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' Soil Suitability/ Nitrate Loading Study 1��rracon Avanti Nut Co. ■ Stockton, CA May 19, 2016 ■Terracon Project No. NA167038 1 1.4 Groundwater Information 1 .4.1 Groundwater Depth and Gradient Groundwater was not encountered in our percolation test holes excavated to depth of 41 inches and 252 inches on May 5, 2016. The San Joaquin County Flood Control and Water Conservation District Groundwater Report I (SJCWCD) Spring 2015 groundwater depth and elevation maps were reviewed to determine the groundwater levels near the Site. According to the Lines of Equal Depth to Groundwater Spring 2014 and Spring 2015 maps (Plates 3 and 4), depth to groundwater groundwater lies between approximately 100 to 120 feet bgs. Per the Department of Water Resources (DWR) Water Data Library an irrigation well', approximately 1,160 feet north-northwest of the site, had a depth to L groundwater of 130 feet on March 21, 2016. Based on a review of the SJCWCD Lines of Equal Elevation of Groundwater Spring 2015 map, groundwater flow gradient is generally to the north- northeast. The groundwater flow direction and the depth to shallow, unconfined groundwater, if present, would likely vary depending upon seasonal variations in rainfall and other hydrogeological features. Without the benefit of on-site groundwater monitoring wells surveyed to a datum, groundwater depth and flow direction beneath the site cannot be directly ascertained. Based on the topographic map (Plate 1) the approximate site elevation is 55-60 feet above mean sea level. 1 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. 1 ' htto://www.water.ca.covAvaterdatalibrary Groundwater level station site code:380578N1212017N001 Responsive ■ Resourceful m Reliable 5