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The concentration of nitrogen in septic system effluent is normally specified as units of mg NIL. Unfortunately,these units superimpose wastewater flow variability onto nitrogen influent `~ variability,thus creating even greater variability. The above figure for wastewater discharge is estimated at iMals/resident/day (428 Liters , and using the figure of 17 g N/cap/day excreted 17 g-428 L =40 mg N/L/day. This nitrate-nitrogen concentration will be the estimated nitrogen loading in the effluent discharged from the two proposed SFRs. D. CALCULATED IMPACT FROM NITRATE-NITROGEN LOADING The calculated or estimated nitrate impact to the soil originating from septic effluent, and ultimately impacting the groundwater is extremely difficult to determine due to the number of variables involved. With this project, only the two proposed new homesite Parcels will be taken into consideration and not the total area, which includes the existing homesite on the Designated Remainder. This will be done so that a comparison can be made between nitrate loading from the existing almond orchard on proposed Parcels I and 2, and nitrate loading from two new homesites on these same Parcels. It is assumed that a traditional septic system will be installed for each residential structure. Therefore, the following calculations are based upon using a conventional or traditional type of a septic system consisting of a septic tank, leachfield and possibly filter beds or sumps. HANTZSCHEIFINNEMORE EQUATION M,(1 - d) +RN Nr= (I +R) 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 (40 mg NIL/day) d = Fraction(%) of nitrate-nitrogen loss due to denitrification in the soil R = Average recharge rate of rainfall - inches per yr (11) Nb = Background nitrate-nitrogen concentration of rainfall recharge, exclusive of wastewater influences (0.1 ppm NO3-N) Values and Assumptions 113 gals/person/day x 4 people per household x 2 new houses/4.5 Ac x 365 d/yr =2.7 in. I = 43,560 cu ft/Ac ft x 7.48 gal/cu ft x (I.ft/12 in) Nw=40 mg/L - 20% reduction from typ. septic tank = 32 mglL N d — 10% from biomat and 15%from saturated soil conditions under leachlines. Nb = Assumed to be 0.1 ppm NO3-N 8 Vafley dig Research