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HANTZSCHEIFINNEMORE EQUATION CONSIDERING THE EQUATION IN <br /> TERMS OF "INDIVIDUAL RESIDENTIAL SOURCE PER ACRE" <br /> AWx Nw(I -d) +R <br /> Nr= (AW+R) <br /> Where: <br /> Nr= Resultant average concentration of nitrate-nitrogen in recharge water from domestic sources <br /> A =Number of dwelling units per acre on septic tanks (unit/acre) = 1.15 ac. (average Lot land area) <br /> W =Annual wastewater loading per dwelling unit per acre= 3.2 in. (in inches,based on 270 gpd/residence) <br /> Nw=Total nitrogen concentration of wastewater in N mg/L(66 mg N/L/day- See Pg. 9) <br /> d = Fraction(%)of nitrate-nitrogen loss due to denitrification in the soil and biomat formation-assumed <br /> to be 25%min. <br /> r = Annual deep percolation of precipitation = 15.5 inches <br /> Nb= Background nitrate-nitrogen concentration of rainfall recharge, exclusive of wastewater influences <br /> (ppm NO,-N). Assumed to be 0.1 mg/L <br /> Values and Assumptions: <br /> W =270 gpd/residence x 365 d/yr=98,550 gals/res./yr _ 1.15 ac x 27,154 gals/ac-in=3.2 in./res./yr <br /> Nw = 66 mg/L - 10%reduction of N in the septic tank=59 mg/L N <br /> d = 10% from biomat formation and 25% from clay soil under leachlines and observed nitrogen decrease. <br /> 1.15 ac(3.2 me N/L) (59 me/L) (1 -0.35)+ (15.5 in/yr) (0.1 mg/) <br /> Nr = (1.15) (3.2) + 15.5 in <br /> Nr = 7.4 ppm as NO3 N or 33.1 ppm as NO, <br /> IV. CONCLUSIONS AND RECOMMENDATIONS <br /> SSS§ 6.7, 6.8 The percolation test results for this project reveal dramatically varying surface and <br /> subsurface soil conditions. In accordance with EHD rules and regulations, the septic system disposal <br /> area for each individual Lot must be installed within 100 feet of the percolation test location. These <br /> perc test locations were in most cases exclusively dependent upon locating permeable stratum within a <br /> particular Lot. This was particularly evident with Lot 4. Five - 25 ft deep borings were completed on <br /> this Lot in an attempt to find permeable soil. As evidenced, only the surface soils in the"front'of the <br /> Lot were determined to possess acceptable permeability. Consequently, the septic system for this Lot <br /> may have a very limited lifespan. Limited lifespans may also apply to other Lots as well, with the <br /> possibility being that permeability(acceptable percolation)was serendipitously determined in localized <br /> areas, which are not representative of a portion of the subject Lot(front or back), or the Lot as a whole. <br /> Page -11- <br /> Chesney Consulting <br />