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Soil Suitability /Nitrate Loading Study Irerracon Thornton Road Trailer Parking Facility ■ Lodi, California December 15, 2021 ■ Terracon Project No. NA217079 The septic system design should be based on the San Joaquin County On -Site Wastewater Disposal Standards or other engineering recommendations. 1.4 Groundwater Information 1.4.1 Groundwater Depth and Gradient Groundwater was not encountered within our percolation test borings which were Hand Augered between 3.0 and 7.0 feet below grade surface (bgs). According to the California Department of Water Resources Sustainable Groundwater Management Act (SGMA) Data Viewer, in Spring 2021 depth to groundwater was reported between approximately 20 to 30 feet bgs and in Fall 2019 depth to groundwater was approximately 20 feet bgs. Based on a review of the Spring 2021 and Spring 2020 elevation contours groundwater was reported approximately 21.74 to 24.84 feet below mean sea level with a southeast groundwater gradient. 1.4.2 Potential Groundwater Contamination Issues Potential groundwater contamination can occur from a number of sources including historical petroleum hydrocarbon use, agricultural activities, dairies, septic systems, and storm water infiltration. As per EHD requirements nitrate as N and 1,2-dibromo-3-chloropropane (DBCP) have been included as part of the SSS discussion. Identifying potential groundwater contamination other than nitrates and DBCP is beyond the scope of work for this report. 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 milligrams per liter (mg/L) nitrate (NO3) or (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 (dibromo chloropropane) 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. Based on the historical information, the past agricultural land use in the area should be considered potential groundwater contamination sources. According to the State Water Resources Control Board website, there were no nitrate impacted wells reported within 2,000 feet of the site. Responsive ■ Resourceful ■ Reliable 7