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Soil Suitability/ Nitrate Loading Study 1rerracon Ernst Property ■ Tracy, CA February 21, 2019 revised April 9, 2019 ■ Terracon Project No. NA197000 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. Table 5. Potential Quantity of Effluent. Average Average Number of Number of Effluent days of Average Daily Flow Category Bedrooms People per Quantity per use per (gpd*) Bedroom Person (gpd*) year Existing (5 bedrooms x 2 people per bedroom Residence 5 2 70 365 x 70 gal. per day x 365 days per year)/365 days per year=700 gpd Proposed 3 bedrooms x 2 people per bedroom Mobile Home 3 2 70 365 x 70 gal. per day x 365 days per year)/365 days per year=420 gpd Potential Average Daily Flow 1,120 gallons per day *gpd -gallons per day Based on a review of Table 5, the estimated potential sewage flow rate for the existing five bedroom residence is 700 gallons per day. The proposed three bedroom mobile is estimated to add an additional 420 gallons per day for a combined total of 1,120 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 Responsive■ Resourceful ■ Reliable 14