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Nitrate Loading study Irerracon Cho Property a Ripon,California September n, 2048 ■ Terracon Project No. NAI 87038 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 "naturae" conditions, groundwater concentration containing nitrate is no more than about 13.8 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. Agricultural land use and septic systems in the area should be considered potential groundwater contamination sources. The concerns for groundwater contamination in this area are deemed moderate to high based on the agricultural land use and anticipated depth to groundwater between 45 to 60 feet bgs. 2.3 Current and Future On-Site Ground Water Uses According to Mr. Cho, there are no groundwater wells located on the site. fir. Cho indicated the site will be developed with a groundwater supply well for future residential use. Based on the absence of an onsite groundwater well, a groundwater sample was not collected. 3.0 SOURCES AND WFACT OF NITRATE TO GROUNDWATER 3.1 Current Off-Site Sources of Nitrate The adjoining properties consist of agricultural land primarily orchards and rural farm structures and/or residences. Terracon assumes the farm structures and/or residences are connected to individual septic systems based on the absence of municipal sewer systems in the area as reported on the San Joaquin County District Viewer. Therefore, off-site sources of nitrate include residential septic systems, agricultural land use, and natural processes. Based on information obtained from the DWR Water Data Library, between the years 1959 to 2012, dissolved nitrate was reported between 5 and 70.4 rng/L-N at three groundwater wells located within one mile north and northeast of the site. A groundwater study titied Addressing Responsive ■ Resourceful ■ Reliable 5