The URL can be used to link to this page

Home My WebLink AboutCT 16-04; HIGHLAND VIEW HOMES; INFILTRATION TESTING; 2016-09-30-----·----.. .. ----.... .. --.. ----Iii -----.. ,. -,.. .. -.. 11111 -lilt ... .. INFILTRATION TESTING Proposed Bioretention Basin 3758 -3794 Highland Drive Carlsbad, California RECEIVED DECO 1 2016 CITY OF CARLSBAD PLANNING DIVISION HETHERINGTON ENGINEERING, INC. ----.. ---.. ... .. -... --------------.. ----.. .. -.. .. .. HETHERINGTON ENGINEERING, INC. SOIL & FOUNDATION ENGINEERING• ENGINEERING GEOLOGY• HYDROGEOLOGY Carlsbad Coastal Views, LLC 3 7 5 8 Highland Drive Carlsbad, California 92008 Attention: Mr. Brian Sullivan Subject: INFILTRATION TESTING Proposed Bioretention Basin 3758 -3794 Highland Drive Carlsbad, California September 30, 2016 Project No. 8047.1 Log No. 18544 References: 1. "Preliminary Grading Plan, 3758 -3794 Highland Drive, Carlsbad, California," by Coastal Land Solutions, Inc., dated April 28, 2016. 2. "Geotechnical Investigation, Proposed Eight-Lot Residential Subdivision, 3758 -3794 Highland Drive, Carlsbad, California," by Hetherington Engineering, Inc., dated September 30, 2016. Dear Mr. Sullivan: In response to your request, we have performed infiltration testing of existing terrace deposits in the area of the proposed bioretention basin at the subject site. No groundwater was encountered to the maximum depth explored of 15.5-feet in borings excavated at the site (see Reference 2). Infiltration testing was performed by this office on September 23 and 26, 2016 in accordance with the Open Pit Falling Head test method. The approximate locations of the infiltration tests are shown on the attached Plot Plan, Figure 1 and the test results are shown on the attached Infiltration Data Sheets, Figures 2 and 3. The infiltration rates based on the infiltration testing are 7 .6-inches/hour and 4.4-inches/hour (without considering safety factors). Completed I-8 and I-9 Forms are attached to this report. 5365 Avenida Encinas, Suite A• Carlsbad, CA 92008-4369 • (760) 931-1917 • Fax (760) 931-0545 333 Third Street, Suite 2 • Laguna Beach, CA 92651-2306 • (949) 715-5440 • Fax (760) 931-0545 www.hetheringtonengineering.com ------------------------.. -.. .. .. • -• .. .. .. .. INFILTRATION TESTING Project No. 8047.1 Log No. 18544 September 30, 2016 Page2 The opportunity to be of service is sincerely appreciated. If you have any questions, please call this office. Sincerely, HETHERINGTON ENGINEERING, INC. n on Civil Engineer 30488 Geotechnical Engineer ( expires 3/31/18) Attachments: Plot Plan Infiltration Data Sheets I-8 and I-9 Forms ogseth ofessional Geologist 3 772 rtified Engineering Geolo rtified Hydrogeologist 5 ~ Distribution: 1-via e-mail (bsully59@hotmail.com) 1-via e-mail (sean@coastal-land-solutions.com) 5-Addressee HETHERINGTON ENGINEERING, INC. l/ ~~ G5 0 1 2 0 20 40 60 80 LEGEND IT-2 ~ APPROXIMATE LOCATION OF INFILTRATION TEST PLOT PLAN HETHERINGTON ENGINEERING, INC. GEOTECHNICAL CONSULTANTS 3758 -3794 Highland Drive Carlsbad, California PROJECT NO. 8047.1 I FIGURE NO. 1 INFILTRATION DATA SHEET Proiect: 3794 Highland Drive Job No.: 8047.1 Test Hole No.: 1 Soil Classification: SM Excavation by: Mansolf Date Excavated: 9/23/2016 Pre-soak by: CF Pre-soak Date: 9/23/2016 Infiltration Testing by: CF Infiltration Date: 9/26/2016 Excavation and Pre-soak Data Trench Width (ft) Trench Length (ft) Trench Depth (ft) Pre-soak Start Pre-soak Water 2 4 1.5 Infiltration Testing Time Time Initial Water Final Water Interval Level Level (min) (inches) (inches) 0752 60 12.0 3.25 0852 0856 0956 60 12.0 4.125 1001 60 12.125 4.5 1101 Time 1550 A in Water Level (inches) 8.75 7.875 7.652 Level (inches) Infiltration Rate (min/inch) 6.86 7.62 7.87 12.0 % Change from Previous 11.1 3.3 Figure 2 Project No. 8047.1 Log No. 18544 INFILTRATION DATA SHEET Project: 3794 Highland Drive Job No.: 8047.1 Test Hole No.: 2 Soil Classification: SM Excavation by: Mansolf Date Excavated: 9/23/2016 Pre-soak by: CF Pre-soak Date: 9/23/2016 Infiltration Testing by: CF Infiltration Date: 9/26/2016 Excavation and Pre-soak Data Trench Width (ft) Trench Length (ft) Trench Depth (ft) Pre-soak Start Pre-soak Water 2 4 1.75 Infiltration Testing Time Time Initial Water Final Water Interval Level Level (min) (inches) (inches) 0820 60 0920 12.12 6.48 0923 60 1023 12.12 7.56 1026 60 12.12 7.68 11 26 Time 1500 ~ in Water Level (inches) 5.64 4.56 4.44 Level (inches) Infiltration Rate (min/inch) 10.64 13.1 6 13.5 1 12.0 % Change from Previous 23.7 2.7 Figure 3 Project No. 8047.l Log No. 18544 Appendix I: Forms and Checklists C . . fl fil . F ·1 ·1· C d'. Forml-8 atcgonzat10n o n 1 tratton cast Jt tty on 1t10n Part 1 -Full Infiltration feasibility Scttcning 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 must be based on a comprehensive evaluation of the factors presented in Appendix C.2 and Appendix D. Yes No X Provide basis: Two infiltration tests using Open Pit Falling Head test method were performed in the terrace deposits in the area of the proposed bioretention basin. The test results were 7.6 in/hr and 4.4 in/hr (without considering safety factors). See "Infiltration Testing ... ," by Hetherington Engineering, In., dated September 30, 2016. 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 cann ot be mitigated to an acceptable level? The response to this Screening Question must be based on a comprehensive evaluation of the factors presented in Appendix C.2. X Provide basis: Infiltration in the area of the proposed bioretention basin is considered acceptable from a geotechnical standpoint provided that the geotechnical recommendations included in the "Geotechnical Investigation ... " (Reference 2) are implemented during design and construction. Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/ data source applicability. 1-3 February 26, 2016 Criteria 3 Appendix I: Forms and Checklists Form 1-8 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 must be based on a comprehensive evaluation of the factors presented in Appendix C.3. Yes No X Provide basis: Storm water pollutant concerns in the area of the proposed bioretention basin are unknow at this time. Borings at the site with a maximum depth of 15.5-feet did not encounter groundwater. Infiltrated water will migrate at least 15.5-feet before reaching groundwater. In addition we are not aware of any known soil contamination present at the site. 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 must be based on a comprehensive evaluation of the factors presented in Appendix C.3. X Provide basis: No ephemeral streams are present at the site. Groundwater was not encountered to a depth of at least 15.5-feet and we are not aware of any contaminated groundwater in the site vicinity. 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 ::i LL *To be completed using gathered site information and best professional judgment considering the definition of 11:EP in the MS4 Permit. Additional testing and/ or studies may be required by Agency /Jurisdictions to substantiate findings I-4 February 26, 2016 Appendix I: Forms and Checklists Form 1-8 Page 3 of 4 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 5 Screening Question Do soil and geologic conditions allow for infiltration in any appreciable rate or volume? The response to this Screening Question must be based on a comprehensive evaluation of the factors presented in Appendix C.2 and Appendix D. Yes No X Provide basis: Due to providing a "Full Infiltration" result to Part 1, this criteria need not be answered. See response to Criteria 1. 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. 6 Can Infiltration in any appreciable quantity 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 must be based on a comprehensive evaluation of the factors presented in Appendix C.2. X Provide basis: Due to providing a "Full Infiltration" result to Part 1, this criteria need not be answered. See response to Criteria 2. 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-5 February 26, 2016 Criteria 7 Appendix I: Forms and Checklists Form 1-8 Page 4 of 4 Screening Question 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 must be based on a comprehensive evaluation of the factors presented in Appendix C.3. Yes No X Provide basis: Due to providing a "Full Infiltration" results to Part 1, this criteria need not be answered. See response to Criteria 3. 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 must be based on a comprehensive evaluation of the factors presented in Appendix C.3. X Provide basis: This question requires the expertise of water-rights lawyers to determine if any violation can be expected downstream by reducing the runoff via infiltration of the water into the bioretention basin. I 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. Part2 Result* If 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. C 0 :.::; g ij:: C ::i LL *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 Agency /Jurisdictions to substantiate findings 1-6 February 26, 2016 Appendix I: Forms and Checklists Factor of Safety and Design Infiltration Rate Worksheet Form 1-9 Factor Category Factor Description Assigned Factor Product (p) Weight (w) Value (v) p=wxv Soil assessment methods 0.25 1 0.25 Predominant soil texture 0.25 1 0.25 Suitability Site soil variability 0.25 1 0.25 A Assessment Depth to groundwater / impervious 0.25 1 1.00 layer Suitability Assessment Safety Factor, SA = :Ep 1.00 Level of pretreatment/ expected 0.5 sediment loads 2 1.00 B D esign Redundancy/ resiliency 0.25 2 0.50 Compaction during construction 0.25 2 0.50 Design Safety Factor, SB = :Ep 1.00 Combined Safety Factor, S,0,,.1= S,1 x Sn 2.00 Observed Infiltration Rate, inch/hr, Kobserved 7.6 & 4.4 (corrected for test-specific bias) Design Infiltration Rate, in/hr, :Kiesign = Kobscrvcd / S,oral 3.8 & 2.2 use 3.0 (ave) Supporting Data Briefly describe infiltration test and provide reference to test forms: Two Open Pit Falling Head tests were performed. See "Infiltration Testing ... " by Hetherington Engineering, Inc., dated September 30, 2016. I-9 February 26, 2016