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30 August 2019 <br />AGE Project No. 19-4819 <br />Page 13 of 15 <br /> <br /> <br />I = Volume rate of wastewater entering the soil averaged over the gross developed area <br />(acres) in inches per year. The total wastewater volume for proposed project will be <br />560 gpd (existing system) + 280 gpd (proposed system) x 365 days of proposed operation <br />= (560 + 280) x 365 days ÷ 7.48 gallons per cubic foot = 40,989 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% for silty clayey fine-grained sand soil). <br />R = Estimated Deep percolation / average rainfall recharge rate per year: 3.12 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 HOME AND PROPOSED HOME CALCULATIONS (COMBINED): <br /> <br />Nr = I x Nw (1-d)+ R x Nb ÷ (I+R) <br /> <br />Assumptions: <br /> <br />I = 306,600 gallons = 40,989 cubic feet wastewater ÷ [(1.67 acres x 43,560 feet2) ÷ 12 <br />inches] = 6.76 inches/year <br />NW = 34.425 mg/L-N <br />d = 25 percent denitrification <br />R = 3.12 inches/year <br />Nb = 1.0 milligram per liter <br />Nr = [6.76 inches/year x 34.425 mg/L-N (1-0.25)] + (3.12 inches/year x 1.0 milligram per <br />liter) ÷ (6.76 inches/year + 3.12 inches/year) <br />Nr = 177.65 ÷ 9.88 = 17.98 <br />Nr = 17.98 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 flat, AGE does not anticipate percolating <br />effluent will affect any nearby water sources. Based on the volume of wastewater to be