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Soil Suitability/ Nitrate Loading Study Ripon Winery Proposed Warehouse ■ Ripon, CA 1rerracon January 20, 2017 ■ Terracon Project No. NA167059 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 Onsite Wastewater Disposal Standards (2003), Crites and Tchobanoglous (1998), and EPA (1980). The references indicate that 15 gallons per day is typical for each employee and 5 gallons per day for visitors, when utilizing a low-flow flush system. 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. Careful examination, professional judgment, and experience are necessary to select a reasonable flow rate estimate. The flow rates selected for the uses associated with this project are presented below. Table 7. Typical Quantity of Effluent. Total Average Quantity Category People per Person Average days of Average Daily Flow per Day (gallons) use per year Permanent (30 person x 15 gal x 260 Employees 30 `15 260 days)/365 days per year = 320.55 gpd (16 person x 5 gal x 260 Visitors 16 *5 260 days)/365 days per year =56.99 gpd , Average Daily Flow 377.54 gallons per day Note:gpd is gallons per day.'Value cited from the San Joaquin County On-Si Wastewater Disposal Standards(2003)6.1.15. The average total nitrogen concentration of domestic wastewa nermally_consider o be 20- 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. It is estimated that the average concentration for total nitrogen in wastewater for the project is approximately 85 mg/L-N over the long term. 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 j percent. Soils with higher clay content, moist soil conditions, high pH, and organic material denitrify by about 35 percent, and soils with high sand content and fast percolation rates are estimated to denitrify at a lower rate, about 10 percent to 15 percent. Responsive ■ Resourceful ■ Reliable 14