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Nitrate Loading Study Irerracon Guillermo Ramirez Property ■ Ripon, California April 29, 2019 ■ Terracon Project No. NA197019 reported on the San Joaquin County District Viewer. Therefore, off-site sources of nitrate include residential septic systems, agricultural land use, and natural processes. Based on information obtained from the DWR Water Data Library, between the years 1959 to 2012, dissolved nitrate was reported between 5 and 70.4 mg/L-N at three groundwater wells located within one mile north and northeast of the site. A groundwater study titled Addressing Nitrate In California's Drinking Water Technical Report 2 Nitrogen Sources and Loading to Groundwater dated 2012 prepared by the University of California Davis for the Tulare Lake Basin and Salinas Valley, indicated crop land contributed 96% of the human-generated nitrate sources to groundwater. The study indicated other minor contributors to nitrate in groundwater included waste water treatment plants, septic systems, corrals, lagoons and urban runoff. Based on the groundwater study, agricultural land use on the site and vicinity is anticipated to be the highest contributor to nitrates in groundwater. 3.2 Contribution of Rainfall An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. The estimate of deep percolation of rain is based on the average monthly precipitation of rain fall and evapotranspiration for Ripon, California. The estimate first determines whether the average monthly precipitation exceeds average monthly potential evapotranspiration. If so, then the difference is potential deep percolation. This method does not consider runoff, although due to the relatively flat nature of the site, runoff should be minimal. Average precipitation and potential evapotranspiration were obtained from the California Irrigation Management Information System (CIMIS)website. Refer to Appendix B for the data and calculation. Table 2. Estimate of Deep Percolation of Rain for the Site Location Deep Percolation of Rain Ripon 2.54 inches per year Based on this method, the average deep percolation of rain for the Ripon area is estimated to be 2.54 inches/year. The nitrate concentration of rainfall is estimated to be 1 mg/L-N (Hantzsche and Finnemore, 1992). 3.3 Current On-Site Sources of Nitrate The site is developed with an orchard; therefore, the current on-site sources of nitrate include the existing agricultural land use and natural processes. 3.4 Future On-Site Sources of Nitrate The site is proposed to be developed with a residence and septic system. Therefore, the future on-site sources of nitrate will include the proposed septic system and natural processes. Responsive ■ Resourceful ■ Reliable 6