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Soil Suitability/ Nitrate Loading Study Irerracon Thor Property w Stockton, CA July 19, 2018 m Terracon Project No. NA187029 1.4.2 Potential Groundwater Contamination Issues The presence of nitrates is not uncommon in shallow groundwater aquifers in San Joaquin County and other parts of the Central Valley. Nitrate in groundwater occurs as a result of the application of fertilizers, livestock waste, and untreated septic tank waste. Nitrate is mobile and often accumulates in the shallow groundwater zones. In the early 1900s, natural levels of nitrate in groundwater were measured in forty-three (43)wells throughout the Sacramento Valley by Kirk Bryan (1923). It was thought that groundwater at that time was close to "natural" conditions. Based on the work by Bryan, it is estimated that under "natural" conditions, groundwater concentration containing nitrate is no more than about 13.5 mg/L-NO3 (3 mg/L-N). Areas having 24.75 mg/L-NO3 (5.5 mg/L-N) or more are those in which nitrate concentrations may be increasing (Hull, 1984). DBCP (dibromochloropropane) is a nematocide and soil fumigant for vegetables and grapes. It is thought to cause health problems consisting of kidney damage, liver damage, and cancer. The use of DBCP was discontinued in 1979. EDB (ethylene dibromide) was used in gasoline to prevent lead deposits and build up. It was also used in pesticides and fumigants. Exposure to EDB is linked to many adverse health effects stemming from organ damage to cancer. Agricultural activities and the use of septic systems in the area should be considered potential groundwater contamination sources.The concerns for groundwater contamination in this area are deemed low to moderate due to the depth to groundwater of 50 to 70 feet bgs. 1.4.3 Water Sample Location According to Mr. Thor, there are no funct' ing groundwater wells on the site. On June 14, 2018, Terracon spoke with Mr. Michael I�iiff;9 ,the San Joaquin County Environmental Health Department who indicated a groundwatersample was not required. 1.4.4 Groundwater Sample Analysis Not applicable. Refer to Section 1.4.3. 1.4.5 Groundwater Sample Handling Not applicable. Refer to Section 1.4.3. 1.5 Soil Profile and Geologic Information Based on a review of the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS)website for San Joaquin County, site soils consist of Stockton silty clay loam with 0 to 2 percent slopes. Parent material is alluvium derived from mixed rock sources. Typical soil profiles consist of 0 to 12 inches silty clay loam soils, 12 to 34 inches clay, 34 to 47 inches clay loam, and 47 to 60 inches cemented soils. Drainage class is considered somewhat Responsive ■ Resourceful ■ Reliable 7