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y� The characteristics or composition of septic tank effluent is'dependent upon several parameters because of idiosyncrasies within each household. Certain appurtenances change the character- istics of the wastewater effluent such as filter vaults within septic tanks and kitchen food-waste grinders. Since this study is concerned with nitrogen, this constituent is quantified in the effluent, as illustrated below: In determining nitrogen concentrations of septic influent and effluent, per capita intake of nitrogen per day must be estimated. The average American consumes between 70 and 140 g of N/day. Since nitrogen comprises 16% of the weight of the average protein, 16% of 70 g N = 11 g N/capita/day and 16% of 140 g N =22 g N/capita/day. The average of these two values is 17 g N/capitalday of theoretical influent. The concentration of nitrogen in septic system effluent is normally specified in the scientific literature as units of mg NIL. Unfortunately, these units superimpose wastewater flow variability onto nitrogen influent variability, thus creating even greater variability. One researcher, (Bauman), has averaged the means from 20 other studies to arrive at a concentration of 62 f 21 mg NII, in septic tank effluent. If the above figure for wastewater discharge is estimated at 68 gals/resident/day (257 liters) and using the figure of 17 g N/cap/day excreted= 17 g - 257 L = 66 mg N/L/day estimated for the proposed project. This concentration will be the estimated nitrogen loading in the effluent discharged throughout the project. D. 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 total area of the two parcels will be taken into consideration and the nitrate loading from the all three structures will be quantified and compared with the current nitrate concentration in the groundwater. HANTZSCHEIFINNEMORE EQ UATION INW(1 - d) + RNb Nr— (I + R) Where: Nr= Resultant average concentration of nitrate-nitrogen in recharge water- (ppm NO,-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 N mg/L (66 mg NIL/day) d = Fraction (%) of nitrate-nitrogen loss due to denitrification in the soil R = Average recharge rate of rainfall - inches per yr (13 in.) Nb= Background nitrate-nitrogen concentration of rainfall recharge, exclusive of wastewater influences (ppm NO,-N) Values and Assumptions: Page -6- Vaffey Ag Research