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7RESIDENTIAL ,3.5,3.6. PREDICTED NITRATE-NITROGEN LOADING FROM THE EXIST G TWO STRUCTURES,WITH ONE TOILET EACH,USING THEA D Y FLOW ASED ON THE SAN JOAQUIN COUNT E GE STANDARDS O 150 g P R AND TAKING THE ENTIRE PROJECT AREA F 1.95 CRES INTO CONS ION: HANTZSCHEIFINNEMORE EQUATION IN. (1 -d) +R Nb Nr= (I+R) Whcre: 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 mg NIL d Fraction(%)of nitrate-nitrogen loss due to denitrific ions e soil R = Average recharge rate of rainfall-inches per yr N § 3.2 Nb= Background nitrate-nitrogen concentration of rainfall recharg , exclusive of wastewater influences (ppm NO3-N) Values and Assumptions I= 150 gpd x 2 houses x 65 d/Yr of o eration= 109,500 gals=total WWI ` 14 639 cu ft 2.1 in. 1.95 Ac x 43,560 sq ft/Ac x(I ft/12 in.) `� 1 Nw =66 mg N/L.(D mestic/Household Nitrogen Concentration: 10%reduction from the septic tank = (1-0.1)66=59 mg NIL d = Assume 20% as referenced above. R = 13 in/yr. Ne= Assumed to be 0.1 ppm NO3-N 2.1 in/yr(59 mg N/L)(1 -0.2)+ (13 inti x 0.1 mg/L) i� Nr = (2.1 in/yr+ 13 in/yr) Nr = 6.7 ppm s nitrate-nitrogen NNO.- ) r�29.6 pm as nitrate(NO3) The calculrate/nitrate loading concentration in the recharge effluent from the Restrooms is calculated to be under the Maximum Contaminant Level limit for nitrate in drinking water. The variables used in the calculations above are conservative. For example, the use of 113 mg NIL, which was determined from actual septic tank effluent from three commercial facilities is a much higher nitrogen concentration than those concentrations published in the.scientific literature. Secondly, a value of 66 mg N/L was used for residential nitrate-nitrogen loading calculations,also as indicated in the scientific literature. Thirdly, various researchers place the nitrogen reduction occurring in septic tanks at 10%to 20%. From the May 8, i 2003 Symposium"Onsite Wastewater Treatment-Nitrogen Removal,"Dr, Stuart Oakley of Chico State University states that"approximately 20%of the total nitrogen generated is removed in the septic tank."As noted above, a conservative estimate of 10%was used for the grease interceptor tank that will eventually have to be installed, then 10% for a septic tank that will handle wastewater from the public restroom and the employee restroom, and thirdly, 10%nitrogen reduction for the septic tank that will handle wastewater flows from the two residential structures. 10 Chesney Consulting