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As a nitrate mitigation measure,shallow-rooted landscaping grasses may be used to absorb a percentage of the nitrogen in the effluent pumped to the filter bed. This is provided the pressurized pipes are installed high in elevation, typically assumed to be six inches below the soil surface. Most plants assimilate only two forms of nitrogen: nitrate and ammonium (NH4). Approximately 75% of conventionally treated septic effluent is ammonium. However, the proposed septic systems will discharge under the MCL for nitrate of 10 ppm nitrate-nitrogen or 45 ppm nitrate. Therefore, percentages of the maximum nitrate concentration in the effluent will be correlated with the amount estimated to be synthesized by lawn grasses: For eight months out of each year (March-October), it is theorized the plants will use 50% of available nitrate molecules nitrified from the treated septic effluent (the remaining 50% is lost to denitrification, immobilization and leaching). The colder four months of the year, the lawn grass may synthesize 20% available nitrate. Consequently, an additional 40% (50% (0.67) + 20%(0.33) =40%) reduction in nitrate concentrations may occur: 45 ppm maximum nitrate (as NO3) concentration emanating from the new septic system minus 40% reduction from landscape grasses= 27 ppm NO3 potentially entering the water table. SEPTIC SYSTEM DESIGN EXAMPLE SEPTIC TANKS Dual tanks with a filter vault in the second septic tank is recommended. By using two tanks with a filter, organic matter is trapped and digested within the septic tank environment. In addition, there is scientific evidence that denitrification may occur within the septic tank, particularly with two tanks in series. Septic tanks affect the sludge, scum and effluent volumes, which in turn affect treatment of nitrogen within the tanks. Typically, the volumetric capacity of septic tanks serving non- residential facilities should be equal to approximately 5 times the average daily flow (ADF or QAVE). In the following equations, the numerical value times the QAVE the peaking value (PF) correlate with the pump-out time interval in yrs. The peaking value is normally taken to be 2.5 for commercial, or nonresidential projects: SEPTIC TANK CAPACITY EXAMPLE FOR THE NEW RESTROOM: Recommended tank capacity for a pump out interval of three yrs: 2.8(QAVE) x Peaking Factor(PF) = 2.8(10,000 gals WW/wk_ 5 d/wk=2,000 gals/day x 0.3 (3 restrooms) = 600 gals) x 2.0 (PF) _ 3,360 gal tank capacity required: Use one - 2,000 gallon tank and one - 1,500 gallon tank, in series SEPTIC TANK DETENTION TIME EXAMPLE FOR THE NEW RESTROOM: Detention Time = 3,500 gal tank capacity x 0.70 (30% volume lost to sludge/scum accumulation) 2.0 (Peaking factor) x 600 gals/day from new restroom Detention Time = 2.0 days. The minimum acceptable detention time is 1.0 day. Page 2 of 4 Na!!ey�(g�eseareh