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Nitrates Loading Study Irerracon Cho Property ■ Ripon. California September 6, 2018 ■ Terracon Project No. NA187038 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 fail 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 Finnernore, 1992). 3.3 Current On-Site Sourres 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 I itr The site is proposed to be developed with an approximately 3,100-square foot(SF)four bedroom residence and septic system. Therefore; the future on-site sources of nitrate will include the proposed septic system and natural processes. 3.5 Quantity and Quality of Wastewater from Proiect The following discussion is for determining the longterm wastewater flow generated from the proposed development for the nitrate loading analvsis and should not be used for septic system Responsive ■ Resourceful ■ Reliable 6