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SEPTIC TANKS Septic tank designs which affect the sludge, scum and effluent volumes, affect the treatment of nitrogen within the tanks. Therefore,two septic tanks in series have been specified for each Site Approval. The pump-out interval should be based on a periodic inspection by the Environmental Health Department. After two years, a determination can be made as to sludge and scum formation and wastewater flows to possibly extend this pump-out interval. Since it is anticipated that the Lawson firm will have the greatest wastewater flow, the following calculations demonstrate adequate capacity and detention time: CAPACITY: Required septic tank capacity: 2.4(QAvE)x Peaking Factor(PF)=2.4(435 gals/day) x 2.0 = 2,100 gal tank capacity required- 3,200 gal provided. DETENTION TIME: Detention Time= 3,200 gal tank capacity x 0.70 (30% volume lost to sludge/scum accumulation) 2 (Peaking factor)x 435 gallon/day Detention Time= 2.6 days. The min. acceptable detention time should be approximately 0.5 day. LEACHFIELDS/FILTER BEDS Appendix D contains the calculations, design parameters and orientation for each leachfield/filter bed for the three Site Approvals. Several scientific studies have demonstrated the infiltration capacity of a soil absorption system is dependant primarily by the formation of the biomat and not by the permeability of the soil. The biomat is a biological, slimy substance which forms on the soil-effluent interface over time. Hydraulic loading rates range from a conservative criterion of 0.125 gal/ftz/day to 1.0 gal/ft2/day for a percolation rate of approximately 15 min/in. These application rates are based on trench side wall areas only. NITROGEN IMPACT MITIGATION Nitrogen mitigation will be primarily accomplished by the use of two septic tanks through the following processes: It has been well documented that gaseous nitrogen emanates from septic tanks. The gaseous formation is apparently attributable to denitrification which is the biological reduction of nitrate (NO3) and nitrite (NO2)to volatile gases. The biochemical processes which occur in septic tanks are highly complex but can be described simplistically - A microbe digesting a waste organic molecule with an attached nitrogen atom may have the freed nitrogen as a surplus atom. To digest the N atom,the microbe can combine it with dissolved molecular oxygen O2 and release it in solution as a molecule of nitrite and possibly nitrate. This occurs under aerobic conditions and is referred to as nitrification. If a microbe needs oxygen within an anaerobic environment, it can take the oxygen from nitrite or nitrate molecules. Not requiring 7 Nalfey Mfg Ppearch