HomeMy WebLinkAboutPD 2021-0004; NORTH COUNTY ACADEMY; RESPONSE TO CITY REVIEW OF STORM WATER QUALITY MANAGEMENT PLAN (SWQMP); 2021-06-02Carlsbad Unified School District June 2, 2021
Mr. Derrick Anderson NOVA Project 2020187
6225 El Camino Real
Carlsbad, CA 92009
Subject: Response to City Review of Storm Water Quality Management Plan (SWQMP)
North County Academy, Campus Consolidation
1640 Magnolia Avenue, Carlsbad, California
References:
MBI 2021. Review/Redlines by Michael Baker International of: Priority Development Project (POP) Storm
Water Quality Management Plan (SWQMP) for North County Academy - Campus Consolidation prepared
by PLSA, dated December 17, 2020.
NOVA 2020. Report, Preliminary Geotechnical Investigation, Proposed Portable Classrooms, North
County Academy, 1640 Magnolia Avenue, Carlsbad, CA 92008, NOVA Services, Inc., Project No.
2020187, December 7, 2020.
NOVA 2021. Update Report, Geotechnical Investigation, North County Academy, Campus Consolidation,
1640 Magnolia Avenue, Carlsbad, CA, NOVA Services, Inc., Project No. 2020187, June 2, 2021.
PLSA 2021. Grading Plans For: North County Academy, Campus Consolidation, 1640 Magnolia Avenue,
Carlsbad, California, Pasco Laret Suiter & Associates, Inc., Project No. 687995, undated, received by
NOVA May 11, 2021.
Dear Mr. Anderson:
The intent of this letter is to respond to the redlines within the review of the project 1-8 Form.
These redlines are a portion of the project SWQMP review conducted by Michael Baker
International (MBI 2021), on behalf of the City of Carlsbad for the above-referenced
geotechnical reporting and plans (NOVA 2020 and PLSA 2021).
NOVA Services, Inc. (NOVA) is retained by Carlsbad Unified School District as Geotechnical
Engineer-of-Record (GEOR) for the project.
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For the convenience of the reviewer, the redlined 1-8 Form (MBI 2021) is attached to this
response. MBI 2021 raises concerns about the site being designed by PLSA as "No Infiltration",
considering that NOVA 2020 concludes in Form 1-8 that the site has the potential for "Partial
Infiltration". This conclusion was based on planning phase infiltration rates utilizing a factor of
safety (FS) of FS=2. Since the time the form was submitted, NOVA has worked with the BMP
design team to determine a reliable infiltration rate for the final design by completing Form 1-9.
4373 Viewridge Avenue, Suite B www.usa-nova.com 24632 San Juan Avenue, Suite 100
San Diego, CA 92123 Dana Point, CA 92629
P 8582927575 P 9493887710
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Response to SWQMP Review Comments
North County Academy, Carlsbad, CA
NOVA Project 2020187
NOVA June 2, 2021
Based on Form 1-9, the Factor of Safety and Design Infiltration Rate Worksheet, the factor of
safety has increased to FS=3.375.
Utilizing a factor of safety FS=3.375 as determined for the site based on Form 1-9, design
infiltration rates are now 0.01-inch per hour. Infiltration rates equal to or less than 0.01-inch per
hour indicate that the soil and geologic conditions do not allow for infiltration in any appreciable
rate or volume without increasing the risk of geotechnical hazards. Based on this comment, and
other geotechnical review comments, NOVA's report, including Forms 1-8 and 1-9 for the site
have been updated/added (NOVA 2021).
Based on the very low projected infiltration rates at the site, it is NOVA's judgement that the site
is not suitable for permanent stormwater infiltration.
s1'1Iu1A :1
NOVA hopes the responses to the MBI redlines are clear. Should you have any questions
regarding this letter or other matters, please do not hesitate to contact the undersigned at
858.292.7575.
Sincerely,
NOVA Services, Inc.
_
Melissa Stayner, CEG
Senior Engineering Geologist
.. r•..
/ . .
John F. O'Brien, P,E, G.E.
Principal Geotechnical Engineer
Attachment 1: MBI 2021
Attachment 2: Revised Project 1-8 Form (NOVA 2021)
Attachment 3: Project 1-9 Form (NOVA 2021)
. . Response to SWQMP Review Comments
North County Academy, Carlsbad, CA
NOVA Project 2020187
NOVA June 2, 2021
CITY OF CARLSBAD
PRIORITY DEVELOPMENT PROJECT (PDP) STORM WATER QUALITY MANAGEMENT PLAN
(SWQMP)
FOR
NORTH COUNTY ACADEMY - CAMPUS CONSOLIDATION
DWG
GR2O?O
ENGINEER OF WORK,.
WILLIAM J. SUITER, P.E. RCE 68964 EXP., 12-31-21
PASCO LARET SUITER & ASSOCIATES, INC.
27127 CALLE ARROYO, SUITE 1904
SAN JUAN CAPISTRANO, CA 92675 .J
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PREPARED FOR:
NORTH COUNTY ACADEMY
1640 MAGNOLIA
CARLSBAD, CA 92008
PREPARED BY:
P`Azicuoft L ARET I'
& ASSOCIATES
VU ENGI NEE RING LAND PLANNING;AN SURVEYING
27127 CALLE ARROYO
SAN JUAN CAPISTRANO, CA 92615
858-259-8212
DATE:
December 17, 2020
Appendix I: Forms and Checklists r 1L III
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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) t
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a
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cannot be mitigated to an acceptable level? 'the response to this Screening Qncstinn shall be based on a c sprthcnsive evaluation of the factors presented in Appendix G1.
Provide basis:
Water contamination was not evaluated by NOVA Se
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maps, d.atis sources, etc. Provide narrative discussion of study/data source applicability.
Can itltrtiozs.greaier tham 05 inches per hour he ,iUoed 'aithout c using potential 'aiscr Iaiice iiue such a
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If all answers to rows 1 --4 are "Yes" a full infiltration design is potentially feasible. The feiucibilitv screening category is Full Infiltration .art
Result
Proceed to * If aia .m-'cr
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o ' row 1-4 is 'No, in filtration nfiltration may be possible lx. somv -tcn: but
Part 2 w iiiild oi i'cncral; he fcaible or desirable to achieve a "full infiltration" Ieiej itta\! i. Paii
V0 bc ci impkud using :ithcvcJ site ii ii tints and best pi-i naI judgten1 onl~I&Tlng, tbc.6 titiun nf MI Till the MS4 Permit., Additional testing and/or studies may be re
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14 February 2016
Appendix I Forms and Checklists
T.I T7 JU
Can I-ardustion in any appreciable quantity be allowed without posing significant risk for groundwater related Cc)nccrfl8 (shallow water table, storm water pollutants or other factors)? The response to this Screening Question
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Appendix .C3.
Provide basis:
Water contamination was not evaluated by NOVA Services.
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rrizc findings of studies; provide refereucc, io tWics, csktilrins, maps. data
5ot. etc. Provc narrative dlscu~~Ian of study/data source applicability and v. t was not li ibk to mitigate low inifltr&ai rat.
Can in 1rUinn be alloxved without kiotating downstream water rights ihc u nn Qta n
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The potential for water balance was not eval
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to mitigate tow infihration rate,.
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The fi 'they screening category is Partial Infiltration. Part 2
Result*
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Infiltration
It any answer from row 5-8 is, no, then thltrataun of any volume . s considered it)b infeasible within the drainage area. The feasibiikv scre
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"I'o be completed Using ncr J siry and best n oal jmi~,nwnt the dolt)~'Toon 41NIFT in. the MS4 permit. Additional teone and/ut tudics may be required by the City to substantiat
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J-6 February 2016
. I Response to SWQMP Review Comments
Ali
North County Academy, Carlsbad, CA
NOVA Project 2020187
NOVA June 2, 2021
Appendix I: Forms and Checklists
F :WT!
Part I - Full Inflhlratiun T &-a'ihihi Scret'mn Criteria
\Vuuld infiltration uf the full dcin oluinc he feasil)lc from a phYi(al j)CI pcctI I.' itho&ii dlP ufldcslJal)lC
Cu! cqtIcncc' 111M cannot hc rca'onabh nitiiatcd
Criena i 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 X evaluation of the factors presented in Appendix C.2 and Appendix
D.
Provide basis:
The infiltration rate of the existing soils for locations P-I and P-2, based on the on-site
infiltration study was calculated to be less than 0.5 inches per hour (0.01 inches per
hour) after applying a factor of safety (ES) of FS 3.375.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of stud/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
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:
No. See Criterion 1.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
1-3 February 2016
Appendix I: Forms and Checklists
i
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 I)aS1S:
Water contamination was not evaluated by NOVA Services.
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 potential for water balance was not evaluated by NOVA Services.
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 tows 1 4 are "Yes" a full infiltration design is potentially feasible.
Part The feasibility screening category is Full Infiltration
Result Proceed to
If any answer from row 1-4 is "No", infiltration may be possible to some extent but Part 2
would not generally he 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 maybe required by the City to substantiate Findings.
1-4 February 2016
Appendix I: Forms and Checklists
W IPâ!!T T1Y rs
P:irt - Partial tnfiitratiii v',. No Infiltration F(. ,Jihr rue!aT1±ritiria
\\ ti]d infiltration Of IAMCr in ati\ apprcci.thlc .triiuiint hu 1)hy,,icalk, fcaihle wit iutlt an'. ncgati\c
ciieiaiicc, that cdflflol he r .nabl niitijted?
ril a,. a 1Ui' t)iR'- aq
Do soil and geologic conditions allow for infiltration in any
5 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:
The infiltration rate of the existing soils for locations P-i and P-2, based on the on-site
infiltration study was calculated to be 0.01 inches per hour, after applying a factor of safety
(FS) of FS=3,375.
Infiltration rates equal to or less than 0.01 inches per hour indicate that the soil and geologic
conditions do not allow for infiltration in any appreciable rate or volume.
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 in any appreciable quantity be allowed
without increasing risk of geotechnical hazards (slope
stability, groundwater mounding, utilities, or other factors) X 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.
C2.1 A geologic investigation was performed at the subject site.
C2.2 Settlement and volume change due to stormwater infiltration is not a concern with: (I)
low expansive soils,(ii) no potential for liquefaction, and (iii) no potential for hydro collapse.
C2.3 Infiltration has the potential to cause slope failures. BMPs are to be sited a minimum
of 50 feet away from any slope.
C2.4 Infiltration can potentially damage subsurface and underground utilities. As planned,
BMPs are not located within 10 feet of underground utilities.
C2.5 Stormwater infiltration can result in damaging ground water mounding during wet
periods. Mounding is not considerd to be a hazard of infiltration at this site due to the depth
of groundwater.
C2.6 BMPs are not anticipated to be located near foundations or retaining walls. Infiltration
has the potential to increase lateral pressure and reduce soil strength which can impact
foundations and retaining walls.
C2.7 Other Factors: NOVA is not aware of all subsurface conditions on nearby sites and
cannot address the potential effects of added saturation to geotechnical hazards like
saturation, heave, settlement or hydrocollapse, liquefaction, etc. Accordingly, NOVA
recommends potential for lateral migration of water from stormwater BMP's be limited by
siting any such structures away from property lines.
1-5 February 2016
Appendix I: Forms and Checklists
Can Infiltration in any appreciable quantity be allowed
N C 4)
without posing significant risk for groundwater related
concerns (shallow water table, storm water pollutants or other
factors)? The response to this Screening Question shat] be based
on a comprehensive evaluation of the factors presented in
Appendix (:3.
Provide basis:
Water contamination was not evaluated by NOVA Services.
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 (13.
Provide basis:
The potential for water balance was not evaluated by NOVA Services.
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.
Part2 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 udgme.nt 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
S . A A M Response to SWQMP Review Comments
North County Academy, Carlsbad, CA
NOVA Project 2020187
NOVA . June 2, 2021
S 0
Appendix I: Forms and Checklists
-...-.-....-
I I
Soil assessment methods 1 0.25 0.25
Predominant soil texture 025 2 0.50
Site soil variability 0.25 2 0.50 Suitability
Assessment Depth to groundwater / impervious 1 layer 025 0.25
Suitability Assessment: Safety Factor, S\ Ep 1.5
Level of pretreatment! expected
sediment loads 0.5 3 1.5
B Design Redundancy/resiliency 0.25 2 0.50
Compaction during construction 0.25 1 0.25
Design Safety Factor, SiA = P 2.25
Combined Safety Factor, S,>F S\ x Sii 3.375
Observed Infiltration Rate, inch/hr, I<<,brce P-1=0.03
(corrected for test-specific bias) P20.06
P-1=0.01
Design Infiltration Rate, in/hr, Kd,, = /sulal P-2=0.01
Smip1 rting Data
Br.ieflv describe infiltration test and provide reference to test forms:
Design Phase Borehole percolation tests were utilized for all percolation borings (P-i
and P-2) at the bottom of the prospective infiltration BMP structure accompanied by
an exploratory engineering boring (B-4) to depths of at least 10 feet below the bottom
elevation of the BMP structure. In coordination with the design engineer, a factor of
safety of FS = 3.375 was determined following the guidance in the BMP Manual.
1-7 February 2016