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11 October 2019 <br />AGE Project No. 19-4782 <br />Page 12 of 14 <br />9.5. DENITRIFICATIONS CAUSED BY SOILS <br /> <br />The process of denitrification is important when utilizing subsurface septic lines and <br />regularly occurs in the soil within the leach fields where bacteria utilize oxygen in the <br />nitrate to release nitrogen gas out to the atmosphere. The denitrification process is <br />controlled by waste concentrations, soil type, annual rainfall, pH of the soils, total organic <br />concentration of the soil (TOC) and exposure time to nitrogen. The soils with a high or <br />moderate clay content, higher organic content, high pH and adequate soil moisture <br />denitrify the concentrations by approximately 30 percent and less desirable soils with <br />more sands and faster percolation rates (less moisture and clay content) denitrify only <br />about 10 percent. <br /> <br />A denitrification factor of 15 percent was selected for the calculation based on the silty <br />sands existing at the site. <br /> <br /> <br />9.6. MASS BALANCE OF NITROGEN LOADING <br /> <br />The EHD requires the user to consider all potential sources identified for wastewater <br />generation. Further, the EHD supports the use of Hantzsche/Finnemore, or other <br />appropriate formula/model to calculate a mass of nitrogen loading. <br /> <br />RESIDENTIAL: <br /> <br />The Hantzsche / Finnemore (Nr) equation for residential home application: <br />Nr = I x Nw (1-d) + R x Nb ÷ (I+R) <br /> <br />Definitions: <br /> <br />Nr = The average concentration of nitrate-nitrogen in the recharged waste water parts per <br />million of nitrate-nitrogen. <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 /> <br />420 gpd (proposed system) x 365 days of proposed operation = 450 x 365 days ÷ 7.48 <br />gallons per cubic foot = 20,495 cubic feet of wastewater. Does not account for <br />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 (15 percent for silty sand type soils). <br />R = Estimated Deep percolation / average rainfall recharge rate per year: 3.64 inches.