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Addendum Revised Soil Suitability Nitrate Loading Study Manteca Unified School District 241 4th Street, French Camp, CA Page 8 barium at concentrations exceeding their respective MCLs but Condor could find no sampling results on record since 2010. Results of a well located approximately 1,800 feet south of the Site contained nitrate- NO3 at concentrations exceeding 100 mg/L (samples of record were collected between 2001 and 2003). A copy of water sample results gathered from the on-site wells, as well as the well 1,800 feet south of the site, are included in Appendix E. 2.2.3 Current Use of Groundwater at the Site and of the Future Expected Use of Groundwater as Related to the Proposed Development Project Shallow groundwater in much of San Joaquin County has been impacted by agricultural chemicals, including nitrates, 1,2,3-trichloropropane (TCP), arsenic, and a variety of herbicides/pesticides as a result of historical agricultural use. Testing of Site water supply wells have confirmed the presence of nitrates and arsenic in groundwater beneath/near the Site. On-site wells are strictly used to provide irrigation water. The facility is on municipal drinking water. 2.3 SOURCES AND CALCULATED IMPACT OF NITRATE TO GROUNDWATER 2.3.1 Current Off-Site Sources of Nitrate to Soil and Groundwater in the General Up Gradient Area and the Contribution of Nitrate Load from These Sources to the Project Site Septic systems and agriculture in the area may be the most significant sources of nitrate. As discussed in Section 1.3, septic system density for the vicinity of the Site was based on 70-80 buildings/residencies within 0.5 miles of the Site. It is assumed that at least each building has one septic system. The up-gradient area is predominantly agricultural farmland with intermittent residential housing. Refer to Section 1.3.5 for descriptions of septic tanks in the general area. 2.3.2 Description of Impact of Rainfall Contribution of Nitrate Load to the Project Site An estimate of the quantity of rainfall was required for the nitrate loading analysis. The estimate of deep percolation of rain is based on the average monthly precipitation of rainfall for French Camp, California, based on the nearest weather station to the Site available (Stockton Airport). The estimate first determines whether the average monthly precipitation exceeds average monthly potential evapotranspiration. If so, then the difference is potential deep percolation. Based on the California Irrigation Management Information System (CIMIS) monthly report and the Western Regional Climate Center (www.wrcc.dri.edu), the average monthly climate summary average rainfall was found to be 13.91 inches per year (in/yr) for the years 2010 through 2019. Adjustments to the evapotranspiration factor were made based on site specific landscape conditions, as referenced from the University of California Division of Agriculture and Natural Resources. Based on the average monthly rainfall totals and the adjusted monthly evapotranspiration totals, deep percolation of rain for the French Camp Elementary School area is estimated to be 8.99 in/yr. The nitrate concentration of rainfall was estimated to be 1 mg/L-N (Hantzsche and Finnemore, 1992). Precipitation data provided in Appendix F. 2.3.3 Current On-Site Sources of Nitrate to Soil and Groundwater and the Contribution of Nitrate Load from These Sources to the Project Site Current on-site sources of nitrate include existing septic tanks discussed and identified in Section 1.3 and agricultural use in the area. 2.3.4 Proposed Future On-Site Sources of Nitrate to Soil and Groundwater and the Contribution of Nitrate Load from These Sources to the Project Site Proposed on-site sources of nitrate are discussed in Section 1.3.7.