CITY PROJECT - 1821 & 1823 E Chestnut Ave - Plan

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ASSOCIATED SOILS ENGINEERING, INC. Project No.: 7160.23 2860 Walnut Avenue, Signal Hill CA 90755 January 23, 2024 Tel: (562) 426 -7990 * Fax: (562) 426 -1842 Page 27 and fill compaction should be performed under the observation of and testing by a Geotechnical Consultant or his representative. 6.0 FIELD PERCOLATION TEST DATA Initial seepage rates obtained during the "Reading Time Interval Test" in Borings B-P1 and B-P2 after overnight pre-soaking indicated the time interval between readings should be 10 minutes maximum, i.e. the “Sandy Soil” category. The percolation tests were therefore performed using the sandy soil method (i.e. one hour test maximum) for Borings B-P1 and B-P2, in accordance with the State of California Regional Water Quality Board Technical Guidance Document Appendices (Appendix VII) procedures modified to test the cross sectional zone of typical soils within the level of anticipated storm water infiltration (e.g. approximately 5 feet to 10 feet and 1 foot to 5 feet below existing grade for Borings B-P1 and B-P2, respectively). Field percolation testing was conducted on December 2, 2023. Stabilized field percolation test data indicates preadjusted percolation test rates ranging from 0.690 to 5.714 minutes per inch (mpi) for clean water at the locations of Borings B-P2 and B-P1, respectively. Field percolation test data is presented on the attached Plates H-1 and H-2 in Appendix A. Tabulated below are the results of percolation testing conducted at the locations of Boring B-P1 and B-P2, including the infiltration rate derived from the Porchet Method of Percolation Rate Conversion procedures outlined in Appendix VII of the Technical Guidelines Document Appendices. Boring No. Test Depth (ft) Percolation Test Rate (Minutes/Inch) Infiltration Rate* (Inches/Hour) B-P1 5-10 0.690 0.570 B-P2 1-5 5.714 5.559 *Infiltration Rate derived from Porchet Method Conversion from Percolation Rate using a Factor of Safety of 3. The rates presented on the previous page are anticipated to be the fastest rates that can be absorbed by the site soils at the boring locations. However, with time and depending on the degree of saturation of soils and other factors, the percolation rate may reduce which is typical for sewage disposal or stormwater dispersal fields. Per Appendix VII, the results of the field percolation testing (i.e. measured infiltration rate greater than 0.3 inch per hour) indicate that site soils only at Boring B-P1 location are deemed suitable for the planning and installation of an on-site stormwater LID system within the approximate upper five to ten (5-10) feet from existing grade. Please be informed that during installation of on-site stormwater dispersal system, the following factors should be noted: • The degree of compactive effort in the upper 1 to 1.5 feet of soils above any filter material should be between 90 and 92 percent relative compaction. As any greater compactive efforts in the soil strata