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Soil Suitability/Nitrate Loading Study Irerracon Soares Property■ Escalon, CA December 13, 2019 ■ Terracon Project No. NA197095 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. The EHD recommends a residential use rate of 70-gallons per person/day times two persons per 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. Table 10. Typical Quantity of Effluent. Average Number Number of effluent Average days Building of people per quantity per of use per Average daily flow bedrooms bedroom person year (gpd ) (gpd") (3 bedrooms x 2 people per bedroom x 70 gal. Residence 3 2 70 365 per day x 365 days per year)/365 days per year=420 gpd Total 420 gpd 'gpd-gallons per day Based on a review of Table 10, the average daily flow for the proposed three bedroom residence is approximately 420 gallons per day. The average total nitrogen concentration of domestic wastewater is normally considered to be 20 to 85 mg/L-N with 35 to 45 mg/L-N being typical (Crites and Tchobanoglous, 1998). It is estimated that commercial use will have higher concentrations of total nitrogen when compared to residential use. For the purposes of the nitrate loading estimate, it is estimated that the average concentration for total nitrogen in wastewater for the residence is 45 mg/L-N. 2.3.4.2 Denitrification Estimate Denitrification is an important process which occurs within the leach field whereby certain bacteria utilize the oxygen in the nitrate (NO3) and release nitrogen gas (N2) to the atmosphere. Denitrification is expressed as a percentage, and the normally accepted range is 10 percent to 35 percent. Soils with higher clay content, moist soil conditions, high pH, and organic material Responsive ■ Resourceful ■ Reliable 15