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Hill, Christi A., August 2000, "A Geochemical and Hydrological Assessment of Groundwater in the Portuguese Bend Landslide, CA" A GEOCHEMICAL AND HYDROLOGICAL ASSESSMENT OF GROUNDWATER IN THE PORTUGUESE BEND LANDSLIDE, CALIFORNIA BY CHRISTI A. HILL A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (GEOLOGY) August 2000 11 ACKNOWLEDGEMENTS I would like to thank the members of my Ph.D. dissertation committee(Dr. Robert Douglas,Dr.Doug Hammond,Dr.Jean Morrison,Dr. Carol Kendall,and Dr. Dennis Williams)for their guidance and reviews of this dissertation. A special thanks goes to Bob Douglas for his many hours of discussion and fact-gathering. My work in the field could not have been completed without the help of Fay Woodruff and Daphne Clark in collecting samples. The late Dr. Perry Ehlig was extremely helpful in providing background information and valuable discussion. Many thanks go to the following lab personnel for their hours of work on analyses: Doug White at a USGS Water Resources Division Lab under the direction of Dr. Carol Kendall,Zhihong Zheng of the Upper Ocean Process Lab under the direction of Dr. Burt Jones,the Environmental Isotope Lab at the University of Waterloo,and the soil/water lab at M.J. Schiff and Associates, Inc under the direction of Dr.Graham Bell. Financial assistance for the project was provided by the City of Rancho Palos Verdes,the Department of Earth Sciences Graduate Student Research Fund,Dr. Robert Douglas,and Dr. Jean Morrison. I want to thank my family for their continued support of my"lifelong"education. During these past few years,I have come to understand the great personal sacrifice it takes to achieve the goal of earning a Ph.D. degree. The sacrifice was not so much mine, but that of the person closest to me,who had to pay the bills,feed the "kids", and generally keep life running smoothly when I was gone or spending endless hours writing. _ J,I'll never be able to express my thanks for your boundless support. You're the best! TABLE OF CONTENTS ACKNOWLEDGEMENTS ii LIST OF TABLES vi LIST OF FIGURES viii ABSTRACT x CHAPTER I. INTRODUCTION 1 A. PURPOSE OF RESEARCH 3 B. TECTONIC SETTING 3 C. GEOLOGY 4 D. LANDSLIDE HISTORY 5 E. LANDSLIDE STABILITY 7 Subsurface Conditions 7 Mechanics of Movement 8 General Effects of Water on Landslide Movement 9 F. ORGANIZATION OF STUDY 10 G. TERMS AND DEFINITIONS 11 II. HYDROLOGIC PARAMETERS AND BUDGET CALCULATIONS l2 A. ALTAMIRA CANYON BASIN—SURFACE WATER BUDGET 12 Input Variables 12 Rainfall 12 Landscape Irrigation 21 Output Variables 23 Surface Runoff to Ocean 23 Loss to Subsurface Within the Canyon 28 Evapotranspiration 29 B. ALTAMIRA CANYON BASIN—SUBSURFACE WATER BUDGET 31 Input Variables 31 Precipitation Recharge and Infiltration 31 Domestic Water 31 Output Variables 32 Pumping of Groundwater 32 Subsurface Outflow 32 Flow Along the Abalone Cove Head Graben 34 C. PORTUGUESE BEND BASIN—SURFACE WATER BUDGET 36 Input Variables 36 Rainfall 36 Landscape Irrigation 36 iv TABLE OF CONTENTS(cont'd) Output Variables 37 Surface Outflow 37 Evapotranspiration 37 Loss to Subsurface 38 D. PORTUGUESE BEND BASIN—SUBSURFACE WATER BUDGET 38 Input Variables 38 Infiltration and Fissure Recharge 38 Domestic Water 39 Flow Along the Abalone Cove Head Graben 39 Output Variables 39 Pumping of Groundwater 39 Subsurface Outflow 41 E. GROUNDWATER AND LANDSLIDE RESPONSE TO RAINFALL 43 Groundwater Levels 43 Kelvin Canyon Spring 43 Response of Groundwater 46 Annual Storage for 1997-98 51 Long-term Groundwater Budget 52 Response of Landslide Mass 53 F. SUMMARY 57 III. GEOCHEMISTRY 60 A. MAJOR ION CHEMISTRY 60 Rainfall 60 Storm Runoff 62 Domestic Water 62 Groundwater 63 B. STABLE ISOTOPE CHEMISTRY 80 Rainfall 83 Storm Runoff 93 Domestic Water 93 Groundwater 93 C. TRITIUM 102 Rainfall 104 Domestic Water 104 Groundwater 106 D. SUMMARY 110 IV.CONCLUSIONS 112 REFERENCES 119 V �I I TABLE OF CONTENTS (cont'd) APPENDICES A. WELL CONSTRUCTION DETAILS 123 B. GEOCHEMICAL DATA 125 vi LIST OF TABLES TABLE PAGE 1. Total weekly precipitation from rain gauge stations in the study area(1997-98) 15 2. Net effective uniform depth(EUD)of precipitation in the Altamira Canyon drainage basin for the study year(1997-98) 17 3. Net effective uniform depth(EUD)of precipitation in the Portuguese Bend drainage basin for the study year(1997-98) 18 4. Water consumption data for Altamira Canyon and Portuguese Bend basins 22 5. Runoff discharge data from Altamira Canyon during 3 February 1998 storm event. 27 6. Evapotranspiration estimates for Altamira Canyon(1997-98) 30 170 7. Surface water budget for Altamira Canyon(1997-98) 31 8. Dewatering well production in the Altamira Canyon basin(1997-98) 33 9. Groundwater budget for Altamira Canyon(1997-98) 36 10. Surface water budget for Portuguese Bend(1997-98) 38 11. Dewatering well production in the Portuguese Bend basin(1997-98) 40 12. Groundwater budget for Portuguese Bend(1997-98) 41 13. Depth-to-water measurements in the Portuguese Bend monitoring wells 44 14. Discharge measurements at Kelvin Canyon spring 47 15. Long-term groundwater budget for Altamira Canyon basin 52 16. Long-term groundwater budget for Portuguese Bend basin 53 :411' 17. Summary of average chemical and physical data from groundwater samples65 vii LIST OF TABLES(cont'd) TABLE PAGE 18. Factor analysis interpretation 81 19. Calculated annual weighted average 8180 values for rainfall at Station BD 86 20. Monthly rainfall and weighted average 6180 at Station BD 87 21. Estimates of potential elevation effects on 6180 composition of rainfall 90 22. 8l80 and 8D concentrations for selected samples 91 23. Stable isotope mass balance parameters 98 24. Results of tritium analyses on groundwater,rainwater, and domestic water samples 105 t viii 8 LIST OF FIGURES FIGURE PAGE 1. Map showing location of Pleistocene landslide and reactivated Portuguese Bend and Abalone Cove landslides 2 2. Vertical cross sections through active portions of landslides 6 3. Drainage basins and rain gauge network for study area 14 4. Effective uniform depth(EUD)of precipitation over the study period in Altamira Canyon and Portuguese Bend drainage basins 19 5. Correlation of total event rainfall with elevation in the study area 20 6. Monthly domestic water consumption in the study area(1997-98) 22 7. Groundwater and storm runoff sample locations 25 for 8. Graph of discharge from 3 February 1998 storm event 27 9. Altamira Canyon groundwater budget for 1997-98 35 10. Portuguese Bend groundwater budget for 1997-98 42 11. Monitoring well locations in Portuguese Bend landslide 45 12. Graph of discharge measurements at Kelvin Canyon spring during the study period 47 13. Comparison of groundwater levels in the Portuguese Bend landslide with rainfall measurements collected during the study period 48 14. Graph showing relationship of rainfall to movement of the Portuguese Bend landslide between 1956 and 1986 55 15. Fingerprint diagram of major ion chemistry of rainfall and domestic water in the study area and seawater 61 16. Piper tri-linear diagram for wells located in the Abalone Cove landslide 67 17. Piper tri-linear diagram for wells located in the Portuguese Bend landslide 68 ix LIST OF FIGURES(coned) FIGURE PAGE 18. Hydrochemical classification system for natural waters 69 19. Fingerprint diagrams of groundwater data from study area 71 20. Fingerprint diagram of beach well and seawater major ion concentrations 72 21. Fingerprint diagrams of major ion concentrations in wells CB and W6K over the sampling period 75 22. Factor loadings for major elements in water samples from the study area 77 23. Yearly average concentrations of major ions and conductivity in groundwater plotted as a function of total dissolved ions 82 24. Stable isotope composition of rainfall in Santa Maria,California 85 C, 25. Correlation of 8180 with amount of rainfall in each event 87 26. Graph of 8180 versus elevation within the study area 90 27. Stable isotope compositions of selected groundwater,rainfall,and domestic water samples 92 28. Graph of decay-corrected tritium concentrations in rainfall at Santa Maria, California from 1954 through 1993 103 29. Graph of tritium data from locations in study area 105 30. Model showing possible groundwater flow paths within study area 118 x ABSTRACT The influence of water as a driving force in landslide movement is well known. This study incorporated geochemical,isotopic,and hydrological techniques to examine the sources and mechanisms of recharge to groundwater within the Portuguese Bend and Abalone Cove landslides of the Palos Verdes peninsula. During the 1997-98 study year, El Nino conditions were prevalent with total precipitation twice the amount experienced during a normal rainfall year. Under these conditions,recharge in both the Altamira Canyon and Portuguese Bend groundwater basins was dominated by flow down surface fissures and soil infiltration,with modest amounts(<20%)contributed by domestic water recharge via septic systems. These C=1 recharge percentages contrast with the contributions expected for an average rainfall year, in which domestic water is estimated to contribute from 20 to 60%of the recharge to the groundwater system. In both landslides,tritium data indicate that groundwater residence time is on the order of several decades. In light of this estimated age,the rapid response(within one to three months) of groundwater levels to rainfall suggests the propagation of hydraulic pore pressure through the groundwater body rather than the rapid flow of water itself. In addition, an older,warmer,and chemically unique mass of water is present near the toe of the Abalone Cove landslide,indicating the possible presence of a deeper circulating body of water. The presence of a deeper circulation pattern could have important implications for movement in either landslide in the form of possible pore pressure from beneath the slide plane,and presents a topic for future research. 1 CHAPTER I INTRODUCTION The effects of water on the stability of earth material is well known to anyone who has ever built a sand castle.•Dry sand falls in a heap,unable to retain shape or form other than that dictated by the angle of repose. However,just the right amount of added moisture maximizes the water's cohesive properties,allowing the sand particles to be molded into and retain shapes. Further addition of water to the sand results in loss of the cohesion and the castle collapses. The effects of water operate on much larger scales,causing both short-term mass wasting as the result of excessive rainfall and long-term persistent landslide movement. On the Palos Verdes peninsula in southern California favorable geologic conditions have allowed for persistent landslide movement to occur in two adjacent landslide areas, Abalone Cove and Portuguese Bend(Figure 1). The two agents which appear to continuously influence the movement of both the Portuguese Bend and the Abalone Cove landslides are the wave erosion at the toes of the slides and the dynamics of groundwater within the landslide masses. Correlations have been established between the amount of groundwater present and the amount of landslide movement(Ehlig, 1979). 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PURPOSE OF RESEARCH In order to mitigate the influence of groundwater dynamics on landslide movement,it is essential to have an understanding of the sources of groundwater within the landslide mass. Previously identified sources of recharge within the study area include infiltration from rainfall,storm runoff infiltration,and domestic water inflow from septic systems and irrigation(Proffer, 1992).However,the proportions of these sources contributing to the groundwater reservoir and their role in groundwater dynamics have not been well established. The purpose of this research was to confirm and quantify the sources, mechanisms,and relative importance of recharge to groundwater within the Portuguese Bend and Abalone Cove landslide areas.Because landslide movement,especially in Portuguese Bend,is persistent and not just confined to periods of heavy rainfall,a better understanding of the role of all water sources in the recharge of groundwater is essential in comprehending the relationship between groundwater dynamics and Iandslide movement,and in making decisions on mitigation options. B. TECTONIC SETTING The Palos Verdes peninsula is a northwest-trending,doubly-plunging anticlinal structure,- 14 km long and up to 8 km wide(Figure 1). The overall structure has been created by Quaternary uplift within the hanging wall of the Palos Verdes fault,resulting in seaward-dipping marine strata on the southern portion of the peninsula. Multiple marine terraces ring the peninsula,providing evidence of this recent uplift(Woodring, 1946). 4 .rill C. GEOLOGY The regional geology of the area was first described by Woodring et al. (1946). The Mesozoic Catalina Schist forms the basement(core)of the anticline. The Catalina Schist is stratigraphically overlain by the Monterey Formation,which is subdivided into the Middle Miocene Altamira Shale,the late Middle to early Upper Miocene Valmonte Diatomite,and the late Upper Miocene to early Pliocene Malaga Mudstone. The Altamira Shale is predominant in the study area and is composed of tuffaceous, cherty, and phosphatic members. The tuffaceous member was deposited during the infilling of a submarine tectonic basin south of the peninsula and was subsequently uplifted during formation of the anticline. Its thickness throughout the peninsula ranges from- 90 to 1,200 meters. It includes biogenic cherty and phosphatic shale, siltstone and fine-grained sandstone, pillow basalts, basaltic sills,tuffturbidites,ashfall and debris flow tuffs, and dolostone. The dolostone was formed by diagenesis of calcareous muds(Conrad and Ehlig, 1983). Dolomite also occurs near basaltic intrusions both as concretionary lens and as veins in the basalt. There is extensive development of dolomite,barite,and quartz veining within and adjacent to the basalt intrusions suggesting significant geothermal activity(Conrad and Ehlig, 1983). In the vicinity of Portuguese Bend,the most easily-recognized stratigraphic unit within the tuffaceous member is the- 20m-thick Portuguese Tuff. It is an irregularly-bedded tuff which appears to have been deposited by turbidity currents during a single eruptive event(Ehlig, 1992). The tuffaceous member of the Altamira 5 Shale is the most influential unit in terms of landslide activity because its weathered tuffs form weak bentonite beds that serve as slip surfaces. Structurally,the strata in the study area form a topographic amphitheater bounded on the north,east,and south by ridges of fairly stable bedrock. The amphitheater most likely formed by differential compaction of sediments in a basin bounded by fairly incompressible Catalina Schist and basaltic intrusions. Uplift of the compacted sediments on the limb of the peninsular anticline resulted in undulating,southward- dipping strata,more steeply tilted under the landward portion of the amphitheater than under the seaward portion(Ehlig, 1992). Cross sections of each of the two landslides are illustrated in Figure 2. 1111 It is the combination of seaward-dipping strata and weak bentonite layers that provides a favorable environment for landslide activity throughout the southern portion of the Palos Verdes peninsula(Ehlig, 1992). D. LANDSLIDE HISTORY One of the first descriptions of landslide activity in the Portuguese Bend area was provided by Woodring et al. (1946). They mapped the extent of an ancient landslide complex in which the most recent movement appeared to be Pleistocene in age. The entire Pleistocene complex encompasses—3.5 km2 of the structural embayment described above(Figure 1). The origin of the ancient complex is still under debate. Jahns and VonderLinden (1973)suggested that the complex originated as several semi-independent slides which formed during three separate time intervals. Ehlig(1992)interpreted the origin of the complex as a single megaslide. In 1956,the coastal portion of the ancient fib it) IS A Portuguese Bend Landslide Cross Section A' 600- - soo ;qq' Secondary failure surface 300- i c• �.�► p..0"• '��-300 fe z 0- w" 1 _._ Basal Rupture Surface - 0 Q Approximate groundwater level(September 1996) Ed -300 I I I I I I I I I I I I -300 0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 Abalone Cove Landslide Cross Section B B' -400 200- graben .-r------ 300 200 100- -100 0411EAV - Approximate groundwater level(1991) Icti,L -100- Basal rupture surface Q -200- Secondary failure surface a III Figure 2. Vertical cross sections through active portions of landslides. See Figure 1 for locations of cross sections. os 7 complex was reactivated as the Portuguese Bend landslide. Portions of it have moved as much as 240 meters and resulted in the destruction of 130 of approximately 160 homes within the area. The current Portuguese Bend landslide is moving as a series of five semi- independent subslides. The five subslides occupy- 1 km2 and can be divided into two groups:one group which moves into Portuguese Bend, and a second group in the western portion that moves into an unnamed cove between Inspiration Point and Portuguese Point (Figure 1). The Abalone Cove Landslide occurs immediately adjacent to the west of the Portuguese Bend landslide and occupies- 0.3 km2 of the ancient complex(Figure 1). The coastal segment of this slide started moving by February 1974,and the upper portion began moving in 1978,apparently in response to high rainfall. A portion of the slide moved nine meters and damaged several homes prior to stabilization by dewatering. E. LANDSLIDE STABILITY Subsurface Conditions Most pyroclastic glass in the study area has been diagenetically altered. The composition of the clay material in the landslide area has been studied by several investigators. Kerr et al. (1967)analyzed the x-ray diffractometer patterns for five different samples of bentonite(collected from five separate locations in the vicinity of the Portuguese Bend landslide). All five samples were identified as montmorillonite with calcium as the dominant interlayer cation. Novak(1982)and Ehlig and Yen(1997)also f,= used x-ray diffractometer patterns but identified the clay as sodium montmorillonite. The • 8 tested shear strength of the landslide bentonite lies between the reported strength envelopes of both calcium and sodium montmorillonite but more closely resembles the curve of sodium montmorillonite(Ehlig and Yen, 1997). Because of the cation exchange ability of clay,it appears likely that both types of montmorillonite occur in the landslide area. During weathering,which is prominent in the uphill areas of the study area, calcium is typically exchanged for sodium in the clays. In the less-weathered downhill areas more sodium is retained,resulting in clay material that holds more water and is weaker overall(Ehlig and Yen, 1997). The slide planes for both the Abalone Cove and Portuguese Bend landslides occur slightly above or within the altered Portuguese Tuff. Important to the understanding of 1-11 landslide movement is the observation of Ehlig and Yen(1997)that the clay strength in the Portuguese Bend landslide area is dependent upon the rate of displacement. As a result,the slower the rate of shear displacement,the lower the apparent clay shearing strength resisting the displacement. This relationship between clay strength and displacement could possibly explain the slower,but continuous movement of the Portuguese Bend landslide even in the absence of rainfall. Mechanisms of Movement Terzaghi,is his classic 1950 landslide paper,discussed the delicate balance between the fundamental shearing resistance(or strength)of a material and the shearing stresses which can act on that material. He divided the causes of landslide movement into external and internal ones. External causes produce an increase in shearing stress 71 while leaving the shearing resistance unaltered. Examples of external causes include • 9 steepening or heightening of slope by natural (i.e.erosion)or human(excavation) processes,deposition of material on the upper edge of a slope, increase in weight of material from saturation with heavy rainfall, or earthquake shocks. Internal causes create a decrease in shearing resistance and lead to slope failure without altering surface conditions. Loss in cohesion of material or increase in pore water pressure are examples of internal causes. In the cases of both subject landslides,probable external causes have been identified. The Portuguese Bend landslide began moving not long after the placement of roadfill along the upper portion of the slope. The Abalone Cove landslide began moving following periods of heavy rainfall. Both landslides continue to be plagued by the undercutting at the base of the slides by wave erosion. The influence of water(or lack of water)on the movement of both landslides as an internal cause is reflected in different ways. An aggressive dewatering program has slowed the movement of the Abalone Cove landslide to an almost imperceptible creep. The Portuguese Bend landslide has not responded as favorably to dewatering and shows an increase in movement following periods of heavy rainfall. General Effects of Water on Landslide Movement A common misconception about subsurface water is that it has a lubricating effect on soil material. Almost any soil has enough moisture present at any time to"lubricate" the particles,yet mass movement is not a constant phenomenon on every slope. A small amount of water occurring as a film on soil particles actually helps to hold particles together through water's adhesive and cohesive properties. However,replacement of air 10 within the pore spaces with water eliminates the surface tension, resulting in a loss of cohesion. Water cut also cause loss of soil cohesion by dissolution of binding materials in the soil (Terzaghi. 1950). infiltration of water into subsurface pore spaces can result in an increase in hydrostatic pore pressure. This type of pressure can result from an increase in hydraulic head accompanying a rise in the local water table. The effective stress of soil material, or its shear strent;tll, is highly dependent on frictional contact between soil particles. i lydrostatic ilressure decreases the strength of the soil material in one of two ways: 1) it increases the spacing between soil particles, thereby reducing their frictional contact; or 2) the weight of the overlying material is increasingly supported by the pore water which has no shotir strength (Watson and Burnett, 1993). in addition, groundwater can have an increased effect in compound landslides (slide masses with more than one slide plane) such as the Portuguese Bend slide for several rc,isons: 1) multiple slide planes provide a greater surface area than a single slide plane upon which the water can act; 2) the subslides are more rapidly saturated by water infiltration; and 3) movement-inducing pore pressures can often he reached more rapidly in secondary slides (Cronin, 1992). ORGANIZATION OF STUDY '1 his study integrates hydrological, geochemical, and isotopic data to examine the sources, mechanisms, and effects of groundwater recharge on landslide movement. [lyclrologic data from rainfall,runoff, domestic water, and groundwater measurements were used to develop surface and groundwater budgets for each landslide area. The 11 geochemical section includes chemical analysis of major ions,the stable isotopes of oxygen and hydrogen,and the radioactive isotope tritium. The major ions provided clues to the possible influences on groundwater chemistry(i.e. subsurface lithology or seawater intrusion). The isotopic data were used as tracers of groundwater sources and to assess groundwater age. In addition,the isotopes were used in mass balance calculations as an independent check on the results of the hydrologic budget calculations. G. TERMS AND DEFINITIONS The following terms appear throughout the paper and definitions are provided here for easy reference: • 96o—parts per thousand(per mil). `1 Y • SD—concentration of hydrogen-2 isotope(deuterium)determined in similar manner to 5180. • 5180—concentration of oxygen-18 isotope in sample determined from the equation: 8180sam0o J 180/160 sam to 1- 1} x 1000 96o 1 ( 0/ O)rcferenceJ • Effective uniform depth(EUD)of precipitation —average areal precipitation falling within a given drainage basin in linear units(i.e.mm or in.)for a defined time period. • Local meteoric water line(LMWL)—linear relationship between SD and 5180 of precipitation; determined from sampling of local rainfall. • Total dissolved ions(TDI)—total sum of cation and anion concentrations for a given sample. • Tritium unit (TU)—concentration of tritium where: 1 TU= 1 3H per 1018 hydrogen atoms. 12 CHAPTER II HYDROLOGIC PARAMETERS ANI) BUDGET CALCULATIONS As stated previously,identified sources of input to the groundwater system include rainfall and storm runoff infiltration,and domestic water seepage from septic systems. Groundwater in each basin generally flows toward the ocean with an average hydraulic gradient of—0.08 ft/ft in Altamira Canyon and—0.15 in Portuguese Bend. Hydraulic conductivity of the subsurface material in the area ranges from—0.12 m/day (0.39 ft/day)in Altamira Canyon to—0.08 m/day(0.26 ft/day)in Portuguese Bend(Ehlig and Yen, 1997;Proffer, 1992). For the purpose of these calculations,it was assumed that the boundaries of both groundwater basins closely paralleled the surface drainage basins in areal extent. In order to gain an initial estimate of the percent contribution of each hydrologic source component to the water within the slide masses,a hydrologic budget was calculated for both the Altamira Canyon and Portuguese Bend drainage basins. Budgets were first derived for the surface drainage basin and the output from the surface into the subsurface was then incorporated into the groundwater budget. A. ALTAMIRA CANYON BASIN-SURFACE WATER BUDGET Input Variables Rainfall Rainfall measurements were taken on a weekly basis from a nine-station rain �, gauge network in the study area. At one of the stations(BD),rainfall measurements were 13 taken for each individual rainfall event. Figure 3 illustrates the rain gauge station locations and the extent of the Abalone Cove and the adjacent Portuguese Bend drainage basins. Rain samples were collected in a small bucket at a central location in the study area(Station BD). The samples were mixed and placed into vials at the end of each particular stone. Rainfall measurements were taken from plastic rain gauges attached to fixed points throughout the sample area. The gauges could measure up to 126 millimeters of rainfall per event. The Altamira Canyon surface drainage basin is—3.3 km2(815 acres)in size while the Portuguese Bend basin measures- 2.5 km2(618 acres). Data for three of the stations(1011B,SF,and 1216)were obtained from the Los Angeles County Department of Public Works. The data from all 12 stations are presented in Table 1. Three stations had missing data as a result of stolen or broken gauges. The missing data at a given station(Z)were estimated from the data of three surrounding index stations(A,B,and C) using the following equation(Fetter, 1988): Pz= 1/3 [(Nz/NA)PA+(Nz/NB)PB+(NzINc)Pc] where P represents the actual precipitation at the index stations and N is the mean annual precipitation at each of the stations. In order to estimate the weekly effective uniform depth(EUD)of precipitation in each of the drainage basins,the Theisson polygon method was used. This method is effective when the distribution of rain gauges is non-uniform. Polygons of appropriate size are constructed around each rain gauge to account for their varied distribution. The c,� polygon area surrounding each gauge is expressed as a percentage of the total area of the . 14 fit) L > ` l 1r c ee p ?.• • ▪ �y, •�� ayKl. 51\< c� '<2 `'£ �'4 -a+� rr ,r, ..�,y '4A �• s'1�1 g '^114( t` •.4t F<a' £:\11,7411111? .,. ',^ ':.' > A .. "'A e ie y,'v A`S�+4w` - ?s,.y,;y� .itf . Ur i E'6, "... f••:•.,0.:•••-; • 1 •h i : ' ?9 \ :'L+ rw� 4 ? z+ P � ! < V,. ;,�r9kiG: S>>°;.;:.2�c:: h ♦ r �S.aic}s f >� e3 " k : S� .,,,mow•. �r''..r�' �wcp�l.,.c<.� a a� @ %....‘, • �. ...>': r:.:::..z : `„ - DCPA. • s <�c � 5 .c::.t: :,'.:;:? s r ii ti� 4y (:•'.'?:�t� f' y • ,z, a6<p `,�I. 1216 .z„.,,:. s s. :. • ^�,• w c ,\+,S ? :vF.... ::c:-:•.\ . ::?:4 ups`.`:l:n.i _'p,�,'",i�>:: •,• ;:`C• �t:`c'''. .LY: .:S?:. ':' iia: i air...,:.... •r ,'''''''' .t.';' .-\ Fh < 't.i'.�' {o 0 �.l<�l80.gd.• Y�'"� ?y _ r '` � '._ � y 4 '�e,Q A JS C q • 4 . • Y . -'.*.- l v �<Nc 'Ifl',. • `4.1k—,k;:. X� 2i Y.•*). .0hyr �; .4.,„..,...., .1.....Y . , 7C ,.:,..,-,.,..#5.:AY.';,..,. .-,,,.....,.i;'irso.i„.* "--•:,,,,• :•-.: ...'•••••••..."...-.1., .<:•.,:.m •,••%•:-..,..:, •::c 1pp.r e. ' t': • < 4;:: 0,S •F. ''':::`( • a • '• _ 'ti 'k g^^ ... a Abevi. �, ` a Fry DC' y e • • • \ :t • .`troll i.m�...4.1..........;. K \\W, as , `4y 1000 0 1000 2000 3000 4000 5000 6000 70400 FEET " .. r�' .\. 1 0S 0 1 KLONET13t k 1 CONTOUR INTERVAL 20 FEET Figure 3. Drainage basins and rain gauge network for study area. Gray areas represent each drainage basin (dark gray-Altimira Canyon, light gray-Portuguese Bend). Polygons represent weighted areas for each rain gauge. •NC represents rain gauge station. . . 15 TABLE 1. TOTAL WEEKLY PRECIPITATION FROM :. RAIN GAUGE STATIONS IN THE STUDY AREA (1997-98). Rain Gauge Designations Week 1011B DCP SF 1216 VD BD NE RC POM NC ISH DC elevation 1265 1180 1140 810 510 430 422 404 356 270 182 162 9/1-9f7/1997 - - - 9/8-9/1 4 - - - - 9/15-9/21 - - - . - . 9/22-9/28 11.7 - 8.9 7.9 - - - - - - 9/29-10/5 - - - - - - - - 10/6-10/12 - - - .- - - - - - 10/13-10/19 - - -. - - - .. - - 10/20-10/26 - - .. - - - - 10/27-11/2 - - - - - - 11/3-11/9 - -. - - - - - - - - 11110-11/16 45.0 32.0 45.5 38.4 30.0 28.0 23.5 24.0 20.0 22.5 19.0 17 5 11;17-11/23 - - - 3.0 - - - 11/24-11/30 19.6 12.0 18.5 14.2 26.0 - 21.5 13.0 12.0 14.0 9.0 ' 18.0 16.5- 12/1-12/7 62.5 44.0 50.8 58.7 53.5 56.0 47.0 50.0 44.0 45.0 42.0 45.5 12/8-12/14 - - 10.2 - - _ - - - 12/15-12/21 57.9 17.0 42.2 25.7 36.0 37.0 27.0 31,0 26.5 27.0 35.0 29.5 12/22-12/28 - 5.1 12/29-1/4/1998 10.9 7.0 89.4 168 11.5 13.0 8.5 10.0 8.0 7.5 7.0 8.5 1/5-1/11 30.5 16.0 30.5 28.2 26.0 24.0 24.0 22.0 24.0 18.0 23.8 24.0 1/12-1/18 5.8 5.5 57.7 20.3 6.0 3.0 3.5 3.0 2.5 2.0 2.8 2.5 1/19-1/25 - - _ 5.0 - - - - 1/26-2/1 20.6 11.5 20.1 25.7 19.5 18.0 13.5 14.0 12.0 11.0 14.5 _13.0 2/2-2/8 139.2 278.0 97.0 145.5 117.0 133.0 108.0 114.0 102.5 101.0 110.0 104.0 2/9-2/15 50.8 24.5 50.8 33.0 50.0 47.5 45.0 42.0 41.5 37.0 44.0 40.5 2/16-2/22 61.0 46.0 74.9 T 64.0 61.7 67.5 62.0 61 0 57.5 540 61.0 58.0 2/23-3/1 48.0 31.0 : 55.9 47.8 43.5 43.0 34.0 38.0 35.0 32.0 36.0 38.0 3/2-3/8 9.9 ' 10.2 - _ - - - . - 3/9-3/15 16.5 18.9 12.7 30.5 28.0 26.0 19.0 21.0 15.5 16.0 15.0 18.0 3116-3/22 -. - _ - - - - - 3/23-3129 45.7 34.3 43.2 35.8 31.3 38.0 28.5 26.0 28.5 20.5 31.0 26.5 3/30-4/5 31.2 23.5 31.2 24.1 21.7 22.0 19.5 18.0 19.5 14.5- 21.0 18.5 4/6-4/12 26.7 21.4 30.5 15.2 ' 17.0 ' 17 5 16.0 19.5 16.0 19.5 18.0 17.0 4113-4/19 1.0 - - - - 4/20-4/26 .. - 4/27-5/3 - . • 2.5 - - - - - 5/4-5/10 21.6 17.8 8.9 20.3 16.5 17.0 16.5 17.0 13.0 13.5 10.0 12.5 5/11-5/17 25.1 20.7 20.8 19.5 20.0 19.0 16 0 18.5 13.5 18.0 16.0 5/18-5/24 - 5/25-5/31 - - - 6/1-6/7 - 2.5 - - - - . 6/8-6/14 . 1.0 0.8 - - - . 6/15-6/21 - - 1.0 1.0 - - . - . - - . - 6/22-6/28 - - - .. _ 6/29-7/5 _ - - 7/6-7/12 - - - - 7/13-7119 - - - • 7/20-7/26 .. . 7/27-8/2 - - - - - 8/3-8/9 - - - . . - 8/10-8/16 - .. .. _ - 8/17-8/23 - _ 8/24-8/31 TOTAL 728.5 661.2 787.1 672.8 614.7 640.0 527.5 538.5 498.5 463.5 526.1 506.0 Stations are listed from left to right in order of decreasing elevation(see Figure 3 for locations). All measurements in millimeters and dashes(-)=no rainfall measured. Numbers in bold are estimates of missing data(derived from surrounding stations as detailed in text). 16 8 basin and the amounts of rainfall for each gauge are weighted as a function of the polygon area. This method has two advantages: 1)it adjusts for the non-uniform distribution of rain gauges by applying a weighting factor, and 2)allows repeated use of the established polygon network to process large numbers of data sets. The polygon network established for the study area is illustrated in Figure 3 and the calculated weekly EUDs of precipitation for Altamira Canyon and Portuguese Bend drainage basins are presented in Tables 2 and 3, respectively. Although both Tables 2 and 3 have the same stations headings listed,only the stations with polygons falling within the drainage basin of interest have values listed in each respective table. The total net EUD of precipitation during the study year was 632 mm(--25 in.)in TI the Altamira Canyon drainage basin and 592 mm(—23 in.)in the Portuguese Bend drainage basin. These totals represent almost twice the annual mean rainfall of—328 mm (12.9 in.)reported in the study area(Ehlig, 1992). Figure 4 shows a graph over time of the weekly EUD of precipitation in each of the drainage basins.The profiles are almost identical in form with the Altamira Canyon basin reflecting its greater total EUD of precipitation. The amount of rainfall in the study area shows a rough,positive correlation with increasing topographic elevation(Figure 5). Total volume of rainfall in the Altamira Canyon basin for the study year was calculated by multiplying the total EUD for the basin(632 mm)by the basin surface area (3.3 km2)yielding a total of 20.9 x 105 m3 (— 1,694 acre-ft). It TABLE 2. NET EFFECTIVE UNIFORM DEPTH (EUD) 17 OF PRECIPITATION IN THE ALTAMIRA CANYON DRAINAGE BASIN FOR THE STUDY YEAR (1997-98). Rain Gauge Designations Week 1011B DCP SF 1216 VD BD NE RC POM NC ISH DC , Net EUD 9/1-9/7/1997 - - - - _ - 9/8-9/14 - _ -. - .- - 9/15-9/21 - - - - - - - 9/22-9/28 1 -- 0 0 - - - - - - 1 9/29-10/5 - - • - - - 10/6-10/12 - .. - - - _ - - - - 10/13-10/19 - - - - _ .. - 10/20-10/26 - - - - - - - _ 10127-11/2 - - - - - - - 11/3-11/9 - - - - - - - - 11/10-11/16 3 17 0 1 - 3 3 1 2 1 0 0 0 30 11/17-11/23 - - - 0 - - - - - 0 11/2411/30 1 6 0 0 2 2 0 1 1 0 0 0 15 12/1-12/7 4 23 0 1 5 6 2 4 2 _ 1 0 1 48 12/8-12/14 - - 0 - - - - - - 12/15-12/21 3 9 0 1 3 4 1 3 1 0 0 0 26 12/22-12/28 - - 0 - .. - - - - - _ 12/29-1/4/1998 1 4 0 0 1 1 0 1 0 0 0 0 9 1/5-1/11 2 8 0 1 2 3 1 2 1 0 0 0 20 1/12-1/18 0 3 0 0 1 0 ' 0 0 0 0 0 0 5 1/19-1/25 - - - 1 - - - - - 1 1/26-2/1 1 6 0 1 2 2 0 1 1 0 0 0 14 2/2-2/8 8 145 0 4 10 14 4 10 5 2 0 1 203 219-2/15 ' 3 13 ' 0 1 4 5 2 4 2 1 0 0 34 2/16-2/22 4 24 0 2 5 7 2 5 3 1 0 1 54 2/23-3/1 3 16 0 1 4 5 1 3 2 1 0 0 36 3/2-3/8 1 0 _ - - 1 3/9-3/15 1 10 0 1 2 3 1 2 1 0 0 0 21 3/16-3/22 - - .. - - - - - - .. 3/23-3129 3 18 0 1 3 4 1 2 1 0 0 0 34 3/30-4/5 2 12 0 1 2 2 1 2 1 0 0 0 23 4/6-4/12 2 11 . 0 ' 0 2 2 1 2 1 0 0 0 20 4/13-4/19 - - 0 - - - - - - - 4/20-4/26 - - - - - - - - - 4/27-5/3 - 0 - - - - 0 5/4-5/10 1 9 0 0 1 2 1 1 1 0 0 0 17 5/11-5/17 1 11 - 1 2 2 1 1 ' 1 0 0 0 20 5/18-5/24 - - - - - - - - .. - 5/25-5/31 - - - - - - - - - 6/1-6t7 - 0 - 0 6/8-6/14 0 0 - - - - 6/15-6/21 - 0 0 - - - - - 6/22-6/28 - - - - - 6/29-7/5 - - _ - - - - - 7/6-7/12 - _ - - - - 7/13-7/19 - - - - 7/20-7/26 - - S - - - - 7/27-8/2 - - - - - - 8/3-8/9 - - - - - - - - 8/10-8/16 - - - - .. - ' - - 8/17-8/23 - - - - - - - - - 8/24-8/31 - - - - - _ - - - - - - Total 632 All measurements are in millimeters and dashes(-)= no rainfall measured. Shaded stations do not fall within the drainage basin and are not applicable. TABLE 3. NET EFFECTIVE UNIFORM DEPTH (EUD) 18 OF PRECIPITATION IN THE PORTUGUESE BEND DRAINAGE BASIN FOR THE STUDY YEAR (1997-98). Rain Gauge Designations Week 10118 DCP SF 1216 VD BD NE RC POM NC ISH DC Net EUD 9/1-9/7/1997 - - - - _ - - - - - 9/8-9/14 - - - - - - - - - - - - 9/15-9/21 - - - - - - - - - - 9/22-9/28 4 - 0 0 - - - 4 9/29-10/5 ` - . - - - - - - - - 10/6-10/12 - - - - - - . - _ _ - 10/13-10/19 - - - - _ - - .. - - - 10/20-10/26 - - - _ - - - - 10/27-11/2 - - - - . - - - - - - - - - 11/3-11/9 - - - - - - - - - - - 11/10-11/16 14 0 0 0 1 0 5 0 1 0 5 2 28 11/17-11/23 - - - - 0 - - - - - - - 11/24-11/30 6 0 0 0 1 0 3 0 1 0 5 2 17 12/1-12(7 190 0 0 2 0 9 0 2 0 11 6 50 12/8-12/14 - l - 0 - - - - - - 0 12/15-1221 18 0 0 0 1 0 5 0 1 0 9 4 39 12/22-12/28 - - 0 - - - - - - - - - 12/29-1/4/1998 3 0 1 0 0 0 2 0 0 0 2 1 10 1/5-1/11 9 0 - 0 0 1 0 5 0 1 0 6 3 26 1/12-1/18 2 0 0 0 0 0 1 0 0 0 1 0 4 1/19-1/25 - - - - 0 - - - - - 1/26-2/1 6 0 0 0 1 0 3 0 1 0 4 2 16 2/2-2/8 43 0 1 0 3 0 22 0 6 0 28 15 117 2/9-2/15 16 0 0 0 1 0 9 0 2 0 11 6 46 2/16-2122 19 0 1 0 2 0 12 0 3 0 15 8 61 2/23-3/1 15 0 " 0 0 1 0 7 0 2 0 9 5 40 3/2-3/8 3 - 0 - - - - - - - 3 3/9-3/15 5 0 0 0 1 0 4 0 1 0 4 3 17 3/16-3/22 - - - - - _ - - 3/23-3/29 14 0 0 0 1 0 6 0 2 0 8 4 34 3130-4/5 10 0 0 0 1 0 4 0 1 ' 0 5 3 24 4/6-4/12 8 0 0 0 ' 0 0 3 0 1 0 5 2 20 4/13-4/19 - - - 0 - - - - - - - - - 4/20-4/26 - - - - - - - - - - r - 4127-5/3 - - - 0 - - - - - -5/4-5/10 7 ' 0 0 ' 0 0 0 3 0 1 0 3 2 16 5/11-5/17 8 0 - 0 1 0 4 0 1 0 5 2 20 5/18-5/24 - - - - - - - - - 5/25-5/31 - _ ' - - - - - - - - 6/1-6/7 - - - 0 - - - - - - - 6/8-6/14 - 0 0 - - - - - - - - 6/15-6/21 - - 0 0 - - - - - - - 6/22-6/28 - - - - - - - - - - - - 6/29-7/5 - - - - - - - - - - - - 7/6-7/12 ., - - - - - - ' - - 7/13-7/19 • - - ' - - _ _ - - - 7/20-7/26 - - - - - - - - - - 7/27-8/2 - - - - - - - - - 8/3-8/9 - - - - - - - - - - - 8/10-8/16 - - - - - - - - - . 8/17-8/23 - - - - - - - 8/24-8/31 - - - . - - - - ( -1_ ' 1_7utal 592 + Ali measurements are in millimeters and dashes (-) = no rainfall measured. Shaded stations do not fall within the drainage basin and are not applicable. 1=,' 0 no ••,•��r �.pn Rainfall(millimeters) Rainfall (millimeters) C o tti coli § § 51, g in3 o bii S g R ilg 51 9/22-9/28 4 9/22-9/28: 10/13-10/19 I 10/13-10/19: CI a* ril 003 11/3-11/9 11/3-11/9" O 11/24-11/30 ,• 11/2411/30 5. 12/15-12/21 : 12/15-12/21 1-81 00 Co1/5.1/11 1/5-1/11 " 0 S 1/26-2/1 . C 1/26-2/1 - ' ? D, = • 2/16-2/221 i C 2/16-2/22 I 1 tth, a = - I <o p ! 1 } ? } ! 3 G in 3t9-3115 Sfr i ? ? i 3/9-3115 CI 0 80 . . i } ! to 1• 0 3/30-4/5; ' 3/30-415 I } } } lZ it 4120 4126" m 4/20-4/26; 1 ? } '�' ; O �o• 5111-5/17 I G 5/11-5/171 ? }rn CI. ! 1 C } ct - 1 I 1 ! i I � ' I 1 p0,• 6/1-6/7: 1 j cn } 6/1.617: I i i0) i I - I , 1 ? 1t1 8/22-6/28: !3 6/22-6/28: I 1 j I `N : !3 g g.888 eV7113-7119_ I 3 7/13-7119_ } I I 3 i `° • x-6/9: 8/3-8/9: I j } 1 } i 11 } 1 ' 1 3' h 44 8/24-8/31 8/24-8/31 l . • 8. . Q. rr 20 Event Rainfall vs. Elevation 800 - E 700 e • E 600 R2=0.7786 s. 500 • • I 400 - 300 W 200 100 0 0 200 400 600 800 1000 1200 1400 Elevation(ft above mean sea level) Figure 5. Correlation of total event rainfall with elevation in the study area. (1 There is a general increase in rainfall amount with increasing elevation. 21 Landscape Irrigation Surface water is also supplied by domestic watering of lawns and plants. Water supply records for each basin were obtained from the California Water Service for the years 1995-1999. Based on these records,a total of 98,907 m3 (- 80 acre-ft)of water was supplied to the Altamira basin area during the 1997-98 study year(Table 4). In practice, landscape irrigation is typically discontinued during periods of rainfall and therefore it is assumed that most domestic water delivered to residences during these periods enters directly into the septic systems. Figure 6 illustrates water consumption in the two basins over the study year. During the study period rainy season, the highest amount of rainfall occurred during the month of February(Table 2). The monthly water consumption for February totaled 4,196 m3(-3 acre-ft). By applying this amount as a base level of monthly household consumption and assuming that any amount over the base level is probably used for landscape irrigation, an estimate of irrigation water can be obtained. For the year-long study,the base level of household consumption would total 50,352 m3 (--41 acre-ft)with the remaining 48,555 m3(-39 acre-ft)available for irrigation watering. Most irrigation occurs during times of little to no rainfall,warmer temperatures,and(in the Mediterranean climate of the study area)conditions of relatively low humidity. For the purposes of these calculatiol ' for irrigation was either evaporated or transpired al , C k C groundwater system. 3( g, r ot r Gqi =, I �Do k6 vo 22 TABLE 4.WATER CONSUMPTION DATA FOR ALTAMIRA CANYON AND PORTUGUESE BEND BASINS 1997.98(El Nino year) Altamira Portuguese Month Canyon Bend Sep 12,268 2,625 Oct 10,866 1,869 Nov 11,769 2,494 Dec 5,345 1,008 Jan 5,246 821 Feb 4,196 756 Mar 4,077 841 Apr 4,680 736 May 7,007 1,062 Jun 8,867 1,693 Jul 10,988 1,554 Aug 13,598 2,950 Year Total 98,907 18,408 (Note:All amounts repotted in cubic meters(=8.107 x 104 acre-ft)) �KII 16000 - E 14000 I ::: 8000 8 6000 wm 4000 3 2000 co 0 Z 0 -A LL Month - -Altamira Canyon -f-Portuguese Bend Figure 6. Monthly domestic water consumption in the study area(1997-98). In general, water use decreases during the wetter winter season. There are fewer residences in the Portuguese Bend area than Altamira Canyon resulting in lower overall consumption rates in Portuguese Bend. 23 Output Variables Surface Runoff to Ocean Initial estimates of the rainfall-runoff relationship in the Altamira Canyon drainage basin were calculated using the rational method. This equation is used to predict peak runoff rates from data on rainfall intensity by employing the following equation: Qp=0.278 CIA where Qp=peak runoff rate(m3/sec),C=fraction of runoff, I=average rainfall intensity(mm/hr),and A=the size of the drainage basin(km2). The coefficient C is based on land use. Less than 'A of the Altamira Canyon drainage basin is developed as single-family residences(Figure 3). With the exception of the developed area at the crest of the basin,most homes are widely-spaced with minimal asphalt coverage. For these calculations,a coefficient(C)of 0.2 was used,based on land use of unimproved property (America Society of Civil Engineers, 1970). Using the average rainfall intensity(I)from the 3 February 1998 storm(—4 mm/hr),and a basin area(A)of 3.3 km2,the peak runoff rate for the basin during this 11-hour storm event was predicted to be— 1.1 m3/sec (39 cfs). In order to assess the role that surface runoff plays in the overall basin surface water budget, rainfall and runoff measurements were collected during a storm event on 3 February 1998. Total runoff-producing rainfall at station BD during the storm event measured 44 mm (— 1.7 in.). This storm amount represented—33%of total rainfall at the station for the week of 2/2 through 2/8. Total basin EUD for the same week was 24 203 mm(—8 in.). Assuming that the storm also represented—33%of the total weekly basin EUD,it is estimated that—67 mm(—2.6 in.)of rain fell on the overall basin during this storm. With a basin area of 3.3 km2(816 acres),the volume of rain falling on the basin during the 3 February storm was—2.2 x 105 m3 (- 179 acre-ft). :eh\ G 4 S Runoff samples were collected from the middle of the runoff stream approximately 3 to 6 inches below the surface. A General Oceanics Inc. flowmeter was lowered into the water for a 10-second interval and a meter reading was taken at the beginning and end of each interval. Three readings were taken for each sampling and averaged to obtain the final measurement. During low stages of stream flow,three float measurements were taken over a given distance and averaged to obtain a velocity I measurement. The measurements were taken at two locations along Altamira Canyon: 1)the Sweetbay culvert,located upgradient of the upper edge of the Abalone Cove landslide and;2)the Narcissa culvert,located within the Abalone Cove landslide(Figure 7). The culverts are large 10-foot-diameter pipes which direct water flowing down Altamira Canyon beneath surface streets crossing over the canyon. The Sweetbay location was selected to measure runoff along the canyon prior to entering the Abalone Cove landslide area while the Narcissa location allowed for measurement of runoff prior to leaving the landslide area. Rainfall in the storm started at approximately 5:30 AM. The greatest amount of discharge was measured at the Sweetbay location and was manifested as two separate pulses of water movement. This separation of water masses corresponded to a short Al,,,,..s 25 r - • • �r —. i ; 7 ::-. i �,. ^ -rte- .=--_- ,sem '!KC• S a 1 ( 800 ., ..._,-..-_-......:_--_,-- -i-.;,. \i�j".0.,. s.\, • .1 S ?y • •)C• ��_ ..�- �•,�,. _,.,;-�_ �� r . • 4 4 !SES; • • $B u st, ' I. ..\ iN973 -�� 444,:s:.:. •` J' G' W11 �%W6A ': , ,�� pr' ` r` `, 1 44 4 Krfairpril ace ' \-'WW3 � / / � , ii^ i ; ! (<4mooWW2A Wwa� w-----c. -0.-3..,;,--„:1---, , i=- . �j T. G. `.d.', � .at ISE r �• Port Inspiration`' Roo N Point 1000 0 1000 2000 Feet ' mg — _ aimmi■mo .* 0.5 0 1 Kilometer me — mm i Contour Interval 20 Feet Figure 7. Groundwater and storm runoff sample locations. • =groundwater samples; X=storm runoff samples 26 break in rainfall intensity and demonstrates the rapid response of runoff to precipitation in this small basin. Discharge at the Narcissa location also exhibits two corresponding pulses but had less volume overall than the Sweetbay location. Discharge rate was calculated from velocity measurements by multiplying the flow velocity by the stream channel cross-section(Table 5)and the average results over the length of the storm ranged from— 1.1 m3/sec(39cfs)at Sweetbay station to—0.3 m3/sec(9 cfs)at Narcissa station. By plotting the discharge measurements versus time (Figure 8)and calculating the area under the curve,the total volume of discharge at each runoff location during the storm was calculated. Total runoff at the Sweetbay station was calculated at- 42,062 m3 (34 acre-ft)while runoff at the Narcissa location measured 13,305 m3(11 acre-ft). Values of runoff discharge at Sweetbay during the storm equal the discharge predicted by the rational equation. The total volume of runoff at this location(42,062 m3)represents— 19%of the total event rainfall,again closely approximating the 20% runoff expected on unimproved property. The total storm runoff for the lower Narcissa culvert portion(- 13,305 m3)constitutes only 6%of total event rainfall(2.2 x 105 m3 or 179 acre-ft)and represents the volume of water leaving the surface drainage area through the canyon during the storm event. Discharge measurements of 0.3 m3/sec at this location represents—27%of predicted discharge(1.1 m3/sec). These lower-than- predicted values suggest a loss of runoff water between the upper(Sweetbay)and lower (Narcissa)canyon stations. Because the Narcissa station is located within a more developed area where runoff is expected to increase as a result of surface improvements, 27 TABLE 5. RUNOFF DISCHARGE DATA FROM ALTAMIRA CANYON DURING 3 FEBRUARY 1998 STORM EVENT Sweetbay Narcissa Discharge Discharge Discharge Discharge Time (cfs) (m3/sec) lime (cfs) (m3/sec) 5:30 0 0.0 5:30 0 0.0 7:00 7 0.2 6:45 2 0.1 7:40 87 2.5 8:20 20 0.6 9:30 42 1.2 10:10 11 0.3 11:05 6 0.2 11:40 1 0.0 12:25 1 0.0 13:30 34 1.0 13:55 147 4.1 15:30 4 0.1 14:40 40 1.1 17:40 0 0.0 16:20 1 0.0 18:30 0 0.0 150 - Sweetbay 125 — —Narcissa 100 ar a- 75 c� t o 50 25 0 , 0 0 0 0 0 0 0 0 0 .. .. .. .. .. .. .. .. .. O M CD co N Cri co v- O r r 1- N Time Figure 8. Graph of discharge from 3 February 1998 storm event. Although runoff is similar:in both portions of the basin, total volume is less in the lower Narcissa portion indicating possible loss to the subsurface through canyon fractures. 28 the loss may be even greater than suggested. This apparent loss of runoff water within the canyon is discussed further in the next section. In order to assess the total amount of storm runoff over the year-long study period, it was assumed that similar percentages of runoff from each event exited the drainage basin. In reality,the actual percentage of runoff would be expected to vary and would depend on such factors as duration of rainfall intensity and the saturation conditions of the soil during each event. Not every rainfall event,however,produced runoff down the canyon. Review of field notes indicated that runoff was most likely to occur during single storm events with greater than 20 mm(—0.8 in.)of total rainfall. Thirteen separate events met this criterion and the EUD was calculated for each storm. The total storm rainfall amount for the 13 events was calculated to be 14.2 x 105 m3 (- 1,151 acre-ft); assuming 6%of this total event rainfall left as surface flow(as occurred during the 3 February event)indicates 0.9 x 105 m3(- 73 acre-ft)of total surface runoff to the Pacific Ocean over the 1997-98 study period. Loss to Subsurface Within the Canyon Total runoff for the 3 February 1998 storm at the two locations measured 42,062 m3(-34 acre-ft)in the upper portion of Altamira Canyon and 13,305 m3 (� 11 acre-ft)in the lower portion. Since the canyon is continuously connected,the discharge would be expected to be greater at the lower portion than at the upper portion. There is instead air apparent loss of water(.28,757 m3 or 23 acre-ft)within the canyon between the two sample locations. Because the lower sample location also receives 29 diverted surface street drainage from other areas of the basin during the storm,the above estimate actually represents a minimum amount of loss. Altamira Canyon crosses the head of the Abalone Cove landslide about 350 meters north of Palos Verdes Drive South. There is a significant drop of— 1.2 meters (—4 feet)in the floor of the canyon at this location and,during storm runoff,ponded water temporarily builds up before it continues down the canyon. The fracture zone at this location would provide a direct route for the surface drainage water to enter the subsurface,resulting in the indicated loss of water(— 13%of the storm event rainfall). Assuming a similar canyon response during each qualifying storm,it was estimated that 1.8 x 105 m3(— 146 acre-ft)entered the subsurface through fractures in the canyon over the entire 1997-98 study period. Evapotranspiration Evapotranspiration is the transfer of moisture from the ground to the atmosphere, primarily through evaporation of soil moisture and transpiration from plants. Estimates of evapotranspiration were calculated using several methods. The climate of the study area is classified as Mediterranean,with typical average annual precipitation of 38 to 64 cm(— 15 to 25 in.). The summer months are typically dry,producing semi-arid conditions. The methods of Thornwaite(1957)and Muller and Oberlander(1978)are widely used but are most appropriate in humid climates. They are presented in Table 6 below for reference but are not considered appropriate for application to the study area. The methods of Turc(1955)and Thomwaite(1948)can be applied to semi-arid and arid ii regions and are therefore more applicable to the study area. Both methods require the use 30 • of temperature and precipitation values as input. The temperature values were obtained from the County of Los Angeles stations(1216, 1011B, and SF)which are located near the study area(Figure 3). The precipitation values were measured during this study and obtained from the three County of Los Angeles stations.The Turc(1955)and Thomwaite (1948)estimates are also listed in Table 6 and range from- 509 mm to- 548 mm(—20 to 22 in.)for the 1997-98 study year. The total volume of rainfall leaving the surface basin as evapotranspiration is estimated to range from— 16.8 x 105 m3 to 18.1 x 105 m3 (1,313 to 1,467 acre-ft),approximately equal to 81 to 85%of total rainfall. This amount is added to the assumed evapotranspiration amount from irrigation water(0.5 x 105 m3 or 39 acre-ft)to arrive at total evapotranspiration from the surface F. area for the study year. TABLE 6. EVAPOTRANSPIRATION ESTIMATES FOR ALTAMIRA CANYON(1997-98). Method Application Est.Evapotrans.(mm) Total Volume(105 m3)* Turc(1955) humid-arid climates 548 18.1 Thornwaite(1948) arid regions of U.S. 509 16.8 Thornwaite(1957) any area** 266 8.8 Muller et al(1978) any area** 258 8.5 *The above estimates do not include an additional 0.5 x 103 m3 of domestic irrigation water postulated to evapotranspire during the study year. **Equations are used for all climatic conditions,but are most applicable in humid climates. The remaining(—0.1 x 105 to 1.4 x 105 m3 or 8 to 113 acre-ft)of rainfall during the study period is assumed to have entered the subsurface through infiltration or scattered surface fissures. Table 7 summarizes the annual surface water budget components and their percent contribution. 31 TABLE 7.SURFACE WATER BUDGET FOR ALTAMIRA CANYON(1997-98). Surface Budget Component Volume(105 m3) Volume(acre-ft) %Contribution Input—Rainfall 20.9 1694 —98 Landscape irrigation 0.5 41 —2 Total Input 21.4 1735 100 Output—Surface runoff 0.9 73 —4 Total evapotranspiration 17.3— 18.6 1403- 1508 —81 —86 GW recharge through canyon 1.8 146 —9 Infiltration/fissures to subsurface 0.1 - 1.4 8—113 — 1 —6 Total Output 21.4 1735 100 B. ALTAMIRA CANYON BASIN—SUBSURFACE WATER BUDGET Input Variables Precipitation Recharge and Infiltration As stated above, an estimated volume of 1.8 x 105 m3(— 146 acre-ft)of water entered the subsurface of the Altamira Canyon basin during the study period via canyon recharge and—0.1 x 105 to 1.4 x 105 m3(-8 to 113)of precipitation infiltrated during the same period. This total amount of recharge(1.9 x 105 to 3.2 x 105 m3 or 154 to 259 acre-ft)from precipitation to the groundwater system represents—9 to 15 %of total rainfall over the basin for the 1997-98 study period. Domestic water Residences and commercial properties in the Altamira Canyon drainage basin are serviced by septic systems. As discussed earlier,it is estimated that the base level of 1997-98 internal household consumption for the entire study area totaled 50,352 m3(—41 acre-ft). This represents the amount of domestic water directly recharging the groundwater body through septic system percolation. 32 Output Variables Pumping of Groundwater Fourteen wells are currently in operation to remove groundwater from the subsurface in the Altamira Canyon basin(Figure 7). Although wells EB and CB are located within the Abalone Cove landslide,they are outside the limits of the Altamira Canyon basin and are not included in the calculation of the subsurface budget. Most wells are evacuated using pumps which run when a preset,well-specific level of water is reached and therefore are not in constant operation. Pump readings are made regularly and are tabulated on a monthly basis. Well production data for the study period are presented in Table 8. Pumping from wells in the Altamira Canyon basin removed a total of 3.6 x 105 m3 (—289 acre-ft)of water from the subsurface during the study period. Subsurface Outflow Groundwater flow is typically toward the ocean and it is assumed that the groundwater basin geometry is closely coincident with the surface drainage basin. In this geometry, groundwater could exit the study area through a fairly narrow(—83 meter or 270 feet wide) area at the lower basin boundary with the ocean. Using Darcy's law: Q=Av, where: A=L x b and v=-K(Ah/Ax),with Q=flow(m3/day),L=distance across the boundary in meters,b=the saturated aquifer thickness in meters,K=hydraulic conductivity(m/day),and Ah/Ax=average hydraulic gradient(m/m),the estimated discharge of groundwater flow from the study area across the lower boundary can be calculated. The bottom of the saturated zone is typically associated with the bottom of ( ei.,. er,)-. TABLE 8. DEWATERING WELL PRODUCTION IN THE ALTAMIRA CANYON BASIN (1997-98). Well 8126-9124 9124-10116 10/16-1111411/14-12/13 12/30-1126 1126-2/24_2124-3/30 3130-4/27 4/27-6/18 6/18-6126 6126-7/16 7116-8/11 Study period WW-1 8,172 7,995 7,583 6,603 3141' 17,676 12,128 11,717 12,246 14,010 17,218 19,780 12,284 WW-2 8,778 7,717 5,735 7,317 5,631 4,480 5,393 2,291 4,727 3,585 2,778 1,377 4,984 WW-3 6,886 6,457 6,426 5,801 4,437 9,139 301' 6,387 5,619 5.032 4,853 5,185 6,020 WW-4 6,410 316' 6,456 4,197 4,392 9,797 12,197 5456' 9,703 5,586 2,604 2,562 6,390 WW-6 3.134 2,904 2,652 _ 1,109 772 1,540 0' 0' 9,707 6.648 7,131 8,546 4,414 WW-7 2,834 2.837 2,746 2,833 2,697 2.846 3.142 3.228 3,379 3,361 3,410 3,319 3,053 WW-8 2,417 2,132 1,859 1,924 1,374 1,407 1,285 1,542 1,671 2,053 2,825 3,637 2.011 WW-11 15,487 15,409 20.719 14,106 9,096 11,082 19,864 20,572 22,702 23,569 24,360 25,540 18,542 WW-12 21,618 20,073 19,298 17,612 16,304 16,493 18,520 22,127 25,787 25,024 27,154 26,044 21,338 WW-13 95,023 103,477 95,641 92,821 87,873 83,669 87,047 92,093 99,110 81,034 78,145 95,385 90,943 LCC1 17,600 16,491 15,128 14,055 12,552 12.259 12,547 13,439 14,995 17,297 18,965 18,907 _ 15,353 r UN 38,617 46,818 _ 60,228 61,259 61,074 60,462 33,159 44,961 40,929 39,695 39,230 38,874 47,109 - SB 35,143 35.673 31,928 30,866 37,056 43,714 58.982 50,646 46,495 47,142 44,930 44,000 42,215 Thyme(SG) 11,677 11,687 10,901 11,279 11,695 13,798 14,471 _ 13,005 13,762 11,501 6,605 5,760 11,345 Total/period 8.2x106 6.2x108 83x108 79x108 69x106 84x106 9.5x108 7.9x108 6.5x108 11x108 5 6x 106 8.1x106 *pump temporarily out of order part or all of period Total(gallons) 9.4 x 107 Well production data for each sample period given in average gallons per day. Total(m') 355,664 \/4,\ 2S l Q-5 w w 34 the landslide(Ehlig, 1979)resulting in a saturated thickness at the boundary of-' 12 meters(40 feet). Based on nature of subsurface materials and previous studies(Proffer, 1992)the estimated hydraulic conductivity of the Altamira Canyon subsurface basin is 0.08 to 0.12 m/day(2 to 3 gpd/ft). Based on groundwater flow maps(Ehlig, 1992),the average hydraulic gradient at the boundary is 0.08. The resulting calculation yielded an estimated range of subsurface outflow from the area of 2,387 to 3,581 m3/year(- 1 to 3 acre-ft/year). This estimate is based on the assumption that there is sufficient hydraulic head to promote outflow. The pumping of groundwater from upgradient wells would likely decrease the hydraulic head within the groundwater body,therefore the above outflow amount represents a maximum range of flow across the lower boundary. Flow Along the Abalone Cove Head Graben During most times of the year,a component of water flows from the Altamira Canyon basin toward the Portuguese Bend basin via the head graben of the Abalone Cove landslide. This flow of water is estimated at-20,000 gallons/day(-76 m3/day)and could reverse during times of heavy rainfall (P.L. Ehlig,personal communication,August 1999). For this annual calculation it was assumed that flow continued in the direction away from the Altamira Canyon basin and totaled 27,740 m3(-'23 acre-ft)for the study year. The annual subsurface budget of the Altamira Canyon basin is illustrated in Figure 9 and summarized in Table 9. Net change in groundwater storage: -1.48 to -0.16 (105m3) (-120 to -13 acre-ft) Upslope infiltration 4 to 37% Canyon fissure recharge 49 to 75% Domestic Water Pumping wells 14 to 21% N 92% J. .,-— Approximate groundwater level {1991) 4110 =.-- Flow along Abalone Cove head graben \Basal Rupture ^) 7% Subsurface outflow Surface 7 �0 N 1% Figure 9. Altamira Canyon groundwater budget for 1997-98. Striped arrows show percent input to groundwater body and shaded arrows show percent output. Pumping and infiltration are distributed across the canyon and not localized(as indicated). Percentages represent percent contribution of each component to their particular category of input or output. N 36 TABLE 9.GROUNDWATER BUDGET FOR ALTAMIRA CANYON(1997-98). Subsurface Budget Component Volume(105 m3) Volume(acre-ft) %Contributions Input—Canyon recharge • 1.8 146 —49—75 Upslope infiltration 0.1 — 1.4 8—113 —4—37 Domestic water 0.5 41 — 14—21 Total Input 2.4—3.7 195—300 Output—Pumping from wells 3.6 289 —92 Subsurface outflow 0.02—0.04 1-3 — 1 Flow along the head graben 0.3 23 —7 Total Output 3.86—3.88 313—315 Predicted change in groundwater storage: -1.48 to-0.16 -120 to-13 *%Contribution indicates the percentage of a particular component within each input or output category (ex."pumping from wells"component constitutes—92%of total output). PORTUGUESE BEND BASIN—SURFACE WATER BUDGET Input Variables Rainfall rip Total rainfall for the study year in the Portuguese Bend drainage area was calculated in the same manner as that of Altamira Canyon and totaled— 14.8 x 105 m3 (1,200 acre-ft). Landscape Irrigation Total reported water consumption in the Portuguese Bend area for the 1997-98 study period was 18,408 m3 (— 15 acre-ft). Water consumption in the Portuguese Bend basin for the month of February totaled 756 m3 (0.61 acre-ft). By applying the same assumptions discussed for Altamira Canyon,the study-period-amount of household consumption would total 9,072 m3 (—7 acre-ft)leaving 9,336 m3(—8 acre-ft) for irrigation and subsequent evapotranspiration. 37 Output variables Surface Outflow The surface water budget calculation for the Portuguese Bend basin is less straightforward. Prior to landslide activity,three primary canyons drained water from the upper hillside areas,through the current landslide area to the ocean. Landslide activity has significantly modified this drainage pattern and currently no canyon completely traverses the area. Any surface drainage is conducted from the area by half-open,steel corrugated pipes on the ground surface. It was therefore not possible to conduct runoff measurements such as those obtained in Altamira Canyon. For the purposes of these calculations, it was assumed that the percentage of total rainfall leaving the Portuguese Bend basin was similar to that measured in the Altamira Canyon basin(—5%). For the study year,this would total- 0.7 x 105 m3(57 acre-ft). Evapotranspiration Evapotranspiration calculations for the Portuguese Bend basin were conducted in the same manner as those for the Altamira Canyon basin. The areal extent of the basin is 2.5 km2(618 acres)and the estimated amount of water lost to evapotranspiration from this area over the study period ranges from- 13.1 x 105 to 13.4 x 105 m3(1,062 to 1,086 acre-ft). Including the amount of irrigation water lost to evapotranspiration,the total volume of water leaving the surface basin as evapotranspiration is estimated to range from- 13.2 x 105 m3 to 13.5 x 105 m3(1,070 to 1,094 acre-ft). 38 a Loss to Subsurface Landslide activity has created many surface fissures which could allow runoff to move very quickly into the subsurface. Because surface drainage is so disrupted,much of the water remaining at the surface accumulates in depressions where it remains until it evaporates or infiltrates into the ground. In order to balance the surface water budget,it is estimated that—0.7 x 105 to 1.0 x 105 m3(57 to 81 acre-ft)of rainfall entered the subsurface of the Portuguese Bend basin during the study year. The annual surface water budget is summarized in Table 10. TABLE 10.SURFACE WATER BUDGET FOR PORTUGUESE BEND(1997-98). Surface Budget Component Volume(105 m3) Volume(acre-ft) %Contribution Input—Rainfall 14.8 1200 —99 Landscape irrigation 0.1 8 — 1 Total Input 14.9 1208 100 Output—Surface runoff 0.7 57 —5 Total evapotranspiration 13.2— 13.5 1070— 1094 —88—90 Infiltration/fissures to subsurface 0.7— 1.0 57—81 —5—7 Total Output 14.9 1208 100 D. PORTUGUESE BEND BASIN—SUBSURFACE WATER BUDGET Input Variables Infiltration and Fissure Recharge As stated above,an estimated—0.7 x 105 to 1.0 x 105 m3(57 to 81 acre-ft)of rainwater falling in the Portuguese Bend drainage basin enters the subsurface via infiltration or down surface fissures. This total amount of recharge from precipitation to the groundwater system represents—5 to 7%of total rainfall over the basin for the 1997-98 study period. 39 Domestic Water Assuming similar household water usage as in the Altamira Canyon basin,it is estimated that a total of 9,072 m3(—7 acre-ft)of water were contributed to the groundwater system via septic system recharge. This volume constitutes—6 to 8%of total input to the groundwater system. Flow Along the Abalone Cove Head Graben Water is also assumed to be entering the Portuguese Bend groundwater basin via the connection between the two basins at the head graben of the Abalone Cove landslide. The total estimated input is 27,740 m3(—23 acre-ft). Output Variables Pumping of Groundwater A total of 22 wells are present in the Portuguese Bend for potential removal of groundwater(Table 11). Removal of water in this basin is more difficult that in the Altamira basin for several reasons. Because of the increased landslide activity in the Portuguese Bend area,subsurface material has been significantly altered both physically and chemically,producing clay-rich material with increased porosity but decreased permeability. This decrease in permeability slows the retrieval of water from the subsurface via pumping wells. In addition,increasingly finer-grained material can pass through the screens in the wells,eventually filling the wells with sediment or clogging the pumps. As a result, groundwater removal is not as productive in this area. Approximately 13 of the wells remained operational throughout the entire study period. . _ 400,..J TABLE 11. DEWATERING WELL PRODUCTION IN THE PORTUGUESE BEND BASIN (1997-98). Well 8/25.9/24 9/24-10/29 10/29-11/21 11/21-12116 12/16-1/13 1/13-2/6 2/6-3/9 3/9-4/13 4/13-6/11 6/11--6/9 6/9-7/13 7/13.8/6 8/6-8/31 `Study Period W6A 12,284 11,086 9,790 9,196 8,025 8,052 7,777 7,763 8,361 10,471 13,094 14,945 14,728 10,429 W6B 400 391 387 380 375 370 81 31 232 459 401 336 424 328 W61 39 27 0 0 0 0 0 0 0 0 0 0 0 5 W6J 1,350 639 123 626 688 0 0 0 0 0 - 0 0 286 W6K 987 0 2,709 1,541 1,425 1,360 1,303 1,314 1,226 1,334 1,226 1,241 1,265 1,302 FW 4,394 2,951 2,692 2,198 1,739 1,575 1,468 1,501 1,818 2,268 - 6,782 7,184 3,048 FSW 510 0 409 194 896 756 713 584 449 615 610 582 454 521 INE 0 0 0 0 0 0 0 0 0 - 438 461 470 114 IEC 0 0 0 0 0 0 0 0 0 0 0 - 242 20 ISE 321 253 293 277 300 304 88 15 195 339 327 319 318 258 IW 117 19 38 66 2 1 32 41 68 83 - 256 267 83 N 1.423 1,389 1,343 1,284 1,250 1,230 1,178 757 1,239 1,255 1,238 1,125 1,152 1,220 P 38 0 0 0 0 0 0 0 0 - _ 2,148 1 292 207 T 776 739 820 904 954 1,047 1,002 963 584 0 1,127 1,648 564 856 W sump 0 0 0 0 0 0 0 0 0 0 0 171 19 15 C sump 385 349 340 329 336 327 368 16 0 646 542 507 468 355 E sump 0 0 0 0 0 0 0 0 0 0 387 329 302 78 PTG 1,861 1,718 1,726 1,476 1,583 2,022 1,782 1,806 2,134 2,253 2,058 912 1,763 1,776 W971&2 580 441 263 256 278 308 337 297 586 547 535 522 512 420 W973 - - 501 371 1,140 1,019 1,351 937 690 527 477 404 65 680 LT - - - - - - - - - 188 36 25 21 68 W98E&W - - - - - - - - - - - 170 80 125 Total/period 7.6x105 7.0x105 4.9x105 _ 4.8x105 5.3x105 4.2x105 5.6x105 5.6x105 4.9x105 6.1x105 8.4x105 7.4x105 7.6x105 Total(gallons) 8.0 x 105 Well production data for each sample period given in average gallons per day. Total(m ) 30,091 .p 0 41 These wells,combined with partial operation of other wells,produced a total of 30,091 m3(—24 acre-ft)of water over the study year. Subsurface Outflow Subsurface outflow was conducted using the same method employed above with the following parameters: L=— 1,372 meters(4,500 ft);b=— 15 meters(50 ft);K= 0.008 to 0.08 m/day(0.03 to 0.26 ft/day); and Ah/Ax=0.15. The K values were selected to represent subsurface materials ranging in composition from silty to clayey soils(Fetter, 1988). The annual calculated range of subsurface outflow was 9,325 to 93,252 m3/year (—8 to 76 acre-ft/year). Subsurface outflow is dependent on the presence of sufficient hydraulic head to drive the flow. Should a sufficient hydraulic head be absent,the CI amount of water leaving the area at the lower basin-ocean boundary would be possibly decrease below the above range. The total estimated subsurface budget of the Portuguese Bend basin over the study period is illustrated in Figure 10 and summarized in Table 12. TABLE 12.GROUNDWATER BUDGET FOR PORTUGUESE BEND(1997-98). Subsurface Budget Component Volume(105 m3) Volume(acre-ft) %Contribution* Input—Recharge/Infiltration 0.7- 1.0 57—81 66—73 Domestic water 0.09 7 6-8 Flow along the head graben 0.28 23 21 —26 Total Input 1.07-137 87—111 Output—Subsurface outflow 0.09-0.93 8—76 25-76 Pumping from wells 0.3 24 24—75 Total Output .39-1.23 32—100 Predicted change in groundwater storage: -0.16 to 0.98 -13 to 79 Observed change in groundwater storage: 0.7 57 *%Contribution indicates the percentage of a particular component within each input or output category (ex."pumping from wells"component constitutes—24-75%of total output). t Net change in groundwater storage: -0.16 to 0.98 (105m3) (-13 to 79 acre-ft) Fissure recharge/ Surface infiltration 66 to 73% Pumping wells 24 to 75% s, ? Domestic Water 6to8% 11 alms.. s�IVkau li \ Approximate groundwater .:46,"1".' level (September 1996) iii 41 Flow along Abalone Basal Rupture Cove head graben Surface 21 to 26% Subsurface outflow 25 to 76% Figure 10. Portuguese Bend groundwater budget for 1997-98. Striped arrows show percent input to groundwater body and shaded arrows show percent output. Pumping and infiltration are distributed across the canyon and not localized (as indicated). Percentages represent .N percent contribution of each component to their particular category of input or output. 43 E. GROUNDWATER AND LANDSLIDE RESPONSE TO RAINFALL Groundwater Levels Groundwater measurements collected over the 1997-98 study period were obtained from Dr. Perry Ehlig. Depth-to-water measurements were collected by Dr. Ehlig on a monthly basis from groundwater monitoring wells in the study area. Table 13 lists depth-to-water measurements in the Portuguese Bend monitoring wells during a two- year period, including the year-long study period. Monitoring well locations in the Portuguese Bend area are illustrated in Figure 11 and available well construction details are presented in Appendix A. According to Dr. Ehlig,there are three monitoring wells in the Abalone Cove area that are measured regularly but their proximity to pumping wells L1 makes the data less useful in assessing groundwater levels and movement(P.L.Ehlig, personal communication,August 1999). Groundwater elevations in the Portuguese Bend landslide range from— 102 meters(335 feet)above mean sea level(asp in the upper portion of the basin to—27 meters(90 feet)asl near the ocean. Kelvin Canyon Spring Discharge measurements from the Kelvin Canyon spring(KCS on upper part of Figure 7)were obtained and provided to me by the City of Rancho Palos Verdes. The measurements of surface runoff were taken at a weir by measuring the time needed to accumulate five gallons of water in a bucket.At least three measurements were taken during each sampling episode and averaged. The measurements obtained during the study period are listed in Table 14 and range from 9 to 33 gallons per minute TABLE 13. DEPTH-TO-WATER MEASUREMENTS IN THE PORTUGUESE BEND MONITORING WELLS Month Year Well No. Well elev. J-97 F-97 M-97 A-97 M-97 J-97 J-97 A-97 S-97 0-97 N-97 D-97 W2D 343 126 77 126 42 125 42 126 67 126 57 126 68 126 71 126 61 126.49 126.84 126.61 126.79 W4E 303 52 48 51 92 51 71 51 57 51 16 51 09 51 22 51 59 61.83 52.52 62.74 62.87 WLT 281 93 96 93 85 93 74 93 68 93 65 93.74 93 98 94 19 94.29 94.77 94.94 96.21 888-4 343 12 9 11 11 11 88 12.47 13 02 13 07 12 99 12 98 13.14 13,82 13.96 14.01 888-5 299 28 75 29 43 28 43 32.97 30 51 30.2 30 82 30 74 31.26 31.51 31.76 31.39 888-9 304 36 48 35 91 36 12 35 46 34 78 35 47 36 12 36 45 36.63 37.04 37.2 37.56 PBS-1 180 73 42 73 17 79 95 81 62 84 21 80 08 83 82 85 23 85.68 86.36 86.77 87.14 PBS-2 156 28.19 26.82 26 66 27 71 28.33 29 02 28.34 28 28 28.72 - - - PBS-3 216 96.47 95 59 94 93 94 45 94.38 94 06 93 87 93 67 93.72 93.81 93.87 94.63 PBS-4 249 77 36 77 23 77 13 77 02 76 45 76 28 76 29 76 21 76.98 76.41 76.28 76.68 PBS-5 288 68 48 67 76 60 24 52 93 52 32 52 11 52 39 52 51 60.69 50.63 50.52 60.66 PBS-6 310 50 54 48.28 48.29 47 94 47 91 47 92 47.96 48 01 47.94 48.24 48.32 48.39 PBS-7 299 10 81 2 22 5.72 7.3 8 72 9.86 10.78 11 88 12.39 13.16 13.24 13.67 P65-9 185 38.25 36 23 37 56 38.47 39.02 39 69 41 78 45 75 49.17 60.64 50.96 61.34 PBS-10 170 49 11 48 93 48 86 48 98 48 83 48 83 48 93 48.91 48.74 49.06 49.24 49.44 Well No. Well elev. J-98 F-98 M-98 A-98 M-98 J-98 J-98 A-98 A-98 S-98 0-98 N-98 D98 W2D 343 126.86 126.80 126.67 126.48 126.14 126.04 126.98 125.89 125 68 125 74 125 62 125 67 125 93 W4E 303 63.36 53.65 53.32 62.83 52.55 62.64 62.79 63.33 53 47 53 94 54 54 54 82 55 59 WLT 281 96.47 96.71 95.89 96.42 - - - - - - - B88-4 343 14.04 12.96 8.76 10.78 11.66 12.18 12.87 12.76 12 01 11 77 11 64 11 57 11.57 B88-5 299 31.47 - 24.92 29.22 30.52 31.43 3174 .. - - 888-9 304 37.74 37.95 37.32 36.08 34.02 34.52 34.9 35.04 35 02 34 69 35 41 35 82 36 12 PBS-1 180 87.31 87.34 85.86 86.91 79.48 - 87.1 86.28 87 29 87 31 88.23 88 64 88 99 PBS-2 156 - - - - - - - PBS-3 216 94.73 94.76 94.56 94.66 96.03 94.98 94.78 94.74 94 79 94.83 94.66 94 67 94.76 P8S-4 249 76.66 76.63 76.18 76.08 76.94 _76.04 76.21 76.04 76 06 76.28 76.38 76 69 77 04 PBS-5 288 61.70 63.24 52.36 64.64 53.08 58.66 60.2 60.04 58 15 55 9 52.28 51 74 51 61 PBS-6 310 48.49 48.44 47.46 46.86 44.92 46.18 46.81 46.91 46 89 47 47 13 47 27 47 39 PBS-7 299 13.97 14.74 7.39 6.03 9.26 7.03 8.03 8.72 9 33 9 92 10 53 11 23 11 91 PBS-9 185 51.76 61.89 60.12 48.94 48.67 48.21 48.09 48.08 47 87 47 89 47 89 48 02 48 24 P85-10 170 49.49 48.76 49.42 49.64 49.64 49.69 49.83 49.84 49 66 49 78 49 76 49 97 50 02 Bold entries represent 1997-98 study period. Wellhead elevations are presented in feet above mean sea level and water level measurements are in feet below mean sea level. See Figure 6 for well locations. 4i) 10 t.:, ...: :":41-:!..,..,1;4...wcgo::::::.z.....-::;;y1 \,,.... .,... -. ,....,.. ..,.......r:,...„-ve„, )iititt.7( ._. ,..,,, • 41..'•'' ..,_.::34;•::.:.-4.1.1,... 4 .•7:-.....,Z. ..;=i4.'ii'....,:..::.• . .44., Mitaltri';,:.:.3. 4;>`::.. .:i; 11.,.•-k .17* • ...-_,..,.... 1.t. : ''..2 ,•:,j'•\.,,4' ' .71'......rarliiff.:2;;^•::: ::.. •• *;:; -....:: : • Groundwater monitoring well ,.. ___ .." e.se olotf-:,.. ,,,, v. . ,....x..,_ :«, - .... ...4,44,_-,..:.:.-:.......,-. . :.. '!•::•----4kv.2. , :,:-.'‘ ::,...:,'.-,i; (7,1 -.H i ft• t.\ 417.7.Sif* .... - '''' *" 2 .1:—.. '' .:.'-±' ..`t.' .., ."•7'1K '.:1:1,.:7,. ..-:.4 .,.. , Ai... . 1. .:./' •-.., .6..... ' 1 . 9.\N.\.. : ..' -. :..,:.•=1,.,..! -.,... i. c--- 4 .... .„,,.... ..„.4* v4. Well in which groundwater .-..,.,:,.. ,$ .• „ „..::. ; , .....,.*..5' • 4 .' 1388 . `.`,„" • • c, , .1 iitl V.... : *`-ify- .,,.:'it .. :-. •: -kt,.::. i.' . „ •• N.... '''...,‘.';::' ,,,::; v•... :....i4 ,,2.•1 "* ,!...s4 . • ... • --.:.: . 1.4..: 1::.:::::, 'Y 7 levels rise within 1-3 months ..• •• .P•/ ,..-:... :;.''''t..). 911; t • B8-7 '',' --+.-., ' 'ir: following rainfall. - - •P.. r. , a'.,.A ' 0,es. ..-k. :::g: :, ...-211-ii,r,-'\' B88-9 ... N:41, ::••,', •4••;." $ ,,,,• • , _h, ?•:::-:,. t--- . _-gs4 •••:.% :•••:••:.„t-,%,. :'':s....:'"!..... • ..._: ,.i;';:;;; 4:::A"..., .../ j t....- vtta4yA IP , ,,,-.. . .- . ‘ tt7flif'PM,4!'4'..44'.?wr- ...?''..ii,:' "7: ....." (X1-3P'4W2WW4Eill''':A i • "4:::'... .."',7,- A Multi-stage, pneumatic piezometer . •if. ., ..7%k.:.:::. .:::..i ..,,,Zor„.., .:.-. ...-:-,.....,.,! :,..piliv ., -,-- '....t.:::.1...- 4:: •,:-.?-ir::::....,...54. • .:)3ift .... 'Aikedt:. ..,:,. .„-,e,,,. . .:. .:.,,.• ••,;;;....-; 44: ..; --...c,. ..e.r.,,,:u..),/;,---7:/a.L.." : -:::::,:::::.;,, .,..4;...4 i:;0.:,......... . ••••••1 • '..e4.....it,541F:,•..:'.... r' A 1.• s:•••• k;:ilt;Z:::7i ";....,,,-.& .,t i , ::. .-„:701, ....t::„. ....):,- ,:.....„-45,.PB8•4: et: Vi...;:-..."--:'.': . : ...i::.. ,.... .,•;-, . .• :..?;;P , .,,,.;:c• :;::.:,.,.: :-/erz,,,,,,:b lite•.:“...,..0;...... ' .....• .;:i5 .4:-.... 4 ,0 ligu:-: z, -,:, • .0,- iPBS•a ,q' •::::‘,„... .::::. .':-... .... : ' 4,..r4•;;;:,.... :::, .::::‘,........s.....:: :::::::',. , ..(.7:t.:'::::.::A... .1....."...7:`'';' PBS•lb...:\7P1 \''./. ...C42 06 ....... ''t i::.:('''' , :-..,.• , :.;::: •. .,...-........::::-....•.....,&:::.... ,:',::: P BS-1e4474 ,...'$' ::."...!?,-...'•' : ..:•..---•,.... ...,,:::•,.....„.... -.... ...:,:„.... ..../.ct,) •.) „..........,.t...4,..:::: ,:: 0,,,,...,...:.i.,.::::•.,, isZ:'" ••••.. / , 2 .. ,, ' ''•:, -,.:- , .! ,•, .;•':..i,--ks,`n•-- "., ft4.414,:..-.,-,>si,. f •..c..— - :..., -.1 .:7 =, ------ . ,:• „..... , 4 :..i,...-..,. 40. -... „, .,:::::;•.:: .:', , ,, • ,„t.A k,, :.- .....\\.i?,..- .,: zet. ,‘; • .. :' :-,, - •,. • i,: ,, •... 71i* .:„. ''.\ :,.1 ,7 , . 44110191119 t.4••TI y: . '''POOlt ' 7Alk .. ,•; \.„, N ,..:. ..• ... .... .. Volition Ilhi .. : : i,61:-.. 1000' s' -:." 1000 : •-4000 Feet .....:-.: '•:i ,..iii: •,. ... •.,:: • - • amomit 05 ,0 1 Kilometer um mm sing 1 Contour Interval 20 Feet Figure 11. Monitoring well locations in Portuguese Bend landslide. (See Table 13 for well data.) _0. ,.... 46 (51 to 182 m3/day). Unfortunately,the weir was non-functional during the months of January and February 1998 so no samples were collected during that time. A graph of the available discharge measurements versus time is shown in Figure 12 with the apparent maximum discharge occurring during the month of April. Response of Groundwater The response of groundwater levels to rainfall can be observed by examining hydrographs(plots of groundwater elevation versus time)of the Portuguese Bend monitoring wells(Figure 13). Several of the wells(PBS-3,PBS-10, WLT,PBS-4,and W2D)show no apparent increase in groundwater levels following the wet portion of the 1997-98 study period. Other wells(PBS-9, B88-9,PBS-6,and W4E)show modest and gradual increases of several feet which occur within or immediately-following the three months of peak rainfall in the area. Wells PBS-1,PBS-7,B88-5,and B88-4 show sharper increases of 1.5 to 3 meters(5 to 10 feet)within one to two months following peak rainfall (Figure 13). These four wells are in close proximity to major slide boundaries with PBS-1 located near the southeastern margin and the others near the head scarp(Figure 11). Well PBS-5 shows a trend which cannot be easily correlated with rainfall patterns. However,rises in groundwater levels in this well correspond to periods of time in which nearby sump wells were not actively pumping. Wells located progressively inward from the boundaries show slower response to rainfall with the innermost wells showing no significant response. It appears then,that despite the presence of smaller fissures in the interior of the landslide area, most of the 47 -t TABLE 14. DISCHARGE MEASUREMENTS AT KELVIN CANYON SPRING Date Readings (seconds) Average gal/sec gpm m3/day 11-Sep-97 27 25 27 26 0.2 11 62 09-Oct-97 26 25 25 25 0.2 12 65 20-Oct-97 23 24 23 23 0.2 13 70 23-Oct-97 27 30 29 29 0.2 10 57 04-Nov-97 28 27 28 28 0.2 11 59 17-Nov-97 35 31 31 32 0.2 9 51 16-Mar-98 13 12 13 13 0.4 24 129 17-Mar-98 14 14 14 14 0.4 21 117 23-Mar-98 9.4 9.7 9.6 10 0.5 31 171 26-Mar-98 9.6 8.3 9 9 0.6 33 182 30-Apr-98 10.5 10.4 10.3 10 0.5 29 157 14-May-98 12.9 12.8 13 13 0.4 23 127 01-Jun-98 12.9 12.5 12.8 13 0.4 24 128 15-Jun-98 12.9 12.3 12.9 13 0.4 24 129 13-Jul-98 15.6 15.3 15.9 16 0.3 19 105 27-Jul-98 14.7 15.4 15 15 0.3 20 109 18-Aug-98 16.3 16.7 17.2 17 0.3 18 98 (measurements taken in 5-gallon bucket) Ai 2501 - 250 200 200 ea E 150 - 150 a) - v) 100 3 100 aco .c_ N 50 50 0 _ LILA AA& rn rn rn rn rn a) rn rn rn rn rn rn rn Q (A 0 z o 5) U... g Q ca z Q Sample Date Figure 12. Graph of discharge measurements at Kelvin Canyon spring during the study period. Diamonds=spring discharge; triangles = rainfall. Spring discharge shows a peak- 2 months following peak rainfall indicating fairly rapid response of groundwater system to rainfall recharge. 120 48 1.100 Study 80 Period Ts• 60 40 N • 20 0 111111 I Ii, f 150 �,� R 140 • 130 cow 120 i• 110 • 100 v 90 II ♦ PBS-1 -40—PBS-3 -AM—PBS-9 Jll--PBS-10 —190 0160 m▪170 *160 1 60 ti 11111111111 8wti ti; as ti ' m m 4 O t 7 R "5 R 7al W g2 Z 2 "" O p A WLT tPM-4 Figure 13. Comparison of groundwater levels in the Portuguese Bend landslide with rainfall measurements collected during the study period. Groundwater elevations in well PBS-1 show a 1 to 2-month delayed response to rainfall. 120 49 9 00 Study „ 80 Period os 60 cea 40 3 20 0 ' LI iii 250 a LC. 240 El 230 W y 220 c 210 0 hi j 200 t W2D --i—PBS-5 300 c 290 > 280 W 270 w 260 250 -, *,,----r ✓ n n i. n ti n ao a) m m co a) co C) co C) co CO 0) 0) al C) C) C) ti t to Z -) 2 ck 0 0 — -W4E • B88-5 --i--888-9 --f—PBS-6 —W-PBS-7 Figure 13 (cont'd). Comparison of groundwater levels in the Portuguese Bend landslide with rainfall measurements collected during the study period.Groundwater levels in wells B88-5, B88-9,PBS-6 and PBS-7 show a "1 delayed response to rainfall. 120 50 100 E Study 80 Period 7 60 Y 40 • d ' 20 0 I 1111i1 � Ii , 0 c 350 0 34o d 330 f f - . 1-+d.ild=m 320 d t310 300 II T 1 1 1 1 1 1 1 1 o . n n►� ti ti rCO CO ao ao CO CO aw o� CA w CO w o) w C) CO a) CD 91- c t 3 d > c c 6 02 g Z - g - < 0 —f--888.4 Figure 13(cont'd). Comparison of groundwater levels in the Portuguese Bend landslide with rainfall measurements collected during the study period. Groundwater levels in well B88-4 show a delayed reponse to rainfall of 1 month. 51 rapid recharge occurs via the larger,bounding landslide scarps. This phenomenon was also observed by Ehlig and Yen(1997). Annual Storage for 1997-98 The predicted change in storage in each of the groundwater basins during the 1997-98 study year was estimated in the previously-discussed groundwater budget calculations. These calculations contain uncertainties in the estimation of evapotranspiration,subsurface outflow,and flow along the graben. However,the validity of the predicted change in storage can be evaluated by comparison with actual observed changes in groundwater levels during the same time period. Because functional groundwater monitoring wells are virtually absent in the Altamira Canyon basin,the only ` k"'' available groundwater level measurements are those from Portuguese Bend. The average groundwater level change throughout the Portuguese Bend basin during the study year was+0.07 m. Assuming a porosity of 0.35 (representative of silty to clayey lithologies)over the basin area of 2.5 x 106 m2, the observed change in groundwater storage during the study year was a gain of 0.6 x 105 m3. This value falls within the predicted range of values of-0.16 to 0.98(x 105m3)obtained from the groundwater budget calculations. The observation that the predicted storage closely approximates the observed storage suggests that the uncertainty in the selected evapotranspiration and subsurface runoff estimates used in the budget calculations was small. 52 Long-term Groundwater Budget A long term budget was calculated by examining input and output values for the water year 1995-96. This year was chosen because annual rainfall in the area was 12.74 inches,closely approximating the long-term average rainfall for the area of 12.9 inches. Based on budget calculations for the 1995-96 year,the Altamira Canyon basin is predicted to experience a loss in storage of—-2.4 x 105m3(Table 15)and the Portuguese Bend basin is predicted to experience a loss of—-0.8 to 0(x 105m3)(Table 16). This range in Portuguese Bend basin compares favorably to the observed storage loss of -0.4 x 105 m3 during 1995-96. Again,lack of monitoring wells in the Altamira Canyon basin prohibits comparison with actual observed groundwater level changes. I TABLE 15.LONG-TERM GROUNDWATER BUDGET FOR ALTAMIRA CANYON BASIN. Subsurface Budget Component Volume(105 m3) Volume(acre-ft) %Contribution Input—Recharge/Infiltration 0.4 32 --43 Domestic water 0.5 41 —57 Total input 0.9 73 Output—Subsurface outflow 0.04 3 < 1 Pumping from wells 3 243 —91 Flow along head graben 0.3 24 —9 Total output 3.3 270 Predicted change in storage: -2.4 x 105 -197 �1 53 • TABLE 16.LONG-TERM GROUNDWATER BUDGET FOR PORTUGUESE BEND BASIN. Subsurface Budget Component Volume(105 m3) Volume(acre-ft) %Contribution Input—Flow along graben 0.3 24 77 Domestic water 0.09 7 —23 Total input 0.4 31 Output—Subsurface outflow 0.09—0.93 7—76 < 1 Pumping from wells 03 24 —91 Total output 0.4—1.2 31—97 Predicted change in storage: -0.8 to 0 -66 to 0 Observed change in storage: -0.4 -32 A significant difference between the long-term budget and the study year(El Nino)budget is the percentage of recharge which comes from domestic water. During the 1997-98 study year, domestic water constituted— 14 to 21%of recharge to the Altamira Canyon basin. During an average rainfall year, domestic water makes up —57%of the recharge. The remaining—43%of recharge is provided through canyon fissure recharge during storm runoff and some surface infiltration. In the Portuguese Bend basin,—6 to 8%of the input to groundwater was contributed by domestic water recharge during the 1997-98 study year. By contrast, —23%of the recharge in an average rainfall year(1995-96)was domestic water. This estimate was based evapotranspiration calculations which indicated little to no recharge via infiltration or fissure flow. The amount of recharge expected via fissures and infiltration is difficult to constrain in the Portuguese Bend area. If significant fissure recharge did occur during an average rainfall year,the domestic water contribution would be less than the predicted 23%. Response of Landslide Mass The relations between rainfall,groundwater levels, and landslide movement in the landslide areas have been fairly well documented(Merriam, 1960;Easton, 1973;EhIig, 54 4 1986;Proffer, 1992; Ehlig, 1992). The Abalone Cove landslide exhibits little overall movement,mostly in the form of creep in the upper portion and near the beach. Previous studies have examined recharge by observing the response of groundwater(rise of water levels in wells)to rainfall(Proffer, 1992). Wells in the upper portion of the Altamira Canyon basin typically exhibit a delayed response to rainfall, extending from one to eight months. Some wells within the Abalone Cove landslide area were observed to have rapid responses due to the movement of water down open fissures. Movement of the Portuguese Bend landslide occurs constantly but increases in the rate of movement have been observed in conjunction with rainfall events. Easton(1973) observed movement of the Portuguese Bend landslide during two storms in November tand December, 1970. Each storm produced nearly a doubling of the rate of landslide movement. He also observed that the response of the landslide movement to even small amounts of rainfall(5 to 10 mm)was almost immediate(within a few hours). Figure 14 illustrates the relationship between rainfall occurrence and landslide movement of a survey monument located within the Portuguese Bend landslide(Ehlig, 1992). This fluctuating response of persistent landslides to rainfall events has been observed in other areas. Baum and Reid(1995)studied a smectite-rich landslide in Hawaii,observing that water movement through the slide mass is limited by the fairly impermeable slide base. In Hawaii,where rainfall occurs frequently,the slide mass remained fairly saturated year round. During periods of rainfall,pore pressures within the landslide increased significantly within one to two days following the onset of #it rainfall. The result was a diffusive propagation of pore pressure waves through the slide 55 so- • of - 50 u) 40- -40 L 30- . 30 20- • 1-20 — 10- - 10 0 . . • ,. ice• � —. 0 -10- __ . --10 Cumulative deviation of annual rainfall from 12.9 inches 12- -12 10- -10 a i 8' - 8 L 6 _ g U L.1 JAL Ali J.1.1111, ) il. II IL 1 1 1, {ii ii ►II .L.IJ�II1-11-i 11 i o 1.6- Monthly Rainfall -1.6 >,1.4- -1.4 0 1.2- P.,0,,, '::•-: -1.2 a`� 1.0 ,. 0.8 a-f a � '',r. �.-0.8 0.2f'k 1 _ 0 C e 3 s� za �.,a, ,,` a 0.2 0.0 � I, im1 o(_ 1rIM . r i'� "-tiimlaio1 _I ..4r.-,1si „ , �I 0.0 a s g a a Ci a w w P a w a a a a m ^ a T, a w m r. m Average daily rate of movement between survey measurements Figure 14. Graph showing relationship of rainfall to movement of the Portuguese Bend landslide between 1956 and 1986 (modified from Ehlig, 1992). Movement of the landslide is closely correlated to increases in rainfall. t • 56 mass to the slip surface,triggering landslide movement(Baum and Reid, 1995). Similar findings were reported in a study by Iverson and Major(1987)who observed that single rainstorms produced short-period pore pressure waves that attenuated before reaching the slide base,while seasonal rainfall cycles produced long-period waves that modified pore pressures at the base of the landslide. These pore pressure effects are significant in an already saturated slide mass such as the Portuguese Bend landslide. The clay-rich nature of the slide mass at Portuguese Bend creates conditions of high porosity but low permeability,allowing for retention of water for long periods of time. The water table within the Portuguese Bend landslide area typically occurs above the slide plane, creating an average of 40 feet(12 m)of saturated material above the slide R>"'Y base(Ehlig and Yen, 1997). Thus internal slide conditions are present for a pore pressure response to winter season rainfall events. While increased pore pressure seems a likely explanation for movement of the Portuguese Bend landslide,there is a question of potential pressure from beneath the slide base. It has been reported in previous studies that groundwater flow occurs entirely within the slide mass where the Portuguese Tuff serves as a barrier to vertical groundwater movement(Ehlig, 1979). To further investigate the potential for flow across the basal rupture surface,Ehlig and Yen(1997) installed multi-stage pneumatic piezometers in three locations within the landslide area(Figure 11). Two piezometers located in the northern portion of the landslide measured a higher piezometric level above the rupture surface than below,indicating negligible downward flow across the rupture titsurface. By contrast,the most southerly,downgradient piezometer measured 57 41/ approximately ten feet of hydraulic head beneath the rupture surface and none above, indicating potential for upward flow of water and/or associated hydraulic pressure on the underside of the rupture surface. These fmdings were preliminary but significant in assessing the potential driving forces for landslide movement(Ehlig and Yen, 1997). The extent of the upward trend is unclear and further work would be required to constrain its influence. F. SUMMARY In general,groundwater in the study area flows from the upper part of the topographic basin to the ocean where it has,in the past, been observed seeping from the toe of the slides during low tides. Since the inception of groundwater pumping,the - 1_7) seepage has not been observed(P.L. Ehlig,personal communication,Augit ust 1999). The two groundwater bodies are essentially independent with the exception of a small subsurface graben connecting the western edge of the Portuguese Bend landslide with the upper margin of the Abalone Cove landslide. Groundwater flow between the Portuguese Bend landslide and the Abalone Cove landslide along this trough has been observed(P.L. Ehlig,personal communication,August 1999). In both basins, analyses of water budgets indicates the majority of water entering the subsurface comes from rainfall via infiltration or direct recharge through surface fissures. For the study year,only a modest percentage(- 14-21%in Altamira Canyon and 6-8%in Portuguese Bend)comes from domestic water influx. However,this study year witnessed a rainfall amount(— 24 inches)that was approximately double the decadal 58 II average of 12.9 inches,and these domestic water influx estimates increase at least two- fold over the long term. The percentage of recharge contributed by infiltration versus surface fissure flow is difficult to assess. Aside from flow down the head scarp fissure within Altamira Canyon, it is likely that recharge via infiltration in the upslope areas is the more dominant process in the Altamira Canyon basin. The Abalone Cove landslide is smaller in area and its movement has resulted in less disruption of the overall ground surface in the form of fissures. The surface area of the basin is also more developed,resulting in more overland runoff from asphalt and concrete ground coverings. Both of these factors would decrease the amount of water which could rapidly recharge to the subsurface via fissure flow. The opposite is expected in the Portuguese Bend basin where extensive disruption of ground surface has produced multiple subslides and numerous surface fissures. The opportunity for rapid recharge is greater but the relative contribution of fissure recharge versus upgradient infiltration and inflow is difficult to constrain. Where rapid recharge does occur,it appears to be most prevalent along the larger,bounding landslide scarps. Based on water budget calculations for the 1997-98 study year,the Altamira Canyon basin groundwater budget appears to experience a net loss in storage ranging from-1.48 x 105 m3 to-0.16 x 105 m3 (-120 to-13 acre-ft). Predicted change in storage in the Portuguese Bend basin ranges from-0.16 x 105 m3 to 0.98 x 105 m3 (-13 to 79 acre-ft). The range is, in Iarge part, due to the difficulty in constraining the evapotranspiration factor. In addition, subsurface outflow may fluctuate and is difficult 59 t to determine. It appears,by comparison of the predicted storage values with those actually observed,that the uncertainties are rather small. . Groundwater plays a significant role in the persistent,long-term movement of the Portuguese Bend landslide. Although a few wells show a rapid response to rainfall in the area,most wells show a small,delayed or negligible response. Increases in overall landslide movement during high rainfall yearscould be explained by increases in pore pressure at depth. The potential for upward hydraulic pressure from beneath the slide plane requires further investigation because of its implications for landslide movement, even in areas with no apparent response to rainfall. 60 CHAPTER III GEOCHEMISTRY A. MAJOR ION CHEMISTRY The objective of the geochemical portion of the research was to employ both geochemical and isotopic techniques to constrain the contributions of various source waters to the overall groundwater body in the study area. In addition,important information was obtained on the sources of groundwater composition and on the approximate residence time of water within the groundwater system. Combined,this information presents a picture of the dynamics of groundwater recharge and movement, allowing consideration of the effects of groundwater on landslide movement. Rainfall Two rainwater samples were collected during the 3 February 1998 storm event and analyzed for major ion composition,the results of which are listed in Table B-3 of Appendix B. There is a large difference in the two results,reflecting a rainout effect. A weighted average of these data was obtained by multiplying the data by the percentage of . the storm they represent. These weighted values,along with the average data from Kadera(1997), are plotted in Figure 15. K, SO4,and HCO3 were below detection limits. Both sets of rainfall data parallel the seawater pattern(diluted—5,000 to 10,000 times), suggesting a strongly marine influence for rainfall in the study area. As a result of this influence,rainfall chemistry is dominated by Na and Cl. 61 100000.0 10000.0 E 1000.0 0 100.0 4.1 10.0 xrr c 1.0 O 0.1 0.0 K Na Ca Mg SO4 Cl HCO3 Major ions -•--wavg rain —u—Kadera avg rain -- seawater - domestic water Figure 15. Fingerprint diagram of major ion chemistry of rainfall and domestic water in the study area and seawater. Rainfall composition closely resembles a diluted version of seawater suggesting a marine source for precipitation. 62 IP Storm Runoff Runoff samples were collected from two areas during two separate rainfall events and analyzed for major ion concentrations(see Table B-2). Samples collected during the January 1998 event were relatively small in volume and only one sample from each area had sufficient volume to be analyzed for the major ion concentrations. Samples from the February 1998 storm were collected at intervals throughout the storm. All the runoff samples contain greater concentrations of ions than those reported for rainfall,about three times greater for Na,ten times greater for Mg,and fifty times greater for Ca. These increases in concentration probably reflect interaction with surface material during runoff through the canyon. Domestic Water Four water samples were collected over the study period and the results of chemical analyses are provided in Table B-2. According to Mr.David Delsigne,of the California Water Service,domestic water provided to homes in the study area is obtained from the Metropolitan Water District and is composed of an approximate 50-50 mix of water from the Colorado River aqueduct and from the northern California State Water Project. This approximate mix has been maintained over the past eight years. With the exception of sample DW2-12-1,which has an extraordinarily high Na concentration,all the samples are similar in composition. The Na concentration of DW2-12-1 isnearlyseven times the average of the other three samples. The Na measurements on that sample were repeated several times with similar results. However, this sample is so far outside the standard deviation of the sample population,that it was 63 disregarded for this interpretive analysis.Average domestic water values are plotted on the fmgerprint diagram in Figure 15. This plot reveals that the average domestic water chemical composition is significantly different from that of seawater and rainwater. Groundwater Major element ion concentrations in groundwater are helpful for distinguishing various water types and potential water-rock interactions. Based on preliminary observations,the groundwater in the study area occurs as two distinguishable bodies underlying the two prominent drainage basins. Limited interaction between the two bodies occurs along the head graben of the Abalone Cove landslide. Groundwater samples were collected on a monthly basis from 21 pumping wells ti=r throughout the study area(Figure 7). All sampled wells were equipped with a faucet near the wellhead. Most wells were continuously pumping and water was allowed to flow from the faucet for approximately 1 to 2 minutes prior to the collection of a sample. If a well was not continuously pumping,it was turned off for a period of time to allow for water to accumulate in the well. The period of time ranged from 5 minutes to several hours depending on the well. Water samples were also collected on a bi-monthly basis from Kelvin Canyon spring(Figure 7). Spring samples were collected from two areas:the middle of a small surface stream,and from seepage emerging from between sedimentary layers in the side wall of the canyon. While both sets of samples were analyzed,it is assumed that the sidewall samples are the most direct measurement of subsurface water and more indicative of groundwater composition. The isotopic and chemical composition of 64 surface water can vary as a result of interaction with surface materials and evaporative processes in the atmosphere. All groundwater samples were collected in a plastic beaker and measurements of temperature and conductivity were taken immediately. Temperature and conductivity measurements were taken for each sample at the time of collection using a portable conductivity meter. Samples to be analyzed for major ions and nitrates were filtered through 0.45 µm syringe filters and placed in a cooler of ice. Upon returning to the lab, samples to be analyzed for cations were acidified with 600µl of 6N HC1. Nitrate samples were transferred to a freezer at the lab and the remaining water samples were refrigerated. Average annual values of temperature and conductivity for the wells and the spring were calculated and are presented in Table 17. Temperatures ranged from 21°C at well WWII and Kelvin Canyon spring to 27°C at well EB. In general, average temperatures in the study area tend to increase downgradient with the highest temperatures occurring near the ocean. The exception to this trend is beach well CB with an average annual temperature of 23°C. Annual average conductivity values range from 3,913 µmhos at well WWII to 9,433 µmhos at well W6K. Well CB also exhibits a high average conductivity of 9,375 µmhos. The major cations of calcium,magnesium,sodium,and potassium were analyzed by the author at the University of Southern California(USC)using atomic absorption spectroscopy(AAS). An air/acetylene flame was used to analyze sodium and potassium, while calcium and magnesium were analyzed using a nitrous oxide/acetylene flame. All TABLE 17. SUMMARY OF AVERAGE CHEMICAL AND PHYSICAL DATA FROM GROUNDWATER SAMPLES elev.of elev.of avg. Sample Well Temp. Cond. No. elev.' (°C) {µmhos) Cat Na Mg K Cl SO4 HCO3 Si023 NO3 TDI4 61808 3H6 well slide daily boftomt base' prod.? Comments KCS 770 21 3420 18 9 20 1 7 36 9 588 0 101 -5.7 1.2 - osl - LCC1 415 23 4486 26 16 18 7 1 13 , 43 7 482 0 125 -6.3 7 na 267 osl 58 , UN 404 23 4378 22 11 25 0 13 42 9 606 0 123 -5.8 1.8 224 osl 178 WW13 386 22 4189 22 15 23 0 13 39 8 606 0 121 -6,1 3.2 273 osl 344 WW12 383 23 4757 22 20 21 1 13 47 7 544 0 131 -6.3 na 257 osl 81 SG 364 7 23 4245 , 23 15 23 0 7 13 41 7 9 629 0 124 -6.0 na 164 osl 43 SB 364 23 4150 23 11 25 0 12 41 9 708 0 121 , -5.9 na 184 osl 160 WW8 350 23 4332 23 11 27 0 16 39 8 540 0 125 -6.0 na unk osl 8 WW11 315 21 , 3913 20 12 , 20 0 14 36 8 482 0 111 , -6.2 , na 199 osl 70 WW3 279 24 4228 23 14 22 0 11 43 7 537 0 120 _ -6.0 na unk 117 23 WW4 221 22 ' 4398 25 17 , 25 0 11 47 8 506 0 133 -5.9 1.2 137 140 24 WW2A 170 26 4302 22 16 21 1 9 44 7 529 0 120 -6.4 na unk 10 19 sulfide smell,some EB 86 27 8192 4 69 20 2 28 , 62 9 535 0 194 -6.0 <0.8 -59 -20 31 seawater influence CB 64 23 9375 19 , 38 85 1 33 108 7 369 0 292 -6.1 3.7 -69 <-80 221 some seawater influence W6A 386 22 4689 28 16 23 0 16 45 7 ' 682 0 134 -6.7 na 226 unk 39 N 377 23 6124 26 18 26 0 16 60 6 663 1 143 -6.9 3 unk 233 6 FW 373 23 6177 29 , 17 28 , 0 20 , 49 _ 7 594 1 151 -6.3 na 261 unk 12 , W973 355 23 5564 27 23 33 1 18 63 11 372 0 166 -6.4 na unk unk 3 PTG 184 26 6623 21 27 24 1 _ 9 , 55 7 626 0 , 144 n -6.6 na unk unk 7 yellow color,possible W61< 181 26 9433 27 24 , 126 0 24 118 3 77 4 324 -6.0 81 71 -61 6 animal waste influence ISE 179 26 8400 34 20 63 0 42 49 6 355 16 219 -6.7 4.6 7 -0 1 possible fertilizer influence FSW 167 26 ; 6010 31 22 27 0 24 61 6 427 2 164 -6.6 na . 60 -60 2 DW - - - 3 7 2 0 2 4 2 59 0 20 -11.3 6.5 - - - Average values for domestic water(DW)are also included for comparison. Entries in bold are from the Portuguese Bend basin. (unk=unknown value) Notes: 1 Wellhead elevations expressed at feet above mean sea level(ft asp. 2 Major ion concentrations expressed as milliequivalents per liter(meq/I). 3 SiO2 concentrations expressed as micromoles per liter(1iPM) °TDI=total dissolved ions in meg/I. 6180 concentrations expressed in parts per thousand(%o). 6 Tritium concentrations expressed as tritium units(TU)where 1 TU= 1 3H per 1010 hydrogen atoms. cN Average daily well production is expressed in m3 per day. 66 t''' samples were diluted to within the detection range with a 1,500 ppm cesium ionization suppressant. Chloride analyses were also conducted at USC using coulometric titration. All the above results(except where noted)are within 3%uncertainty. Exceptions are within 10%uncertainty and were typically the result of small sample size or low ion concentration. Nitrate and SiO4 were analyzed by the Upper Ocean Process Lab operated by Dr. Burt Jones at USC. The analyses were performed using a continuous-flow analyzer according to the methods described in the 1996 Joint Global Ocean Flux Study,Report 19(SCOR, 1996). Sulfate and bicarbonate analyses were conducted by M.J. Schiff& Associates,Inc. of Upland, California. %i► Results of chemical analyses of groundwater samples for major ions are included �� in Table B-1 in Appendix B. The yearly averages for the major ions are listed in Table 17 and were plotted on a trilinear Piper(1944)diagram(Figures 16 and 17),along with plots of the average concentrations of domestic water and rainwater samples collected during the study period. Average seawater composition(Goldberg et al., 1971)is also plotted on Figures 16 and 17. Comparison of the resulting plot with the classification scheme in Figure 18 reveals that the majority of the groundwater in the study area is dominated primarily by SO4 but,with the exception of wells EB and CB, contains no dominant cation type. Groundwater in wells EB and CB is dominated by Na and Mg, respectively. Total dissolved ion concentrations range from 3,435 to 9,163 milligrams per liter(mg/1). t 67 i. Piper Diagram - Abalone Cove Wells A •Abalone Cove Wells =�=� Well Domestic ess tic Water ^ ® Rainfall . 9-.-�,Y�' k ov ® Seawater �A '. (Syrnbds oepresentyealy CO A AVATA A 0 averam concenbaticns in%me41) A A CAVAI►��I%'I "AL AVA M g V��V SO 6V VAVAT'9 A ail 9A��AVA`a wAyAw amort' dAYA 4YAVA � VAV ATA At AWAW�A VA. AYAJ A A AAAYAY�A, Ca 80 60—40 20 Na+K CO3+HCO3 20 40--17-60 80 Cl Ca . CI CATIONS ANIONS Figure 16. Piper tri-linear diagram for wells located in the Abalone Cove landslide. Groundwater is classified as a sulfide-type and is relatively constant in composition. Well EB is the exception and plots in the vicinity of seawater and rainfall compositions. 68 OA i Piper Diagram - Portuguese Bend Wells A • Portuguese Bend Wells &--GS Q Domestic Water AV Ak ® Rainfall ® Seawater ,941. LAT, ; (S,is representyealy O /All. 1' k ge averaoonceltmatlms in%meo,4) Cl p AL.�1, A Ave r9A. voli6 AYAVAYATAY f. �►A YAVAVAVAVAVAWW AVAY Mg ': :::::::A AVff 1 504A �AV�a Yom ,A ��VAYA p o (8)A.:::. 1 te...... 6 ��SwA .0::�' .► LA A Vo A��r� A (9A��rA��ATAYA,a ��AVAt vsr Ai A TA r ATAi TA IA A TA��'I��I►��A, Ca 80 60 —40 20 Na+K CO3+HCO3 20 40--p--60 e0 —CI Ca CI CATIONS ANIONS Figure 17. Piper tri-linear diagram for wells located in the Portuguese Bend landslide. Groundwater is classified as sulfide-type and exhibits a wider range in composition than groundwater within the Abalone Cove landslide area. Q". 69 / \ 0 / \ •, Y. p man x /\`� o / \ try. , ' r9 / p \ Ta / � \ / o \ 1\ c. /\e A \ / \ x / Mg \ "'—V .� / �' SO4 Is / x %\ / \CP lb - O 2 4 c\ • /-/ �G Sulfate Magnesium \ / p • v ��i � type x �o \ / `� X o, type Y. � 7 \I is \ / 0 'V ° P \ No / oo /\ \ No / o • \ dominant / \ dominant / \ /Sodium ��typetype o Calcium \ / P potassium Bicarbonate Bicarbonate / c0 \ / Chloride . type \ / type type \ / type Ca 80 60 —40 20 Na+K CO3+HCO3 20 40--p- 60 80 CI Ca CI CATIONS ANIONS Figure 18. Hydrochemical classification system for natural waters. Q f . © 70 Siinilarilics and differences n7 chemical composition can also be seen in lintierprint diagrams Uf major ions (Figure 19). The Altars ira Canyon wells show ion concentrations etre fairly tightly clustered. The most variation occurs in the tnottovale it ions ofK. and Cl. The Portuguese Bend wells show minor differences, with the exception of well W6K, which has a higher Mg concentration. Of the two beach wells, CB resembles well \VGK. in composition and ELI exhibits a pattern unlike any other. Figure 20 shows the major ion concentrations of the beach wells compared to those of'seawater. The cation concentrations in well EB are parallel but diluted patterns i ilea compared to seawater. However,the anion concentration patterns are dissimilar, with seawater showing significantly high Cl coneentrotions compared to well L'13, The different, but very consistent,chemical composition in well E13, along with warmer average temperatures and a strong sulfide smells suggest that groundwater in the vicinity of this well may reflect a source or body of water which is different from that tapped by the other wells in the area. Kaden (1997)used strontium isotope ratios and the higher temperatures in well EB to conclude that water in this well represented a hybrid mix of groundwater within the landslide,seawater,and water which circulated much deeper within the peninsula. Evidence of deeper, warns water circulation has been found elsewhere on the Palos Verdes peninsula in the form of coastal, hydrothermal springs. 'lie influence of seawater is also apparent in association with well C13. Well CB is a nested well, with an adjacent one-inch-diameter pipe (CI3A)which extends to a depth below the Abalone Cove slick,plane. As with well Eta, which also terminates below the slide plane, Mc cation concentrations in well CBA show parallel, yet diluted patterns .•._ l000 Altamira Canyon 71 f 100 - K45 Na Ca Mg SO4 CI HCO3 Major ions -4-WW2A-avg ••-9_,LCC1-avg —33E—WW4-avg —0—WW3-avg --1—SG-avg —e—WW1 2-avg --M--•UN-avg —0—WW1 3-avg —a—SB-avg —fr—WW1 1-avg —e--WW8-avg —♦—KCS-avg Portuguese Bend 1000 413 15 100 - a �. H � - ��- / . m 1 - K Na Ca Mg SO4 CI HCO3 Major ions -31E-W6A-avg t N-avg -I-FW-avg W973-avg -4--ISE-avg -410-FSW-avg -e-W6K-avg --Ar-PTG-avg -•-CB-avg Beach Well - EB 1000 4, 100 - . a N E 10 - m 1 - E K Na Ca Mg SO4 CI HCO3 Major ions —4—EB-avg Figure 19. Fingerprint diagrams of groundwater data from study area. Variation (, in Portuguese Bend composition could be result of adsorption effects. Well EB composition suggests possible deep-circulating water source. 72 1000 L 100 00,4 otli Q \ C CO i 7 CT aa) 1 - 0 1 r I I 1 I K Na Ca Mg SO4 CI HCO3 Major ions —o—EB-avg --E--CB-avg --is—seawater —x--CBA2 •••• ••••CBA Figure 20. Fingerprint diagram of beach well and seawater major ion concentrations. Groundwater in well CBA may represent a transition 466,.<. ,,,IIIPP mix between a lower seawater wedge and upper landslide water body. (Data on CBA and CBA2 from Kadera, 1997) • 73 compared to seawater concentrations suggesting that water beneath the slide surface in the vicinity of this well has a seawater component. The anion concentrations of well CBA show similar SO4 and HCO3 concentrations compared to wells CB and EB,but show Cl concentrations intermediate between the more shallow beach wells(CB and EB) and seawater. Water collected from the CB well,which terminates above the slide plane, has a composition more reflective of the other wells in the Portuguese Bend basin. The bottoms of both wells CB and EB terminate at a depth below mean sea level (Table A-1). The chemical behavior of chloride ions in groundwater tends to be fairly conservative (Hem, 1992). In the majority of the study area, chloride concentrations range from approximately 250 to 700 mg/1. Two areas of relatively high chloride concentration are observed surrounding wells EB and CB and well ISE near the coastline. Well ISE extends to a depth near mean sea level(7 feet above mean sea level). The chloride concentrations in well ISE may result from a combination of seawater intrusion and evaporative recharge as will be discussed in the stable isotope section. The one exception to this chloride observation in coastal wells is well PTG,which along with well WW2A,exhibit the lowest chloride concentrations in the slide area. The lower chloride concentrations may reflect dilution by domestic water. Nitrate analyses were performed on groundwater samples,and average values ranged from 0 mg/1 at the beach wells(EB and CB)to 971 mg/1 in well ISE. The average measured nitrate concentration in domestic water was 1 mg/l. The highest average nitrate concentration reported in the Altamira Canyon portion was 28 mg/1.The Portuguese Bend portion of the study area typically contained higher values,including 74 111, wells W6K and FSW with reported nitrate concentrations of 256 and 138 mg/1, respectively. Kelvin Canyon spring contained an average nitrate concentration of 4 mg/1. The presence of nitrate concentrations in many of the wells indicates probable domestic water influence. Nitrate is indicative of waste products and would be closely associated with septic system discharge. Wells FSW and W6K,which have higher nitrate concentrations than nearby wells are located in close proximity to a horse corral. The extremely high nitrate concentrations reported in well ISE are most difficult to explain. There are currently no buildings in the vicinity of the well. There are residences upgradient on the crest of the peninsula which are serviced by septic systems,but indications of domestic water input, specifically 5180 values more negative than—6.0, are not present in the well. According to local residents,well ISE is located in a former ir agricultural area near a former fertilizer storage location. It is possible that,during extensive regrading of the Portuguese Bend landslide,nitrate-laden soil was buried and is slowly leaching nitrates into the groundwater in the vicinity of well ISE. With some exceptions,the major ion chemistry of water in any given well remained consistent(within 10%deviation from the mean)over the 12-month sampling period(see Table B-1). Analytical uncertainties can account for—3%of the variations. The exceptions,in which more than two ions showed significantly greater than 10% variation, include wells CB and W6K. Well CB also shows unusual temperature variability. Fingerprint diagrams of these wells are shown in Figure 21. Well CB, located near the shoreline of Abalone Cove,showed fairly significant variation in Na, K and Cl over the study period,but only small variations in Ca,Mg, and SO4. Well W6K 75 CB 1000 1000 10 ar • 1 0 K Na Ca Mg SO4 CI HCO3 ions -+-CB-9-1 - -CB-1O-1 --*-CB-11-1 •-X-CB-12-1 -41E-CB-1-1 - -CB-3-1 -+-CBS-1 CB-5-1 CB-6-1 -*-CB-7-1 W6K 1000 I E 1 • V C U• 0 , K Na Ca Mg SO4 CI HCO3 ions -4-W6K-9-1 •••NI-•W6K-11-1 -a-W6K-12-1 ---1E-W6K-1-1 -*--W6K-2-1 W6K-3-1 i W6K-4-1 W6K-5-1 W6K-6-1 Figure 21. Fingerprint diagrams of major ion concentrations in wells CB and W6K over the sampling period. The fluctuations in Na and Cl in well CB may result from seawater intrusion. Well W6K appears to be influenced by two separate water sources. 76 (Figure 7)exhibits fmgerprint patterns showing two fairly distinct types of water. One type,with higher concentrations of the above-mentioned ions, appeared during the months of September and the following January and February.The two types are distinguished by variations in K,which could be explained by decomposition of animal waste, and Mg, SO4,and HCO3,which could be caused by differential weathering of subsurface materials. In order to better identify and discriminate among the potential influences on groundwater chemistry,multivariate factor analysis was conducted on the average major ion results for each well. This type of analysis results in a set of factors which can hopefully be used to explain interrelationships among a large number of variables. Figure 22 illustrates that results of the analysis,displaying the loadings of each variable on a specific factor. The loadings have numerical values between+1 and—1 and measure the extent to which each factor is associated with a particular variable. The closer the variable loading is to 1 (regardless of the sign),the greater the association of that variable to the factor. Factors were judged to be significant if their percent variance was greater than ten. • Kelvin Canyon spring is located in the upper portion of the Altamira Canyon drainage basin and would therefore be a likely candidate to represent groundwater at or near the recharge area for the basin. As a representation of recently-recharged rainfall, the spring water might be expected to most closely reflect the chemical composition of rainwater,although weathering may be important. As discussed earlier,rainfall 77 Kelvin Canyon Spr. Factors 1 2 3 4 +1 Ca, Mg SO4 Na Ca c Mg CI J CI CI -1 HCO3 Altamira Canyon Factors 1 2 3 4 +1 Na, SO4 Mg HCO3 Ca Mg,CI m K HCO3 Na HCO3 -1 K Portuguese Bend I Factors 1 2 3 4 +1 Ca Mg, SO4 Na c CI HCO3 HCO3 Ca Mg SO4 HCO3 Ca,Na Na • -1 K CI Figure 22. Factor loadings for major elements in water samples from the study area. Within each factor,the closer the variable (such as Na)is to 1(regardless of the sign),the greater the association of that variable to the factor. See the text and . Table 17 for an interpretation of the factors in each analysis. 78 4p composition reflects a marine source with the dominant ions being Na and Cl. The ion composition of water in Kelvin Canyon spring is enriched in K,Ca,Mg, SO4, and HCO3 relative to rainwater. Factor analysis of the spring water shows 4 dominant factors. Factors 1 and 2 show high loadings on Ca,Mg,and HCO3 suggesting weathering of subsurface dolomite material which is prominent in the study area. Factor 3 has a high loading for SO4 and an intermediate loading for Ca. There is abundant pyrite present in the lithologic units throughout the study area which can be oxidized to release SO4 as sulfuric acid. Oxidation occurring in the presence of calcite would proceed according to the following reaction: FeS2+3.7502+ 1.5H20+2CaCO3=Fe(OH)3 +2Ca2++2S042-+2CO2, r'''''' or, if CO2 does not escape and reacts further: FeS2+3.7502+3.5H20+4CaCO3=Fe(OH)3+4Ca2++2S042-+4HCO3. Weathering of dolomite is likely to release Mg as well as Ca. Factor 4 shows a high loading for Na,possibly derived from weathering of sodium montmorillonite in the subsurface. As stated earlier,the groundwater within the study area can be classified as sulfate-type. The weathering reactions discussed above will proceed in the presence of oxygen. At ambient air temperatures experienced in the study area,the dissolved oxygen concentration expected in groundwater in equilibrium with the atmosphere would be 200 pm(Truesdale et al., 1955). Based on the stoichiometric reaction,- 100 pm of SO4 will be produced for each 200 pm of oxygen. Concentrations of SO4 in groundwater ,i of the study area range from— 18,000 to 59,000 pm. In order to produce the amount of 79 4111. SO4 measured in the groundwater,large volumes of oxygen must be supplied. This must reflect interactions of gas,water,and solids in the vadose zone. Factor analysis of Altamira Canyon groundwater shows high loadings of Na and SO4 with an intermediate loading of Ca on factor 1 suggesting pyrite oxidation with some possible exchange of Ca for Na. As mentioned earlier,Ca adsorption is most likely to occur in uphill,highly weathered areas. Factor 3 has a high loading for Mg,and an intermediate loading for HCO3,once again supporting dolomite dissolution. Any variation present in ion concentrations in groundwater primarily effects the monovalent ions. This occurrence supports the process of adsorption in the study area because divalent ions are more easily adsorbed and therefore tend to vary less as a result of this buffering effect. The Portuguese Bend samples are more varied in composition and the factors are much more difficult to interpret. Again there are high loadings on Ca,Mg,and SO4 although not associated with the same factors. The high loading on K in factor 1 may be indicative of animal waste decomposition(there are numerous horses in the area)or past applications of fertilizer in the agricultural areas.This explanation is supported by significant concentrations of nitrate present in several Portuguese Bend wells. Because the lithology underlying Portuguese Bend is similar to that underlying the Altamira Canyon basin, any differences in groundwater composition may reflect variations in weathering patterns. For example, the SO4 concentrations in the Portuguese Bend area,which are even higher than those found in the Altamira Canyon basin,suggest one or more of several possible geochemical scenarios: 1)there is significant gas • 80 exchange within the vadose zone;2)there is potentially more material (i.e.pyrite) exposed in the subsurface; 3)more evaporative concentration has occurred; or 4)the residence time of water in the weathering zone is prolonged. The landslide activity has significantly disrupted the continuity of subsurface sedimentary units in the Portuguese Bend area creating the potential for more reactive surface area to be exposed to groundwater interaction. In addition,the low,and likely variable,permeability typical of disrupted, clayey landslide material would result in the potential for variable residence times of groundwater in the subsurface. A more detailed discussion of groundwater residence time is included in a subsequent section on tritium.Table 18 provides a summary of the factor analysis interpretation. The weathering relationships discussed above are also illustrated in plots of individual ion concentrations from wells in the study area versus TDI(Figure 23). A positive correlation is seen between TDI and the ions of Na,Ca, Mg,and Cl. A strong positive correlation is observed between SO4 and TDI as well as between conductivity and TDI. The HCO3 concentrations show a negative correlation versus TDI. In all plots, except Mg,SO4,and conductivity,ion concentrations from wells CB,EB,ISE,and W6K consistently plot separately from the trend exhibited by the rest of the wells. B. STABLE ISOTOPE CHEMISTRY As suggested by the hydrologic calculations,rainfall appears to be the primary source of recharge for the groundwater body in the study area. Recharge is inferred to occur via two primary processes: infiltration through the unsaturated zone and directly down fissures in the landslide body. The relative importance of these two processes can C)3! TABLE 18. FACTOR ANALYSIS INTERPRETATION Kelvin Canyon spring Factor No. Associated Elements Interpretation 1 Ca, Mg weathering of subsurface dolomite 2 HCO3 3 SO4 pyrite oxidation 4 Na weathering of montmorillonite Altamira Canyon groundwater Factor No. Associated Elements Interpretation pyrite oxidation in presence of calcite; Ca released 1 Na, SO4 exchanges for Na 2 K possible waste decomposition 3 Mg, HCO3 dolomite dissolution Portuguese Bend groundwater Factor No. Associated Elements Interpretation 1 K, Ca, Na waste decomposition,weathering of montmorillonite 2 Mg, SO4 pyrite oxidation, possible basalt weathering? 3 CI possible seawater intrusion Elements have their highest correlation with Factor 1, next highest with Factor 2, etc. 00 • 82 .-.:'Pe' 1.8 80 1.6 • • 1.4 • 60 • 1.2 -t- .13 1.0 m E 0.8 • • E 40 • Y 0.6 1° 0.4 • z 20 * . • 0.2 4. • • 0 100 200 300 400 0 100 200 300 400 40 140 •ISE 120 • 30 offr A. •W5K 100 c _ • • E 20 • • 80 v CB co 60 • 10 40 •EB 20 de• 0 , 0 , 0 100 200 300 400 0 100 200 300 400 50 140 :17,..?i - 40 _ • 120 • 100 • 30 • • • • 0 80 V 20 •• CD 40Ot. • 10 20 0 100 200 300 400 0 100 200 300 400 12 • 10000 •• 10 Tn 8000 "48: 8 A . 2 6 6)• • ? 6000 : 0 4 • c 4000 = 2 • v 2000 0 0 , 0 100 200 300 400 0.0 100.0 200.0 300.0 400.0 TDI(meq/1) TDI(megll) Figure 23. Yearly average concentrations of major ions and conductivity in groundwater plotted as a function of total dissolved ions. The correlations between Ca, ev.• HCO3,Mg, and SO4,and total dissolved ions(TDI)support weathering of subsurface dolomite and pyrite. 83 be evaluated using stable isotopes. Stable isotopes are excellent tracers of groundwater source and movement for two reasons: 1)the isotopes of oxygen and hydrogen are part of the water molecule and therefore will not act independently; and 2)in the environmental conditions of the study area, water isotopic composition can only be altered by evaporation or mixing with other waters. Water samples to be analyzed for stable isotopes were collected directly into plastic vials with polyseal caps to prevent evaporation and stored at room temperature. Analyses of oxygen and hydrogen isotopes were conducted in the Water Resources Division laboratory at the United States Geological Survey(USGS)in Menlo Park, California. Analyses for 5180 were conducted by equilibrating the water samples with CO2 in a shaking water bath for 9 hours(Epstein and Mayeda, 1953)followed by analysis on a Finnigan MAT 251 mass spectrometer. Reproducibility is 0.05 per mil. Samples were analyzed for hydrogen isotope ratios(ED) on a Finnigan Delta E mass spectrometer using the methods described by Kendall and Coplen(1985). Reproducibility is 1.5 per mil. Isotopic results are reported relative to the Vienna Standard Mean Ocean Water standard. • Rainfall This study was conducted during the 1997-98 El Nino event,one of the strongest on record. While this is beneficial in providing us with a worst-case scenario in studying the effects of rainfall on landslide movement, the question arises as to how representative the El Nino rainfall isotopic compositions are of typical rainfall years. To examine the possible isotopic variations in rainfall due to El Nino years,oxygen isotope records were 84 obtained from Santa Maria, California(IAEA/WMO, 1998). Eight full water-year(Sept- Sept)records were available and weighted annual 00 values are illustrated in Figure 24. As illustrated in the diagram,three significant El Nino events occurred during the subject years,with weighted 5180 values of-5.4, -6.4,and-4.9%o. These particular years do not represent a significant deviation from the overall weighted average 5180 value of rainfall of-5.4± 1.1 %o suggesting that El Nino rainfall events do not have significantly different isotopic averages. During the study period,at least one rainfall sample was collected at Station BD for each storm event and analyzed for 8180. As a result,-94.5%of total measured rainfall at Station BD,located in the approximate center of the Altamira Canyon drainage basin,was sampled. Sample collection dates,rainfall amounts,and stable isotope analytical results are listed in Table 19. As stated earlier,rainfall occurred during the months from November 1997 through May 1998. Rainfall 8180 values at Station BD ranged from-1.1 3.o to-11.5 %o with an annual weighted average of-5.7 %o. Table 20 lists the amount of rainfall and weighted monthly 8180 values for each month during the study period. Local variations in rainfall isotopic composition can occur as a result of seasonal trends, intrastorm and interstonn variations,and elevation changes(Dansgaard, 1964; Kendall and McDonnell, 1993). Seasonal trends are typically most apparent in temperate climates where rainfall occurs all year round and temperatures vary (Clark and Fritz, 1997). In the Mediterranean climate of the study area, rainfall primarily occurs during a ipp winter rainy season,thereby reducing seasonality. There is significant isotopicvariation 85 74 -3 • -4 - Weighted average • for 8 years=-5.4±1.1%o - _________......„...................._____..: ♦ CO CO t - N CI N ce) to V CO CO Co Co I� Water Year Figure 24. Stable isotope composition of rainfall in Santa Maria,California. El Nino years are indicated with arrows(WeatherNet4, 1999). El Nino events do not have significantly different isotope averages from non-El Nino events. TABLE 19. CALCULATED ANNUAL WEIGHTED AVERAGE 86 \'`` 6180 VALUES FOR RAINFALL AT STATION BD Sample No. Date gauge (mm) 6180 (%o) weekly wgted 5180 RD-1 13-Nov-97 -6.0 RD-2 13-Nov-97 16 -5.4 RD-3 14-Nov-97 12 -5.1 -5.5 RD-4 20-Nov-97 3 -2.2 -2.2 RD-5 26-Nov-97 12 -4.4 RD-6 30-Nov-97 4.5 -7.1 -5.2 RD-7 06-Dec-97 20.5 -2.8 RD-8 06-Dec-9744 6..6 cumulative for storm RD-9 07-Dec-97 12 -5.6 -6.4 RD-10 19-Dec-97 37 -5.5 -5.5 _ RD-11 05-Jan-98 13 -5.4 -5.4 RD-12 10-Jan-98 24 -4.6 -4.6 RD-13 14-Jan-98 3 -2.7 -2.7 RD-14 19-Jan-98 5 -1.1 -1.1 RD-15 01-Feb-98 18 -4.0 -4.0 RD-16 02-Feb-98 1:4 2.7 RD-17 03-Feb-98 20 . -6.3 collected at intervals RD-18 03-Feb-98 .:.24 -13.1 -.. :during same storm ., RD-19 06-Feb-98 12 -4.4 RD-20 08-Feb-98 32 -5.2 RD-21 09-Feb-98 27 -5.0 -6.5 ` i_i_i_l_ RD-22 16-Feb-98 47.5 -4.0 -4.0 RD-23 21-Feb-98 42 -11.5 RD-24 23-Feb-98 25.5 -2.5 -8.1 RD-25 25-Feb-98 43 -5.3 -5.3 RD-27 31-Mar-98 38 -42 several rains RD-28 01-Apr-98 22 -7.0 -7.0 RD-29 13-Apr-98 17.5 -6.6 -6.6 RD-30 05-May-98 17 -2.9 -2.9 RD-31 13-May-98 20 -5.3 -5.3 DCP-R1 04-Feb-98140 -6.3 DC-R1 04-Feb-98 :57 86 .:cumulative for storm BD-R1 04-Feb-98 62 84> .at each location 605 Annual weighted rainfall 6180 at Station BD: -5.7 Percent of total rainfall sampled at Station BD: 94.5 Note: Weighting of annual 6180 rainfall value determined from the following equation: 3180A=Eh 8180 Eh; where:h;=event rainfall in millimeters and 00,=average event value in%o. 87 TABLE 20. MONTHLY RAINFALL AND WEIGHTED AVERAGE 6180 AT STATION BD Month Amount of Average rainfall (mm) September 0 - October 0 - November 47.5 -5.1 December 93.0 -6.0 January 45.0 -4.3 February 305.0 -6.1 March 38.0 -4.2 April 39.5 -6.8 May 37.0 -4.2 June 0 - July 0 - August 0 - 8180 vs. Rainfall Amount 0 - • -2 * • • a -4 • 0 6 • • • • • • • w -8 - R2= 0.2571 -10 -12 1 • 0 10 20 30 40 50 60 70 Rainfall amount per event Figure 25. Correlation of S'$0 with amount of rainfall in each event. In general, rainfall 6180 values show a rainout effect, becoming lighter with increasing amounts of precipitation. 'f� 88 between individual storms within the study area(Table 19),and no apparent correlation relating isotopic composition to time of year(Table 20). Rainfall 5180 values appear to get more negative with increasing amounts of rainfall,but the correlation is weak(Figure 25). In addition,there is a negative correlation between 5180 and timing of rainfall within an event. Specifically,the earliest rainfall within a given storm event is typically heavier in 5180,with oxygen isotopic values becoming lighter as the storm progresses. This trend is also apparent in storm runoff 5180 measurements(Table B-2). The majority of storm events dropped between 10 and 50 mm of rain and had 5180 values ranging from —4%o to—7%o. Because of the topographic change within the study area(a total of about 366 op meters from shoreline to crest),the potential orographic effect on rainfall isotopic composition must be considered. During placement of the rain gauge network,stations were selected to evaluate the effect of altitude during storm activity. Station DCP was located at the top of the study area at an elevation of approximately 360 meters(1,180 feet)asl,while station DC was located near the bottom at an approximate elevation of 50 meters(162 feet)asl. Station BD(— 131 meters asl)was located near the middle of the study area and was the location selected for collection of a complete set of storm samples (every storm event). Isotopic values typically become progressively lighter with increasing elevation (Dansgaard, 1964). In two studies in similar coastal settings(Clark, 1987;and Fontes et al., 1977),the observed change in isotopic composition was between—0.1 and—0.155%o per 100 meters,respectively. By applying this isotopic gradient to the elevation change 89 411/ in the study area relative to station BD,the effect of isotopic change with elevation can be predicted to range from—5.6%o at station DC to—6.1 %o at station DCP(Table 21). During the 3 February 1998 storm event, samples were collected at all three stations to observe the actual isotopic difference with elevation. Contrary to expectations,the rainfall isotopic composition became heavier with increasing altitude. Because of the unexpected results during the 1998 storm,additional samples were collected during the 1999 winter rainy season in an attempt to clarify the 6180-altitude . relationship. During the first 1999 sampled event,the isotopic values again became heavier with increasing altitude(DC=-6.8;BD=-2.4, and DCP/RM=-2.5%o). During the second event,the values showed no trend at all (DC=-6.7,BD=-3.4,DCP/RM= -8.6%o)(Figure 26). It appears then,that there is no apparent and/or predictable isotopic elevation effect in the study area. This may be attributable to the varied storm paths and rainfall patterns which are prevalent on the peninsula(D. Gales, personal communication,August 1998). Selected rainfall samples representing different storm events in different months and of different magnitude were analyzed for SD. 8D results from these samples are listed in Table 22 and range from-90 to 0%o. 6D results are plotted versus 6180 in Figure 27 to produce a local meteoric water line(LMWL) with an slope of 8D=7.77 8180+ 11.36. The use of a LMWL is preferable to comparison of samples with a global meteoric water line because the LMWL is composed of local rainfall and more closely reflects the environmental conditions present in the study area. 90 TABLE 21. ESTIMATES OF POTENTIAL ELEVATION EFFECTS ON 5180 COMPOSITION OF RAINFALL Weighted avg 8180 at station BD: -5.7 At station DCP A 5180/100m m elev totl change range 5180 potential 8180-altitude change based on: Clark(1987) -0.1 229 -0.2 -5.9 Fontes et al. (1977) -0.155 229 -0.4 -6.1 At station DC A 5180/100m m elev totl change range 5180 potential altitude change based on: Clark (1987) -0.1 82 -0.1 -5.6 Fontes et al. (1977) -0.155 82 -0.1 -5.6 400 - n. 350 o 300 - L a 250 200 o 150 — > 100 - F — as a� 50 0 — 0 -- -10.0 -8.0 -6.0 -4.0 -2.0 5180 (%o) —4-1998 storm --IN-1999 storm A —6-1999 storm B —X--predicted DCP —0—-predicted DC Figure 26. Graph of 6180 versus elevation within the study area. Measured rainfall 5180 values vary from the trend predicted based on elevation change in the area. 91 '\."- !!) TABLE 22. &0O and SD CONCENTRATIONS FOR SELECTED SAMPLES Sample 5180 SD RD-2 -5.4 -31 RD-4 -2.2 -5 RD-9 -5.6 -36 RD-12 -4.6 -23 RD-14 -1.1 0 RD-17 -6.3 -31 RD-18 -13.1 -90 RD-23 -11.5 -80 RD-28 -7.0 -46 RD-31 -5.3 -27 DW1-10-1 -11.2 -98 WW2A-11-1 -6.5 -49 LCC1-11-1 -6.4 -43 FW-12-1 -6.7 -41 W973-11-1 -5.4 -41 W973-3-1 -4.8 -33 ISE-9-1 -5.0 -44 ISE-3-1 -5.9 -43 E:` FSW-11-1 -6.5 -49 W6K 11-1 -6.1 -38 W6K 2-1 -5.7 -42 KCS-12-1 -5.8 -39 KCS-4-1b -5.7 -33 KCS-6-lb -5.5 -29 PTG-10-1 -6.2 -41 PTG-4-1 -6.6 -39 seawater 0 0 Concentrations in parts per thousand(la) r,� cit -7:7,4 11 10 0 • 0 Local Meteoric Water Line -10 NA y= 7.7709x+ 11.357 -20 R2 =0.988 -30 • ,A. X A -40 .4:K • X w— 50 �® -60 e i -70 - e Potential mixing line between -80 domestic water and average rainfall i -90 e - -100 ,'# . -14 -12 -10 -8 -6 -4 -2 0 2 8180(%o) • rainfall A KC spring ♦ domestic water + WW2A X W973 • W6K X ISE Cl PTG — LCC1 ■ RN o FSW 0 seawater(SMOW) —Linear(rainfall) Figure 27. Stable isotope compositions of selected groundwater, rainfall, and domestic water samples. Kelvin Canyon spring samples plot on the meteoric water line suggesting that spring water reflects rainfall recharge with little evaporation in subsurface. Samples which plot to right of line indicated either evaporation(i.e. W973 and ISE) or possible mixing with domestic water. (Uncertainties are 0.05 per mil for 8180 and 1.5 per mil for SD) N 93 a Storm Runoff Storm samples from both the January and February rainfall events were analyzed for 8180 with values ranging from—2.8 to—12.5 %o(see Table B-2). In general,5180 values in runoff samples became lighter as the storm event progressed,reflecting the patterns seen in precipitation. Domestic Water Four domestic tapwater samples were collected from two homes in the area.The • samples were analyzed for 5180 and ranged from—11.4 to—10.7%o. Sample DWI-10-1 was analyzed for deuterium with a reported value of-98.3 %o. DW1-I0-1 plots significantly below the LMWL in Figure 27. Groundwater Monthly groundwater samples were analyzed for 5180 and selected samples were analyzed for SD. The 5180 values for each sample location are listed in Table B-1. SD results are listed in Table 22 and groundwater samples with both 5180 compositions and SD values are plotted in Figure 27. Several groundwater samples,including those from Kelvin Canyon spring,plot along or close to the LMWL. Other samples,including FSW, WW2A,ISE,and W973,plot below the LMWL. Yearly average 8180 values of groundwater in the study area range from—6.6 to —5.4%o(Table 17). The average 5180 composition at Kelvin Canyon spring is—5.7%o and,in general, 5180 values for groundwater in the Altamira Canyon basin become isotopically lighter as you enter developed areas downgradient within the study area. In • addition,average 8180 values in wells located in or adjacent to the canyons appear to 94 ft deviate less from the Kelvin Canyon spring 5180 value than wells located farther from the canyons. Rainfall recharge within the study area can occur by direct infiltration through the vadose zone or by movement down surface fissures. Each route will potentially affect the influence that rainfall variability has on groundwater isotopic composition. In some semi-arid to arid regions,groundwater isotopic composition can closely resemble the mean composition of rainfall as a result of fairly rapid recharge through preferential flow channels(Mathieu and Bariac, 1996). This direct recharge of rainfall to the groundwater body via surface fissures also provides an opportunity for an unequal contributions of various rainfall events to occur,potentially resulting in a groundwater isotopic ems composition that varies from the overall weighted average of rainfall. { Direct infiltration places water in the vadose zone where evapotranspiration is by far one of the most dominant mechanisms of removal of water,with important implications for groundwater recharge. While the process of transpiration is non- fractionating, direct evaporation of water from the soil zone can result in alteration of groundwater isotopic composition by fractionation(Clark and Fritz, 1997).The potential effect that the evaporative portion of this process had on groundwater isotopic composition in the study area was considered. With the exception of arid climates,seasonal variations in rainfall are typically attenuated during passage through the vadose zone,resulting in groundwater isotopic values that closely approximate those of weighted annual rainfall (Clark and Fritz, 1997). er,t This attenuation occurs because of the flow of water via differential flow paths in porous 95 111/ subsurface materials. In arid regions, evaporation is prominent on both the surface and in the vadose zone. As a result,there is an isotopic enrichment of soil water in the vadose zone. As successive recharge pulses of soil water progress through the vadose zone to recharge the groundwater body,the groundwater will exhibit a 5180-8D composition which will plot below but parallel to the local meteoric water line(Allison et al.,1984). The spring in Kelvin Canyon provides a unique opportunity to access "groundwater" in the recharge area. The average 8180 for the spring water was—5.7%o and the 8D was—34%o,closely matching the weighted average values for annual rainfall in the study area. These similar values suggest that the groundwater issuing at Kelvin Canyon spring is recharged from infiltration of rainwater with virtually no fractionating evaporation in the vadose zone. This interpretation is supported by the observation that the isotopic composition of several spring water measurements plot roughly on the local meteoric line(Figure 27). Evaporative fractionation would result in heavier 5180 and 8D values in water,with the resulting sample composition plotting to the right and below the meteoric water line. This trend was not observed in the Kelvin Canyon spring samples. Upgradient sources of water to the spring were explored but ruled out. Immediately upgradient from the stream the developed properties are serviced by sewer systems. One developed area,northeast and upgradient of the study area,remains on septic systems. Any mixture of water in the spring from upgradient domestic sources is likely to be reflected in lighter 8180 values,possible elevated nitrate concentrations,and younger tritium ages in the spring than are currently found. 96 The potential for recharge of groundwater through fissures is greatest in the active slide areas of the study area. This type of surface fissure recharge is most likely to occur once runoff begins overland and through the canyons.As mentioned in the section on water budgets, single storm events with rainfall totals>20 mm were most likely to produce excess runoff and the potential for fissure recharge. In a fairly steady rainfall event,runoff typically occurs after about 20 to 30 minutes of rainfall.It is likely that the water with the heavier isotopic values is involved in initial saturation of ground and contributes little to runoff. The calculated weighted 5180 average for these events, and therefore fissure recharge water, is-6.2%o. Assuming recharge from either infiltration or fissure recharge,the groundwater isotopic composition would then be expected to range from-53 to-6.2%o. It is likely . that both methods of recharge play a role and that groundwater isotopic composition reflects a balance between the two values. An examination of the groundwater isotopic values in individual wells reveals some interesting observations. Several wells (WW2A, LCC1,WW12,FW,FSW,and PTG)have annual 8i8O averages more negative than-6.2 %o. Several wells with annual 5180 averages within the -5.7 to-6.2%o range stated above have monthly values lighter than -6.2%o. These isotopically-lighter values suggest that groundwater in some areas is influenced by an isotopically-depleted source or that mixing does not perfectly homogenize the groundwater reservoir that may be episodically recharged. As mentioned before,the residences in the area are serviced by septic systems. In addition, groundwater recharge in urbanized areas can be increased by leaking pipes and irrigation. • 97 6,401S As discussed previously,landscape irrigation is less likely to contribute significantly to recharge because of high summertime evaporation potential and the potential for undetected leaking from water supply pipes has been greatly lessened by the placement of the pipes above ground where leaks can be detected quickly and easily. Because septic system discharge places water directly into the subsurface and therefore into the groundwater body,the need for evaluation of this potential source is great. Domestic water 818O values averaged—11.3±0.1 %o during the study period. Because the groundwater isotopic composition(-5.7%o)flowing into the housing area is so close to the range of rainfall-recharged isotopic values stated above(-5.7 to—6.2%o),it is difficult to distinguish between groundwater inflow and rainfall sources. Combining •``' ` - those two sources as one and using mass balance calculations,the percentage of recharge within the Altamira Canyon groundwater basin attributable to domestic water input can be estimated. Table 23 lists the stable isotope endmembers used and the general mass balance equations. In order to use mass balance calculations to estimate domestic water contribution, steady-state conditions must be met. These steady state conditions would be reached if the groundwater body in Altamira Canyon was homogeneous and had a residence time of less than 50 years. The area has been developed for approximately 50 years and a residence time of water less than that would allow for complete mixing of domestic water into the groundwater body. However,if residence time of the groundwater body is longer than 50 years, it is unlikely that domestic water would be completely mixed into the ti., i ,, 98 • TABLE 23. STABLE ISOTOPE MASS BALANCE PARAMETERS. Stable isotope endmembers (5180 in%o): Domestic water -11.3 Rainfall/subsurface water -5.7 to—6.2 Groundwater in Altamira Canyon wells -5.8 to—6.4 Groundwater in Portuguese Bend wells -5.4 to—6.6 General mass balance equations: QT=QD+QR Q11:31.`QD6D+QR6R where QT,QD,and QR represent total%of groundwater in wells,domestic water,and rainfall/groundwater inflow,respectively,and ST,SD,and SR represent their respective 5180 values. „?),, Results: Domestic water contributed—4 to 13 %of recharge to groundwater in Altamira Canyon and—0 to 16%of recharge in Portuguese Bend. 99 system(therefore indicating non-steady-state conditions)and the fraction of domestic water contribution predicted by mass balance calculations would be low. Average isotopic compositions in the Altamira Canyon basin wells range from —5.8 to —6.4%o. Based on stable oxygen isotope mass balance calculations,the percentage of domestic water involved in groundwater recharge ranges from 4 to 13 %, comparable to the 14 to 21 %range obtained from the 1997-98 water budget calculations, but significantly lower than the long-term(average year)expected contribution of—57%. These results imply that,during the El Nino study year,domestic water input played a small role in groundwater recharge. However,the significantly lower percentages obtained via the mass balance calculations suggest that conditions in the groundwater 47,71 body are probably not steady-state. This conclusion can be tested by calculating the residence time of water in the Altamira Canyon basin. An approximation of residence time can be obtained by estimating the volume of groundwater in the basin and dividing it by the rate of input of water to the groundwater body. However,the accuracy of this calculation is hindered by several limitations. Within the landslide,the slide plane provides a reasonable lower boundary for the saturated zone. However,the lower limit of the saturated zone in areas topographically higher than the landslide is undefined and difficult to determine. The thickness of the saturated zone throughout the basin can be approximated by extending the average saturated thickness in the landslide over the entire basin area. Because it is not uncommon for a saturated zone to thin out as it approaches the lateral boundaries of a basin,this extrapolated thickness would represent a maximum value. The porosity of the 100 subsurface material is also unknown and can be approximated based on likely subsurface lithologies. A porosity of 0.35 is typical for silty/clayey soils and was chosen for the calculation. The groundwater basin boundaries are also assumed to coincide with the boundaries of the surface drainage basin. Keeping in mind the limitations discussed above,a first-order approximation of groundwater residence time in the Altamira Canyon basin was calculated. The resulting age was— 135 years and was based on an average saturated thickness of 10.4 meters (—34 feet),a porosity of 0.35, and a basin area of 3.3 km2. This residence time is longer than the 50 years supporting the likely presence of non-steady-state conditions in the Altamira Canyon basin. Residence time estimates were also calculated using tritium tconcentrations and will be discussed in that particular section of this dissertation. Average isotopic compositions in the Portuguese Bend wells range from—5.4 to —6.6%o. Using the same mass balance technique and assumptions from above,the estimated amount of groundwater recharge provided by domestic water input in the Portuguese Bend groundwater basin ranges from 0 to 16%. Again,these values correspond closely with the 6 to 8 %range obtained in water budget calculations and are slightly less than the long-term,average estimate of—'23%. Hydrological parameters are even less constrained in the Portuguese Bend basin,making quantitative estimates of residence time difficult. In the Portuguese Bend basin, average groundwater 5180 values in the wells remain close to rainfall,or slightly lighter in developed areas. Well W973 is an W 101 exception;with an yearly average concentration of-5.4%o,it is slightly heavier isotopically than other groundwater well samples and heavier than average rainfall (-5.7%o). Heavier groundwater isotopic values could be obtained in several ways: 1)evaporative fractionation prior to or during recharge,2)mixing with heavier water from another source,and/or 3)recharge with a higher percentage of isotopically-heavier rainfall. No other sources of isotopically-heavier water have been identified in the study area, and the rainfall events with heavier isotopic compositions tend to be smaller in amount or at the beginning of storms. Therefore, options 2 and 3 seem unlikely. Because little natural surface drainage remains in the area,much of the Portuguese Bend landslide area has surface depressions and,according to Perry Ehlig(personal communication,August 1999),a significant amount of water received during rainfall . events and concentrated canyon runoff sits in these depressions prior to infiltration into the ground. This collection of water prior to infiltration could allow for evaporative fractionation of the water,with the remaining heavier portion serving as recharge to the groundwater body in the vicinity of well W973. The occurrence of evaporative fractionation prior to recharge is supported by the plotting of W973 samples below but parallel to the meteoric water line(Figure 27). Recharge by direct rainfall infiltration, and subsequent dilution of groundwater,is also supported by the observation that ion concentrations and conductivity in well W973 generally decrease following the start of the rainy season. Rainfall contains less dissolved ions than groundwater and a decrease in groundwater TDI might indicate dilution by infiltrating precipitation. Well ISE also plots below the LMWL. 5180 values in this well were heavier in the dryer initial part of 102 the study period(September through January),suggesting potential evaporative recharge conditions. However,the 5180 composition became lighter following periods of rainfall. This suggests fairly rapid recharge of rainfall to the well,an observation supported by a corresponding rise in groundwater levels in nearby monitoring wells. Several other wells(WW2A,FSW,LCC1,PTG,and W6K)also plot below the meteoric water line,but might be best explained as resulting from mixing of domestic water with average rainfall composition as indicated by the mixing line shown on Figure 27. 5180 values in well N change to become significantly lighter from March to April and remain so through the end of the 1997-98 study period. This difference indicates an 4?_ilapparent change in source contribution during the latter part of the study period with an increase in domestic water contribution. This may be an indication of flow along the previously-discussed head graben of the Abalone Cove landslide which is currently conducting water from the more developed Abalone Cove landslide to the Portuguese Bend landslide(P.L.Ehlig,personal communication,August 1999). C. TRITIUM Tritium,the radioactive isotope of hydrogen with a half-life of 12.43 years (Unterweger et al., 1980), can be used to estimate relatively young groundwater ages. During the 1960s,testing of nuclear bombs released significant amounts of tritium into the atmosphere(Figure 28). As this tritium rained out and recharged groundwater,a tritium spike could be identified in groundwater recharged during this time period. Today,groundwater with tritium concentrations greater than 15 probably contains some 103 Tritium in Precipitation at Santa Maria, California 120 100 v E eo 60 40 et 20 3 (0 W O til 3 2O 0) O N g t0 O O N (0 m O N O) a) a) a) a) a) 0) 0) a) 0) W W 0)) 00) 00 0) 0) W 0) 00) 0) Year Figure 28. Graph of decay-corrected tritium concentrations in rainfall at Santa Maria, California from 1954 through 1993. The data are corrected to 1998 values. The peak records the influx of tritium resulting from testing of nuclear bombs. 104 tqii bomb component in its composition. Even for younger waters a quantitative interpretation of groundwater age can be made if the tritium input values and the dynamics of mixing in the recharge zone are known. Water samples to be analyzed for tritium were collected directly into 500 ml HDPE bottles and stored at room temperature. Tritium samples were analyzed at the Environmental Isotope Laboratory at the University of Waterloo,Canada. The samples were enriched approximately 15 times by electrolysis(Taylor, 1977)and then counted using a liquid scintillation counting technique(Drimmie et al., 1993). The detection limit for enriched samples is 0.6±0.8 TU. Rainfall Two rainfall samples were collected after the initial study period(during March 1999)and analyzed for tritium concentration. Reported tritium values for samples RT1 and RT2 were 2.0 and 2.8 tritium units(TU),respectively(see Table 24). Tritium values for rainfall samples are illustrated on Figure 29. These values are similar to decay- corrected values of 2 TU determined(using the Ottawa correlation)for Santa Maria, California, a location with a similar coastal setting to the study area(J. Izbicki,personal communication, Dec. 1998). Figure 28 shows a graph of the tritium concentrations at Santa Maria over an approximate 40-year period. Domestic Water One domestic water sample(H1)was collected in March 1999 and analyzed for tritium. As stated earlier,the domestic water supply to the study area is a mixture of northern California and Colorado River water. Sample Hl had a reported tritium value of 105 TABLE 24. RESULTS OF TRITIUM ANALYSES ON GROUNDWATER RAINFALL, AND DOMESTIC WATER SAMPLES Sample Collection Dates Sample Type Sep-97 Feb-98 May-98 Mar-99 N well 2.4 3.5 WW4 well 0.9 1.5 CB well 3.2 4.2 UN well 1.5 2.1 W6K well 5.8 10.4 ISE well 4.2 4.9 WW13 well 3.2 EB well <0.8 KCS spring 1.2 KCW well 3.7 RT1 rainfall 2.0 RT2 rainfall 2.8 H1 domestic water 6.5 (Results are reported in tritium units(TU)with an average uncertainty of+0.6) Tritium Data - PB/AC Landslides 12 ♦Sep-97 10 —•May-98 4 ti ♦Mar-99 IA 8 —■Feb-98 4 4 t T ►- 2 c.) Z M Z `r cW W 23 H I Y Y � >.`t CC Q' Sample Figure 29. Graph of tritium data from locations in study area. Samples are plotted from left to right in order of decreasing elevation. Error bars represent+ 0.6 TU uncertainty. Wells with ages from—2 to 8 TU suggest a modem age (<5 to 10 years),possibly influenced by mixing with domestic water. Well EB shows age greater than —45 years. 106 6.5 TU(Figure 29). Tritium concentrations in the Pacific northwest and the northern interior of the continental U.S.are typically higher than those found in the south(Michel, 1989). These concentrations are produced by the latitudinal dependence of stratospheric exchange of water vapor and a decreasing influence of oceanic water vapor exchange as air masses move inland. As a result,water supplied from those areas would be expected to have higher tritium concentrations that those measured in local rainfall. Groundwater Several groundwater samples were analyzed for tritium and selected samples were analyzed from two different months during the study period. The results of these analyses are reported in Table 24 and a graph of the values is presented in Figure 29. Tritium concentrations in groundwater ranged from<0.8 to 10.4 TU and without exception,in wells sampled more than once,the values appear to have increased from September 1997 to May 1998. However,with the exception of well W6K,which showed an increase from 5.8 TU in September to 10.4 TU in May,the increases are within analytical uncertainty and could essentially represent similar values. In the study area,the lack of known tritium input values for past years limits a more quantitative approach. The spring at Kelvin Canyon has a reported tritium concentration of 1.2 TU. Assuming no mixing during recharge, an estimated age range of the spring water can be obtained by using tritium input rainfall values from Santa Maria,California and the following decay equation: t=-17.93 ln(at3H/ao3H)) 107 IP where t=the age in number of years,at3H=the measured tritium value in groundwater, and ao3H=the input tritium value of rainfall. The low tritium concentration rules out the presence of a"bomb"tritium spike and therefore constrains the time of recharge to before the mid-1950s or after the 1970s. Decay calculations yield potential age estimates for spring water of-9 or 45-50 years. The spring occurs naturally as the result of flow along sedimentary bedding planes,with flow emerging where the canyon wall intersects the strata. It is reasonable to assume that flow along the bedding planes will occur more rapidly than through the relatively less- permeable strata on either side. Although there is no clear way to further constrain the age estimate,the potential for more rapid flow through the subsurface along bedding planes and the proximity of the spring to the recharge area in the upper portion of the basin lend support to the shorter residence time of—9 years. Even shorter residence times(less than a decade)can be ruled out with several lines of evidence. If the spring represented rapidly-recharging water,the tritium values would mirror rainfall values and the stable isotopic and chemical composition of the spring water would fluctuate with rainy season precipitation. Although the flow from the spring increased in response to increased periods of rainfall,the chemical composition and 5180 concentrations remained remarkably constant throughout the study period. It appears thenthat groundwater in the upper portions of the study area has a minimum residence time of approximately a decade resulting in attenuation of tritium signals and other geochemical parameters in the spring water. The increase in spring flow following rainy periods most likely represents flow 108 t. pulses of older,well-mixed water being pushed by increasing pore pressure from episodic upgradient recharge. . As groundwater flow continues downgradient,there would be an expected increase in age,yielding tritium concentrations below the detection limit. However,this trend is not observed in the lower portions of the Altamira Canyon basin. Instead,tritium concentrations vary throughout the basin(from<0.8 to 4.2 TU). In wells along Altamira Canyon(UN and WW4),tritium concentrations resemble those found in Kelvin Canyon spring(Figure 29). These similar tritium concentrations, as well as fairly uniform ion and isotope compositions,suggest a more rapid passage of groundwater downgradient within Altamira Canyon,possibly through more permeable alluvial material. The presence of ,,e_i) this alluvial material is supported by the larger volumes of water removed by pumping from wells located in close proximity to the canyon(Figure 7 and Table 8). In wells located away from the canyon,where groundwater compositions are more varied and pumping rates drop off,it is reasonable to assume that groundwater is flowing through less permeable materials and therefore may have a longer residence time. These wells(i.e. WW2,CB,and SG)are typically located in developed areas of Altamira Canyon where mixing of various water sources prohibits direct use of decay equations for age determination. 109 When it is difficult to obtain quantitative age values, for instance if mixing of multiple sources is possible,qualitative interpretations can be made using the following guidelines (Clark and Fritz., 1997): <0.8 TU Submodem—recharge prior to 1952 0.8 to—4 TU Mixture between submodem and recent recharge 5 to 15 TU Modem(<5 to 10 years) 15 to 30 TU Residual "bomb"tritium present;and > 30 TU Considerable component of recharge from 1960s or 1970s. In wells away from Altamira Canyon,tritium concentrations range from 3.2 to 4.2 TU(Table 24). These values fall within the qualitative range of 0.8 to—4 TU suggesting mixture between submodem(>—45 years)and recent recharge(i.e. domestic water or rainfall). Approximations of groundwater residence time based on reservoir volume and input rates(see stable isotope section) yielded an estimated age of 135 years. Considering the potential for lithologic heterogeneities within the basin,the mixing relationships present,and the uncertainties in the calculations,it is likely that groundwater residence time in the Altamira Canyon basin falls somewhere between the decade-old water at Kelvin Canyon spring and the> 135-year age approximated from hydrologic parameters,perhaps on the order of several decades. The one exception to wells sampled in the lower portion is well EB(Figure 7). The measured tritium concentration in this well is<0.8, suggesting that recharge of water currently found in this well occurred prior to the 1950s. This qualitative estimate,along with the unique geochemical signature and wanner temperatures,supports the idea that water in the vicinity of this well may represent deeper circulation patterns of water within fir. the peninsula. 110 m In the Portuguese Bend basin,with the exception of well W6K,tritium concentrations range from 2.4 to 4.9 TU(Table 24)suggesting a mixture of submodem water with recent recharge. Well W6K has tritium concentrations ranging from 5.8 to 10.4 TU which fall within a modem age range of<5 to 10 years. D. SUMMARY In general,the chemical compositions of the groundwater bodies in both basins are dominated by sulfate with no apparent dominant cation. The ion concentrations between wells in the Altamira Canyon basin are less varied than those wells in the Portuguese Bend basin. With few exceptions,the groundwater composition of the study area reflects the titweathering of dolomitic rocks,driven by the oxidation of pyrite and accompanied by some cation exchange. Differences in the compositions between the two basins likely reflects the enhanced weathering environment present in the Portuguese Bend basin as a result of continued landslide movement. During the study period,recharge to the groundwater body within the Altamira Canyon basin appears to be the result of fissure flow within the canyon,with contributions from infiltration of rainfall in the upper portions of the basin and domestic water within the Abalone Cove landslide area. Groundwater appears to have a residence time of several decades and responds fairly quickly to rainfall as a result of pore pressure waves. Recharge within the Portuguese Bend basin occurs primarily through infiltration from surface depressions or flow down surface fissures with minor contributions from domestic water. 111 There appears to be a component of water which circulates deeper within the peninsula,manifesting itself in the unique geochemical properties in well EB. This deeper water circulation could have an influence on landslide movement and presents a topic for further study. 112 qt CHAPTER IV CONCLUSIONS The correlation between rainfall and landslide movement in the Portuguese Bend landslide area has been clearly documented(Ehlig, 1992). The purpose of this study was to clarify the sources and mechanisms of recharge to the groundwater systems in the area and discuss the potential effects of groundwater dynamics on landslide movement. This investigation was completed by using geochemical and isotopic methods to complement more traditional hydrologic techniques of investigation. The results of the research suggest that geochemical and isotopic techniques provide additional information which can prove valuable in interpreting hydrologic systems. The groundwater dynamics of a landslide area are influenced by the sources of water to the area,the residence time of the water in the area,the interaction of water with other sources of water and with the surrounding lithologies,and the movement of water. through the area. The extensive groundwater dewatering and monitoring program in the Portuguese Bend and Abalone Cove landslides provided a unique opportunity to examine groundwater in great detail and over a significant period of time. The conclusions from this study are presented below: • Recharge to the groundwater body in Altamira Canyon basin during the 1997-98 study year(El Nino period)was accomplished via fissure flow within the canyon(49-75%),with contributions from infiltration of rainfall in the upper portions of the basin(4-37%),and domestic water influx(14-21%). This 1. 1 contrasts with recharge expected during a normal rainfall year,when domestic 113 IP water constitutes over 50% of input to the groundwater system with canyon fissure recharge and infiltration making up the remainder. The contribution of domestic water is readily apparent in the lighter 5180 concentrations in the lower elevation wells in developed areas. Influence of residential septic systems is also indicated by the increase in nitrate concentrations in groundwater within the developed areas. • During the study year(1997-98 El Nino period),recharge to the groundwater body in the Portuguese Bend basin was provided by infiltration and fissure recharge(66-73%)with minor contributions from subsurface graben inflow (21-26%) and domestic water influx(6-8%). In contrast,long-term recharge(as evidenced by a normal rainfall year)is anticipated to occur primarily through contributions from domestic water(-.23%)and graben inflow. It is difficult to distinguish between the amounts of water contributed by fissure recharge versus infiltration. Longer-term recharge estimates could be better refined by constraining the amount of water recharging down fissures during storms and the volume of water moving along the graben. • In both landslides,groundwater response to rainfall occurs within one to three months following periods of higher rainfall.It appears that this response is not the actual movement of water through the groundwater system(which could take decades),but rather a propagation of hydraulic pore pressure through the groundwater system. 114 This increased flow is manifested as larger volumes of discharge at Kelvin Canyon spring in the Altamira Canyon basin and as periodic rises in groundwater levels in portions of the Portuguese Bend basin. The most rapid groundwater level response in wells in the Portuguese Bend landslide occurs near landslide boundaries or surface fissures. Elevations in pore pressure which extend to the landslide base would be expected to intensify during winter rainy periods and indeed, during periods of high rainfall,landslide movement increases. The effectiveness of the dewatering wells in the Abalone Cove landslide area is evident by the lack of landslide movement response even in periods of heavy rainfall such as those experienced in this El Nino study year. Although small amounts of creep are occurring,the Abalone Cove slide has been fairly stable over the past few years. f A decades-long residence time of groundwater is supported by several lines of evidence. Groundwater emerging at the spring possessed a fairly consistent geochemical and isotopic composition over the 1997-98 study year,suggesting that groundwater represented in the spring had remained in the subsurface long enough for storm or seasonal variations to become attenuated. The tritium value reported in the spring yielded an age of approximately nine years. In addition,the groundwater in the spring also exhibited a major ion chemical composition which differed from average rainfall, suggesting that time had passed to allow interaction with and dissolution of subsurface materials. Residence time of groundwater in the Altamira Canyon basin may vary AP somewhat. Lower-elevation wells near the canyon(i.e. WW4,UN,and SB)may be 115 1111 receiving water from upslope areas via passage through alluvial material within the canyon. Water flowing through this material would be expected to move more quickly and have less interaction with domestic water. This hypothesis is supported by the observation that wells near the canyon have similar 8180 and tritium values to those found in Kelvin Canyon spring. In contrast,wells located farther from the canyon have a more varied chemical composition and 8180 values indicative of domestic water influence. Tritium concentrations in these wells suggest a mixture of submodern (>—45 years)water and recent recharge. Qualitative assessment of groundwater residence time in Portuguese Bend reveals an estimated age ranging from recent(<5— 10 years)to submodern. 8 • There may be a component of water which circulates deeper within the peninsula. The presence of deeper circulating water could have important implications for landslide movement,potentially exerting hydraulic pressure from beneath the landslide plane. This deeper circulation pattern may be reflected in well EB which exhibits a warmer average temperature than those in other wells,a tritium age of greater than >45 years, a strong sulfide smell,and a geochemical signature that is unique from any other well in the study area. It appears to have some seawater influence,but its longer residence time and warmer temperatures suggest a possible association with a deeper-circulating water source. If there is a source of deeper water circulating upward,there is the potential for upward pore pressure to be applied on the underside 1!11 of the Abalone Cove slide plane. This interpretation would require further work to 116 confirm. Other unique wells may also reflect combinations of water and recharge . conditions that in general do not reflect the overall conditions of the study area. • Movement of the Portuguese Bend landslide increases following periods of rainfall(Ehlig, 1992). During the study year,there was an observed gain in groundwater storage of—0.7 x 105 m3(57 acre-ft). In a normal rainfall year, there was an measured loss in storage of'—-0.4 x 105 m3(32 acre-ft)with landslide movement continuing even during periods of little to no rainfall. The weathering and mechanical breakdown in the landslide mass has produced fine-grained clay material which impedes the easy flow of groundwater. This results in lower groundwater recharge as evidenced by the lower groundwater recovery rates i!!!!11 measured in dewatering wells within the landslide. This lower recharge rate hinders attempts to slow landslide movement by pumping groundwater. As a result,the landslide moves continuously,even during periods between rainfall seasons. The lower permeability results in a slide mass that is fairly saturated year-round,as evidenced by consistent groundwater levels in most monitoring wells. An already saturated slide mass is quick to respond to periods of rainfall with an increase in hydraulic head, in turn producing increased pore pressure which can result in increased landslide movement. Because of the low permeability of landslide material the recovery of the groundwater system to pre-rainfall levels is a slow process requiring several months,and allowing a high potential for landslide movement to extend for a significant period after precipitation events. 117 fiKs This persistent movement could also be aided by the continuous erosion of material supporting the toe of the landslide and/or hydraulic pressure acting on the underside of the landslide base. The conclusions of this investigation are significant in recognizing and constraining the dominant mechanisms of recharge to the groundwater bodies of these two landslides. However, the specifics of the relationship of groundwater to landslide movement are still unclear. It is possible that groundwater exerts pressure on the slide planes from both above and below. Figure 30 presents a simple model of possible groundwater influence in the landslides of the study area. The potential for hydraulic pressure on the underside of the slide planes in both landslides has not been fully investigated, but has important implications for the mitigation of landslide movement. In addition,it is important to recognize that the residence time of groundwater within the groundwater body appears to be on the order of decades,and further supports the concept that the relationship between groundwater dynamics and landslide movement may be the result of pore pressure propagation and not the actual movement of groundwater through the saturated materials. Shallow movement through landslide 1 to 3 decades Interaction with seawater Ocean • ♦ `� • circulation ♦ Fresh waterDeeper Salt water ♦ > 4 decades • • Figure 30. 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(ft as') (ft as!) EB AC PW 4174465 4017965 6 145 125-105 86 -59 -20 CB AC PW 4174123 4017982 6 133 113-53 64 -69 <-80 WW2A AC PW 4174722 4018965 6 unk unk 170 unk 10 LCC1 OAC PW 4173514 4020337 6 148 unk 415 267 osl WW4 AC PW 4175284 4018914 unk 84 unk 221 137 140 WW3 AC PW 4174945 4019372 unk unk unk 279 unk 117 SG OAC PW 4175303 4019870 6 200 160-140 364 164 osl WW12 OAC PW 4174290 4020874 6 126 unk 383 257 osl UN OAC PW 4175849 4020933 6 180 140-120 404 224 osl WW13 OAC PW 4175024 4020674 6 113 unk 386 273 osl SB OAC PW 4175570 4020603 6 180 160-120 364 184 osl WW11 OAC PW 4175696 4019915 6 116 unk 315 199 osl WW8 OAC PW 4176311 4020265 unk unk unk 350 unk osl W6A PB PW 4176975 4020030 6 160 150-80 386 226 unk N PB PW 4177539 4019795 unk unk unk 377 unk 233 FW PB PW 4177153 4019995 6 112 unk 373 261 unk W973 PB PW 4177587 4020235 unk unk unk 355 unk unk ISE PB PW 4178680 4018028 6 172 ?172-152 179 7 -sea level FSW PB PW 4177425 4018265 6 117 105-75 167 50 -60 W6K A=120 A=61 (2 wells) PB PW 4177051 4018245 6 B=110 unk 181 B=71 51 PTG OPB PW 4175850 4017654 unk unk unk 184 unk unk W2D PB MW 4177050 4019400 2 150 unk 343 193 unk W4E PB MW 4177935 4019412 4 unk unk 303 unk 219 WLT PB MW 4177206 4018809 6 114.5 unk 281 166.5 164 B88-4 PB MW 4177677 4020278 2 23 unk 343 320 281 B88-5 PB MW 4178530 4019770 6 43 unk 299 256 254 _ B88-9 PB MW 4178305 4019723 6 70 unk 304 234 233 PBS-1 PB MW 4178700 4018018 2 180 unk 180 0 4 PBS-2 PB MW 4177724 4018166 2 115 95-75 156 41 60 PBS-3 PB MW 4177839 4018412 2 216.5 unk 216 -1 96 PBS-4 PB MW 4177855 4018818 2 100 90-70 249 149 152 PBS-5 PB MW 41779484019248 2 100 80-60 288 188 201 PBS-6 PB MW 4178109 4019632 4 100 90-70 310 210 77, PBS-7 PB MW 4178274 4019938 2 141.6 unk 299 157 269 PBS-9 PB MW 4179010 4018552 2 90 70-50 185 95 98 PBS-10 PB MW 4178218 4018350 unk 212 unk 170 -42 44 B96-12 PB MW 4178393 4019950 2 14 unk 294 280 283 Notes: 'Location of well with respect to landslides(ex.OAC=outside Abalone Cove landslide,PB=Portuguese Bend). 2 Type of well,either pumping or monitoring(ex.PW=pumping well). unk=value unknown osl=outside slide limit as!=above mean sea level 125 APPENDIX B GEOCHEMICAL DATA TABLE B-1. GEOCHEMICAL AND ISOTOPIC DATA FOR GROUNDWATER SAMPLES Sample No.1 Date Temp. Cond.' Ca' Na Mg K CI SO4 HCO3 Si02 NO3 8180 5 EB-9-1 03-Sep-97 28 8100 72 - 1738 237 64 1032 3019 539 - -6.0 EB-10-1 09-Oct-97 27 8500 92 1611 243 66 1158 2815 520 29 0 -6.0 EB-11-1 13-Nov-97 26 8200 89 1509 248 - 62 1014 2861 505 - - -6.0 EB-12-1 10-Dec-97 27 8900 83 1541 241 62 1137 2704 520 28 0 -5.9 EB-1-1 16-Jan-98 26 8050 95 1629 254 67 1081 2662 520 - - - -5.9 EB-1-2 16-Jan-98 26 8050 81 1645 _ 252 67 - 1064 2966 508 30 0 -6.1 EB-2-1 13-Feb-98 27 8200 88 1678 25562 1005 3033 - 476 37 0 -6.0 EB-3-1 16-Mar-98 25 8100 91 1643 243 67 833 3176 520 34 0 -5.9 EB-4-1 16-Apr-98 28 8500 82 _ 1627 246 63 901 3358 517 36 1 -6.0 EB-5-1 15-May-98 27 8400 74 1483 219 63 951 2941 639 34 0 -6.0 EB-6-1 24-Jun-98 28 7900 83 1526 225 62 902 2888 520 31 0 -6.0 EB-7-1 22-Jul-98 28 7400 73 1497 233 61 835 3515 542 31 0 -6.0 20-Aug-98 ns ns ns ns ns ns ns ns ns ns ns ns Average 27 8192 84 1594 241 64 993 2995 527 32 0 -6.0 Samp.St.Dev. 1 370 6 81 11 2 110 252 39 3 0 0.1 %Deviation 3 5 9 5 5 4 11 8 7 10 124 1 Sample No.1 Date Temp.2 Cond.3 Ca4 Na Mg K Cl SO4 HCO3 Si02 NO3 8180 5 CB-9-1 03-Sep-97 24 10500 390 1052 1112 67 1224 5489 466 -. - -5.7 CB-10-1 09-Oct-97 24 10500 406 1265 1084 74 ' 1489 5139 449 30 0 -6.2 CB-11-1 13-Nov-97 24 10200 398 1051 1159 56 1539 5283 410 22 0 -6.3 CB-12-1 10-Dec-97 26 13100 356 1561 842 83 2642 4392 434 23 0 -5.7 CB-1-1 16-Jan-98 24 8500 367 ' 553 1004 40 811 5181 405 21 0 -6.0 13-Feb-98 ns ns ns ns ns ns ns ns ns ns ns ns CB-3-1 16-Mar-98 21 8200 439 539 1180 39 593 5362 422 26 1 -6.4 CB-4-1 16-Apr-98 21 7950 391 528 850 38 758 4773 386 23 0 -5.9 CB-5-1 15-May-98 21 8800 389 734 1162 48 818 4980 432 17 0 -6.1 CB-6-1 24-Jun-98 22 8700 380 847 984 58 1050 5229 447 19 0 -6.4 CB-7-1 22-Jul-98 23 7300 367 575 940 43 852 6076 425 20 0 -6.3 20-Aug-98 ns ns ns ns ns ns ns ns ns ns ns ns Average 23 9375 388 871 1032 55 1177 5190 428 22 0 -6.1 Samp. St.Dev. 2 1711 24 355 127 16 604 444 23 4 0 0.3 % Deviation 8 18 6 41 12 29 51 9 5 17 205 4 N TABLE B-1 (cont'd). GEOCHEMICAL AND ISOTOPIC DATA FOR GROUNDWATER SAMPLES Sample No.' Date Temp.2 Cond.3 Ca' Na Mg K CI SO4 HCO3 Si02 NO3 6180 5 WW2A-9-1 03-Sep-97 28 4650 420 368 236 20 335 2009 403 - - -6.2 WW2A-10-1 09-Oct-97 28 4500 449 362 238 21 340 2098 388 - - -6.6 WW2A-11-1 14-Nov-97 26 4410 443 371 249 19 342 2069 442 39 5 -6.5 WW2A-12-1 10-Dec-97 27 4260 454 368 247 20 353 2044 386 38 8 -6.4 WW2A-1-1 16-Jan-98 27 4400 458 380 257 21 351 2031 417 34 7 -6.5 WW2A-2-1 13-Feb-98 26 ' 4420 459 404 273 21 332 2038 481 27 6 -6.5 WW2A-3-1 16-Mar-98 26 4380 468 384 ' 257 22 284 1757 422 27 7 -6.5 WW2A-4-1 16-Apr-98 27 4410 457 399 257 21 334 2024 417 26 9 -6.4 WW2A-5-1 15-May-98 24 4320 441 393 289 22 308 2129 474 29 7 -6.4 WW2A-6-1 24-Jun-98 25 4100 442 389 266 22 309 2108 417 26 5 -6.5 WW2A-7-1 22-Jul-98 25 3980 441 363 265 21 272 2315 459 38 6 -6.4 WW2A-7-2 ' 22-Jul-98 25 3980 429 371 255 20 272 2249 456 35 6 -6.5 WW2A-8-1 20-Aug-98 26 4110 396 347 222 20 336 2341 _ 420 32 7 -6.4 Average 26 4302 443 377 255 21 321 2093 429 32 7 -6.4 Samp.St.Dev. 1 204 19 16 17 1 29 150 31 5 1 0.1 %Deviation 4 5 4 4 7 4 9 7 7 17 17 1 Sample No.1 Date Temp.2 Cond.3 Ca' Na Mg K CI SO4 HCO3 S102 NO3 5180 5 LCC1-9-1 03-Sep-97 25 4840 553 386 233 24 472 2162 364 - - -6.3 LCC1-10-1 09-Oct-97 24 4520 587 385 233 25 472 2129 347 25 12 -6.3 LCC1-11-1 13-Nov-97 21 .. 4510 576 391 239 23 473 2110 410 27 13 -6.4 LCC1-12-1 10-Dec-97 22 4680 567 393 234 24 482 2090 339 32 21 -6.2 LCC1-1-116-Jan-98 23 4520 514 356 220 25 478 1782 400 30 21 -6.3 LCC1-2-1 13-Feb-98 - 22 4540 540 383 230 23 481 2121 437 34 21 -6.3 LCC1-3-1 16-Mar-98 22 4570 507 355 - 211 24 453 2030 422 40 22 -6.3 LCC1-4-1 16-Apr-98 23 4610 517 380 217 r 24 457 2192 339 27 22 -6.3 LCC1-5-1 15-May-98 24 4400 500 379 247 24 463 2143 312 22 23 -6.4 LCC1-5-2 15-May-98 24 4400 520 - 379 245 25 461 2066 - 351 26 23 -6.2 LCC1-6-1 24-Jun-98 23 4330 484 351 199 21 _ 477 - 2021 447 31 23 -6.3 LCC1-7-1 22-Jul-98 22 4150 555 383 230 22 438 2332 - 515 27 - 24 -6.4 _ LCC1-8-1 20-Aug-98 23 _ 4250 438 307 179 24 337 _ 1935 491 27 24 -6.4 Average 23 4486 528 371 224 24 457 2086 398 29 21 -6.3 Samp.St.Dev. 1 182 41 24 19 1 38 131 63 5 4 0.1 %Deviation 5 4 86 9 5 8 8 16 16 19 1 N J TABLE B-1 (cont'd), GEOCHEMICAL AND ISOTOPIC DATA FOR GROUNDWATER SAMPLES Sample No.' Date Temp.2 Cond.3 Ca4 Na Mg K CI SO4 HCO3 Si02 NO3 8180 5 WW4-9-1 03-Sep-97 24 4700 496 400 291 20 423 2239 459 - - -5.9 WW4-10-1 09-Oct-97 4 19 4060 472 364 274 + 19 450 2061 425 - - -5.9 WW4-11-1 14-Nov-97 22 4730 526 404 317 18 422 2304 498 - - -6.0 WW4-12-1 10-Dec-97 22 4550 535 403 321 18 417 2360 456 35 9 -5.9 WW4-1-1 16-Jan-98 22 4500 532 401 327 20 4 423 - - 31 10 -5.9 WW4-2-1 13-Feb-98 21 4310 510 401 331 18 432 2232 503 37 21 -5.6 WW4-3-1 16-Mar-98 21 4330 513 402 324 19 349 2306 508 32 16 -6.1 WW4-4-1 16-Apr-98 22 4380 494 372 322 18 393 ' 2309 481 28 17 -6.0 WW4-4-2 16-Apr-98 22 4380 489 392 321 1 18 388 2194 474 28 16 -5.9 WW4-5-1 15-May-98 23 4470 452 367 305 19 360 2258 476 25 11 -6.0 WW4-6-1 24-Jun-98 22 4320 498 403 317 20 404 1700 498 30 10 -5.8 WW4-7-1 22-Jul-98 23 4240 389 300 4 240 19 339 2554 510 29 9 -6.0 WW4-8-1 20-Aug-98 22 4210 - 497 370 297 _ 18 406 2430 493 30 9 -6.0 Average 22 4398 492 383 307 19 401 2246 482 30 13 -5.9 Samp.St.Dev. 1 190 39 30 26 1 34 211 25 4 4 0.1 %Deviation 5 4 8 8 8 4 8 9 5 12 34 2 Sample No.' Date Temp.2 Cond.3 Ca' Na Mg K CI SO4 HCO3 Si02 NO3 8180 5 - WW3-9-1 15-Sep-97 26 4400451 332 253 18 365 2045 351 - - -5.9 WW3-10-1 ' 09-Oct-97 24 4280 - 472 340 268 18 401 2085 412 - - -5.9 WW3-11-1 13-Nov-97 23 4300 467 330 270 16 395 2111 415 38 5 -6.0 WW3-12-1 10-Dec-97 24 4330 484 343 4 281 17 403 2037 420 31 4 -5.9 16-Jan-98 ns ns ns ns ns ns ns ns ns ns ns ns 13-Feb-98 ns ns ns ns ns ns ns ns ns ns ns ns WW3-3-1 16-Mar-98 — 22 4230 453 340 _ 268 18 388 1921 425 39 5 -6.1 WW3-4-1 16-Apr-98 23 _ 4280 465 346 275 17 400 2059 427 19 ' 5 -5.9 15-May-98 ns ns ns ns ns ns ns ns ns ns ns ns 24-Jun-98 ns ns ns ns ns ns ns ns ns ns ns ns WW3-7-1 22-Jul-98 23 3900 410 296 240 16 362 - 2216 417 34 6 -6.0 WW3-8-1 20-Aug-98 24 4100 418 _ 320 253 16 400 _ 2234 415 33 _ 6 -5.9 Average 24 4228 452 331 264 17 389 2089 410 32 5 -6.0 Samp.St.Dev. 1 158 26 16 14 1 17 101 24 7 1 0.1 %Deviation 5 4 6 5 5 5 4 5 6 22 12 1 t') 00 t., TABLE B-1 (conttl). GEOCHEMICAL AND ISOTOPIC DATA FOR GROUNDWATER SAMPLES Sample No.' Date Temp.2 Cond.' Ca4 Na Mg K CI SO4 HCO3 SiO, NO3 8180 5 SG-9-1 03-Sep-97 25 4520 464 356 269 18 455 1958 549 -6.1 .. SG-9-2 03-Sep-97 25 4520 475 359 268 17 463 1802 559 - -6.0 .. SG-10-1 09-Oct-97 24 4330 462 355 280 16 423 1925 544 - - -6.1 SG-11-1 13-Nov-97 21 4320 448 352 286 15 456 1903 542 40 9 -5.9 SG-12-1 10-Dec-97 22 4260 495 355 289 15 465 1923 559 38 10 -5.8 SG-1-1 16-Jan-98 22 4090 499 356 288 16 452 1838 549 43 9 -5.7 - SG-2-1 13-Feb-98 22 3880 441 338 261 14 416 1721 520 40 9 -5.9 SG-3-1 16-Mar-98 22 4330 _ 532 376 305 17 479 1906 530 39 8 -6.1 SG-4-1 16-Apr-98 23 - 4220 466 355 272 16 449 1949 537 28 10 -6.0 SG-5-1 15-May-98 24 4280 420 355 274 - 16 468 1906 564 30 10 -6.1 24-Jun-98 ns ns ns ns ns ns ns ns ns ns ns ns SG-7-1 22-Jul-98 23 4120 458 326 - 26714 480 2126 608 43 11 -6:0 SG-8-1 20-Aug-98 24 4160 442 368 285 16 453 2253 571 40 10 -6.0 SG-8-2 20-Aug-98 24 4160 379 321 251 14 473 _ 2167 559 36 10 -6.0 Average 23 4245 460 352 277 16 456 1952 553 38 9 -6.0 Samp.St. Dev. 1 173 38 15 14 1 19 148 22 5 1 0.1 %Deviation 5 4 8 4 5 7 4 8 4 13 7 2 Sample No' Date Temp.2 Cond.3 Ca4 Na Mg K Cl SO4 HCO3 Si02 NO3 8180 5 VVVV12-9-1 15-Sep-97 24 5000 479 525 255 25 479 2260 393 - -6.3 WW12-10-1 09-Oct-97 23 4910 468 513 266 24 493 2187 391 - - -6.3 WW12-11-1 13-Nov-97 21 4910 436 500 259 24 499 2087 449 30 24 -6.3 WW12-12-1 10-Dec-97 22 4880 509 560 289 25 508 2221 415 31 25 -6.3 WW12-12-2 10-Dec-97 22 4880 479 ' 513 264 24 502 2258 398 - - -6.2 WW12-1-1 16-Jan-98 22 4800 448 483 254 23 507 2110 395 31 25 -6.1 VVVV12-2-1 13-Feb-98 22 4820 439 491 250 23 503 2236 425 31 25 -6.3 VVVV12-3-1 16-Mar-98 22 4800 402 436 233 23 481 2148 405 30 24 -6.3 WW12-4-1 16-Apr-98 23 4790 391 447 224 23 469 2310 378 25 24 -6.3 WW12-5-1 15-May-98 23 4600 384 413 247 20 409 2288 408 34 25 -6.3 VVVV12-6-1 24-Jun-98 24 4620 446 405 262 19 432 2158 508 38 30 -6.3 WW .12-7-1 22-Jul-98 22 4400 371 315 217 16 434 2589 525 ' 39 30 -6.2 WW12-8-1 20-Aug-98 23 4430 447 425 281 20 420 2559 527 39 29 -6.2 Average 23 4757 438 463 254 22 472 2262 432 33 26 -6.3 Samp.St.Dev. 1 188 41 65 21 3 36 154 53 5 3 0.1 %Deviation 4 4 9 14 8 12 8 7 12 14 10 1 r.) L:) TABLE B-1 (cont'd). GEOCHEMICAL AND ISOTOPIC DATA FOR GROUNDWATER SAMPLES Sample No' � Date Temp.2 Cond.3 Ca° Na Mg K CI SO4 HCO3 Si02 NO3 5180 5 UN-9-1 03-Sep-97 25 4750 490 281 317 , 20 462 1930 515 - - -5.8 UN-10-1 09-Oct-97 24 4470 493 286 337 20 440 2017 476 - - -5.6 UN-10-2 09-Oct-97 24 4470 488 262 335 20 459 2004 503 44 6 -5.8 ..UN-11-1 13-Nov-97 22 4420 444 263 310 19 456 1915 542 35 9 -5.9 UN-12-1 10-Dec-97 22 4380 485 272 320 - 19 460 1993 486 38 9 -5.6 UN-1-1 16-Jan-98 22 4300 469 258 300 20 456 2010 513 40 9 -5.8 UN-2-1 13-Feb-98 22 4310 448 270 304 18 457 2029 574 31 9 -5.8 UN-3-1 16-Mar-98 ' 22 4310 ' 404 231 282 18 405 1964 532 44 9 -5.7 UN-4-1 16-Apr-98 22 4320 408 231 282 19 382 1990 503 34 9 -5.8 UN-5-1 15-May-98 22 4350 415 245 289 17 470 2018 515 33 11 -6.1 UN-6-1 24-Jun-98 23 4330 345 193 244 17 483 1881 596 37 12 -6.1 _ UN-7-1 22-Jul-98 23 4210 448 227 309 18 490 2210 596 34 13 -6.0 UN-8-1 20-Aug-98 24 4300 441 258 321 21 546 2312 622 31 13 -6.0 Average 23 4378 444 254 304 19 459 2021 536 36 10 -5.8 Samp.St.Dev. 1 133 43 27 25 1 39 117 46 5 2 0.2 %Deviation 4 3 10 11 8 7 9 6 9 13 21 3 Sample No.1 Date Temp.2 Cond.3 Ca Na Mg K CI SO, HCO3 Si02 NO3 5150 5 WW13-9-1 03-Sep-97 24 4500 456 371 263 20 461 1864 488 - - -6.2 WVV13-10-1 09-Oct-97 23 4170 450 350 273 20 471 1808 476 - - -6.1 WW13-11-1 13-Nov-97 21 4210 433 338 274 18 445 1956 505 34 12 -6.2 WW13-12-1 10-Dec-97 23 4220 468 351 276 19 451 1802 452 32 11 -6.2 WW13-1-1 18-Jan-98 22 4130 471 362 283 20 457 1817 478 36 12 -5:7 WW13-1-2 16-Jan-98 22 4130 411 311 242 18 463 1735 456 37 12 -6.2 WW13-2-1 13-Feb-98 21 4150 460 373 282 18 457 1795 554 38 12 -6.1 WW13-2-2 13-Feb-98 21 4150 431 343 261 18 457 1845 544 40 12 -5.6 WW13-3-1 16-Mar-98 22 4220 476 366 294 21 391 1816 547 44 13 -6.2 WW13-3-2 16-Mar-98 22 4220 448 346 277 20 407 1850 552 42 13 -6.2 WW13-4-1 16-Apr-98 21 4230 449 353 277 20 412 1926 505 42 13 -6.2 WW13-5-1 15-May-98 22 4110 410 357 269 20 457 1881 500 34 13 -6.3 24-Jun-98 ns ns ns ns ns ns ns ns ns ns ns ns WW13-7-1 22-Jul-98 23 4080 451 - 329 280 20 490 2221 561 31 14 -6.3 WW13-8-1 20-Aug-98 23 4130 445 326 288 20 470 2225 620 28 14 -6.3 Average 22 4189 447 348 274 19 449 1896 517 36 13 -6.1 Samp.St.Dev. 1 101 20 18 13 1 27 149 48 5 1 0.2 %Deviation 4 2 5 5 5 5 6 8 9 13 8 3 i-:.) TABLE B-1 (cont'd). GEOCHEMICAL AND ISOTOPIC DATA FOR GROUNDWATER SAMPLES Sample No.' Date Temp.2 Cond.3 Ca4 Na Mg K CI SO4 HCO3 Si02 NO3 5180 5 SB-9-1 03-Sep-97 26 4600 471 238 ' 286 19 422 1890 483 - - -5.9 SB-10-1 09-Oct-97 23 4270 493 261 310 20 424 1894 466 - -5.8 SB-11-1 13-Nov-97 21 4200 462 239 296 19 401 1956 520 - - -5.8 SB-12-1 10-Dec-97 22 4160 496 256 315 19 422 1860 493 44 8 -6.0 SB-1-1 16-Jan-98 22 4110 504 254 316 20 420 2694 495 48 _ 8 -5.8 SB-2-1 13-Feb-98 22 4040 489 255 308 19 402 1850 476 44 8 -5.8 SB-3-1 16-Mar-98 22 4060 484 251 330 20 363 1861 569 41 9 -6.0 SB-4-1 _16-Apr-98 21 4090 471 251 323 20 388 1850 471 42 11 -6.1 SB-5-1 15-May-98 22 4000 409 240 301 19 404 1862 508 37 12 -6.0 SB-6-1 24-Jun-98 23 4110 439 243 310 19 441 1803 574 46 19 -5.8 SB-6-2 24-Jun-98 23 4110 407 232 305 19 437 1786 605 39 19 -5.8 SB-7-1 22-Jul-98 23 4060 423 223 287 18 477 2072 620 46 20 -5.9 SB-8-1 20-Aug-98 23 4140 495 253 320 20 513 2106 642 40 19 -5.9 Average 23 4150 465 246 308 19 424 1960 532 43 13 -5.9 Samp.St.Dev. 1 152 34 11 13 0 38 240 62 3 5 0.1 %Deviation 5 4 7 4 4 3 9 12 12 8 41 2 Sample No.' Date Temp.2 Cond.3 Ca4 Na Mg K Cl SO4 HCO3 S102 NO3 5180 5 WW11-9-1 03-Sep-97 24 4290 440 301 256 17 506 1761 486 - - -6.2 W11-10-1 09-Oct-97 22 4020 436 283 254 17 518 1704 486 - - - W -6.1 WW11-11-1 14-Nov-97 22 3970 441 - 289 264 16 504 1683 454 26 24 -6.3 WW11-11-2 14-Nov-97 22 3970 458 298 267 16 512 _ 1728 442 22 24 -6.1 WW11-12-1 10-Dec-97 22 4030 440 284 262 17 522 1647 427 21 24 -6.4 WW11-1-1 16-Jan-98 20 3810 391 - 269 239 16 520 1692 422 20 24 -6.0 WW11-2-1 13-Feb-98 21 3920 464 306 264 17 550 1782 383 40 24 -6.2 WW11-3-1 16-Mar-98 22 3980 390 284 239 _ 16 504 1636 508 46 22 -6.1 WW11-4-1 16-Apr-98 21 3920 388 _ 265 241 17 475 1688 459 28 21 -6.3 WW11-5-1 15-May-98 20 3790 324 248 208 14 420 1637 474 30 20 -6.2 WW11-5-2 15-May-98 20 3790 367 258 235 16 451 1612 ` 520 32 20 -6.1 WW11-6-1 24-Jun-98 21 3760 356 258 230 15 426 1599 557 28 19 -6.1 W W 11-7-1 22-Jul-98 21 3730 396 291 _ 252 16 466 2030 ` 564 30 19 -6.1 WW11-8-1 20-Aug-98 21 3800 457 310 254 18 390 2038 + 549 r 25 _ 17 _ -6.0 Average 21 3913 411 282 248 16 483 1731 481 29 21 -6.2 Samp.St.Dev. 1 149 43 20 17 1 47 139 54 7 2 0.1 %Deviation 5 4 11 7 7 5 10 8 11 26 11 2 w TABLE B-1 (cont'd). GEOCHEMICAL AND ISOTOPIC DATA FOR GROUNDWATER SAMPLES Sample No.1 Date Temp.2 Cond.3 Ca4 Na Mg K CI SO4 HCO3 Si02 NO3 5180 s WW8-9-1 04-Sep-97 23 4800 485 255 324 16 ' 608 1888 469 - - -6.0 WW8-10-1 09-Oct-97 24 4490 470 255 323 18 606 1801 476 - - -6.0 WW8-11-1 14-Nov-97 22 4440 494 260 327 16 594 1942 478 25 26 -6.1 WW8-12-1 10-Dec-97 24 4480 490 256 334 17 605 1771 491 28 27 -6.0 WW8-1-1 16-Jan-98 22 4290 468 268 331 17 598 1810 461 - - -6.0 WW8-2-1 13-Feb-98 22 4.340 497 270 323 16 607 1909 425 - 39 28 -5.8 WW8-3-1 16-Mar-98 24 4500 478 276 333 17 553 1820 574 41 29 -5.9 WW8-4-1 16-Apr-98 22 4250 483 263 336 18 497 1856 425 36 29 -6.1 WW8-5-1 15-May-98 22 4200 463 268 340 17 531 1836 500 33 26 -6.1 WW8-6-1 24-Jun-98 22 4140 394 228 294 15 498 1761 522 31 27 -6.2 WW8-7-1 22-Jul-98 23 4090 376 221 281 16 547 2029 576 33 29 -6.1 WW8-7-2 22-Jul-98 23 4090 448 _ 263 332 16 530 2054 574 31 29 -6.1 WW8-8-1 20-Aug-98 23 4210 497 271 323 17 545 _ 1831 576 28 29 -6.0 Average 23 4332 465 258 323 17 563 1870 504 32 28 -6.0 Samp.St.Dev. 1 204 39 16 17 1 42 92 56 5 1 0.1 %Deviation 4 5 8 6 5 5 7 5 11 16 5 2 Sample No.' Date Temp.2 Cond.3 Ca4 Na Mg K CI SO, HCO3 SlO2 NO3 8180 5 W6A-9-1 04-Sep-97 24 4950 548 364 - 271 19 537 2155 456 - - -5.7 Oct-97 ns ns ns ns ns ns ns , ns ns ns ns ns W6A-11-1 14-Nov-97 22 4680 580 371 285 18 532 2140 461 31 22 -5.7 W6A-12-1 10-Dec-97 23 4710 567 358 288 19 534 2127 425 34 19 -5.8 W6A-12-2 10-Dec-97 23 4710 580 366 288 19 536 2197 469 36 - 21 -5.5 W6A-1-1 16-Jan-98 22 4620 500 293 254 19 531 2081 427 38 22 -5.5 W6A-2-1 13-Feb-98 22 4610 597 388 287 19 487 2191 347 44 24 -6.0 16-Mar-98 ns ns ns ns ns ns ns ns ns ns ns ns W6A-4-1 16-Apr-98 22 4660 585 387 297 20 508 2180 452 32 23 -5.7 W6A-5-1 15-May-98 23 4570 534 365 298 20 512 2078 469 29 23 -5.6 24-Jun-98 ns ns ns ns ns ns ns ns ns ns ns ns 22-Jul-98 ns ns ns ns ns ns ns ns ns ns ns ns _ 20-Aug-98 ns ns ns ns ns ns ns ns ns ns ns ns Average 22 4689 561 362 283 19 522 2144 438 35 22 -5.7 Samp-St.Dev. 1 117 32 30 15 1 18 46 41 5 2 0.2 %Deviation 3 2 6 8 5 3 3 2 9 14 7 3 W IQ.) TABLE B-1 (cont'd). GEOCHEMICAL AND ISOTOPIC DATA FOR GROUNDWATER SAMPLES Sample No' Date Temp.2 Cond.3 Ca' Na Mg K CI SO, HCO3 Si02 NO3 8180 5 N-9-1 04-Sep-97 25 5500 547 452 329 20 589 2312 378 -5.8 N-10-1 09-Oct-97 24 5300 557 452 343 20 587 2335 386 - - -5.8 N-11-1 14-Nov-97 22 5100 521 422 320 18 588 2341 400 22 36 -5.7 N-12-1 10-Dec-97 23 5300 532 433 ' 334 20 594 2396 381 24 33 -5.9 N-1-1 16-Jan-98 23 5100 472 405 309 18 589 2365 393 25 34 -5.8 N-2-1 13-Feb-98 22 5100 523 430 324 18 606 2462 351 46 37 -5.8 N-2-2 13-Feb-98 22 5100 564 461 346 19 603 2411 361 44 36 -5.9 N-3-1 16-Mar-98 23 5050 524 451 338 19 459 2291 420 43 37 -5.7 N-4-1 16-Apr-98 24 5200 501 410 323 20 568 2353 354 39 37 -6.2 N-5-1 15-May-98 24 5100 4-46 375 309 19 554 2332 417 39 36 -6.3 N-6-1 24-Jun-98 24 5000 409 361 265 18 502 2370 449 33 36 -6.3 N-7-1 22-Jul-98 24 4860 412 352 277 16 468 2672 422 31 35 -6.0 N-8-1 20-Aug-98 24 4900 521 419 303 21 527 2728 425 27 33 -6.3 Average 23 5124 502 417 317 19 557 2413 395 34 35 -5.9 Samp.St.Dev. 1 171 52 36 24 1 51 135 30 9 1 0.2 %Deviation 4 3 10 9 8 7 9 6 8 26 4 4 Sample No.' Date Temp.2 Cond.3 Ca' Na Mg K CI SO, HCO3 Si02 NO3 8180 5 FW-9-1 04-Sep-97 23 5500 624 410 345 13 712 2410 405 - - -6.2 FW-10-1 09-Oct-97 24 5200 492 373 317 13 695 ' 2150 398 41 23 -6.4 FW-11-1 14-Nov-97 22 5200 618 395 347 11 692 2520 447 33 37 -6 3 FW-12-1 10-Dec-97 22 5400 598 376 345 12 696 2325 400 42 37 -6.7 FW-1-1 16-Jan-98 23 5100 609 398 357 13 693 2161 410 36 39 -6.2 FW-2-1 13-Feb-98 22 5000 633 408 362 11 677 2177 400 36 41 -6.4 - 16-Mar-98 ns ns ns ns ns ns ns ns ns ns ns ns FW-4-1 16-Apr-98 23 5200 616 399 360 14 694 2328 391 34 47 -6.3 FW-5-1 15-May-98 24 5100 469 323 312 12 673 2152 232 41 48 -6.2 FW-6-1 24-Jun-98 24 5100 527 370 319 12 620 2227 466 32 46 -6.1 FW-7-1 22-Jul-98 23 5100 610 420 373 ' 13 748 2521 520 28 47 -6.3 FW-8-1 20-Aug-98 24 5050 646 434 349 13 749 2755 508 33 _ 47 -6.1 Average 23 5177 586 391 34-4 12 695 2339 416 38 41 -6.3 Samp.St.Dev. 1 151 60 30 20 1 35 196 76 5 8 0.2 %Deviation 3 3 10 8 6 6 5 8 18 13 18 3 f.) ls) TABLE B-i (cont'd). GEOCHEMICAL AND ISOTOPIC DATA FOR GROUNDWATER SAMPLES Sample No.' Date Temp.2 Cond.3 Ca4 Na Mg K CI SO4 HCO3 Si02 NO3 &80 5 Sep-97 ns ns ns ns ns ns ns ns ns ns ns ns W973-10-1 10-Oct-97 25 6200 562 569 460 26 609 2945 586 26 0 ' -6.1 W973-11-1 14-Nov-97 24 6200 548 603 465 27 593 3067 632 14 1 -5.4 _ W973-11-2 14-Nov-97 24 6200 542 597 466 27 591 3077 637 16 1 -5.7 10-Dec-97 ns ns ns ns ns ns ns ns ns ns ns ns W973-1-1 16-Jan-98 22 5900 536 600 468 28 ' 601 2889 588 21 6 -4.9 W973-2-1 13-Feb-98 21 5200 585 522 366 15 610 2440 661 31 4 -5.4 W973-3-1 16-Mar-98 23 5500 599 524 384 15 802 1963 779 34 11 -4.8 W973-4-1 16-Apr-98 23 5400 527 480 372 19 692 2381 588 29 7 -5.4 W973-5-1 15-May-98 23 5200 514 515 398 18 647 2307 732 26 2 -5.4 W973-6-1 24-Jun-98 24 5200 438 416 312 16 538 2138 788 18 3 -5.5 W973-7-1 22-Jul-98 23 5200 535 502 384 17 656 2455 754 11 6 -5.5 W973-8-1 20-Aug-98 23 5000 580 ' 514 358 16 663 2129 810 _ 20 5 -5.4 Average 23 5564 542 531 403 20 637 2526 687 22 4 -5.4 Samp.St.Dev. 1 470 43 58 54 6 69 401 87 7 3 0.4 %Deviation 4 8 8 11 13 27 11 16 13 33 75 7 Sample No.' Date Temp.2 Cond.3 Ca4 Na Mg K CI SO4 HCO3 Si02 NO3 8180 5 15E-3-1 05-Sep-97 28 9300 672 481 669 13 1529 2281 271 - -5.0 ISE-10-1 10-Oct-97 ' 28 9200 706 476 660 13 1552 2192 281 15 973 -5.6 Nov-97 ns ns ns ns ns ns ns ns ns ns ns ns 10-Dec-97 ns ns ns ns ns ns ns ns ns ns ns ns ISE-1-1 16-Jan-98 24 8300 709 493 627 14 1569 2319 256 17 848 -5.5 ISE-2-1 13-Feb-98 22 8000 718 490 666 12 1537 2151 293 32 1027 -5.8 ISE-3-1 16-Mar-98 25 8800 705 510 ' 636 13 1483 2029 276 24 1035 -5.9 ISE-4-1 16-Apr-98 27 8500 697 495 696 12 1482 2306 268 26 1058 -5.6 ISE-5-1 15-May-98 27 8200 641 444 613 ' 12 1378 2308 286 22 1046 -5.7 24-Jun-98 ns ns ns ns ns ns ns ns ns ns ns ns ISE-7-1 22-Jul-98 24 7600 667 449 641 12 1371 2806 281 12 760 -5.7 ISE-8-1 20-Aug-98 25 7700 649 403 . 624 _ 13 1482 2584 286 23 1019 -6.0 Average 26 8400 685 471 648 13 1487 2331 278 21 971 -5.7 Samp.St.Dev. 2 608 28 33 27 1 71 234 11 6 109 0.3 %Deviation 8 7 4 7 4 5 5 10 4 29 11 5 Xa TABLE B-1 (cont'd). GEOCH€MICAL AND ISOTOPIC DATA FOR GROUNDWATER SAMPLES Sample No.' Date Temp.2 Cond.' Ca' Na Mg K CI SO4 HCO3 Si02 NO3 8180 5 FSW-9-1 05-Sep-97 27 6500 643 517 333 15 890 2526 312 - - -6.6 Oct-97 ns ns ns ns ns ns ns ns ns ns ns ns FSW-11-1 14-Nov-97 25 6200 651 503 333 14 904 2401 327 37 131 -6.5 10-Dec-97 ns ns ns ns ns ns ns ns ns ns ns ns FSW-1-1 16-Jan-98 26 6200 665 504 322 15 922 ' 2322 847 - - -6.5 FSW-2-1 13-Feb-98 - 26 6200 641 512 453 13 909 2228 317 24 146 -6.6 FSW-3-1 16-Mar-98 26 6400 623 520 334 14 868 2427 317 24 150 -6.5 FSW-4-1 16-Apr-98 23 5800 615 488 319 13 894 2505 303 22 141 -6.6 FSW-5-1 15-May-98 22 5700 574 499 307 13 802 2399 320 23 148 -6.6 FSW-6-1 24-Jun-98 26 5900 578 467 305 13 755 2348 315 25 123 -6.6 FSW-7-1 22-Jul-98 24 5600 654 515 333 13 831 2752 + 322 23 132 -6 6 FSW-8-1 20-Aug-98 25 5600 596 _ 424 296 _ 12 877 2549 337 27 131 -6.7 Average 25 6010 624 495 334 14 865 24-46 372 26 138 -6.6 Samp.St.Dev. 1 331 32 29 44 1 53 146 167 5 10 0.1 %Deviation 6 6 5 6 13 6 6 6 45 18 7 1 Sample No.1 Date Temp.2 Cond.' Ca' Na Mg K CI SO4 HCO3 5102 NO3 8180 5 W6K-9-1 05-Sep-97 30 12200 469 584 2480 22 724 8444 383 - - -6.0 _ Oct-97 ns ns ns ns _ ns ns ns ns ns ns ns ns W6K-11-1 14-Nov-97 22 8600 616 505 1051 10 898 l 5142 137 4 188 -6.1 W6K-12-1 10-Dec-97 22 8400 532 516 1080 9 914 4474 134 4 227 -6.1 W6K-1-1 16-Jan-98 24 10200 610 ! 542 2140 21 784 + 7108 273 - - -6.0 W6K-2-1 13-Feb-98 23 12200 571 ' 597 ' 3170 19 761 7716 312 12 324 -5.7 W6K-3-1 16-Mar-98 23 _ 8300 - 565 569 1018 9 _ 823 4496 112 4 255 -6.1 W6K-4-1 16-Apr-98 24 8200 - 518588 1008 _ 10 911 4495 90 2 253 -6.0 W6K-5-1 15-May-98 27 8300 445 - 518 - 852 9 909 4580 73 2 287 - -6.1 W6K-6-1 24-Jun-98 27 8500 469 565 840 9 806 4617 78 5 254 -5.9 22-Jul-98 ns ns ns ns ns ns ns ns ns ns ns ns 20-Aug-98 ns ns ns ns ns ns ns ns ns ns ns ns Average 25 9433 533 554 1516 13 837 5675 177 5 255 -6.0 Samp.St.Dev. 3 1682 63 34 856 6 73 1609 115 3 43 0.1 %Deviation 10 18 12 6 56 43 9 28 65 72 17 2 v� c.n TABLE B-1 (cont'd). GEOCHEMICAL AND ISOTOPIC DATA FOR GROUNDWATER SAMPLES Sample No' Date Temp.2 Gond 3 Ca` Na Mg K CI 504 HCO3 Si02 NO3 8150 5 PTG-9-1 05-Sep-97 27 6000 444 700285 38 324 2813 412 -6.4 PTG-10-1 10-Oct-97 26 6100 444 661 292 37 346 2771 447 36 11 -6.2 PTG-11-1 14-Nov-97 24 5800 425 598 275 34 341 2919 461 32 19 -6.5 PTG-12-1 10-Dec-97 26 5800 424 602 274 34 - 355 2666 415 36 20 -6.2 PTG-1-1 16-Jan-98 24 5500 451 605 274 35 355 2700 422 37 16 -6.5 PTG-2-1 13-Feb-98 25 5500 439 633 _ 391 33 355 2564 425 39 22 -6.6 PTG-3-1 16-Mar-98 25 5700 423 585 280 31 324 2584 474 44 24 -6.6 PTG-3-2 16-Mar-98 25 5700 442 615 289 33 345 2646 464 44 23 -6.6 PTG-4-1 16-Apr-98 25 5600 439 - 632 299 33 341 2648 430 38 21 -6.6 PTG-5-1 15-May-98 25 5300 354 486 249 32 284 2634 444 44 21 -6.8 PTG-6-1 24-Jun-98 26 5500 353 697 230 28 271 1907 474 34 17 -6.2 22-Jul-98 ns ns ns ns ns ns ns ns ns ns ns ns PTG-8-1 20-Aug-98 26 5300 _ 439 530 300 33 282 2952 - 476 30 8 -6.5 PTG-8-2 20-Aug-98 26 5300 - - - - - _ - - - -6.5 Average 25 5623 423 612 286 34 327 2650 445 38 18 -6.5 Samp.St.Dev. 1 259 34 62 39 3 31 265 24 5 5 0.2 %Deviation 3 5 8 10 14 8 9 10 5 13 27 3 Sample No.1 Date Temp.2 Cond.3 Ca4 Na Mg K CI SO4 HCO3 SIO2 NO3 8150 5 KCS-10-1 10-Oct-97 22 3410 446 146 267 27 298 1502 478 35 2 -5.8 KCS-2-1 13-Feb-98 23 2790 445 154 365 25 304 1274 547 40 2 -5.7 KCS-4-1a 16-Apr-98 18 3780 536 183 337 24 298 2393 505 41 4 -5.7 KCS-6-1a 24-Jun-98 - - 490 157 301 25 267 1979 466 34 2 -5.8 KCS-8-la 2.0-Aug-98 20 3400 450 119 284 26 250 1991 537 30 3 -5.9 KCS-12-i L 1 C1.4)0047 1 ',.i':..:31:20> , 347 :11.0 _ 11 11 1�z 4 34 ' .:L:•••'.2,....'....-..,•.:411::.,:. f 1b ! f x- 1 ' ' 3 3k0 24'� • • aids 9 i { a diJ i 4 t� >4 _ .. $#i 14$ b 1 .06 343: :':: : 1.88.:..:. 2b. •31 • 3 "1 O- :..31::::•'". 4 $45 R ib w j , '-Aug- .. '. ... :.:,3 i4::< i8 _ 1, , 3I.. <31 >it :,6345.::: :..,.::'34,•.:,..:' i :-8:8 Average 21 3420 359 207 248 32 253 1722 576 35 4 -5.7 Samp.St.Dev. 1 223 21 28 15 1 24 278 61 5 1 0.1 %Deviation 5 7 6 13 6 2 9 16 11 13 28 2 Sa same es were coect iii center o spring sur ace stream. rn TABLE B-2. GEOCHEMICAL AND ISOTOPIC DATA FOR DOMESTIC WATER (DW)AND SURFACE RUNOFF SAMPLES Sample No.' Date Temp.2 Cond.' Ca4 Na Mg K CI SO4 HCO3 Si02 NO3 8180 5 DW1-10-1 10-Oct-97 - 80 85 - 24 3 80 165 137 3 1 -112 OW212-1 10-Dec-97 - 75 422 23 4 75 W4 154 .4" 1i 401- DW3-6-1 24-Jun-98 61 48 20 2 55 171 149 - - -11.4 DW4-7-1 22-Jul-98 51 55 _, 11 3 73 220 137 3 1 -11.3 Average - 64 63 18 3 69 185 141 3 1 -11.3 Samp.St.Dev. 15 19 7 0 13 30 7 0 0 0.1 %Deviation - 23 31 37 15 19 16 5 6 27 3 Sample No.' Date Temp.2 Cond.3 Ca' Na Mg K CI SO4 HCO3 Si02 NO3 8180 5 S8126-1 26-Jan-98 20 13 8 3 29 41 49 - -2.8 SB126-2 26-Jan-98 - - - - - - - - -9.2 SB126-3 26-Jan-98 - _ - - -8.7 SB126-4 26-Jan-98 - - - .. -. .. -8.7 N126-1 26-Jan-98 13 0 1 3 15 17 10 - - -3.4 N126-2 26-Jan-98 - •• - - .. - - -9.4 N126-3 26-Jan-98 • • -8.8 SB23-1 03-Feb-98 - 20 20 7 1 29 43 36 - - -4.0 SB23-2 03-Feb-98 ' .• 18 17 5 1 18 27 41 - - -5.5 SB23-3 03-Feb-98 - - 15 15 5 0 11 33 37 - -9.1 S823-4 03-Feb-98 • - 23 21 8 1 17 55 56 -9.2 SB23-5 03-Feb-98 30 27 12 0 16 73 71 - -9.1 5B23-6 03-Feb-98 - 20 18 7 1 10 42 49 - -12.5 SB23-7 03-Feb-98 - 31 25 11 1 20 83 66 - -11.9 SB23-8 03-Feb-96 .• - 45 29 15 1 22 129 66 - - -114 N23-1 03-Feb-98 19 24 4 7 39 25 27 - - -3.7 N23-2 03-Feb-98 - - 23 24 7 2 39 37 95 - - -6.7 N23-3 03-Feb-98 - 19 18 6 2 16 36 56 - -9.8 N23-4 03-Feb-98 - -_ 22 19 7 2 22 46 66 - - -9.4 N23-5 03-Feb-98 - 15 11 3 3 7 30 44 - - -11.6 N23-6 03-Feb-98 - 24 21 8 1 16 51 56 - -11.8 N23-7 ' 03-Feb-98 .. 13 29 11 — 2 24 93 76 - - -11.7 S ase. sampe exc used rom calculations. i.) v TABLE B-3. GEOCHEMICAL AND ISOTOPIC DATA FOR RAINFALL SAMPLES Sample No' Date Temp.2 Cond.' Ca4 Na Mg K CI SO4 HCO3 S107 NO3 8780 5 RD-1 13-Nov-97 - - - - - - -6.0 RD-2 13-Nov-97 - - - - - - - - - -5.4 RD-3 14-Nov-97 - - - - - .. - -- -5.1 RD-4 20-Nov-97 - - - - - - - - - -2.2 RD-5 26-Nov-97 - - - - - - - - - - - -4.4 RD-6 30-Nov-97 - - - -- - -. - -7.1 RD-7 06-Dec-97 - - - - .. - - - -2.8 RD-8 06-Dec-97 - - -6.6 RD-9 07-Dec-97 .- .. .- .. - - - .. - - -5.6 RD-10 19-Dec-97 - - - - ., - - - - - - -5.5 RD-11 05-Jan-98 - - - - - - - - - -5.4 RD-12 10-Jan-98 -- - - - - - - - - - -4.6 RD-13 14-Jan-98 - - - - - -2.7 RD-14 19-Jan-98 - - - - .. - - - - - -1.1 RD-15 01-Feb-98 - - - - - - .. - - - - -4.0 RD-16 02-Feb-98 - - - - - - - - - - -2.7 RD-17 03-Feb-98 - -- 0.4 6.7 0.8 0.0 7.8 0.0 0.0 - - -6.3 RD-18 03-Feb-98 0.2 0.4 0.1 0.0 0.0 0.0 0.0 - - -13.1 RD-19 06-Feb-98 - -4.4 RD-20 08-Feb-98 - - - - - - - - - - - - -5.2 RD-21 ' 09-Feb-98 - - - .. - -5.0 RD-22 16-Feb-98 - - - - - - - - - - - -4.0 RD-23 21-Feb-98 - .. -. - - - - - -. -11.5 RD-24 23-Feb-98 - - - - - - - - -2.5 RD-25 25-Feb-98 - - - - - - -5.3 RD-27 31-Mar-98 - - .. .- -4.2 RD-28 01-Apr-98 - - - - - - - - _ - - - -7.0 RD-29 13-Apr-98 -- .. - - - - -. - - -6.6 RD-30 05-May-98 - - - - - - - - - - - -2.9 RD-31 13-May-98 - - - - - - - - - - -5.3 DCP-Rl 04-Feb-98 - - - - - - - - - -6.3 DC-R1 04-Feb-98 - - - - - - - - - -8.6 BD-R1 04-Feb-98 • .. - - - 8.39 �,, e0 Notes for Table B-1: Sample numbers(ex. LCC 1-9-1)represent well(LCC 1)-month collected(Sept.)-sample number(1) 2 Temperature measurements given in degrees centigrade 3 Conductivity measuremei is given in µmhos 'Major ion concentrations given in milligrams per liter. (All results within 3%uncertainty,except bold entries,which are within 10%). 5 Oxygen isotope concentrations given in parts per thousand. ns=no sample collected -=sample not analyzed Notes for Table B-2: ' Sample numbers(ex. SB126-1) represent sample location(SB),collection date(12/6),and sample number(1) 2 Temperature measurements given in degrees centigrade 'Conductivity measurements given inµmhos 'Major ion concentrations given in milligrams per liter. (All results within 3%uncertainty,except bold entries,which are within 10%). 5 Oxygen isotope concentrations given in parts per thousand. ns= no sample collected -=sample not analyzed Notes for Table B-3: ' Sample numbers(cx. RD-1)represent rain gauge location(RD),and sample number(1) 2 Temperature measurements given in degrees centigrade Conductivity measurements given in µmhos 'Major ion concentrations given in milligrams per liter, (All results within 3%uncertainty,except bold entries,which arc within 10%). 5 Oxygen isotope concentrations given in parts per thousand. us= no sample collected =sample not analysed