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WASTEWATER FLOW VOLUME PROJECTIONS <br />Domestic flow volume projections are typically approximated from the USEPA Onsite Wastewater <br />Treatment Systems Manual, Pg. 3-4. However, for nitrate loading calculations, the EHD has mandated <br />wastewater flow volume projections from single family residential structures to be calculated as follows: <br />100 gallons per day (gpd) for the first bedroom and 50 gpd for all subsequent bedrooms within the <br />structure. Therefore, the flow volumes for this project are: <br />4 Bedroom existing structure: 100 + 50 + 50 + 50 = 250 gpd. <br />2 Bedroom ADU structure: 100 + 50 = 150 gpd. <br />Total Wastewater Flow Volume: 250 +150 = 400 gpd. <br />CALCULATED NITRATE -NITROGEN LOADING <br />HA NTZSCHE/FINNEMORE EQUATION <br />INW LL- dib <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 inches per yr <br />Nw = Total nitrogen concentration of wastewater in mg N/L <br />d = Fraction (%) of nitrate -nitrogen loss first in the septic tank and then due to denitrification in the <br />soil environment. <br />R = Average recharge rate of rainfall - inches per yr <br />Nb = Background nitrate -nitrogen concentration of rainfall recharge, exclusive of wastewater influences <br />(ppm NO3-N)- <br />Values and Assumptions: <br />1 = 400 gpd x 365 d/y = 146,000 gals/y = 19,519 cu ft = 3.22 in/yr <br />1.67 Ac x 43,560 sq ft/Ac x (1 ft/12 in) <br />Nw = 45 mg N/L <br />d = Assume 33%N reduction in 2,000 gal septic tank and 40% denitrification due to high clay content soil. <br />R = 3.12 in/yr. <br />Nb = Assumed to be 0.1 ppm NO3-N <br />3.22 in/ (rel; N/L x 0- 0.33)) = 97.1 x (1 - 0.40) = 58.3 + (3.12 in/yr x 0.1 mg/L) = 9.2 ppm <br />Nr = (3.22 in/yr + 3.12 in/yr) <br />Nr = 9.2 ppm as nitrate -nitrogen (NO3-N) or 41 ppm as nitrate (NO3) <br />Page 3 of 7 <br />Chesney Consulting <br />