HomeMy WebLinkAboutSEEPAGE MITIGATION LTS 160-165 TR 28214-5 PETRA
SOLID ASA ROCK
ENGINEERS + GEOLOGISTS + ENVIRONMENTAL SCIENTISTS
December 31, 2015
J.N. 13-578
Mr.Vernell Williams
KB HOME COSTAL DIVISION
36310 Inland Valley Drive
Wildomar, California 92595
Subject: Clarification of Seepage Mitigation, Lots 160-165 and 190-193 of Tract 28214-5,
Alberhill Ranch Development,City of Lake Elsinore,Riverside County,California
References: 1) Petra Geotechnical, 2006, Recommendations for Seepage Mitigation, Tract 28214-5
(Phase 5), City of Lake Elsinore, Riverside County, California, prepared for Castle &
Cooke Alberhill Ranch, Inc., J.N. 160-04, dated June 7
2) Petra Geosciences, Inc., 2015, Geotechnical Update Report, Lots 160-202 of Tract
28214-5 in the Alberhill Ranch Development, City of Lake Elsinore, Riverside County,
California,prepared for KB Home, J.N. 13-578, dated December 8.
Dear Mr. Williams:
In accordance with the request of the City of Lake Elsinore, Petra Geosciences, Inc. (Petra) has reviewed
the seepage conditions affecting the subject lots with respect to prevoius recommendations for seepage
mitigation (Petra, 2006, 2015). In mid-2006 seepage was observed near the toes of the north-facing fill
slopes on Lots 160-165 and 190-193 of Tract 28214-5. The seepage appeared to emanate from relatively
clean coarse-grained fill materials which were underlain by finer-grained fill material. It appeared at the
time that the likely source of the seepage may have been from infiltration of recent rains, day-lighting on
the slope face at the contact with the less permeable finer-grained fill layers. At that time Petra
recommended the construction of subsurface drains at the toes of the affected fill slopes (Petra, 2006).
However, with the curtailment of development activities around the time of the recommendations, the
drains were not installed.
A subsurface drain system was in the process of being installed on October 23, 2015 at the rear and side
yards of Lots 160-163 to mitigate ongoing seepage. Petra also evaluated the condition of Lots 164, 165
and 190-193 October 23, 2105,which were observed to be dry with no evidence of recent seepage. Based
on our observations since the grading of Lots 164, 165 and 190-193, the seepage previously observed
appears to be the result of lateral dissipation of excess water applied in the fill placement process. A
similar condition was noted in the some of the fill slopes constructed for Lots 1-66 in Tract 29214-5. The
fill material was predominantly granular in nature with a large percentage of rock fragments derived from
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KB HOME COASTAL DIVISION December 31, 2015
Lots 160-165 and 190-193, Tract 28214-5/Lake Elsinore J.N. 13-578
Page 2
cuts in the Santiago Peak Volcanics bedrock, which required heavy watering to facilitate the compaction
process. The seepage noted on Lots 164-165 and 190-193 in 2006 gradually dissipated over time and is
not anticipated to be a significant long-term problem, although localized seepage may return with the
onset of post-construction irrigation. If localized seepage does resume on the previously affected lots or
is observed in other areas, these areas will be evaluated for the need of similar subdrains and drains will
be installed, if deemed necessary.
This opportunity to be of service is sincerely appreciated. If you have any questions, please contact this
office.
Respectfully submitted,
PETRA GEOSCIENCES, INC.
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Gra son R. Walker, GE
Principal Engineer sTCccplECNN��P��Q
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Distribution: (1) Addressee(Electronic)
(1) KWC Engineers, Attn. Mike Taing(Electronic)
GRW/nbc
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