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II. SOIL SUITABILITY STUDY FINDINGS A. SUBJECT PROPERTY AND SURROUNDING STUDY AREA INFORMATION SSS§ 1.1. Surrounding land use is, and has been, in agricultural production and rural residential for many decades. To the east and west is open farmland and tree crops, to the north and south is rural residential and farmland. To the northwest is the City of Tracy. The property is zoned R -R, Rural Residential. SSS§ 3.1, 3.2, 3.3, 3.4, 3.5, 3.6. Applications on file with the EHD reveal that there have been two permits issued for repairs/replacements/additions to existing systems on Koster Road. Although the soil has a comparatively high percentage of clay content, the Tracy area clay soils possess significant permeability. Secondly, rural residential structures are sparse in this location. The project site has level terrain; consequently, there will be no need to incorporate design considerations for slopes. B. SOIL PHYSICAL CHARACTERISTICS AND ANALYTICAL TEST RESULTS The United States Department of Agriculture - Soil Conservation Service (USDA -SCS) indicates the on-site soils to consist of Capay clay (#121) and low percentages of Stomar, Vernalis and El Solyo clay soils. SSS§ 5.2. The surface and subsurface soil investigation and testing began with the sampling and testing from the bottom of the percolation test boring (from the 36" to 42" inch depth). NLS§ 1.1, 1.2. As the noted on the A&L Laboratory Soil Analysis Report in Appendix B, the chemical analyses of the retrieved soil sample quantify several constituents that influence nitrate loading from this project. The important parameters for nitrate loading assessment are the organic matter, pH, cation exchange capacity (CEC), clay content percentage, along with nitrate -nitrogen content of the soil. As noted, the organic matter is surprisingly high within the subsurface soils, which may be attributed to previous deep-rooted crops planted, such as alfalfa. This high OM content, in addition to the high clay content can be beneficial for denitrification processes. The nitrate -nitrogen concentration is a medium concentration at 16 ppm. Because septic effluent is composed predominately of ammonium (NH4), the pH, along with the CEC, have significant influence on ammonium molecules. The pH of the soil is alkaline which impedes ammonium formation and stability. The CEC measures the ability of the soil to theoretically trap and hold ammonium molecules and was measured at 19.2; indicative of high clay content soils. Consequently, there is a high potential for the retention of ammonium molecules for microbial uptake, and suppression of nitrification and promotion of denitrification that may occur. Chesney Consulting