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1.5 gals/flush(1.0 gals flush+0.5 hand washing)x 4 flushes/hr x 10 hr/day= 60 gpd Three sinks are proposed: 0.5 gals/use x 50 uses/day =25 gpd Totals= 160 +60 +25 =245 gpd=Average Daily Flow(ADF). 245 gpd x six days/wk x 52 wk/yr= 76,440 gals/yr. This figure will be used in the nitrate loading calculations below and fore design purposes. Wastewater Characteristics The domestic wastewater generated from the Office Building will be composed of blackwater from toilets and graywater from hand washing. There will be no high organic loading from kitchen use, etc. Additionalvastewater constituents may consist of other liquids to the system, such as coffee, juices, low strength cleaning liquids, etc. No industrial or commercial chemicals, solvents, etc. should ever be introduced into the wastewater treatment system. It is imperative that low strength and low volumes of cleaners are used in the restroom since they can disrupt the septic tank biology. A value of 90 mg N/L is typically used for commercial wastewater calculations. i B. CALCULATED NITRATE-NITROGEN LOADING NLS§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 variables unknown at this time. These include: 1.) Impact from upgradient nitrate sources, 2.)Variability in wastewater flows, effluent nitrogen concentrations and dilution effects from rainfall recharge, 3.) Changes in groundwater directional flow and elevation. The Hantzsche/Finnemore Formula is used below to predict the average concentration of nitrate- nitrogen in effluent recharge water from the proposed OWTS and existing modular home. The calculations are based on a total areal loading basis of 21.83 acres, correlated with the annually projected wastewater flows of 76,440 gpy for the modular Office Building. These two factors primarily estimate the average concentration of nitrate-nitrogen in the recharge effluent, which should not exceed 10 ppm nitrate-nitrogen(45 ppm as nitrate). IN,„G - 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 denitrified. R See Section II E,Page 4 Nb = Background nitrate-nitrogen concentration of rainfall recharge, exclusive of wastewater influences (ppm NO3-N). e -6- Chesney Consulting