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Soil Suitability/ Nitrate Loading Study Irerracon Souza Property Tracy, CA February 28, 2020 Terracon Project No. NA207011 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 natural processes and the existing septic system. 2.3.4 Future On-Site Sources of Nitrate Future on-site sources of nitrate include the proposed septic system 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 Treatment Standards (OWTS) dated 2017, 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. On February 27, 2020, a Terracon representative spoke with Ms. Kasey Foley of the EHD. Ms. Foley recommended a long term average discharge rate of 100 gallons for the first bedroom and 50 gallons for each additional bedroom. The following table presents the proposed septic wastewater use for the site. 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