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Where: Nr = Resultant average concentration of nitrate-nitrogen in recharge water - (ppm NO3-N) I = Volume rate of wastewater entering the soil averaged over the gross developed area in inches per yr Nw = Total nitrogen concentration of wastewater in mg NIL d = Fraction (%) of nitrate-nitrogen denitrified. R = Ave. recharge rate of rainfall - inches per yr From San Joaquin County Isohyetal map. NLS§ 3.2 Nb = Background nitrate-nitrogen concentration of rainfall recharge, exclusive of wastewater influences (ppm NO3-N). Values and Assumptions: I = 9,984 gals = total WW/vr = 1,335 cu ft = 0.00547 in/yr 67.19 Ac x 43,560 sq ft/Ac x (1 ft/12 in) Nw = 62 mg N/L d = Assume 10% due to the low percentage of clay soil at the soil-effluent interface. R = 9.5 in/yr. N b = Assumed to be 0.1 ppm NO3-N 0.00547 in/yr (62 mg N/L) (1 -0.10) + (9.5 in/yr x 0.1 mg/L) Nr = (0.00547 in/yr + 9.5 in/yr) Nr = 0.132 ppm as nitrate-nitrogen (NO3 -N), IV. SEPTIC SYSTEM DESIGN: OPERATIONAL PARAMETERS AND COMPONENTS A. SEPTIC TANK Septic tanks store accumulated sludge, scum and effluent (clear zone) volumes, which in turn affect treatment of nitrogen within the tanks. Detention time calculations demonstrate that when the maximum ADF is applied to the existing tank, there remains ample detention time: Detention Time Calculation: Detention Time = 1,200 gal tank capacity x 0.70 (30% volume lost to sludge/scum accumulation) 1.5 (Peaking factor) x 32 gals/day (ADF) Detention Time = 17.5 days. The minimum acceptable detention time is 1.0 day. FILTER BED SIZING CALCULATIONS Base Tank Capacity (BTC) = 1,200 gal. Leachline Equivalent Requirement = 1,200 gallons BTC + 32 gpd ADF x 0.200 sandy loam Soil Factor (SF) = 246 lineal feet of leachline (LFLL). 246 LFLL x 3 (Filter Bed Soil Factor) = 740 sq ft. Filter bed is to be rectangular: 37 ft E-W, 20 ft N-S. Page -6- Chesney Consulting