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Report offindings—Phase 11 Soil ara vroundwater Assessment Page 7 Teixeira-Souza Dairy February 1,2007 WKA No. 6504.45 Soil Analytical Results Soil analytical results identified the highest detected ammonia as nitrogen and nitrate as nitrate concentrations in soil boring SB8, which is located hydrologically downgradient of the former wastewater ponds on the northeastern portion of the site. Currently, the EPA, California-EPA Department of Toxic Substances Control, and RWQCB do not regulate nitrogen in soil aside from protecting water quality and risk to exposure to human health or the environment. Groundwater Analytical Results Grab groundwater results identified the detected presence of ammonia as nitrogen and nitrates as nitrogen in most of the grab groundwater samples analyzed. The detected nitrate and TDS concentrations that exceed their corresponding MCLS indicate possible impacts to shallow groundwater, and may be representative of previous on-site dairy related activities. Nitrate contamination can come from application of synthetic fertilizer, confined animal operations, septic system discharge, or oxidation of nitrogen in organic rich soils. Based on the nutrient rich nature of Central Valley soils, shallow depth to groundwater, and presence of finer-grained organic rich sediments encountered at the site, elevated nitrate and TDS concentrations may also reflect an overlapping result with general regional groundwater quality conditions. The general distribution of detected ammonia and nitrate concentrations in groundwater correlate roughly with the location of previous on-site diary operations related to livestock and wastewater management on the northeastern and southeastern portions of the site. The relative variability in detected ammonia and nitrate concentrations in groundwater concentrations across the site generally shows higher detected concentrations in groundwater in the former dairy areas on the northeastern and southeastern portions of the site. Regulatory Position Item Number 11 of Section D of the tentative WDR discusses provisions for cessation of dairy operations. The tentative Monitoring and Reporting Program, issued by the RWQCB for ongoing groundwater sites under agency oversight, specifies that laboratory testing should be conducted to "determine the potential for a discharge of pollutants to surface water or groundwater." However, the WDR does not provide established cleanup criteria for ammonia, phosphorous, and total Kjeldhl nitrogen for soil or groundwater. The U.S. EPA has established