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Home My WebLink AboutCT 14-10; POINSETTIA 61; SUPPLEMENTAL INFILTRATION INFORMATION; 2017-12-08• • • • • .. A GFilCUP DEL T .L\ December 8, 2017 Lennar Homes 25 Enterprise, Suite 300 Aliso Viejo, California 92656 Attention: Mr. Jamison Nakaya 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. • Supplemental Infiltration Information Poinsettia 61 Development Lennar Homes GDC Project No. SD412B December 8, 2017 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 HDPE 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 ,~~ ,?/J/1----7!. I ,! / ,, •• 1ti1 //(~AJ. ~ l!llp.12-31-19 * Matthew A. Fagan, G.E. 2569 ~ ~~ Senior Geotechnical Engineer "'~OF~ -----Distribution: (1) Addressee, Mr. Mr. Jamison Nakaya (Jamison.Nakaya@Lennar.com) (1) Addressee, Mr. Mr. Tim Carroll (timc@odayconsultants.com) ll f;_~ GROUP DEL T ..t\ N:\Projects\SD\SD412B Lennar -Poinsettia 61, T&O of Earthwork Construction\5. Reports\17-0145.doc • ' • • • APPEND/XO INFILTRATION ASSESSMENT • • • • • • AppendixD: Geotechnical and Groundwater Investigation Requirements 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 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 the factors presented in Appendix C.2 and Appendix D . Provide basis: Yes No No 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 equilibriu 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. 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: See response to Item 1 above . No Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/ data source applicability . BMP Design Manual-Appendices December 2015 D-1 • • • • • AppendixD: Geotechnical and Groundwater Investigation Requirements Criteria 3 Worksheet C.4-1 Page 2 of 4 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 shall be based on a comprehensive evaluation of the factors presented in Appendix C.3. Provide basis: See response to Item 1 above . Yes No No 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 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: See response to Item 1 above . No 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 all answers to rows 1 -4 are ''Yes" a full infiltration design is potentially feasible. The feasibility screening category is Full Infiltration 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 cons1denng the defirut1on of MEP in the MS4 Permit. Additional testing and/or studies may be required by C:ity Engineer to substantiate findings . BMP Design Manual-Appendices December 2015 D-2 • • AppendixD: Geotechnical and Groundwater Investigation Requirements Worksheet C.4-1 Page 3 of 4 Part2 Partial Infiltration vs, No Infiltration Feasibi1itv Screening Criteria Would initltration 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 5 appreciable rate or volume? The response to this Screening No Question shall be based on a comprehensive evaluation of the factors 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 Inf'dtration in any appreciable quantity be allowed without increasing risk of geotechnical hazards (slope stability, 6 groundwater mounding, utilities, or other factors) that cannot No 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: 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 • • AppendixD: Geotechnical and Groundwater Investigation Requirements Criteria 7 Worksheet C.4-1 Page 4 of 4 Screening Question Can Infdtration 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: See response to Item 5 above. Yes No No 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. 8 Can infiltration be allowed without violating downstream 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: See response to Item 5 above. No 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 . Part 2 Result* lf all answers from row 1-4 are yes then partial infiltration design is potentially feasible. The feasibility screening category is Partial Infiltration. 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. *To be completed using gathered stte 1nformat1on and best professional Judgment cons1der1ng the defin1t1on of MEP 1n the MS4 Pcrmit.1\dditional testing and/or studies may be reguired by Agency/Jurisdictions to substantiate findings BMP Design Manual-Appendices December 2015 D-4 BORING RECORD ' .. -.. ·-I PROJECT NUMBER BORING Lennar Poinsettia 61 Development S0412 P-1 SITE LOCATION I START \ 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 I LOGGED BY I CHECKED BY Pacific Drilling Hollow Stem Auger TSL MAF DRILLING EQUIPMENT BORING DlA. (in) TOTAL DEPTH (ft)I GROUND ELEV (ft) I DEPTHELEV. GROUND WATER (ft Truck Ria (Wolverine) 6 5 247 1' N/A/ na SAMPLING METHOD NOTES Hammer: 140 lbs., Drop: 30 in. (Automatic) ETR-82%, N60 -82/60 • N -1.37 • N w zw->-~ z a. cj Q<.>~ ~ w .... ! ,1'. 0 >-z ,-zw .... "' a; "'"' s1 ~? .... w <( <-=>-Ic, <>'.>-~ ~ ;, z,, W>-I <( • w ~ >-"' i: 0~ I<O I a.a DESCRIPTION AND CLASSIFICATION .... >2 ~ a. ~3 >-W .... ~~ a. w-a. " ~~g 0 i5 o>-a. w ~ " <( ~ >-w "' 0 w <( "' WQ'. a, a, " "' 0 "' a. -0 .. .:·:-\ ·;-:·::-SANTIAGO FORMATION: SIL TY SANDSTONE -~ -(SM); light gray; moist; mostly fine SAND; little fines; .· .' -245 ::·:::·.: . :: :·:· nonplastic . - -~ -: Hole cleaned out to 5' with hand auger. Gravel added to --: bottom prior to filling with water. -5 5 See Figure A-20b for percolation test data. - --Total Depth: 5 feet -240 No groundwater encountered -- - -10 -10- - --235 • -- ~ ~ - -15 ~ 15 - ~ - b 1--230 -" § --8 " -- -20 -20- • -- --225 - -- GROUP DELTA CONSULTANTS, INC. THIS SUMMARY APPLIES ONLY AT THE LOCATION FIGURE OF THIS BORING AND AT THE TIME OF DRILLING. 9245 Activity Road, Suite 103 SUBSURFACE CONDITIONS MAY DIFFER AT OTHER LOCATIONS AND MAY CHANGE AT THIS LOCATION V\/ITH 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 lnfilitration Project Name: Lennar Poinsettia Job No.: SD412 Tested By: GMS Test Hole No: P-1 Date Drilled: 10131/2014 Date Tested: 1013112014 Drilling Method: 6" Hollow-Stem Auger Depth of Hole as Drilled: 5 Depth Before Test: 4' 6" Depth After Test: 4' 6" Reading Time Initial Final Change in Rate Number Time Interval Depth of Water Depth of Water Water Level (min.Jin.) (min.) (ft.) (ft.) (in.) 1 8:16 0:15 4.00 4.04 0.50 6:00 8:31 2 8:31 0:15 4.04 4.04 0.00 0:00 8:46 3 8:46 0:30 404 4.04 0.00 0:00 9:16 • 4 9:16 0:30 4.04 4.04 0.00 0:00 9:46 5 9:46 0:29 4.04 4.04 0.00 0:00 10:15 6 10:15 0:30 4.04 4.04 0.00 0:00 10:45 • 7 10:45 1:00 404 4.04 0.00 0:00 11:45 8 11 :45 1:00 4.04 4.04 0.00 0:00 12:45 9 10 11 12 13 14 15 • 16 ~ GR.CUP CELT A Document No. 14-0188 PERCOLATION TEST DATA (P-1) Project No. SD412 FIGURE A-20 b BORING RECORD 1· nRmc l PROJECT NUMBER BORING Lennar Poinsettia 61 Development SD412 P-2 SITE LOCATION I START IFINISH 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 I LOGGED BY I CHECKED BY Pacific Drilling Hollow Stem Auger TSL MAF DRILLING EQUIPMENT BORING DIA. (In) TOTAL DEPTH (ft)I GROUND ELEV (ft) I DEPTHELEV. GROUND WATER (ft Truck Ria (Wolverine\ 6 10 235 !'. N/A/na SAMPLING METHOD NOTES Hammer: 140 lbs., Drop: 30 in. (Automatic) ETR -82%, N60 -82/60 • N -1.37 • N "' zw- '° z 0 Oo~ ~ >-~ ! <L "' f-0 >-z i= z (D f-"' in "'U) ~ u i= z-f-"' <( <( -~ ::,_ :'i'o "'f-j'" I ~l "' ~ "'f-~ ;: .;, ~c IUl I "-o DESCRIPTION AND CLASSIFICATION f-~ <L f-U) f-"' f- <L <L :,; WU)O 0 6 08, Of-<L ~~ "' ~ :,; j', zw ~ ~ >-"' " D "' <( "'"'"' "' :, "' D U) <L -D <:-.··. . _:.: : ~ :. SANTIAGO FORMATION: SILTY SANDSTONE " '-(SM); light gray; moist; mostly fine SAND; little fines; -·:· ··: .... nonplastic. " ~ -'-_. ~ - -5 L...-230 5 ::. · .. . .. - -.. - >-'-- '-Hole cleaned out with hand auger to 9'. Gravel added to bottom prior to saturating the borehole. '- ~10 L,._225 10 See Figure A-21 b for percolation test data. ~ -Total Depth: 10 feet No groundwater encountered - ~ - >-'-- ~1s -220 15- -'-- ii " -§ 8 '-- " >-~ - ~20 -215 20- >-- -- - - GROUP DELTA CONSULTANTS, INC. THIS SUMMARY APPLIES ONLY AT THE LOCATION FIGURE OF THIS BORING AND AT THE TIME OF DRILLING. 9245 Activity Road, Suite 103 SUBSURFACE CONDITIONS MAY DIFFER AT OTHER LOCATIONS AND MAY CHANGE AT THIS LOCATION WITH THE PASSAGE OF TIME. THE DATA A-21 a San Diego, CA 92126 PRESENTED IS A SIMPLIFICATION OF THE ACTUAL CONDITIONS ENCOUNTERED. FALLING HEAD PERCOLATION TEST FIELD DATA SHEET Storm Water lnfilitration 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: 8' 2" Depth After Test: 8' Reading Time Initial Final Change in Rate Time Interval Depth of Water Depth of Water Water level Number (min.) (ft.) (ft.) (in.) (min.fin.) 1 9:00 9:15 0:15 7.50 7.75 3.00 5:00 2 9:15 9:30 0:15 7.08 7.33 3.00 5:00 3 9:30 0:15 9:45 7.33 7.58 3.00 5:00 4 9:45 0:15 10:00 5.50 6.08 7.00 2:08 5 10:00 0:15 6.08 6.25 2.00 7:31 10:15 6 10:15 0:15 6.25 6.42 2.00 7:31 10:30 7 10:30 015 6.42 6.58 2.00 7:31 10:45 8 10:45 11 :00 0:15 6.58 6.75 2.00 7:31 9 11:00 11:15 0:15 5.50 5.75 3.00 5:00 10 11 :15 11 :30 0:15 5.75 6.17 5.00 3:00 11 11:30 11:45 0:15 6.17 6.33 2.00 7:31 12 11 :45 0:15 12:00 6.33 6.42 1.00 15:02 13 12:00 0:15 6.42 6.46 0.50 6:05 12:15 14 12:15 12:30 0:15 6.46 6.46 0.00 0:00 15 12 30 0:15 12:45 6.46 6.46 0.00 0:00 16 12:45 0:15 6.46 6.46 0.00 0:00 13:00 • • d-4 GROUP OEL TA Document No. 14-0188 PERCOLATION TEST DATA (P-2) Project No. S0412 FIGURE A-21 b