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Pastor Matt Linder ` i May 5,2003 Page 4 Denitrification Estimate Denitrification is an important process which occurs within the leach field whereby certain bacteria utilize the oxygen in the nitrate(NO3)and release nitrogen gas (NZ)to the atmosphere. Denitrification is expressed as a percentage,.and the normally accepted'range is 10 percent to 35 percent. Soils with higher clay content;moist soil conditions,high pH, and organic material denitrify by about 35 percent and soils with high sand content and fast percolation.rates are estimated to denitrify at a lower rate, about 10 percent tot-5 percent.Due to the sandy soils which exist on the site,the.denitrification factor is estimated to be about 10 percent for standard septic system effluent. We understand from OSI that when the effluent has'passed through.a sewage treatment system, leach field denitrification is not as effective due to the loss of available nutrients in the effluent. Therefore the denitrification factor of treated wastewater disposed in the leach field is estimated to be 5%for sandy soils. Nitrate Loading Scenarios Three nitrate loading scenarios were performed to measure.the long term benefit of using a waste water treatment system at the site compared with a standard type septic system. For each scenario,the previously described assumptions were unitized in the Hantzshe and Finnemore equation. The variable Nw(total nitrogen concentration of waste stream)was adjusted in two scenarios to reflect a possible, range of total nitrogen removal using an Orenco Systems Inc. Advantex waste water treatment system. Leach field denitrification(d) is less effective for treated waste water therefore'denitrification was assumed to be 5% for the Advantex scenarios. The.OSI.Advantex.treatment system was designed to reduce BOD,TSS, and nitrate of domestic and commercial waste water. We understand that the Advantex system regularly'teduces BOD5 and TSS to below 20 mg/L and reduces total_nitzogenet�ically 0%, sometimes upto 7, /o. The percent of total nitrogen reduction is.effected by the alkalinity of the water, loading rate, and the circulation settings of the system. Three nitrate loading scenarios were performed using the stated variables except for the influent total nitrogen concentration(Nw). The first scenario considers an Nw of 75 mg/L-N reflecting no treatment other than denitrification in the leach field(Plate 2). The second scenario considers theuse of an Orenco Systems Incorporated Advantex treatment system operating at an efficiency of 50% for total nitrogen reduction(Nw--38 mg/L-l) (Plate 3). The third nitrate loading scenario considers the use of an Orenco Systems Incorporated Advantex treatment system operating at an efficiency of 75% for total nitrogen reduction(Nw--'1.9 mg/L-N). (Plate 4). Please refer to Table 2 for a summary of the results. The variable Ne represents.the average, long-term nitrate concentration of percolating water for the site from Iain water and treated domestic waste water. . . r t . z P