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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. A significant variable found in the <br /> Hantzsche/Finnemore equation below is the average number of people that occupy households in San <br /> Joaquin County. Found in Appendix 6, is the U.S. Census Bureau data illustrating that the "average <br /> household size" for San Joaquin County consists of 3.00 people, which is used in the equation. <br /> The following calculations are based on using a semi-conventional type of septic system consisting of <br /> two septic tanks in series, a leachfield using Infiltrator® Chambers and seepage pits at the ends of the <br /> chambers. <br /> HANTZSCHE/FINNEMORE EQUATION TO QUANTIFY THE NITRATE-NITROGEN <br /> IMPACT POTENTIAL FROM ON-SITE SEPTIC SYSTEMS <br /> INw(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 /> 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 - 8 inches per yr <br /> Nb= Background nitrate-nitrogen concentration of rainfall recharge, exclusive of wastewater <br /> influences (ppm NO3-N) <br /> Values and Assumptions <br /> 68 galE/?erson/day x 3 people per household x 6 new houses- 18.96 Total Ac x 365 d/ —0.868 in/yr. <br /> 1= 43,560 cu ft/Ac ft x 7.48 gal/cu fl x (1 ft/12 in) <br /> Nw=66 mg/L - 20%reduction from two septic tanks in series for each new home= 53 mg/L N <br /> d 10% from biomat formation and 10% from saturated clay soil conditions under chambers. <br /> Nb= Assumed to be 0.1 ppm NO3-N <br /> 0.868 in/3(53 mg N/L) (1 - 0.20) + (8 in/)E x 0.1 mg/L) <br /> Nr = (0.868 in/yr+ 8 in/yr) <br /> Nr = 4.2 ppm as NO3-N or 18.7 ppm as NO3 <br /> LL <br /> 9 <br /> Chesney Consulting <br />