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Nitrate Loading Study Irerracon Arellano Property , Stockton, California April 26, 2019 Terracon Project No. NA187058 A Department of Water Resources Well Completion Record dated 1988 was available for the site address on San Joaquin County Environmental Health online records. Based on a review of the Well Completion Record, the soils within the anticipated vadose zone (<90 feet bgs) are comprised of alternating sand, gravel, and/or clay strata which extend to depths of 244 feet bgs. A copy of the Well Completion record is included in Appendix D. The longer effluent remains near the surface, the more treatment is enhanced due to natural processes within the soil. Layered soils and sediments such as some fine to medium grained soils anticipated on the site typically provide a degree of protection between percolating effluent at the surface and groundwater aquifers. Based on the clay and/or cemented soils anticipated on the site, the leaching potential to groundwater from sewage effluent or other surface contaminants appears low. 2.0 GROUNDWATER ANALYSIS 2.1 Regional Groundwater Based on a review of the San Joaquin County Flood Control and Water Conservation District Groundwater Report, from 2015 to 2016, Spring & Fall depth to groundwater near the site was between approximately 90 and 120 feet bgs. Based on a review of groundwater information available on a California Department of Water Resources (DWR) Water Well Driller's Report for the site address (Appendix D), in 1988 depth to groundwater In the site measured between approximately 100 and 108 feet bgs. 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. 2.2 Potential Ground Water 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 NLS 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 Responsive m Resourceful n Reliable 4