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Home My WebLink AboutCDP 13-30; DE ANDA RESIDENCE; GRADING PLAN REVIEW; 2014-06-04W.O.. 6612-Al-SC rL("- NO. 1934 Certified \ Engineering Geologist •. N'0F c/ c't,r (31° Eli Geotechnical • Geologic • Coastal • Environmental 5741 Palmer Way • Carlsbad, California 92010 • (760) 438-3155 • FAX (760) 931-0915 • www.geosoilsinc.com MEMORANDUM DATE: June 4, 2014 TO: Ms. Veronica DeAnda do Berry G Aim: Mr. John Beery, Mr. Misael Arella From: Robert G. Crisman, CEG 1934 David W. Skelly, RCE 47857 SUBJECT: Grading Plan Review, De Anda Residence, APN 155-140-41, Carlsbad, San Diego County, California References: 1. "Grading plan for: De Anda Residence, APN 155-140-41," Sheets 1-4, J.N. 137109 DeAnda, dated May 16, 2014, by Sampo Engineering, Inc. "Supplement to the Geotechnical Update and Review, 2425 Jefferson Street (APN 155-140-41), Carlsbad, California," W.O. 6612-Al-SC, dated March 28, 2014, by GeoSoils, Inc. "Geotechnical Update and Review, Proposed. Development of 2425 Jefferson Street (APN 155-140-41), Carlsbad, San Diego County, California," W.O. 6612-A-SC, dated October 28, 2013, by GeoSoils, Inc. "Updated Preliminary Geotechnical Evaluation, APN 155-140-41, Carlsbad, San Diego County, California," W.O. 5763-A-SC, dated October 15, 2008, by GeoSoils, Inc. "Stormwater Best Management Practice Design Guideline, Volume 3, Basin Best Management Practices, Nation Risk Management Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency," EPA/600/R-04/121B, dated September 2004, by Clar, M.L., et. al. In accordance with a request from the project architect, the referenced plans (see Reference No. 1) were reviewed for conformance with the intent of the referenced geotechnical reports (Reference Nos. 2, 3, and 4). Based on our review, the grading plans/details (Reference No. 1) appear to be in general conformance with the recommendations provided by this office, with the following additional comments and recommendations (see below). Grading Note #35 and "Soils Engineer's Certificate" Grading note #35, shown on Sheet 1 of Reference No. 1 should be revised to include the above references No. 3 and No. 4, as well as this plan review document. The soils engineer's certificate shown on Sheet 1 of Reference No. 1 should be revised to read as follows: "I, David Skelly, a registered engineer of the state of California, representing GeoSoils, Inc., principally doing business in the field of applied soil mechanics, hereby certify that a sampling and study of the soil conditions prevalent within this site was made by GSI, and/pr under my direction, dated 10/15/08, and 10/28/13. Two, copies of the soils reports compiled from these studies, with GSI recommendations, have been submitted to the office of the City engineer." Paver Section with Concrete Edges The "paver detail with concrete edges," shown on Sheet 2 (section C) of Reference No. 1, indicates an open graded gravel section placed over compacted subgrade, and confined laterally by a concrete edge. This design appears to be undrained, and has the potential to have the paver section fill with water, and overtop the paver section reservoir. Furthermore, water held within the reservoir has the potential to saturate the underlying subgrade, thus increasing the potential for distress to the concrete edges and the adjacent improvements within the City R.O.W. The reservoir appears to be on the order of 10 to 11 inches deep and will not likely be able to fully drain to the street, if provided with a subdrain. Consideration should also be given to providing the base course section with a subdrain that discharges the treated water to either of the adjacent bioretention basins, provided that these basins are also allowed to drain downslope, to the west, as discussed in the following section. Front Yard Bioretention Basins Plans indicate two (2) front yard bioretention basins located at the northeast and southeast corners of the property. These basins (including "engineered soil" thickness) appear to be unlined, undrained, and on the order of 2 feet deep. Per plan, these basins are filled with a permeable "engineered soil" and each basin is provided with an overflow outlet to the adjacent curb and gutter. The relatively dense nature of formational soils and lack of subdrainage will increase the potential for prolonged water retention (below the outlet invert elevation) and resultant saturation of subgrade soils in the vicinity of each basin. This will result in an increased potential for distress to any adjacent, settlement sensitive improvement, especially adjacent to the existing wall located along the east end of the southern side yard property Ms. Veronica DeAnda W.O. 6612-Al-SC APN 155-140-41, Carlsbad June 4, 2014 File: e:\wpl2\6500\6612.gpr.memo Page 2 line. The planned excavation and potential saturation of soil materials in the vicinity of the walls foundation will increase the potential for distress to the wall, due to reduced lateral and vertical bearing support. In order to reduce the potential for distress, the basins may be provided with impermeable liners and subdrainage that convey treated water toward the rear of the property, by either discharging into one of the three planned rear yard bioretention basins, or tight lined directly to any of the planned rip rap energy disapators. Rear Yard Bioretention Basins Plans indicate three (3) rear yard bioretention basins, with one of the basins located adjacent to the planned residential structure. These basins (including the "engineered fill" thickness) appear to be on the order of 18 to 24 inches deep, are lined, and are provided with subdrainage. Plans indicate that each basin is outletted to a planned energy dissipater downslope. The rear yard biobasin located nearest the northwest corner of the building appears to be located immediately adjacent to the building. While the basin appears to be lined, the affected portion of the building foundation should be adequately waterproofed (see Sheet S-2 [shown as a planter] and Sheet SD1 .1, Detail 1 of the structural plans prepared by Delta Engineering for reference). Impermeable Liner Criteria Impermeable liners shall have the following minimum properties: 30mi1 PVC, Specific Gravity (ASTM D792):120 (mm.), Tensile (ASTM D882): 73 (lb/in-width, mm), Elongation at Break (ASTM D882: 380 (%min), Modulus (STM D882): 30 (lb/in-width, mm.), and Tear Resistance (ASTM D1004): 30 (lb/in, mm). Soil Suitability for Storm Water Infiltration It should be noted that subgrade soils will generally consist of compacted fill soils, or relatively dense formational soils. While granular in nature, these soils are considered to belong to Hydrologic subgroup "D" (i.e. very slow infiltration rates due to density/cementation), and are likely not feasible for infiltration, per United States Environmental Protection Agency [USEPA], 2004 (see Reference No. 5). Furthermore, in accordance with Reference No. 5, fill soils are also not recommended for infiltration. As such, the use of liners and basin subdrainage should be considered for all basins. Ms. Veronica DeAnda W.O. 6612-Al-SC APN 155-140-41, Carlsbad June 4, 2014 File: e:\wpl2\6500\6612.gpr.memo GeoSoils, Inc. Page 3 Limitations The soil conditions discussed are believed representative of the area; however, soil and bedrock materials vary in character between excavations and natural outcrops or conditions exposed during mass grading. Site conditions may vary due to seasonal changes or other factors. Inasmuch as our study is based upon our review and engineering analyses, the conclusions and recommendations are professional opinions. These opinions have been derived in accordance with current standards of practice, and no warranty is express or implied. Standards of practice are subject to change with time. GSI assumes no responsibility or liability for work or testing performed by others, or their inaction, or work performed when GSI is not requested to be onsite, to evaluate if our recommendations have been properly implemented. Use of this report constitutes an agreement and consent by the user to all the limitations outlined above, notwithstanding any other agreements that may be in place. In addition, this report may be subject to review by the controlling, authorities. Ms. Veronica DeAnda W.O. 6612-Al-SC APN 155-140-41, Carlsbad June 4, 2014 FiIe:e:\wpl2\6500\6612.gpr.memo Geooi1s, Inc. Page 4