HomeMy WebLinkAboutSDP 2022-0003; FPC RESIDENTIAL; GEOTECHNICAL INFILTRATION; 2022-08-18 ADVANCED GEOTECHNICAL SOLUTIONS, INC.
485 Corporate Drive, Suite B
Escondido, California 92029
Telephone: (619) 867-0487 Fax: (714) 409-3287
ORANGE AND L.A. COUNTIES INLAND EMPIRE SAN DIEGO AND IMPERIAL COUNTIES
(714) 786-5661 (619) 867-0487 (619) 867-0487
H.G. Fenton Company August 18, 2022
7577 Mission Valley Road P/W 2107-12
San Diego, California 92108 Report No. 2107-12-B-6
Attention: Ryley Webb
Subject: Additional Comments, Feasibility of Onsite Infiltration, Proposed Multi-Family
Residential Development, 7200-7294 Ponto Drive, Carlsbad, California
References: See Appendix
Gentlepersons,
In accordance with your request, Advanced Geotechnical Solutions, Inc. (AGS) has prepared this letter
presenting additional comments related to the feasibility of infiltration at the subject residential
development on Ponto Drive in Carlsbad, California. AGS prepared an infiltration feasibility report (2022b)
and recommended that infiltration type BMP’s not be installed as part of the proposed development.
Subsequent to the preparation of the infiltration report, AGS has reviewed the referenced geotechnical
reports by Geotechnics Incorporated and Group Delta for the westerly and northerly adjacent hotel and spa.
Geotechnics Incorporated conducted a geotechnical investigation for the adjacent hotel and spa in 2009,
which included subsurface exploratory work consisting of six exploratory borings, including two within the
footprint of the parking garage located adjacent to the northerly boundary of the subject site. The boring
logs for Geotechnical Incorporated indicated that a 7-foot thick clay layer was encountered in Boring B-4
at a depth of 6 feet, and a 2.5-foot thick clay layer was encountered in Boring B-6 at a depth of 6 feet. A
similar clay layer was encountered in AGS’s borings and test pits at the subject site, also at similar shallow
depths. This would indicate that the clay layer is fairly continuous and extends offsite. This clay layer is
expected to act as an aquitard and preclude any appreciable infiltrating water from flowing vertically
through the clay layer. Infiltrating water is expected to perch atop this clay layer and flow laterally. Over
time groundwater mounding and lateral flow can occur, increasing the likelihood for water intrusion to
occur in adjacent utility trenches and subgrade soils, which can lead to soil piping, settlement, and
premature failure of pavements and other surface improvements. In addition, the clay layer encountered is
highly expansive and capable of significant volume increases when exposed to water, which can lead to
heaving of overlying soils and improvements.
Accordingly, the DMA’s onsite are considered restricted for infiltration based on the guidance provided in
Appendix D of the City of Carlsbad’s BMP manual. Vertical infiltration of appreciable amounts of water
is not considered technically feasible onsite without increasing the risk of geotechnical hazards to adjacent
properties, City utilities, and proposed project improvements that cannot be reasonably mitigated. It is
recommended that stormwater BMPs constructed onsite utilize an impermeable liner/membrane to mitigate
potential negative impacts to improvements both onsite and offsite.
~GS
August 18, 2022 Page 2
P/W 2107-12 Report No. 2107-12-B-6
ADVANCED GEOTECHNICAL SOLUTIONS, INC.
The opportunity to be of service is sincerely appreciated. If you should have any questions, please do not
hesitate to contact the undersigned.
___________________________________
JOHN J. DONOVAN
RCE 65051, RGE 2790, Reg. Exp. 6-30-23
2107-12-B-6 (Additional Comment, Infiltration Feasibility, Aug 18, 2022).docx
Appended Appendix- References
Distribution: (1) Addressee (pdf)
August 18, 2022 Page 2
P/W 2107-12 Report No. 2107-12-B-6
ADVANCED GEOTECHNICAL SOLUTIONS, INC.
APPENDIX
REFERENCES
Advanced Geotechnical Solutions, Inc. (2021). “Due Diligence Geotechnical Study, Proposed Multi-
Family Residential Development, 7200-7590 Ponto Drive, Carlsbad, County of Orange, California,”
dated December 3, 2021, Report No. 2107-12-B-2R.
---. (2022a). “Preliminary Geotechnical Investigation and Infiltration Study, Proposed Multi-Family
Residential Development, 7200-7294 Ponto Drive, Carlsbad, California,” dated March 16, 2022,
Report No. 2107-12-B-4.
---. (2022b). “Preliminary Infiltration Feasibility Study, Proposed Multi-Family Residential Development,
7200-7294 Ponto Drive, Carlsbad, California,” dated March 16, 2022, Report No. 2107-12-B-5.
City of Carlsbad, 2021, Storm Water Standard – BMP Design Manual, February 2016, Revised
September 1, 2021, Edition.
Geotechnics Incorporated. (2009). “Geotechnical Investigation, Hilton Carlsbad Beach Resort and Spa,
Carlsbad, California,” dated April 24, 2009 (Project No. 0703-002-01, Document No. 09-0206).
Group Delta. (2010a). “Response to Review Comments, Hilton Carlsbad Oceanfront Resort & Spa,
Carlsbad, California,” dated May 10, 2010 (Document No. 10-0288, Project No. 0703-002-01.
---. (2010b). “Response to Request for Information, Hilton Carlsbad Oceanfront Resort, Carlsbad,
California,” dated October 6, 2010 (Document No. 10-0526, Project No. SD-126.
---. (2010c). “Grading Plan Review, Hilton Carlsbad Oceanfront Resort & Spa, Carlsbad, California,”
dated November 30, 2010 (Document No. 10-0601, Project No. SD-126.