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II. SOIL SUITABILITY STUDY FINDINGS A. SUBJECT PROPERTY AND SURROUNDING STUDY AREA INFORMATION The subject property has been owned by Mr. Sephos since 1991. The surrounding land use to the north, west and southwest of the project is, and has been, in agricultural production for many decades. This is evidenced by the United States Department of Agriculture (USDA) Soil Map of San Joaquin County for this area. To the east and southeast of the project are relatively high density residential subdivisions as noted on the Site Plan prepared by MCR Engineering, Manteca. Applications on file with the County Environmental Health Department reveal that there have been six permits issued for additions to existing systeLns; and no permits for repairs_inthe one- half mile ra ius studyarea. These additions can probably be attributable to an intermittent hardpan layer throughout the region at approximately 4 ft below grade. It appears that additions to septic systems increase eastward along Southland Avenue. I B. SOIL PHYSICAL AND CHEMICAL CHARACTERISTICS 1. SURFACE AND SUBSURFACE SOILS 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) indicates the existing homesite parcel to consist of Veritas fine sandy loam (#266), and the proposed two new Parcels to be Tinnin loamy coarse sand (#255). Particle Size Analysis under the Unified Soil Classification System (USCS) classifies this soil as a silty fine sand, sandy silt (SM), cemented silts hardpan(ML), and a fine-to-medium well- graded silty sand (SW/SM). According to the USDA Handbook, the main limitation with these soils are the rapid permeability in the substratum, which is evidenced by the percolation test results. However,there is sufficient fine material (clay and silt sized particles) to slow the perc rate sufficiently and to promote biological treatment of the effluent before Le chiM the wa er table 2i ft below rade). Biological treatment includes the destruction of bacteria and viruses. A 12-ft hand boring was completed near the NEC of Parcel 2, in the proposed leachfield area. This boring provided 1.) a profile of the underlying soil characteristics, 2.) hardpan layer determination and 3.) subsurface soil hydraulic conductivity, and 4.) chemical analyses. The log of boring illustrates the subsurface soil characteristics encountered: The surface soils to 4 ft consist of a light brown fine sand silt. Below this strata is a chemically induced cemented silts hardpan, which becomes less compact at 5 ft but increases in density and becomes more severe at 6 ft. This hardpan extends another 1.5 ft and at -9 ft is a very fine sandy silt which was wet. From 10.5 ft to boring termination at 12 ft is a rust mottled fine-to-medium well-graded silty sand. This silty sand strata is where there would be an impedance to downward water flow due to the phenomena of moisture tension. y Iql Ill��e��a. 2 Vafley dig Research