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Soil Suitability / Nitrate Loading Study <br />Thornton Road Trailer Parking Facility ■ Lodi, California <br />December 15, 2021 ■ Terracon Project No. NA217079 <br />Responsive ■Resourceful ■Reliable 7 <br />The septic system design should be based on the San Joaquin County On-Site Wastewater <br />Disposal Standards or other engineering recommendations. <br />1.4 Groundwater Information <br />1.4.1 Groundwater Depth and Gradient <br />Groundwater was not encountered within our percolation test borings which were Hand Augered <br />between 3.0 and 7.0 feet below grade surface (bgs). According to the California Department of <br />Water Resources Sustainable Groundwater Management Act (SGMA)Data Viewer, in Spring <br />2021 depth to groundwater was reported between approximately 20 to 30 feet bgs and in Fall <br />2019 depth to groundwater was approximately 20 feet bgs. Based on a review of the Spring 2021 <br />and Spring 2020 elevation contours groundwater was reported approximately 21.74 to 24.84 feet <br />below mean sea level with a southeast groundwater gradient. <br />1.4.2 Potential Groundwater Contamination Issues <br />Potential groundwater contamination can occur from a number of sources including historical <br />petroleum hydrocarbon use, agricultural activities, dairies, septic systems, and storm water <br />infiltration. As per EHD requirements nitrate as N and 1,2-dibromo-3-chloropropane (DBCP) have <br />been included as part of the SSS discussion. Identifying potential groundwater contamination <br />other than nitrates and DBCP is beyond the scope of work for this report. <br />The presence of nitrates is not uncommon in shallow groundwater aquifers in San Joaquin County <br />and other parts of the Central Valley. Nitrate in groundwater occurs as a result of the application <br />of fertilizers, livestock waste, and untreated septic tank waste. Nitrate is mobile and often <br />accumulates in the shallow groundwater zones. <br />In the early 1900s, natural levels of nitrate in groundwater were measured in forty-three (43) wells <br />throughout the Sacramento Valley by Kirk Bryan (1923). It was thought that groundwater at that <br />time was close to “natural” conditions. Based on the work by Bryan, it is estimated that under <br />“natural” conditions, groundwater concentration containing nitrate is no more than about 13.5 <br />milligrams per liter (mg/L) nitrate (NO3) or (3 mg/L-N). Areas having 24.75 mg/L-NO3 (5.5 mg/L- <br />N) or more, are those in which nitrate concentrations may be increasing (Hull, 1984). <br />DBCP (dibromo chloropropane) is a nematocide and soil fumigant for vegetables and grapes. It <br />is thought to cause health problems consisting of kidney damage, liver damage, and cancer. The <br />use of DBCP was discontinued in 1979. <br />Based on the historical information, the past agricultural land use in the area should be considered <br />potential groundwater contamination sources. According to the State Water Resources Control <br />Board website, there were no nitrate impacted wells reported within 2,000 feet of the site.