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July 13,2001 <br /> ` Job Number:LGOl-191 <br /> Page 8 <br /> The Hantzsche and Fennemore equation takes into account development area, soil <br /> denitrification factor, rainfall volume,rainfall nitrate concentration, the waste effluent quantity, <br /> — and waste effluent nitrate concentration. The formula, assumptions and calculations used for the <br /> analysis are shown on Plates 4 through 8. The units of nitrate used in the mass balance equation <br /> are nitrate-N whose maximum drinking water contaminate level is 10 mg/l. <br /> Variables and Assumptions <br /> Denitrification is an important process in septic systems that normally occurs in the <br /> disposal trench whereby certain bacteria utilize the oxygen in the nitrate(NO3) and release <br /> nitrogen gas(NZ)to the atmosphere. Denitrification is expressed as a percentage, and the <br /> normally accepted range is 10 percent to 35 percent. Soils with higher clay content,moist soil <br /> conditions, high pH, and organic material denitrify about 35 percent and soils with very high <br /> sand content and fast percolation rates are estimated to denitrify at a lower rate, about 10 percent <br /> to 15 percent. Due to the common occurrence of dark colored(organic layer) and clayey moist <br /> surface soils, the denitrification factor is estimated to be nearly ideal. A factor of 35 percent is <br /> assigned for this site. <br /> An estimate of the quantity and quality of rain fall and effluent is required for the analysis <br /> therefore the following information was used in the calculation. The deep percolation of rain <br /> was estimated to be 6.84 inches and the calculation is shown on Plate 4. The nitrate <br /> concentration of rain fall was estimated to be 0.17 mg/L-N.° <br /> The quantity of household waste water was estimated to be 50 gallons per person per day. <br /> In a four bedroom residence the typical occupancy would probably range between two to five <br /> persons resulting in a daily waste water flow between 100 to 250 gallons per day(see Table 6). <br /> The average nitrate concentration of the typical residential septic waste is normally considered to <br /> be 45 mg/]L-N.' <br /> pERSpL <br /> Z • <br /> O � <br /> �'�t O C♦ <br />