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Nitrate Loading Study Irerracon Arriaga Property r Stockton, California April 26, 2019 v Terracon Project No. NA187059 a reasonable flowrate. The below table presents the proposed potential septic wastewater use for the site. The flow rates selected for the uses associated with this project are based on EHD recommendations and estimated double occupancy per bedroom. Table 3. Potential Quantity of Effluent. Potential Average Number Number Effluent Average Potential Average Daily Category of of People Quantity per days of Flow use per Bedrooms per Person year (gpd*) Bedroom (gpd*) (3 bedrooms x 2 people per Existing 2 2 70 365 bedroom x 70 gal. per day x Residence 365 days per year)/365 days per year= 280 gpd (3 bedrooms x 2 people per Proposed bedroom x 70 gal. per day x Residence 2 2 70 365 365 days per year)/ 365 days per year= 280 gpd Potential Average Daily Flow Total 560 gallons per day "gpd -gallons per day Based on a review of Table 3, the estimated potential average daily flow for the existing and proposed residence is 560-gallons of effluent 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 project is approximately 35 mg/L-N over the long term. 3.5.1 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 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 to 15 percent. Based on a review of the site plan, the existing and proposed development is located on the northern portion of the site within the Jacktone clay soil area. Based on the clay soils anticipated at leach field depths (between 36 and Responsive a Resourceful ■ Reliable 8