CC RES 2002-043 RESOLUTION NO. 2002-43
A RESOLUTION OF THE CITY COUNCIL OF THE CITY
OF RANCHO PALOS VERDES SETTING FORTH
CERTAIN FINDINGS REGARDING "ZONE 2" OF THE
LANDSLIDE MORATORIUM AREA BASED UPON THE
REPORT THAT WAS PREPARED BY COTTON, SHIRES
& ASSOCIATES
WHEREAS, in 2001, the City Council approved a professional services
agreement with Cotton, Shires &Associates to review existing geologic data to address
certain issues regarding potential development in the area of the Landslide Moratorium
that has been informally designated as "Zone 2"; and
WHEREAS, pursuant to the direction of the City Council, Cotton, Shires &
Associates prepared a draft report in September, 2001, which was made available to all
interested persons and the public for review and comment; and
WHEREAS, interested persons and members of the public submitted comments
and questions on the draft report, which thereafter were reviewed by Cotton, Shires &
Associates; and
WHEREAS, pursuant to the direction of the City Council, Cotton, Shires &
Associates prepared a report dated January 14, 2002; and
WHEREAS, on May 20, 2002, at a duly noticed public meeting, the City Council
of the City of Rancho Palos Verdes reviewed the report that was prepared by Cotton,
Shires &Associates and discussed certain findings that should be made as a result of
the report; and
WHEREAS, the City Council has directed staff to prepare a resolution setting
forth its findings;
NOW, THEREFORE, THE CITY COUNCIL OF THE CITY OF RANCHO PALOS
VERDES HEREBY FINDS, RESOLVES AND ORDERS AS FOLLOWS:
1. The City Council hereby accepts the following conclusions of the Cotton,
Shires &Associates, January 14, 2002 Technical Review that:
A. There is insufficient subsurface information to properly characterize
either the depth to the base of landslide, the strength properties of the
landslide materials, or the groundwater levels. Without these data, no
accurate slope stability analysis can be undertaken, no reliable factor
of safety can be calculated and no dependable landslide mitigation
scheme can be designed.
B. One cannot quantitatively determine the factor of safety and, therefore,
cannot judge the level of risk of development in the prehistoric
landslide area, which includes Zone 2.
C. The factor of safety of the landslide mass that underlies Zone 2 is
above 1.00, but probably is less than the industry's standard safety
threshold of 1.50 for residential development, which also is the
standard that is used by the City of Rancho Palos Verdes.
D. The City Council finds that the accepted geotechnical standard for new
residential construction, which is a Factor of Safety of 1.5 for slope
stability that is applied throughout the City, also should be applied
within the boundaries of the Landslide Moratorium Area. This is a
common standard among geotechnical professionals and has been
adopted by most, if not all, municipalities in Southern California.
(Cotton Report page 5, 8-9, Cotton Jan. 30, 2002, letter page 1.)
E. No recognized geological agency or standard-setting body has
adopted as a standard for determining whether or not to allow
residential development a standard or test that is based on an inquiry
as to whether or not the development of the property would "further
destabilize" an area, or such similar standard. Accordingly, Rancho
Palos Verdes declines to adopt such a standard within its jurisdiction.
(Cotton Jan. 30, 2002, letter page 1.)
F. Geologically, the level of risk of allowing development of undeveloped
residential lots in Zone 2 is presently unknown. The decision to allow
new building upon undeveloped lots in that area, given the unknown
level of risk, is a policy decision, which must be based on a willingness
to accept the unknown risk. (Cotton Jan. 30, 2002 letter, page 1.)
G. The guidelines suggested by Dr. Perry Ehlig in his Memorandum of
May 26, 1993, appear to be based on Dr. Ehlig's subjective
assessment, based on his experience, judgment and expertise.
However, Cotton, Shires uncovered no geotechnical slope stability
analyses of Zone 2 in Dr. Ehlig's files. (Cotton Jan 30, 2002 letter,
page 2, Report page 2.)
H. Although a number of mitigation measures have been employed, to
date no quantitative geotechnical analysis to determine the
effectiveness of these measures has been undertaken. (Cotton Report
page 2.)
I. It has been noted by various individuals that the apparent long period
of there being no recorded land movement in Zone 2 suggests that the
area is adequately stable to allow building on undeveloped properties
in that Zone. Yet there is no clear evidence of the age of the landslide.
Further, predicting the long-term stability of the landslide in advance of
Resolution No. 2002-43
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detailed surface and subsurface information is founded on ill-advised
technical reasoning. (Cotton Report page 3.)
2. The conclusion noted in the Cotton, Shires January 2002 Report that the
undeveloped ("vacant") lots could be developed "without further destabilizing the
large regional landslide" is a conclusion that is not based on the application of the
accepted standard that seeks a Factor of Safety of 1.5, but instead is based on
the fact that it is feasible to construct new homes without significant redistribution
of earth mass or contributing to groundwater rise. Hence, this conclusion is not
based on an evaluation of the stability of the underlying geology. This response
was the result of a request by the City Council that the report address the issue
of whether or not the development would "further destabilize" the area. (Cotton
Jan. 30, 2002 letter page 1-2.) Because this conclusion is not based on a
standard that is recognized by a geological agency or standard-setting body, the
City of Rancho Palos Verdes declines to adopt that conclusion.
3. Based on the foregoing, the City Council is directing City Staff to continue
to deny requests for development permits for new homes in the Zone 2 area of
the Portuguese Bend landslide complex, because of the current lack of evidence
that the Zone 2 area has a factor of safety of 1.5 or greater, until an applicant
submits a complete Landslide Moratorium Exclusion application that is supported
by adequate geologic data demonstrating a factor of safety of 1.5 or greater of
the Zone 2 area to the satisfaction of the City Geologist; the City Council
approves the Landslide Moratorium Exclusion application, and all other required
permits to develop are issued by the City.
PASSED, APPROVED AND ADOPTED this 12th day of June 2002.
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City Clerk
STATE OF CALIFORNIA )
COUNTY OF LOS ANGELES ) ss
CITY OF RANCHO PALOS VERDES )
I, JO PURCELL, City Clerk of the City of Rancho Palos Verdes, do hereby certify
that the above Resolution No. 2002-43 was duly and regularly passed and adopted by
the said City Council at a regular meeting thereof held on June 1 2002. ,-,
. i_ ii_ _ ,
City Clerk
Resolution No. 2002-43
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