HomeMy WebLinkAboutCT 14-10; SUPPLEMENTAL INFILTRATION INFORMATION; 2017-12-08GROUP DELTA
December 8, 2017
Lenn2r Homes
25 Enterprise, Suite 300
Aliso Viejo, California 92656
RECEIIV1ID
JAN 17201a
Attention: Mr. Jamison Nakaya LAND DEVELOPMENT
ENGIN EL_ RiNG
SUBJECT: SUPPLEMENTAL INFILTRATION INFORMATION
Poinsettia 61 Development
Carlsbad, California
References: Group Delta (2014). Report of Geotechnical Investigation, Poinsettia 61
Development, Carlsbad, California, Document No. 14-0188, November 20.
Mr. Nakaya:
In accordance with the request of Mr. Tim Carroll, we are summarizing herein the infiltration
testing we previously completed in 2014 for the Poinsettia 61 Development in Carlsbad. A
narrative describing the infiltration testing was provided in Paragraphs 3 and 4 in Section 2.0 of
the referenced 2014 report (GDC, 2014). That narrative is summarized below for clarity. We
also previously provided the attached Appendix D, which was intended as an addendum to the
2014 report. Appendix D is attached to the end of this letter, and contains the boring logs and
infiltration test results from the investigation, as well as Worksheet C.4-1 of the 2015 San Diego
County BMP Design Manual. Worksheet C.4-1 is identical to the City of Carlsbad Form 1-8.
Two falling head percolation tests were conducted as part of our 2014 field investigation. The
tests were located in cut areas where retention basins are proposed. Note that several other
retention basins are also proposed in portions of the Poinsettia 61 site that were inaccessible to
the drilling equipment, or in areas where deep cuts or fills will be needed to reach basin
subgrade elevations. Percolation tests were not conducted in those areas, since they would not
be representative of the future as-graded conditions beneath the basins. Additional percolation
testing may be conducted once the basins are rough graded.
For the percolation tests, 6-inch diameter holes were drilled to depths of 5 or 10 feet below
grade. The boreholes were then filled with water, and the water surface drop was measured
repeatedly at 15 to 60-minute time intervals. The percolation test data was initially presented
in Figures A-20 and A-21 from Appendix A of the referenced 2014 investigation, and is also
presented in the attached Appendix D.
9
'7
Supplemental Infiltration Information GD: Project No. SD412B
Poinsettia 61 Development December 8, 2017
Lennar Homes Page 2
The field percolation tests indicated that the unsaturated formational sandstone at the site may
initially take water at a rate of about 5 to 7 minutes per inch. However, once the dense fine-
grained sandstone becomes saturated, the infiltration rate drops to zero. We anticipate that
the compacted fill soils proposed for the site may absorb more water than the dense sandstone
that will be prevalent throughout the cut portions of the site. However, we have
recommended that all of the basins be lined with an impermeable HOPE or PVC membrane to
reduce the potential for slope instability.
We appreciate this opportunity to be of continued professional service. Feel free to contact the
office with any questions or comments, or if you need anything else.
GROUP DELTA CONSULTANTS
(Nea\
Matthew A. Fagan, G.E. 2569
"12-31-19 )
Senior Geotechnical Engineer OF
Distribution: (1) Addressee, Mr. Mr. Jamison Nakaya (Jamison.Nakaya@Lennar.com)
(1) Addressee, Mr. Mr. Tim Carroll (timc@odayconsultants.com)
GROUP DEI...1L N:\Projects\SD\SD412B lennar - Poinsettia 61, i&o of Earthwork Construction\5. Reports\17-0145.doc
APPENDIX D
INFILTRATION ASSESSMENT
Appendix D:
Geotechnical and Groundwater Investigation Requirements
Worksheet C.4-1: Categorization of Infiltration Feasibffitv Condition
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 to this
Screening Question shall be based on a comprehensive evaluation of N 0
the factors presented in Appendix C.2 and Appendix D.
Provide oasis:
Percolation tests were conducted in cut areas where retention basins are proposed (see attached test data).
Several other retention basins are also proposed in areas where fills are proposed. Percolation tests cannot
be conducted in fill areas until the site is graded. The tests indicate that the formational material has an equilibriun
infiltration rate below 0.5 in/hour. We recommend that basins located near the tops of proposed fill slopes be
lined with an impermeable membrane to reduce the potential for slope instability.
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 be
mitigated to an acceptable level? The response to this Screening No
Question shall be based on a comprehensive evaluation of the factors
presented in Appendix C.2.
Provide basis:
See response to Item 1 above.
Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/data source applicability.
I3MP Design Manual-Appendices
December 2015 D-1
Appendix D:
Geotechnical and Groundwater Investigation Requirements
Criteria Screening Question Yes No
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 N
Question shall be based on a comprehensive evaluation of the factors
presented in Appendix C.3.
Provide basis:
See response to Item 1 above.
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 No 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:
See response to Item 1 above.
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 I - 4 are "Yes" a full infiltration design is potentially feasible.
The feasibility screening category is Full Infiltration
Part
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 City Engineer to substantiate findings.
BMP Design Manual-Appendices
December 2015 D-2
Appendix D:
Geotechnical and Groundwater Investigation Requirements
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 I Screening Question Yes No
Do soil and geologic conditions allow for infiltration in any
5 appreciable rate or volume? The response to this Screening
Question shall be based on a comprehensive evaluation of the factors No
presented in Appendix C.2 and Appendix D.
Provide basis:
The percolation tests indicate that basins located within cut areas in the Santiago Formation will have a
negligible equilibrium infiltration rate of about 0.0 inches per hour. We recommend that the basins
proposed at the tops of the fill sloped be lined to reduce the potential for slope instability.
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,
6 groundwater mounding, utilities, or other factors) that cannot
be mitigated to an acceptable level? The response to this Screening No
Question shall be based on a comprehensive evaluation of the factors
presented in Appendix C.2.
Provide basis:
See response to Item 5 above.
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.
BMP Design Manual-Appendices
December 2015 D-3
Appendix D:
Geotechnical and Groundwater Investigation Requirements
Criteria Screening Question Yes No
Can Infiltration in any appreciable quantity be allowed without
posing significant risk for groundwater related concerns
7 (shallow water table, storm water pollutants or other factors)? No
The response to this Screening Question shall be based on a
comprehensive evaluation of the factors presented in Appendix C.3.
Provide Dasis:
See response to Item 5 above.
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 water
8 rights? The response to this Screening Question shall be based on a No
comprehensive evaluation of the factors presented in Appendix C.3.
Provide basis:
See response to Item 5 above.
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 1-4 are yes then partial infiltration design is potentially feasible.
Part 2 The feasibility screening category is Partial Infiltration.
Result*
If any answer from row 5-8 is no, then infiltration of any volume is considered to be
infeasible within the drainage area. The feasibility screening category is No Infiltration.
'1'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 requited by Agency/Jurisdictions to substantiate findings
BMP Design Manual-Appendices
December 2015 D-4
BORING RECORD PROJECT NAME I PROJECT NUMBER I BORING
Lennar Poinsettia 61 Development SD412 P-I SITE LOCATION I START I FINISH I SHEET NO.
Southeast of Cassia Road at the Terminus of Poinsettia Road 10/31/2014 10/31/2014 1 of 1 DRILLING CCMPANY DRILLING METHOD LOGGED BY CHECKED BY
Pacific Drilling Hollow Stem Auger TSL I MAF DRILLING EQUIPMENT BORING DIA. (in) I TOTAL DEPTH (ft) l GROUND ELEV (ft) I DEPTHIELEV. GROUND WATER (ft
Truck Rig (Wolverine) I 6 5 247 I Y N/A / na SAMPLING METHOD NOTES
Hammer 140 lbs Drop: 30 in. (Automatic) ETR 82%, N6082/60*N 1.37 * N
z
Q
w ii >- 0 Z
Z jj ' 00- iZLu z - Lu > I- a)
.
. .
F- Lu -J
w -j 0-
<<- 0 n — I-- CO
Z Lu o o.B
Cl)
WI- IC') I-Lu I I-
1(9
DESCRIPTION AND CLASSIFICATION 0_ Lu O
W - -J Lu
0
0-rn m > 0-
OF- 0- Lu a
0- (9
C') 0
SANTIAGO FORMATION: SILTY SANDSTONE
(SM); light gray; moist; mostly fine SAND; little fines;
—245 nonpiastic.
- ...... :. Hole cleaned out to 5 with hand auger. Gravel added to
- . bottom prior to filling with water.
See Figure A-20b for percolation test data. 5
-
Total Depth: 5 feet
—240 No groundwater encountered
-10 - 10-
-25
—15 - 15-
-2O
—20 - 20-
-
-225
- - - - -
-
GROUP DELTA CONSULTANTS, INC. OF THIS BORING AND AT THE TIME OF DRILLING. FIGURE
9245 Activity Road, Suite 103
HIMPPLIES ONLY AT THE LOCATION
SUBSURFACE CONDITIONS MAY DIFFER AT OTHER
LOCATIONS AND MAY CHANGE AT THIS LOCATION
WITH THE PASSAGE OF TIME. THE DATA A-20 a San Diego, CA 92126 PRESENTED IS A SIMPLIFICATION OF THE ACTUAL
CONDITIONS ENCOUNTERED.
FALLING HEAD PERCOLATION TEST FIELD DATA SHEET
Storm Water Infilitration
Project Name: Lennar Poinsettia Job No.: SD412 Tested By: GMS
Test Hole No: P-i Date Drilled: 10/31/2014 Date Tested: 10/31/2014
Drilling Method: 6-tallow-Stem Auger
Depth of Hole as Drilled: 5 Depth Before Test: 4'6" Depth After Test: 4' 6"
Reading
Number Time
Time
Interval
. (mm.)
Initial
Depth of Water
(ft.)
Final
Depth of Water
(ft.)
Change in
Water Level
(in.)
Rate
(min./in.)
1 8:16 0:15 4.00 4.04 0.50 6:00
2 8:31 0:15 4.04 4.04 0.00 0:00
8.46 0:30 4.04 4.04 0.00 0:00 916
9.16 0:30 4.04 4.04 0.00 0:00
5 0:29 4.04 4.04 0.00 0:00
6 0:30 4.04 4.04 0.00 0:00
7 1:00 4.04 4.04 0.00 0:00
8 1:00 4.04 4.04 0.00 0:00
9
10
11
12
13
14
15
16
Document No. 14-0188
LDUP DEL-r1% PERCOLATION TEST DATA (P-I) Project No. SD412
FIGURE A-20b
BORING RECORD~Lennar
PROJECT NAME I PROJECT NUMBER I BORING
Poinsettia 61 Development SD412 I P-2 SITE LOCATION ISTART FINISH SHEET NO.
Southeast of Cassia Road at the Terminus of Poinsettia Road 10/31/2014 10/31/2014 1 of 1 DRILLING COMPANY DRILLING METHOD LOGGED BY CHECKED BY
Pacific Drilling Hollow Stem Auger I TSL I MAF DRILLING EQUIPMENT j BORING DIA. (in) I TOTAL DEPTH (ft) l GROUND ELEV (ft)
J
DEPTH/ELEV. GROUND WATER (ft
Truck Rig (Wolverine) 6 10 235 Y N/A / na SAMPLING METHOD NOTES
Hammer: 140 lbs., Drop: 30 in. (Automatic) ETR 82%, N82/60*N 1.37 * N
Z o
W
>-
.
0 z
zui2 0- jZo w
I- W _i
W
OI-O)
°
n-. I-
0) Z w o
0) WI- 10) -w 1 I-
10
< DESCRIPTION AND CLASSIFICATION o_ W 0
w- -J Ui
CL < 39 9 > 01- [L W a
X CD
0) 0
SANTIAGO FORMATION: SILTY SANDSTONE
(SM); light gray; moist; mostly fine SAND; little fines;
nonplastic.
_5 -.230 5 - 1
Hole cleaned out with hand auger to 9'. Gravel added to
• — :: •. bottom prior to saturating the borehole.
—10 —225 10 —J. See Figure A-21b for percolation test data.
- —
• Total Depth: 10 feet
— - No groundwater encountered
-15 —220 15-
-20 —215 20-
GROUP DELTA CONSULTANTS, INC. THIS SUMMARY APPLIES ONLY AT THE LOCATION
OF THIS BORING AND AT THE TIME OF DRILLING. FIGURE
SUBSURFACE CONDITIONS MAY DIFFER AT OTHER 9245 Activity Road, Suite 103 LOCATIONS AND MAY CHANGE AT THIS LOCATION
WITH THE PASSAGE OF TIME. THE DATA A-2 1 a San Diego, CA 92126 PRESENTED IS SIMPLIFICATION OF THE ACTUAL
CONDITIONS ENCOUNTERED.
r
FALLING HEAD PERCOLATION TEST FIELD DATA SHEET
Storm Water Infilitration
Project Name: Lennar Poinsettia Job No.: SD412 Tested By: GMS
Test Hole No: P-2 Date Drilled: 10/31/2014 Date Tested: 10/31/2014
Drilling Method: 6 Hollow-Stem Auger
Depth of Hole as Drilled: 10' Depth Before Test: 82 Depth After Test: 8'
Reading
Number Time
Time
Interval
(mm.)
Initial
Depth of Water
(ft.)
Final
Depth of Water
(ft.)
Change in
Water Level
(in.)
Rate
(min./in.)
1 9:00 0:15 7.50 7.75 9:15
3.00 5:00
2 9:15 015 7.08 7.33 9:30
3.00 5:00
3 9:30 0:15 7.33 7.58 3.00 5:00
4 9:45 015 5.50 6.08 10:00
7.00 2:08
5 10:00 0:15 6.08 6.25 10:15
2.00 7:31
6 10:15 015 6.25 6.42 10:30
2.00 7:31
7 10:30 0:15 6.42 6.58 10:45
2.00 7:31
8 10:45 0:15 6.58 6.75 11:00
2.00 7:31
9 _11_ 0:15 5.50 5.75 11:15
3.00 5:00
10 -11 - 0:15 5.75 6.17 5.00 3:00 11:30
I 11
11:45 015 6.17 6.33
______________
2.00 7:31
12 111:45 015 6.33 6.42 12:00
1.00 15:02
13 12:00 0:15 6.42 6.46 12:15
0.50 6:05
14 12:15 0:15 6.46 6.46 12:30
0.00 0:00
15 12:30 0:15 6.46 6.46 12:45
0.00 0:00
16 12:45 0:15 6.46 6.46 0.00 0:00 13:00
ek,'_ IRDUP DELTA PERCOLATION TEST DATA (P-2)
Document No. 14-0188
Project No. S0412
FIGURE A-21 b