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Soil Suitability/ Nitrate Loading Study Schuler Property ■ Tracy, California Irerracon May 30, 2019 ■ Terracon Project No. NA197026 Table 7. Estimate of Deep Percolation of Rain Location Average Deep Percolation of Rain San Joaquin County 1.01 inches per year Based on this method, the average deep percolation of rain for San Joaquin County is estimated to be 1.01 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 The current on-site sources of nitrate include the existing septic system and natural processes. 2.3.4 Future On-Site Sources of Nitrate Future on-site sources of nitrate are discussed in section 1.3.7. 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 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 with an average potential occupancy of two persons per bedroom. The following table presents the proposed potential septic wastewater use for the site based on EHD use rate and occupancy. 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 a reasonable flowrate. Responsive ■ Resourceful ■ Reliable 14