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19 May 2021 <br />Project No. 21-6435 <br />Page 12 of 14 <br />Proposed Commercial System <br />120 gpd x 260 days of proposed operation ÷ 7.48 gallons per cubic foot = 4,171 cubic <br />feet of wastewater. <br /> <br />The total wastewater volume for proposed project will be 17,079 cubic feet of wastewater <br />(existing) + 4,171 cubic feet of wastewater (proposed) = 21,250 cubic feet of wastewater. <br />Does not account for evapotranspiration likely to occur. <br /> <br />NW = Total nitrogen concentration of wastewater at 45 mg/L-N based on the average <br />discharge. Accounting for the loss of mg/L-N in the septic tank at 15% = 45-15%= 38.25 <br />and the loss from the biomat at 10% 38.25 - 10% = 34.425 mg/L-N. <br /> <br />d = Fraction of nitrogen concentration removed from the wastewater due to denitrification <br />within the soil (25 percent for silty sand soils). <br />R = Estimated Deep percolation / average rainfall recharge rate per year: 11.78 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 = 158,950 gallons = 21,250 cubic feet wastewater ÷ [(0.811 acres x 43,560 feet2) ÷ 12 <br />inches] = 21,250 ÷ 2,944 = 7.21 inches/year <br />NW = 34.425 mg/L-N <br />d = 25 percent denitrification <br />R = 11.78 inches/year <br />Nb = 1.0 milligram per liter <br />Nr = [7.21 inches/year x 34.425 mg/L-N (1-0.25)] + (11.78 inches/year x 1.0 milligram per <br />liter) ÷ (7.21 inches/year + 11.78 inches/year) <br />Nr = 186.15 ÷ 18.99 = 9.80 <br />Nr = 9.80 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 subject property is relatively flat, AGI does not anticipate <br />percolating effluent will affect any nearby water sources. A total of 9.80 ppm of additional