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10 May 2021 <br />Project No. 21-6390 <br />Page 12 of 14 <br />gpd (proposed system) x 260 days of proposed operation = 1,200 x 260 days ÷ 7.48 <br />gallons per cubic foot = 41,711 cubic feet of wastewater. Does not account for <br />evapotranspiration likely to occur. <br /> <br />NW = Total nitrogen concentration of wastewater at 85 mg/L-N based on the average <br />discharge. Accounting for the loss of mg/L-N in the septic tank at 15% = 85-15%= 72.25 <br />and the loss from the biomat at 10% 72.25 - 10% = 65.025 mg/L-N. <br /> <br />d = Fraction of nitrogen concentration removed from the wastewater due to denitrification <br />within the soil (25 percent for clay and loamy soils). <br />R = Estimated Deep percolation / average rainfall recharge rate per year: 3.05 inches. <br />Nb = Background nitrate-nitrogen concentration of rainfall recharge: 1.0 mg/l. The Nb is <br />an average value determined for San Joaquin County by the EHD. <br /> <br />EXISTING AND PROPOSED HOME CALCULATIONS: <br /> <br />Nr = I x Nw (1-d) + R x Nb ÷ (I+R) <br /> <br />Assumptions: <br />I = 312,000 gallons = 41,711 cubic feet wastewater ÷ [(22 acres x 43,560 feet2) ÷ 12 <br />inches] = 41,711 ÷ 79,860 = 0.52 inches/year <br />NW = 65.025 mg/L-N <br />d = 25 percent denitrification <br />R = 3.05 inches/year <br />Nb = 1.0 milligram per liter <br />Nr = [0.52 inches/year x 65.025 mg/L-N (1-0.25)] + (3.05 inches/year x 1.0 milligram per <br />liter) ÷ (0.52 inches/year + 3.05 inches/year) <br />Nr = 28.41 ÷ 3.57 = 7.96 <br />Nr = 7.96 ppm nitrogen (NO3_N) <br /> <br /> <br />9.7. IMPACT OF NITROGEN LOADING FROM SITE PROJECT TO <br />DOWNGRADIENT WATER SOURCES <br /> <br />The recharging of groundwater is the most likely potential feature that could impact future <br />nitrogen loading. Since the project area and septic system will be developed on a berm <br />approximately 20 feet above ground surface, AGI does not anticipate percolating effluent <br />will affect any nearby water sources. Based on the volume of wastewater to be generated <br />and the depth to groundwater (10 feet bsg), the potential vertical migration would not likely <br />degrade the local groundwater. A total of 7.96 ppm of additional nitrogen is estimated to