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H. SOIL SUITABILITY STUDY FINDINGS A. SUBJECT PROPERTY AND SURROUNDING STUDY AREA INFORMATION The current surrounding land use to the north, south, east and west of the project site has been the same for several years. Chis is evidenced by the United States Department of Agriculture (USDA) Soil Maps for San Joaquin County for this area. Applications on file with the County Environmental Health Department reveal that there have been seven permits issued for repairs/additions to existing systems in the one-half mile study radius. All of the permits reveal the installation of seepage pits as an addition to existing septic systems, reinforcing the premise that seepage pits should be installed in this locale. The seven permits also indicate that the surrounding surface soils are marginally conducive for the proper management of septic effluent. In the eastern and northeastern areas of San Joaquin County, seepage pits are used to manage most of the septic effluent due to the poor shallow soils. B. SOIL PHYSICAL AND CHEMICAL CHARACTERISTICS The project site has level terrain; consequently, there will be no need to incorporate design considerations for slopes. The United States Department of Agriculture - Natural Resources Conservation Service (USDA-NRCS) shows the on-site soils to consist mostly of San Joaquin sandy loam (9237). The Unified Soil Classification System (USCS) identifies the surface soils as a silt and silty clay (ML and CL-ML). According to the USDA Handbook, the surface layer is a brown sandy loam with a claypan of brown clay below this surface soil. Extending frons 20 inches to 60 inches is light brown hardpan of cemented silts and clays. The main limitations with these soils are the very slow permeability in the substratum, which was evidenced by the failure of the shallow percolation tests. However, effluent that does infiltrate and percolate through this fine soil material (clay and silt sized particles) will undergo biological treatment of the effluent before reaching the water table (--120 ft below grade). Biological treatment includes the destruction of bacteria and viruses. Logs of boring are found on each of the four FIELD PERCOLATION 'NESTING REPORTS and illustrate the subsurface soil characteristics encountered in each of the 25 foot percolation test borings. The logs illustrate the variability of the strata encountered. These strata include a well- graded sand (SW), a clayey, well-graded gravel (GW-CL) and a silty. medium, poorly graded sand (SM-SP). No rust mottling was observed in the upper soil profile, although there was slight mottling occurring at the deeper depths above the sand strata in the parcel 2 and parcel 4 borings. Although rust mottling may be attributed to geologic processes, it may also be due to seasonal soil saturation whereby percolating soil water encounters larger porosity soil and accumulates on top of these strata. Rust mottling can be indicative of seasonal soil saturation. It occurs when anaerobic bacteria decompose organic matter and use iron (Fe") in their metabolic processes. 2