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' Nitrate Loading Study Irerracon Arriaga Property r{ Stockton, California April 26, 2019 Terracon Project No. NA187059 determines whether the average monthly precipitation exceeds average monthly ETo. If so, then the difference is potential deep percolation. This method does not consider runoff. Table 2. Estimate of Deep Percolation of Rain Location Average Deep Percolation of Rain Stockton Area 2.64 inches per year Based on this method, the average deep percolation of rain for Stockton area is estimated to be 2.64 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 current on-site sources of nitrate include the existing residential septic system and natural processes. 3.4 Future On-Site Sources of Nitrate Per information provided by Mr. Solorio, the site is proposed to be developed with an additional 960 SF mobile home south of the existing residence and existing septic system. Therefore, the future on-site sources of nitrate will include the existing residential septic system, the proposed residential septic system, and natural processes. 3.5 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 United States Geological Survey (USGS) California Water Science Center California Water Use 2010 Data, average daily domestic use per capita was estimated at 69-gallons per day. The EHD recommends a residential use rate of 70-gallons per person/day times two persons per bedroom. The rates presented from the references provide general guidance but do not always reflect a match in usage. Should any of the above information provided to our office change or is inconsistent with what is stated, our office shall be contacted to make any necessary modifications to our calculations. Examination and professional judgement,and experience shall be used when selecting Responsive s Resourceful a Reliable 7