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concentrations of 5.5 mg/L-N or more (Hull, 1984). The US EPA has set the Maximum Contaminant Level (MCL) for nitrate at 10 mg/L-N. Although nitrate is a naturally-occurring compound necessary for plant growth, it can cause health problems when present at high levels in drinking water. The most common health effect of nitrates in water is methemoglobinemia, or blue baby syndrome, which results in reduced oxygen supply to vital tissues. Pregnant women and certain others can also develop methemoglobinemia. Symptoms include a bluish color of the skin, as well as headache, dizziness, weakness, and difficulty breathing. Ingestion of high levels of nitrates over time can also lead to gastric problems. DBCP is a nematocide and soil fumigant for vegetables and grapes. It is known to cause male reproductive effects and is classified as a probable human carcinogen. Most domestic use of DBCP was discontinued in 1977 through 1979. The US EPA set the MCL at 0.2 parts per billion (ppb, equivalent to �tg/L) because it believes that given present technology and resources, this is the lowest level to which water systems can 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 /cm Reaction ability absorption Symbol (in) Classification mmhos 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. LOGE 20-60 Page 6