HomeMy WebLinkAboutSDP 16-12; HARDING VETERANS HOUSING; UPDATE GEOTECHNICAL ENGINEERING REPORT; 2020-03-12GEOTE JICAL
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NOVA SPECIAL INSPECTION Initial Date SBE • DVBE
Affirmed Housing Group March 12, 2020
CIO Marie Allen NOVA Project No. 3019097
13520 North Evening Creek Drive
San Diego, CA 92128
Attention: Ms. Allen (via email; marie(ãaffirmedhousing.óom)
JT rr T 'T Subject: Update Geotechnical Engineering Report \/jJ
Project: Proposed Three-Story Apartment Building MAR 16 2020
3606-3618 & 3630 Harding Street, Carlsbad, Califor0 DEVELOPMENT
References: ENGI NEE ER1;G
CWE 2016a. Report of Preliminary Geotechnical Investigation, Affirmed Housing, 3606-3618 & 3630
Harding Street, Carlsbad, California, Christian Wheeler Engineering, June 2, 2016.
CWE 2016b. Report of Preliminary Recommendations, Affirmed Housing, 3606-3618 & 3630 Harding
Street, Carlsbad, California, Christian Wheeler Engineering, April 20, 2016.
KL 2020. Rough Grading Plan (Sheet 3 of 8), Harding Veterans Housing, Kettler Leweck Engineering,
March 11, 2020.
Dear Mrs. Allen,
The intent of this Update Geotechnical Engineering Report is to provide updated
recommendations to address changes in design and to update previously prepared seismic
design parameters for the project. NOVA Services, Inc. (NOVA) has been retained by Affirmed
Housing as Geotechnical Engineer-of-Record (GEOR) for the subject project.
NOVA has reviewed the referenced geotechnical reports and plans for the subject development.
With specific consideration of its roll as GEOR, NOVA has reviewed and agrees with the data,
recommendations, and conclusions contained in the referenced project geotechnical reports
(CWE 2016a and CWE 2016b) except as updated and revised herein.
OBSERVATIONS AND BACKGROUND
A NOVA Services representative recently visited the subject property to observe existing
conditions at the site. Observations made during the visit revealed no apparent significant
changes since the referenced reports were issued. The following Figure 1, presents an image
of the site taken during NOVA's recent site visit.
4373 Viewridge Avenue, Suite B www.usa-nova.com 24632 San Juan Avenue, Suite 100
San Diego, CA 92123 Dana Point, CA 92629
P: 858.292.7575 P: 949.388.7710
Geotechnical Engineering Report
3606-3618 & 3630 Harding Street, Carlsbad, CA
upit Project No.: 3019097
N 0 VA 1 March 12, 2020
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Figure 1. Existing Site Conditions as of December 20, 2019.
Figure 2 (following page) depicts the subsurface exploration locations based on existing site
conditions. Plates IA and IB, provided immediately following the text of this report, present
these locations in larger scale on the existing site condition and on a planned improvements
plan, respectively.
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NOVA
U,.--.e Geotechnical Engineering Report
3606-3618 & 3630 Harding Street, Carlsbad, CA
Project No.: 3019097
March 12, 2020
project construction to verify that the design plans and good construction practices are followed.
This is especially important for sites lying close to the major seismic sources.
Table 1. Seismic Design Parameters, 2016 CBC and ASCE 7-10
Parameter . Value
Site Soil Class C
Site Latitude (decimal degrees) 33.15536°N
Site Longitude (decimal degrees) - 117.33908°W
Site Coefficient, Fa 1.0
Site Coefficient, Fv 1.361
Mapped Short Period Spectral Acceleration, Ss 1.143 g
Mapped One-Second Period Spectral Acceleration, S1 0.439 g
Short Period Spectral Acceleration Adjusted for Site Class, SMS 1.143 g
One-Second Period Spectral Acceleration Adjusted for Site Class; 5M1 0.597 g
Design Short Period Spectral Acceleration,SDS 0.762 g
Design One-Second Period Spectral Acceleration, S01 0.398 g
Modified Peak Ground Acceleration, PGAM 0.452 g
Source: OSHPD Seismic Design Maps, found at: https://seismicmaDs.org/
Review of Geotechnical Feasibility Criteria
It is common that seven factors be considered by the project geotechnical professional while
assessing the feasibility of infiltration related to geotechnical conditions. These factors are:
C2.1) Soil and Geologic Conditions
C2.2) Settlement and Volume Change
C2.3) Slope Stability
C2.4) Utility Considerations
C2.5) Groundwater Mounding
C2.6) Retaining Walls and Foundations
C2.7) Other Factors
The above geotechnical feasibility criteria are reviewed in the following subsections.
Soil and Conditions
The soil borings completed for this assessment disclose the sequence of soil units described
below.
Unit 1, Fill. (Qaf) Fill material was encountered generally in the upper 2 to 4 feet of
the subsurface is predominantly silty sand and placement is undocumented.
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gi U p..ie Geotechnical Engineering Report
3606-3618 & 3630 Harding Street, Carlsbad, CA
Project No.: 3019097
NOVA. March 12, 2020
Unit 2. Old Paralic Deposits (Qop). Quaternary-age old paralic deposits were
previously encountered at depths of 2 to 4 feet below existing, grade. Old paralic
deposits were found to consist of very fine to medium grained silty sand and poorly-
graded sand with silt.
Unit 3. Santiago Formation (Tsa). Tertiary-age sediment deposits of the Santiago
Formation were encountered at depths of about 11 feet below existing grade. When
disturbed by drilling tools, the formational material consisted of silty sand and clayey
sand.
Settlement and Volume Change
The Unit I and Unit 2 soils have very low expansion potential. These soils will not be prone to
swelling upon wetting. The existing fill soils may be prone to hydro consolidation upon wetting.
Slope Stability
BMPs should not be located near slopes. There are no structural slopes at the site.
Utilities
Infiltration can potentially damage subsurface and underground utilities. BMPs should be sited a
minimum of 10 feet away from underground utilities.
Groundwater Mounding
Stormwater infiltration can result in groundwater mounding during wet periods, affecting utilities,
pavements, flat work, and foundations.
Retaining Walls and Foundations
BMPs should not be located near foundations. BMPs should be sited a minimum of 25 feet
away from any foundations or retaining walls.
Other Factors
Historic ground water was found to be at depths of about 26 (+50 feet msl) feet below ground
surface 1500 feet south of the site within monitoring well no. 6 at the address of 970 Tamarack
Road. CWE reporting encountered seeping water at depths of 11 feet bgs during site
subsurface exploration.
Suitability of the Site for Stormwater Infiltration
It is NOVA's judgment that the site is not suitable for development of stormwater infiltration
BMPs. This judgment is based upon consideration of the variety of factors detailed above, most
significantly the location of planned stormwater BMPs and (i) proximity to planned foundations,
and (ii) proximity to existing utility lines and the City Right of Way (ROW).
Appendix A provides completed forms related to stormwater infiltration feasibility.
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A U,1e Geotechnical Engineering Report
3606-3618 & 3630 Harding Street, Carlsbad, CA
Project No.: 3019097
NOVA March 12, 2020
CLOSURE
NOVA considers that the recommendations contained in the referenced geotechnical report are
adequate and NOVA does not have additional recommendations based on the plans provided
other than those specified herein.
NOVA appreciates the opportunity to provide its services on this project. Should you have any
questions regarding this letter or other matters, please do not hesitate to contact the
undersigned at (949) 388-7710.
Sincerely,
NOVA Services, Inc.
(e D. Bearfie
ior Engineer
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Attachments:
Plate IA. Subsurface Investigation Map on Existing Conditions
Plate I B. Subsurface Investigation Map on Proposed Development
Appendix A. Infiltration Feasibility Worksheets
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NOVA
Lspaaie Geotechnical Engineering Report
3606-3618 & 3630 Harding Street, Carlsbad, CA
Project No.: 3019097
March 12, 2020
APPENDIX A
Infiltration Feasibility Worksheets
Appendix I: Forms and Checklists
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Part 1- Full Infiltration Feasibility Screening Criteria
Would infiltration of the full design volume be feasible from a physical perspective without any undesirable
consequences that cannot be reasonably mitigated?
Criteria Screening Question Yes No
Is the estimated reliable infiltration rate below proposed
facility locations greater than 0.5 inches per hour? The response
1 to this Screening Question shall be based on a comprehensive
evaluation of the factors presented in Appendix C.2 and Appendix
D.
Provide basis:
Infiltration rate of on-site soils have not been measured.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
Can infiltration greater than 0.5 inches per hour be allowed
without increasing risk of geotechnical hazards (slope stability,
2 groundwater mounding, utilities, or other factors) that cannot X be mitigated to an acceptable level? The response to this
Screening Question shall be based on a comprehensive evaluation of
the factors presented in Appendix C.2.
Provide basis:
C2.2: Settlement and Volume Change: The existing fills are subject to hydro consolidation as a result of
increased moisture content.
C2.4: Utility Considerations: The site area is relatively small and proposed and existing utility trenches and the
adjacent utility trenches within the City Right of Way are susceptible to saturation and lateral migration of
infiltrated storm water.
C2.6: Foundations: The site area is relatively small, and any proposed infiltration facilities would place infiltration
storm water in close proximity to planned foundations.
1-3 February 2016
Appendix I: Forms and Checklists
Criteri Screening Question Yes No a
Can infiltration greater than 0.5 inches per hour be allowed
without increasing risk of groundwater contamination (shallow
water table, storm water pollutants or other factors) that cannot
be mitigated to an acceptable level? The response to this
Screening Question shall be based on a comprehensive evaluation of
the factors presented in Appendix C.3.
Provide basis:
Risk of groundwater contamination has not been evaluated.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
Can infiltration greater than 0.5 inches per hour be allowed
without causing potential water balance issues such as change
of seasonality of ephemeral streams or increased discharge of
contaminated groundwater to surface waters? The response to
this Screening Question shall be based on a comprehensive
evaluation of the factors presented in Appendix C.3.
Provide basis:
The risk of causing potential water balance issues have not been evaluated at this time.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
If all answers to rows 1 - 4 are "Yes" a full infiltration design is potentially feasible.
Part 1 The feasibility screening category is Full Infiltration
Result If any answer from row 1-4 is "No", infiltration may be possible to some extent but
would not generally be feasible or desirable to achieve a "full infiltration" design.
Proceed to Part 2
'To be completed using gathered site information and best professional judgment considering the definition of MEP in
the MS4 Permit. Additional testing and/or studies may be required by the City to substantiate findings.
14 February 2016
Appendix I: Forms and Checklists
Part 2— Partial Infiltration vs. No Infiltration Feasibility Screening Criteria
Would infiltration of water in any appreciable amount be physically feasible without any negative
consequences that cannot be reasonably mitigated?
Criteria Screening Question Yes No
Do soil and geologic conditions allow for infiltration in any
appreciable rate or volume? The response to this Screening X Question shall be based on a comprehensive evaluation of the
factors presented in Appendix C.2 and Appendix D.
Provide basis:
C2.2: Settlement and Volume Change: The existing fills are subject to hydro consolidation as a result of
increased moisture content.
C2.4: Utility Considerations: The site area is relatively small and proposed and existing utility trenches and the
adjacent utility trenches within the City Right of Way are susceptible to saturation and lateral migration of
infiltrated storm water.
C2.6: Foundations: The site area is relatively small, and any proposed infiltration facilities would place infiltration
storm water in close proximity to planned foundations.
Can Infiltration in any appreciable quantity be allowed
without increasing risk of geotechnical hazards (slope
X 6 factors) stability, groundwater mounding, utilities, or other
that cannot be mitigated to an acceptable level? The response
to this Screening Question shall be based on a comprehensive
evaluation of the factors presented in Appendix C.2.
Provide basis:
C2.2: Settlement and Volume Change: The existing fills are subject to hydro consolidation as a result of
increased moisture content.
C2.4: Utility Considerations: The site area is relatively small and proposed and existing utility trenches
and the adjacent utility trenches within the City Right of Way are susceptible to saturation and lateral
migration of infiltrated storm water.
C2.6: Foundations: The site area is relatively small, and any proposed infiltration facilities would place
infiltration storm water in close proximity to planned foundations.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability and why it was not feasible to mitigate low infiltration rates.
I-S February 2016
Appendix I: Forms and Checklists
Bev P.
Criteria Screening Question Yes No
Can Infiltration in any appreciable quantity be allowed
without posing significant risk for groundwater related
concerns (shallow water table, storm water pollutants or other
factors)? The response to this Screening Question shall be based
on a comprehensive evaluation of the factors presented in
Appendix C.3.
Provide basis:
Risk of groundwater contamination has not been evaluated at this time.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability and why it was not feasible to mitigate low infiltration rates.
Can infiltration be allowed without violating downstream
8 water rights? The response to this Screening Question shall be
based on a comprehensive evaluation of the factors presented in
Appendix C.3.
Provide basis:
Risk of potential water balance issues has not been evaluated at this time.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability and why it was not feasible to mitigate low infiltration rates.
If all answers from row 5-8 are yes then partial infiltration design is potentially feasible.
Part 2 The feasibility screening category is Partial Infiltration.
No Result* . If any answer from row 5-8 Is no, then infiltration of any volume is considered to be Infiltration
infeasible within the drainage area. The feasibility screening category is No Infiltration.
"To be completed using gathered site information and best professional judgment considering the definition of MEP in
the MS4 Permit. Additional testing and/or studies may be required by the City to substantiate findings.
1-6 February 2016