HomeMy WebLinkAboutCDP 05-46; PROPOSED MOSS RESIDENCE; LIMITED GEOTECHNICAL INVESITGATION PROPOSED STORM WATER INFILTRATION BMPs; 2017-10-24~~~.~ ~un.i Geotechnical Exploration, Inc.
SOIL AND FOUNDATION ENGINEERING • GROUNDWATER • ENGINEERING GEOLOGY
24 October 2017
Mr. Steven Moss
25408 Colette Way
Calabasas, CA 91302
Subject: Report of Limited Geotechnical Investigation
Proposed Storm Water Infiltration BMPs
Proposed Moss Residence
5015 Tierra Del Oro
Carlsbad, California
Dear Mr. Moss:
Job No. 07-9342
In accordance with your request, and our proposal dated October 16, 2017, we
herein provide this limited geotechnical investigation to allow evaluation of the
feasibility of utilizing a storm water infiltration BMPs at the location of the proposed
residential project. On October 20, 2017, we placed two test pits within or adjacent
to the proposed bio-retention basin for evaluation of the storm water infiltration
BMPs, per the requirements of the City of Carlsbad Storm Water Standards, BMP
Design Manual in accordance with the Guidelines for Geotechnical Reports
(Appendix C), and Approved Infiltration Rate Assessment Methods (Appendix D).
I. PROJECT SUMMARY AND SCOPE OF SERVICES
It is our understanding, based on communications with you, that the existing
single-family residential structure will be removed, and the lot will be developed to
receive a new single-family residential structure and associated improvements.
7420 TRADE STREETe SAN DIEGO, CA. 92121 • (858) 549-7222 e FAX: (858) 549-1604 • EMAIL: geotech@gei-sd.com
Proposed Moss Residence
Carlsbad, California
Job No. 07-9342
Page 2
We have reviewed the Preliminary Drainage and Grading Plan of the property,
prepared by Coffey Engineering, Inc., with the location of the proposed bio-
retention basin. Final construction plans have not been provided to us during the
preparation of this report, however, when completed they should be made available
for our review. Additional or modified recommendations may be provided as
warranted. We have also reviewed our report titled "Preliminary Geotechnical
Investigation and Geologic Reconnaissance': dated April 20, 2007, for the subject
site.
The scope of work performed for this investigation included a site reconnaissance
and subsurface exploration program, laboratory testing, simple open pit falling head
testing within the location of the proposed bio-retention basin, and the preparation
of this report. The data obtained and the analyses were performed to allow
evaluation of the feasibility of the proposed storm water infiltration BMP.
II. SITE DESCRIPTION
The subject site is known as Assessor's Parcel No. 210-020-15-00, Lot 15,
according to Recorded Map No. 3052, in the City of Carlsbad, County of San Diego,
State of California. For the location of the site, refer to the Vicinity Map, Figure No.
I.
The approximately 0.31-acre property is bordered on the north by an undeveloped
residential property; on the south by an existing single-family residence; on t he
east by Tierra Del Oro; and on the west by the Pacific Ocean . Refer to the Plot
Plan, Figure No. II.
Proposed Moss Residence
Carlsbad, California
Job No. 07-9342
Page 3
Vegetation at the site consists primarily of groundcover, lawn, trees and shrubbery.
The lot is currently developed with a single-story, single-family residential structure
with an attached garage and associated improvements. In general, the lot slopes
gently to moderately to the west.
Elevations across the property range from approximately 39 feet above Mean Sea
Level (MSL) along the east property line, to 13 feet above (MSL) along the west
property line. Information concerning approximate elevations across the site was
obtained from a Preliminary Drainage and Grading Plan prepared by Coffey
Engineering, Inc. Drainage on the site is predominately towards the west.
III. FIELD INVESTIGATION
The field investigation consisted of a surface reconnaissance and a subsurface
exploration program using hand tools to investigate, sample and perform infiltration
testing of the subsurface soils. Two exploratory handpits were excavated in the
southeast corner of the property, within or adjacent to the proposed bio-retention
basin on October 20, 2017. The soils encountered in the exploratory excavations
were continuously logged in the field by our field geologist and described in
accordance with the Unified Soil Classification System. The approximate locations
of the exploratory excavations and simple open pit testing are shown on the Plot
Plan, Figure No. II.
Representative samples were obtained from the exploratory excavations at selected
depths appropriate to the investigation. All samples were returned to our
laboratory for evaluation and testing .
Proposed Moss Residence
Carlsbad, California
IV. SOIL DESCRIPTION
Job No. 07-9342
Page 4
Our subsurface exploration program revealed that the proposed storm water bio-
retention basin, is underlain by approximately 1 foot of silty sand fill materials over
silty sand formational soils. Our review of the geologic map by Kennedy and Tan,
2007, "Geologic Map of Oceanside, 30'x60' Quadrangle, CA," indicate that the site
is underlain by formational soils of the Quaternary-Age Old Paralic Deposits (Qop6_
1 ), as mapped on the eastern portion of the site, and the Tertiary-Age Santiago
formation (Tsa) as mapped on the western portion of the site. The mapped
formational soils of the Old Paralic Deposits were encountered beneath the fill soils
in both of the exploratory excavations on the site to a depth of approximately 36
and 37.5 inches.
The exploratory handpits and related information depict subsurface conditions only
at the specific locations shown on the site plan and on the particular date
designated on the logs. Subsurface conditions at other locations may differ from
conditions occurring at these handpit locations. Also, the passage of time may
result in changes in the subsurface conditions due to environmental changes.
V. LABORATORY TESTS AND SOIL INFORMATION
The following test was conducted on the sampled soils:
1. Determination of Percentage of Particles Passing #200 Sieve
(ASTM D1140-06)
Proposed Moss Residence
Carlsbad, California
Job No. 07-9342
Page 5
The particle size smaller than a No. 200 sieve analysis aids in classifying the tested
soils in accordance with the Unified Soil Classification System and provides
qualitative information related to engineering characteristics such as expansion
potential, permeability, and shear strength. Based on our laboratory test results at
infiltration test location INF-1 and INF-2, 24% and 23% of the soils passed the
#200 sieve, respectively.
VI. GROUNDWATER
Free groundwater was not encountered in the exploratory excavations at the time
of excavation. It must be noted, however, that fluctuations in the level of
groundwater may occur due to variations in ground surface topography, subsurface
stratification, rainfall, and other possible factors that may not have been evident at
the time of our field investigation.
VII. CONCLUSIONS AND RECOMMENDATIONS
The following conclusions and recommendations are based on the field investigation
conducted by our firm, our laboratory test results, infiltration test results, and our
experience with similar soils and formational materials.
We performed simple open pit falling head testing at two locations within or
adjacent to the bottom of the proposed bio-retention basin at a depth of 36 inches
at INF-1, and 37.5 inches at INF-2 per the requirements of the City of Carlsbad
Storm Water Standards, BMP Design Manual, in accordance with Appendix D. The
bio-retention basin has been proposed in the southeast corner of the property.
Testing at the two locations (INF-1 and INF-2), revealed falling head rates of 5.600
and 5.833 minutes/inch, respectively. The simple open pit falling head test rate
Proposed Moss Residence
Carlsbad, California
Job No. 07-9342
Pag e 6
results for INF-1 and INF-2 have been converted to infiltration rates, using the
Porchet Method and indicate infiltration rates of 7.045-and 6.857-inch/hour,
respectively. Refer to Appendix A for simple open pit test rate results and simple
open pit to infiltration rate calculations. Based on our review of USDA soil map
sheet 22, the site has been assigned to hydrologic soil group (HSG) A. As part of
our geologic/geotechnical site evaluation, we considered the following issues:
1. The site is not subject to high groundwater conditions (within 10 feet of the
base of the infiltration facility.
2. The site is not in relatively close proximity to a known contaminated soil
site.
3. Portions of the site are underlain by artificial fill soils over medium dense
silty sand formational soils, but not subject to hydroconsolidation.
4. The proposed bio-retention basin has infiltration rates between of 7 .045-and
6.857-inch/hour without an applied factor of safety.
5 . Portions of the site may have a silt plus clay percentage of greater than 50 .
6. The proposed bio-retention basin is not underlain at relatively shallow
depths by practically impermeable formational soils.
7 . The proposed bio-retention basin is not located within 100 feet from a
known drinking water well.
Proposed Moss Residence
Carlsbad, California
Job No. 07-9342
Page 7
8. The proposed bio-retention basin is not located within 100 feet from an on-
site septic system or designated expansion area.
9. The proposed bio-retention basin is not located adjacent to a slope steeper
than 25 percent.
Based on the results of our simple open pit falling head testing and evaluation of
the infiltration rates, it is our professional opinion that the proposed bio-retention
basin has favorable soil conditions and appreciable infiltration rates for the design
of full infiltration BMPs. However, we recommend the sidewalls of the proposed
basin be lined and the basin be located at least 5 feet away from any proposed
structures, retaining walls and utility trenches.
In addition, based on review of our "Preliminary Geotechnical Investigation and
Geologic Reconnaissance" dated April 20, 2007, it is our professional opinion that
the measured infiltration rates are representative of the soils encountered across
the site.
VIII. LIMITATIONS
The findings, opinions, and conclusions presented herein have been made in
accordance with generally accepted principles and practice in the field of
geotechnical engineering within the City of Carlsbad. No warranty, either
expressed or implied, is made.
Our findings, opinions, and conclusions are specifically limited to the scope of
services described herein, for the evaluation and feasibility of storm water
infiltration, within and immediately adjacent to, the proposed bio-filtration basin.
Proposed Moss Residence
Carlsbad, California
Job No. 07-9342
Page 8
If you have any questions regarding this letter, please contact our office. Reference
to our Job No. 07-9342 will help expedite a response to your inquiry.
Respectfully submitted,
GEOTECHNICAL EXPLORATION, INC.
~a+ e A. Cerros, P.E.
R.C.E. 34422/G.E. 2007
Senior Geotechnical Engineer
VICINITY MAP
Carlsbad State Beach
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Moss Reside nce
5015 Tierra Del Oro
Carlsbad, CA.
Figure No. I
Job No. 07-9342
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PLOT PLAN
Moss Residence
5015 Tierra Del Oro
Carlsbad, CA.
Figure No. II
Job No. 07-9342
al Geotechnfcal 11, Exploration, Inc.
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( October 2017)
APPENDIX A
SIMPLE OPEN PIT TEST RESULTS AND
INFILTRATION RATE CONVERSIONS
Simple Ope 'n Pit Falling Head Test Sheet
Project Name: Moss
Project No. 07-9342
Date Excavated: 10/20/17
Test Hole No: INF-1
Initial Time (Minutes) Final Time (Minutes)
235 255
300 325
330 405
Time interval
(minutes)
20
25
35
Initial Water Level
(inches)
29.750
29.750
29.750
Tested By: JAB
Soil Classification: SM
Depth of Test Hole: 36"
Test Hole Dia: 24"
Final Water Level
(inches)
36.000
36.000
36.000
Change in water
(inches)
6.250
6.250
6.250
Falling Head Rate
(min/inches)
3.200
4.000
5.600
Simple Open Pit Falling Head Test Sheet
Project Name: Moss
Project No. 07-9342
Date Excavated: 10/20/17
Test Hole No: INF-2
Initial Time (Minutes) Final Time (Minutes)
239 259
303 328
333 408
Time interval
(minutes)
20
25
35
Initial Water Level
(inches)
31.500
31.500
31.500
Tested By: JAB
Soil Classification: SM
Depth ofTest Hole: 37.5"
Test Hole Dia: 24"
Final Water Level
(inches)
37.500
37.500
37.500
Change in water
(inches)
6.000
6.000
6.000
Falling Head Rate
(min/inches)
3.333
4.167
5.833
Simple Open Pit Rate to Infiltration Rate Conversion (Porchet Method)
Project Name: Moss
Project No. 07-9342
Test Hole No: INF-1
Test EB Depth Delta T
No. (inches) (min)
1 36 20
2 36 25
3 36 35
4
5
6
7
8
9
Water Depth
1 (inches)
29.750
29.750
29.750
Calculated By: JAB
Checked By:
Test Hole Dia: 24"
Date: 10/23/2017
Date:
Depth of Test Hole: 36"
Porchet Corrections
Infiltration rate=((delta h*60r)/(delta t*(r+2 h avg))
Water Depth hl h2 delta h h avg
2 (inches) (inches) (inches) (inches) (inches)
36.000 6.250 0.000 6.250 3.125
36.000 6.250 0.000 6.250 3.125
36.000 6.250 0.000 6.250 3.125
r (radius) delta delta t*(r+2 h
(inches) h*60r ~
12 4500 365
12 4500 456.25
12 4500 638.75
Infiltration
rate (in/hr)
12.329
9.863
7.045
Simple Open Pit Rate to Infiltration Rate Conversion (Porchet Method)
Project Name: Moss
Project No. 07-9342
Test Hole No: INF-2
Test EB Depth Delta T
No. (inches) (min)
1 37.5 20
2 37.5 25
3 37.5 35
4
s
6
7
8
9
Water Depth
1 (inches)
31.500
31.500
31.500
Calculated By: JAB
Checked By:
Date: 10/23/17
Date:
Test Hole Dia: 24" Depth ofTest Hole: 37.5"
Porchet Corrections
Infiltration rate=((delta h*60r)/(delta t*(r+2 h avg))
Water Depth hl h2 delta h h avg r (radius)
2 (inches) (inches) (inches) (inches) (inches) (inches)
37.500 6.000 0.000 6.000 3.000 12
37.500 6.000 0.000 6.000 3.000 12
37.500 6.000 0.000 6.000 3.000 12
delta
h*60r
4320
4320
4320
delta t*(r+2 Infiltration rate
h avg) (in/hr)
360 12.000
450 9.600
630 6.857
Moss 07-9342
Appendix I: Fonns and Checklists
Part 1 -Fun Infiltration feHibillty 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
Is the estimated reliable infiltration rate below proposed
facility locations greatet than 0.S inches per hoU1? The response
to this Screening Question shall be based on a comprehensive
evaluation of the factors presented in Appendix C.2 and Appendix
D.
Provide basis:
Yes No
X
The infiltration lest results below the proposed fac!ity location were 3.522 and 3.428 inches per hour with a minimum factor of safety
of 2 applied. Simple open pit tesUng was performed at 2 locations on the site within or adjacent to the proposed Infiltration basin in
accordance with Appendix D of the City of Carlsbad BMP design manual. In addition, a comprehensive evaluation of the site was
conducted in accordance with Appendix C.2.
Please refer lo our "Report of Limited Geotechnical Investigation Proposed Storm Water Infiltration BMPs" ror details of the
comprehensive evaluation and investigation conducted, simple open ptt test rates and simple open ptt rate to Infiltration rate
calculations and maps representative of the study,
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide nanative
discussion of srudy / data source applicability.
2
Can infiltration greater than 0.5 inches per hour be allowed
without increasing risk of geotechnical hazards (slope stability,
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:
X
The infiltration lest results below Iha proposed facility locations ranged from 3.522 to 3.428 Inches per hour with a minimum factor of
safety of 2 applied. In our opinion. any long term full infiltration at the site will not result in geotechnical hazards which cannot be
reasonable mitigated lo an acceptable level.
Please refer to our "Report of Limited Geotechnical Investigation Proposed Stom, Waler Infiltration BMPs" for details of the
comprehensive evaluation and investigation conducted, simple open pit test rates and simple open pit rate to infiltration rate
calculations and maps representative of the study.
Summarize findings of studies; provide reference to studies, calculations, maps, dau sources, ere. Provide narrative
discussion of study/dato. source applicability.
I-3 February 2016
Moss 07 -9342
Appendix I: Forms and Checklists
Ctiteri
a
3
Screening Question
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 shalt be hosed on a comprehensive evaluation of
the f:actors presented in Appendix C.3.
Provide basis:
Yes No
X
The infiltration test results below the proposed facility locations ranged from 3.522 to 3.428 Inches per hour with a minimum factor of
safety of 2 applied. In our opinion, any long term full infillralion at Ille site will not result in a significant risk for groundwater related concems.
Please refer to our "Report of Limited Geotechnlcal Investigation Proposed Storm Water Infiltration BMPs" for details of the
comprehensive evaluation and investig&tion conducled, simple open pit test rates and simple open pit rate to infiltratlon rate
calculations and maps representative of the study.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/ data source applicability.
4
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 dlschargc of
contaminated gioundwater 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:
Question to be answered by the design engineer.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/ data source applicability.
Part 1
Result •
If aU answers to rows 1 -4 arc "Yes" a full infiltration design is potentially feasible.
The feasibility screening category is Full Infiltration
If any answer from row 1-4 is "No", infiltr-,tion may be possible to some extent but
would not generallr 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.
I-4 February 2016
Moss 07-9342
Appendix I: Fonns and Checklists
·,c -,:u .. !I!!,'~ .. r.,.~! ,;; .i .. :,; .. !~ .· la!!YS ' •'. i _,.,. ' . . , . •:t "
. ,;,~
Part 2 -Panial Infiltmlon vs. No Infiluation Feasiblli1y Scw,ning Criteria
Would infiltration of water in any appreciable amount be physically feasible withom any n egative
consequences that cannot be reasonably mitigated?
Criteria Screening Question Yes N o
Do soil and geologic conditions allow for infiltration in any
5 appreciable rate or volume? The response to this Screening X
Question shall be b•scd on a comprehensive evaluation of the
factors presented in Appendix C.2 and Appendix D.
Provide basis:
The infiltration test results below the proposed facillly location were 3.522 and 3.428 inches per hour with a minimum factor of safety
of 2 applied. Based on our infiltration rate findings and our geotcctmcial investigation conducted on the slle. it is our opinion that the
geologic conditions allow for appreciable Infiltration.
Please refer to our "Report of Limited Geotechnical Investigation Proposed Storm Water Infiltration BMPs" for details of the
comprehensive evaluation and investigation conducted, simple open pit test rates and simple open pit rate to infiltration rate
calculations and maps representative of the study.
Summarize findings of swdies; 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
6 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.
Provide basis:
In our opinion, any long term partial infiltration at the site will not result In geotechnlcal hazards which cannot be reasonable mitigated to an acceptable level.
Please refer to our "Report of Limited Geotechnlcal Investigation Proposed Storm Water Infiltration BMPs' for details of !he
comprehensive evaluation and investigation conducted, slmple open pit test rates and simple open pit rate 10 infiltration rate
calculations and maps representative or the study.
Summarize rinding~ of studies; pnwidc rc:forcnce t0 studies, cakulatlons, maps, data sources, etc. Provide narrative
discussion of studr/dara source applicability and whr it was not feasible to mitigate low infiltration rates.
1-5 February 2016
Moss 07-9342
Appendix I: Forms and Checklists
.. --' . --~ ·.• ., :/ -. ·-•~ .,.., \.,.;:: . 1:. ~~:r ~ ,, . ,., :~-·-~., ··-_, 1.-'· .!. • • • l'!!:fl:P.T:,.,,..·~ ·,.-i•• "
Cnteria Screening Question Yee No
Can Infiltration in any appreciable quantity be allowed
without posing significant risk for groundwater related
7 concerns (shallow water table, storm water pollutants or other X factors)? The response to this Screening Question shall be based
on a comprehensive evaluation of the factors presented in
Appendix C.3.
Provide basis:
In our opinion, any long term partial infiltration at the site will not resul1 in a significant risk for groundwater related concerns.
Please refer to our 'Report or Limited Geotechnlcal Investigation Proposed Storm Water Infiltration BMPs" for details of the
comprehensive evaluation and Investigation conducted, simple open pit test rates and simple open pit rate to infiltration rate
calculations and maps representative of the study.
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
Append.ix C.3.
Provide basis:
Question to be answered by the design engineer.
Summarize findings of studies; provide reference to studies, calcu1"tions, maps, data sources, etc. Provide narrative
discussion of study/ data source appLicabili ty and why it was not feasible to mitigate low infiltration rates.
If aU answer.; from row 5-8 arc yes then partial infiltration design is potentially feasible.
Part 2 1be feasibility screening category is Partial Infiltration.
Result* If •ny answer from row 5-8 is no, then infiltration of aoy volume is considered to be
infeasible within the dro.inage area. The feasibility screening category is No Infiltration.
.. *To be completed using gathered SIie mformaaon and best profess10nal Judgment consrdcring the dcfirunon of MEP 10
the MS4 Permit. Additional testing and/ or studies m•y be required by the City co substantiate findings.
I-6 February 2016
Moss 07-9342 Appendix I: Forms and Checklists
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Facror C<1tegory Factor D escription Assigned Factor Product (p)
Weighr(w) Value (v) p=wx,
Soil assessment methods 0.25 2 0.5
Predominant soil texture 0.25 2 0.5
Suitability Site soil variability 0.25 2 0.5
A Assessment Depth to groundwater I impervious 0.25 I 0.25
layer
Suitability Assessment Safety Facror, s,. = I:p 1.75
Level of pretreatment/ expected 0.5 sediment loads
B Design Redundancy/ resiliency 0.25
Compaction during construction 0.25
Design Safety Factor, Sn = I:p
Combined Safety Factor, S,.,,.,= S, x Sa
Observed Infiltration Rate, inch/hr, Koo=-«J
(corrected for test-specific bias)
Design Infiltration lute, in/hr, Neiijo> = Koo.,n-,J I S.,..i
Supporting Data
Briefly describe infiltration test and provide reference to test forms:
Simple open pil testing was performed at 2 locattons within or adjacent to the proposed facility per u,e requirements of the
City of Carlsbad Storm Water Standards, BMP Design Manual, in accordance with Appendix D.
Please refer to our "Report of Limited Geotechnical Investigation Proposed Storm Water lnfillration BMPs" for details of the
comprehensive evaluation and investigallon conducted, simple open pit test rates and simple open pit rate to lnfillraUon rate
calculalions and maps representative of the study.
I-7 February 2016