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Home My WebLink AboutCT 06-27; MUROYA SUBDIVISION; STORM WATER MANAGEMENT CONSULTATION; 2011-05-181E GEOCON INCORPORATED GEOTECHNICAL • ENVIRONMENTAL. M A I E R I A L S Project No. 07671-52-01 March 2, 2011 Revised May 18, 2011 Taylor Woodrow Homes Incorporated 15 Cushing Irvine, California 92618 Attention: Ms. April Tornillo Subject: STORM WATER MANAGEMENT CONSULTATION MUROYA PROPERTY CARLSBAD, CALIFORNIA References: 1. Geotechnical Investigation, Muroya Properly, Carlsbad, California, prepared by Geocon Incorporated, dated July 14, 2009 (Project No. 07671-52-01). 2. Updated Geologic Map, Muroya: Property, Carlsbad, California, prepared by Geocon Incorporated, dated September 30, 2009 (Project No. 07671-52-01). Dear Ms. Tornillo: In accordance with your request, we prepared this letter to discuss storm water management on the subject site from a geotechnical engineering standpoint. We understand the regulatory agency may request storm water management devices for the project. Based on the referenced report, the subject lots will be underlain by compacted fill over Lindavista Formation and Santiago Formation. The fill materials within the planned development possess a "very low" to "low" expansion potential (expansion index of 50 or less). A review of the grading plan and discussions with the design team indicate that storm water management systems may be requested by the City Of Carlsbad. These systems usually include permeable pavement/payers, grass lined swales, and retention areas. These devices are outlined in the Countywide Model Standard Urban Stormwater Mitigation Plan (SUSMP) or Low Impact Development (LID) Handbook. We attempted to perform three permeability tests using a Guelph Permeameter at the planned locations of pervious payers within the driveway areas for Lots 30 through 32, 4 through 11, and 16 through 16. We expect the formational materials will be present at the. base of the planned paver pavement section; therefore, we attempted to perform the permeameter tests within the formational materials. We performed the Guelph Permeameter testing at a depth of about 24 inches within the formational materials. The results of the permeability testing indicate a saturated permeability rate in inches per hour as presented in Table 1. 6960 Flanders Drive E San Diego, California 92121.2974 0 Telephone 858.558.6900 m Fax 858.558.6159 TABLE 1 SATURATED PERMEABILITY TEST RESULTS Location Field Saturated Permeability [Guelph Permeameter] (m/hr) Driveway of Lots 30-32 0.011 Driveway of Lots 4-11 Too Dense to Perform Test Driveway of Lots 13-16 Too Dense to Perform Test Based on the calculated infiltration rates, the existing soil may not be conducive to water infiltration. In addition, basins that are located adjacent to the planned structures and where distress could occur from infiltration, the storm water management devices should be properly constructed to prevent water infiltration. The planned retention basin areas should be lined with an impermeable liner (e.g. High-density polyethylene, HDPE, with a thickness of about 12 mil or equivalent Polyvinyl Chloride, PVC, liner). We do not expect water will infiltrate the formational materials within the paver pavement areas. The paver areas should be setback from the planned structures at least 5 feet. However, the subgrade should be graded to allow water to flow to a subdrain. The subdrain should be placed at the bottom of the base section along the low point of the driveway to reduce the potential for water to build up within the paving section. The drain should be connected to a drainage device as determined by the project civil engineer. Impermeable liners located below the paver section will not be required if the payers are installed as recommended herein. The drain should consist of a 3-inch diameter perforated Schedule 40, PVC pipe wrapped in filter fabric and placed adjacent to the concrete band. If you have any questions regarding this letter, or if we may be of further service, please contact the undersigned at your convenience. Very truly yours, GEOCONINgORPORATED L 91 UJ EXP.06,O/fl )rn Shawn Foy Weedon cc GE 2714 SFW:dmc OF (2) Addressee (e-mail) Pangea Land Consultants, Incorporated Attention: Mr. Chuck Glass Project No. 07671-52-01 - 2 - March 2, 2011 Revised May 18, 2011 GEOCON INCORPORATED GEOTECHNICAL • ENVIRONMENTAL • MATERIALS (4OV)F Project No. 07671-52-01 March 2, 2011 RECEiVED MAR 09 2011 Taylor Woodrow Homes Incorporated 15 Cushing ENGINEERING Irvine, California 92618 tpARTMENT Attention: Ms. April Tornillo Subject: MUROYA PROPERTY CARLSBAD, CALIFORNIA STORM WATER MANAGEMENT CONSULTATION References: 1. Geotechnical Investigation, Muroya Property, Carlsbad, California, prepared by Geocon Incorporated, dated July 14, 2009 (Project No. 07671-52-01). 2. Updated Geologic Map, Muroya Property, Carlsbaà Calforñia, prepared by Geocon Incorporated, dathd September 30,2009 (Project No. 07671-52-01). Dear Ms. Tornillo: In accordance with yor request, we prepared this letter to discuss stthm water management on the subject site from a geotechnical engineering standpoint. We understand the regulatory agency may request storm water management devices for the project. Based on the referenced report, the subject lots will be underlain by compacted fill over Lindavista Formation and Santiago Formation. The fill materials within the planned development possess a "very low" to "low" expansion potential (expansion index of 50 or less). A review of the grading plan and discussions with the design team indicate that storm water management systems may be requested by the City of Carlsbad. These systems usually include permeable pavement/payers, grass lined swales, and retention areas. These devices are outlined in the Countywide Model Standard Urban Stormwater Mitigation Plan (SUSMP) or Low Impact Development (LID) Handbook. Cexisting milices are did to promote water infiltration; however, the existing soil conditions are noF nducive for water infiltration. We recommend against water infiltration adjacent to structures provements, compacted fill, and slopes. In this regard, distress and possible failure within the and planned improvements will likely occur if infiltration were allowed. The distress could• iñ1*ide einif iviiianxpansion (Downgradient, prop es may l ibjëted to seeps, snn]—,slope instabilitymovementof foundations and slabs, or other impacts as a result of water infiltration. Also, water may enter underground uilitiiones and iiiij,act improvements down gradieñtfroiii the site. (The potential for ditdéëiidsöiitbë amountof water to bedetained,its residence time, soil permeability, and other factors. We have not performed a hydrogeology study at the site. 6960 Flanders Drive • Son Diégà, California 92121.2974 • TeIehone 858.558.6900 U. Fox 858.358.6159 If you have any questions regarding this letter, or if we may be of further service, please contact the undersigned at your convenience. Very truly yours, GEOCON INCORPORATED FE Shawn F. Weedon No. 2714 GE 2714 it Ep.O63WI1 SFW:dmc (2) Addressee (e-mail) Pangea Land Consultants, Incorporated Attention: Mr. Chuck Glass Project No. 07671-52-01 -2- March 2,2011