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If the above figure for wastewater discharge is estimated at 90 gals/resident/day(341 liters), and using the figure of 17 g N/cap/day excreted= 17 g 341 L= 50 mg NIL/day estimated for the proposed If Since it is predicted that there will be increased water usage for the proposed project, this effect may cause a dilution of the nitrogen effluent concentration down to 50 mg N/L. Averaging 50 mg N/L and 62 mg N/L= 56 mg NIL,which will be the estimated nitrogen concentration in the effluent discharged throughout the project (excluding N reduction in the septic tank). . CALCULATED IMPACT FROM NITRATE-NITROGEN LOADING The calculated or estimated nitrate impact to the soil and ultimately to the groundwater is extremely difficult to determine due to the number of variables involved. The groundwater for this project may be the referenced sand stratum (perched water table) at 20 ft to 50 ft, or it may be the static water level of approximately 140 ft. There are various formulas and methods to estimate nitrate loading. The following calculations are based on using a conventional or traditional type of septic system consisting of a septic tank, leachlines and possible shallow sumps. Three different methods are presented, as described by each respective author/researcher, for comparison purposes and comparison with agronomic fertilizer inputs. These three methods include the Hantzsche/ Finnemore Equation, the Crites/Tchobanoglous Formula from Small and Decentralized Wastewater Management Systems and the method presented by O. B. Kaplan in Septic Systems Handbook. It is generally regarded that the Hantzche/F'innemore Equation is the most representative and accurate regarding nitrate-nitrogen loading. The primary variables involved in the assessment or in quantifying nitrate impact to the underlying groundwater are the Total Nitrogen concentrations, volume of yearly wastewater flows, extent of denitrification, and the extent of evapotranspiration. Denitrification capabilities of the indigenous silty surface and shallow subsurface soils are expected to contribute to the denitrification potential, albeit, not to the extent that a clay soil does. Ammonium retention in the clay soils that are present (14%) should also be a factor, as has been observed in other projects with similar soils. Evapo- transpiration has not been factored in any of the three nitrate loading methods; however, it will be a significant part of wastewater management and consequently nitrate-nitrogen loading. I. Hantzsche/Finn„emore Equation INW 1 - d +R Nb Nr= (I+ R) 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. Total wastewater volume: 360 gals/house x 15 houses = 5,400 gpd x 365 days/year= 1,971,000 gals- 7.47 gals per ft3 =263,502 cu ft of wastewater. Does not account for.Evapotranspiration. Page -12- Chesney Consulting s