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rHANTZSCHEIFINNEMORE E UA TION TAKING INTO CONSIDERA TION THE NITRATE IMPACT FROM THE EXISTING SEPTIC SYSTEM A SECOND UNIT DWELLING SEPTIC SYSTEM AND THE ENTIRE PROJECT AREA OF 6.5 ACRES ASA WHOLE: INS„(1 -d) +R Nb ��•� Nr= (I+R) A---,�oz 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 Nw=Total nitrogen concentration of wastewater in N mg/L(66 mg N/L/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: 68gals/person/day, x 4 people per household x-2 h _6.5 Ac x 365 d/ = 1.1 in/yr I= 43,560 cu ft/Ac ft x 7.48 gal/cu ft x '(116-12 in) Nw= 66 mg/L- 10%reduction in each o2 septics=20%reduction total =53 mg/L N %rm d = 10% from biomat formation and 25oclay soil under leachlines and observed nitrogen decrease. Nb = Assumed to be 0.1 ppm NO3-N 1.1 in/yr(53 mg N/L) 1 -0.35 + 9 in/yr x 0.1 mg/L) Nr — (1.l in//yr+ 9 in/yr) Nr =63.8 ppm as NO3-N o lr' 7.s1 ppm as NO3 Typically, the land base area of each individual project to be assessed for nitrate loading is taken as a "whole,"which is the most logical method to quantify nitrate-nitrogen loading. To explain this rationale, which closely correlates with this project, assume that a large area of land is to be carefully assessed for nitrate loading. Under this premise, each individual parcel comprising this land area would have to be individually assessed to quantify nitrogen loading. This would not be the sum total of nitrate loading from each individual parcel. Each individual land area would contribute its calculated nitrate loading in proportion to the entire land area under assessment. IV. CONCLUSIONS AND RECOMMENDATIONS FOR IMPACT MITIGATION Analyses of soil under the DeAngelis leachfield reveals apparent denitrification occurring within the soil environment in a relatively short distance. There was a decrease of 50%in nitrate-nitrogen concentration from the surface (0-24 inches) down to 5 ft which continued throughout the soil profile down to 12 ft. It can be assumed that since there was virtually no ammonia-nitrogen (NH4),which is the precursor to nitrate formation, that only the organic fraction of the total nitrogen quantified can contribute to further nitrate formation. This is going to occur only under aerobic, ideal conditions, which are normally not found within the microscopic pore spaces of clay soil. Page A 0- Chesney Consulting