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The concentration of nitrogen in septic system effluent is normally specified in the scientific <br /> literature as units of mg N/L. Unfortunately, these units superimpose wastewater flow variability <br /> onto nitrogen influent variability,thus creating even greater variability. One researcher, (Bauman), <br /> has averaged the means from 20 other studies to arrive at a concentration of 62 f 21 mg N/L in <br /> septic tank effluent. If the above figure for wastewater discharge is estimated at <br /> 68 gals/resident/day (257 liters) and using the figure of 17 g N/cap/day excreted = 17 g 257 L = <br /> 66 mg N/L/day estimated for the proposed project. This concentration will be the estimated <br /> nitrogen loading in the effluent discharged throughout the project. <br /> D. CALCULATED IMPACT FROM NITRATE-NITROGEN LOADING <br /> The calculated or estimated nitrate impact to the soil and ultimately to the groundwater is extremely <br /> difficult to determine due to the number of variables involved. The total area of the subject parcel <br /> will be taken into consideration and the nitrate loading from the two structures will be quantified. <br /> HANTZSCHEIFINNEMORE EQ UATION <br /> IN,,(1 d) +R Nb <br /> Nr (I +R) <br /> Where: <br /> Nr= Resultant average concentration of nitrate-nitrogen in recharge water- (ppm NO3-N) <br /> I = Volume rate of wastewater entering the soil averaged over the gross developed area in <br /> inches per yr <br /> f Nw= Total nitrogen concentration of wastewater in N mg/L (66 mg N/L/day) <br /> d = Fraction (%) of nitrate-nitrogen loss due to denitrification in the soil' <br /> R = Average recharge rate of rainfall - inches per yr (13 in.) <br /> Nb = Background nitrate-nitrogen concentration of rainfall recharge, exclusive of wastewater <br /> influences (ppm NO3-N) <br /> Values and Assumptions: <br /> 28 gals/person/day x 2 people per household x 2 houses x 1.50 Ac x 365 d/yr=2.3 in/yr <br /> I = 43,560 cu ft/Ac ft x 7.48 gal/cu ft x (I ft/12 in) <br /> Nw= 66 mg/L <br /> d = 10% from biomat formation and 25% from clay soil under leachlines. <br /> Nb = Assumed to be 0.1 ppm NO3-N <br /> 2.3 in/yr (66 mg N/LZ 1 - 0.3 5) + 13 in/yr x 0.1 mg/L) <br /> Nr — (2.3 in/yr+ 13 in/yr) <br /> Nr = 6.5 ppm as NO3-N or 29.1 ppm as NO3 <br /> Page -6- <br /> CFiemey Consulting <br />