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Nitrate Loading Study Irerracon Roque Property a Victor, California July 6, 2018 ■Terracon Project No. NA187032 2.2 Potential Ground Water 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 nematicide 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. 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 based on the anticipated depth to groundwater between 80 and 120 feet bgs. 2.3 Current and Future On-Site Ground Water Uses According to Ms. Roque, there are no groundwater wells located on the site. Ms. Roque indicated an off-site municipal groundwater supply well provides water to the site. Based on the absence of an onsite groundwater well, a groundwater sample was not collected. 3.0 SOURCES AND IMPACT OF NITRATE TO GROUNDWATER 3.1 Current Off-Site Sources of Nitrate The adjoining properties appear to consist of agricultural land primarily vineyards and/or residences. EHD septic permits were available for the adjoining northern and southwestem residential properties. Although septic permits were not found for the adjoining eastern, southern and western properties, Terracon assumes the adjoining properties are connected to individual septic systems based on the absence of sewer systems in the area as reported on the San Joaquin County District Viewer. Off-site sources of nitrate include residential septic systems, agricultural land use, and natural processes. Responsive■ Resourceful ■ Reliable 4