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B. CALCULATED NITRATE -NITROGEN LOADING NLS§ 3.3, 3.4, 3.5, 3.6. The calculated nitrate -nitrogen impact to the soil and potentially to the groundwater is difficult to determine due to the large number of variables involved and unknown at this time. These include: 1.) Variability in wastewater flows, nitrogen concentrations and dilution affects that may occur, 2.) Impact from upgradient nitrate sources, 3.) Changes in groundwater directional flow and elevation, and 4.) Denitrification potential within the soil environment and within the confined and/or unconfined aquifers. Various scientific methods exist to estimate nitrate -nitrogen loading. This Study uses the Hantzsche/Finnemore Equation to predict the average resultant concentration of nitrate - nitrogen in effluent recharge water from the conventional septic system. The effluent concentration should not exceed 10 ppm nitrate -nitrogen (45 ppm as nitrate). Wastewater researchers place the nitrogen reduction occurring in septic tanks at 10% to 20%. From the September 2004 Symposium "University Curriculum Development for Decentralized Wastewater Management - Onsite Nitrogen Removal," Dr. Stuart Oakley of California State University Chico states that "approximately 20% of the total nitrogen generated is removed in the septic tank" (Ref. 5). If Dr. Oakley's premise of an approximate 20% nitrogen removal occurs in septic tanks due to anaerobic digestion and scheduled tank pumping, and if the tank size is increased a specific percentage from a baseline capacity, then it is reasonable to assume that that percentage increase in tank size will remove that percentage of nitrogen above the 20% baseline. Therefore, increasing the tank size for this project from the required 1,200 gallon to 2,000 gallon is a 67% increase in tank capacity, thus substantiating a 67% increase above this 20% N reduction: 20% + (20 x 0.67) = 33% decrease in nitrogen concentrations by installing a 2,000 gallon tank in lieu of a 1,200 gallon tank. This percentage decrease will be used in the nitrate loading calculations below. NITRATE -NITROGEN LOADING CALCULATIONS HANTZSCHE/FINNEMORE EQUATION IN LL- d) + R Nb 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 mg N/L d = Fraction (%) of nitrate -nitrogen loss first in the septic tank and then due to denitrification in the soil environment. R = Average recharge rate of rainfall - inches per yr Nb = Background nitrate -nitrogen concentration of rainfall recharge, exclusive of wastewater influences (ppm NO3-N). C Chesney Consulting