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reasonably be required to remove this contaminant should it occur in drinking water. The Maximum Contaminant Level Goal (MCLG) for DBCP is zero. Soil Profile and Geologic Information The Site is depicted on the Preliminary geologic map of the Tracy quadrangle, San Joaquin County, California (Diblee, 1981). The Site is depicted within a map unit of Holocene alluvium (Plate 8). The surface and near surface soils located at the Site are reported by the USDA Web Soil Survey to be composed of Stomar clay loam (Plate 9) (USDA, 2019). The table below presents some selected properties of this soil: Table 1. Selected Properties of On-Site Soils (USDA, 1992) Soil Name Depth Unified Soil Salinity Soil Perme- Septic tank and Map (in) Class Reaction ability absorption Symbol Classification mmhos/cm pH (in/hr) fields Stomar clay 0-17 Clay loam; CL <2 6.6-7.3 0.2-0.6 Severe: loam, 0-2% 17-47 Clay loam, clay; CL, CH <2 6.6-8.4 0.06-0.2 peres slowly slopes, 252 47-60 Clay loam, silty clay <2 7.4-8.4 0.2-0.6 loam; CL Note: The table descriptions do not necessarily reflect site-specific soil properties. See description of the map unit for composition and behavior characteristics of the map unit. Percolation Test Percolation testing was performed by Chesney Consulting in 2006 and described in the Nitrate Loading Study Soil Suitability Study dated February 20, 2006. According to that report, on January 30, 2006, Chesney excavated two shallow borings near the proposed septic disposal area on the Site for the purpose of conducting percolation tests. The borings were hand drilled to 24 and 36 inches deep (Table 2). The locations of the borings are indicated on Plate 10. The Chesney report describes the soil in the borings as silty lean clay to a depth of 24 inches, followed by lean clay with silt to a depth of 36 inches. Discussion of Soil Lithology Based on the soil described, there appears to be moderate potential for percolation in the shallow soil zone. Sandy soils generally have a much greater potential for percolation than fine-grained or cemented soils. However, a percolation test is the only accepted method for determining the suitability of the soils for a septic disposal area. Percolation test results are discussed in the following section. LOGE 20-19 Page 6