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Soil Suitability/ Nitrate Loading Study Irerracon Proposed Commercial Truck Yard ■ Stockton, CA August 16, 2019 ■ Terracon Project No. NA197053 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). The OWTS manual suggests that 30 gallons per person is typical for a day worker at schools or offices. The truckers and/or visitors to the office will be calculated at 5 gallons per person similar to an airport, passenger. 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 from Sources. Average Total effluent Average days of Average daily flow Category people quantity per use per year (gpd*) per day person (gpd*) Employee 2 30 365 (2 people x 30 gal. per day x 365 days per year) /365 days per year=60 gpd Visitor 8 5 365 (8 People x 5 gal. per day x 365 days per year)/365 days per year=40 gpd Total 100 gallons per day *gpd -gallons per day Based on a review of Table 10, the average daily flow for proposed office effluent is anticipated to be 100 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 Responsive■ Resourceful■ Reliable 15