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/t 1� The characteristics or composition of septic tank effluent is dependent upon several parameters because of idiosyncrasies within each household. Certain appurtenances change the characteristics of the wastewater effluent such as filter vaults within septic tanks and kitchen food-waste garbage disposals. 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/capitalday and 16% of 140 g N L 22 g N/capita/day. The'average of these two values is 17 g N/capita/day of theoretical influen i/The concentration of nitrogen in septic system effluent is normally specified ecified in the scientific literature as units of mg N/L. 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 66±21 mg N/L in septic tank effluent. If the above figure for wastewater discharge is estimated at 90 f gals/resident/day-(341 liters) and using the figure of 17 g N/cap/day excreted= 17 g_ 341 L= 50 mg N/L/day estimated for the proposed project. However, as a safety factor, the concentration of 66 mg NIL will be the estimated nitrogen loading in the effluent discharged from the proposed residences for this project. There are various formulas and'methods ethods to estimate nitrate loading from septic systems. The following calculations are based upon using a conventional or traditional type of septic system consisting of a septic tank and leachlines. The nitrate loading method presented is the Hantzsche/ Finnemore Equation, which is generally regarded as the equation most representative and accurate for nitrate-nitrogen loading from septic systems. The following calculations demonstrate that the nitrate loading potential for the project originating from proposed septic system influence is nil, (NL iman.- ue to the large land area- (110 acres). r S§ 3.5 ant sche/Finnemore E uation INW(1_- d) +RNb 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 22 houses (includes second un;,dwelling)_ 7,920 gpd x 365 days/year=2,891,000 gals_7.47 gals per ft3 = 387,000 cu ft of wastewater. Does not account for Evapotranspiration. Nw = Total nitrogen concentration of wastewater at 66 mg NIL. Accounting for loss of nitrogen in septic tanks (10%) orthrough biomat 10% = b�6.6 = 59 - 5.9 = 53 mg NIL d Fraction(%) of nitrate-nitrogen loss due to itni�atian in he clay soil (15%+) R = Average recharge rate of rainfall- 9 inches p r yr{NLS§ 3.2) Nb= Background nitrate-nitrogen concentration of r 11 rec ge, exclusive of wastewater influences (ppm NO3-N) Page -10- Chesney Consulting