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III. SOIL SUITABILITY STUDY A. de SNAYER DAIRY FACILITY AND STUDY AREA INFORMATION The de Snayer Dairy has been in existence for more than 60 years. It was built circa 1939 by an unknown dairy family. It changed ownership several times until the Sousa Brothers bought the dairy in 1986 and owned it until 1997, when Leen and Paula de Snayer purchased the dairy and surrounding cropland. The subject property and surrounding area are zoned AG-40 with the General Plan designation as agriculture. Interstate 5 is located to the east of the dairy. Surrounding acreage consists primarily crop production for cattle feed and vineyards. Surrounding housing is extremely low density, single family residences (SFRs). It can be assumed that water and sewer from the town of Thornton, which is the nearest "municipality," will not be installed in this area for several decades, and probably never. A review of Application Permits on file at the San Joaquin County Environmental Health Department reveals there have been three Applications for Repairs/Additions within the one-half mile diameter study area, all of which were for the subject dairy facility. These applications were for the installation of two shallow sumps and one filter bed. Considering the dairy has been in existence for several decades,this number of repair applications may be considered predictable and illustrates the surface and subsurface soils have a definite lifespan for effluent management. B. SOIL PROFILES AND PERCOLATION TEST RESULTS 1. SOIL ANALYTICAL TEST RESULTS - FUTURE LEACHFIELD AREA Both soil physical characteristics and soil chemical parameters were examined for the Nitrate Loading Study. The surface soil structure in the proposed area of the future leachfield consists of a silty clay for the top one foot. Below this layer exists a very fine sandy silt with 17% clay. The underlying soil texture analysis at the perc test depth of 42 inches is illustrated below in Table 8. The agronomic description is a sandy loam which is equivalent to a silty, clayey sand in the Unified Soil Classification System (USCS). In addition to soil texture analysis, the retrieved soil sample was chemically analyzed. Considering this area has been an open corral for the last 60 years, the results indicate a medium nitrate- nitrogen concentrations of 22 ppm and a low organic matter content of 0.7%. Soluble salts concentration was medium in concentration at 0.8 mmhos. Additional analyzed constituents relating to nitrate loading potential originating from septic system effluent also include the organic matter content of the soil, pH,and the Cation Exchange Capacity (CEC). The denitrification capacity of the soil is predominately dependant upon the abundance of d. an organic carbon substrate, high soil moisture content leading to anaerobic environment, and high soil pH. The pH is alkaline at 7.7, however, the organic content of the soil is low. Although saturated soil conditions may develop near the soil/effluent interface in the leachfield area during the rainy season, sufficient organic carbon substrate may not be present to promote denitrification. The CEC was also relatively low for the soil type encountered. A low CEC signifies the soil may not possess a large capacity to adsorb ammonium molecules in the septic effluent. s -14- Chesmy ConsuCting