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{ Where: k 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 loss due tddenitrification in the soil R = Average recharge rate of rainfall - inches per yr Nb= Background nitrate-nitrogen concentration!of rainfall recharge, exclusive of wastewater influences (ppm NO3-N) Values and Assumptions {i I= 1,110 als/d x 260 work d/31= 288,600 gais =total WW/)T 38,583 cu ft = 1.41 in. 7.53 Ac x 43,560 sq ft/Ac = 328,007 sq ft Nw — 103 mg NIL: 20% reduction from septic tank+ 1.0% removal from biomat= 74 mg NIL d = Assume 30% R = 10 in/yr. But 80% of total area covered w/roofs and asphalt :. 2 in/yr. i Nb= Assumed to be 0.1 ppm NO3-N f r � - 1.41 in/y(74 mg N/L) 1 - 0.30 + 2 in/yr x 0.1 mg/L)- Nr LNr = (1.41 in/yr+ 2 in/yr) Nr = 21.5 ppm as nitrate-nitrogen (NO3-N) or 96.8 ppm as nitrate (NO3) i PREDICTED NITRATE-NITROGEN IMPACTFROM 61% OF PROJECT ON WASTE- ' WATER TREATMENT SYSTEM AND 39% ON CONVENTIONAL SYSTEMS: ment south of Itis anticipated that wastewater treatment for all 'existing and future development Carmelo Avenue will reduce nitrate-nitrogen concentrations in the effluent to the Drinking Water Standard/Maximum Contaminant Level of 10 ppm nitrate-nitrogen (NO3-N). The Hantzsche/Finnemore Formula was close at predircting nitrate impact in the recharge or top groundwater when compared to the actual analysis (97 ppm NO3 vs. 86 ppm NO3). The Formula E is used again to estimate nitrate-nitrogen concentrations in the treated effluent and conventional septic system effluent: HANTZSCHEIFINNEMORE E Q UA TION FOR 61% OF TREATED WASTEWATER IN,, 1 - d +R Nb r Nr= 0+R) 4 Chesney Consulting