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lierracon Soil Suitability / Nitrate Loading Study Buddhist Temple Proposed Dormitory • Stockton, California July 11,2019 • Terracon Project No. NA177056 2.3.2 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 the Lodi/Stockton California area. 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 potential evapotranspiration and precipitation data was obtained from the California Irrigation Management Information System (CIMIS). The below table was compiled from two inactive stations located nearest the site including Lodi Station 042 and Lodi West Station 166. Table 8. Estimate of Deep Percolation of Rain for the Site Location Deep Percolation of Rain Lodi Area 4.49 inches per year Based on this method, the average deep percolation of rain for the Stockton area is estimated to be 4.49 inches/year. The nitrate concentration of rainfall is estimated to be 1 mg/L-N (Hantzsche and Finnemore, 1992). 2.3.3 Current On-Site Sources of Nitrate Current onsite sources of nitrate include two existing septic systems and natural processes. 2.3.4 Future On-Site Sources of Nitrate Future on-site sources of nitrate will include the two existing septic systems, the proposed septic system for the 12 bedroom dormitory, and natural processes. 2.3.4.1 Quantity and Quality of Wastewater from Project The following discussion is for determining the long-term wastewater flow generated from the proposed development for the nitrate loading analysis and should not be used for septic system design purposes. Typically, use estimates for the sizing of septic systems include a peak use factor, whereas the numbers discussed here are based on long-term averages. The estimated sewage flow rates for use categories are available from a number of references. The uses presented below were guided by the San Joaquin County On-Site Wastewater Disposal Standards (2003), Crites and Tchobanoglous (1998), and EPA (1980). Table 4-2 of the text from Crites and Tchobanoglous indicates that the typical residential use rate is 70-gallons per day per bedroom. The EPA Design Manual (Table 4-6) indicates the typical use rate is 45-gallons per day per resident. Based on a review of the USGS California Water Science Center California Responsive • Resourceful • Reliable 16