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7C. WASTEWATER FLOW CALCULATIONS AND CHARACTERISTICS Domestic wastewater flows have been studied for decades with data published in the scientific literature, specifically Reference No. 16: Small and Decentralized Wastewater Management Systems. Wastewater flows are proposed to be managed by conventional on-site septic systems. The total daily water use is a combination of household and personal uses, as itemized below: HOUSEHOLD PERSONAL USE 25 gal for laundry 2 gal for drinking and cooking 10 gal for dishwashing 3 gal for oral hygiene 5 gal for misc.use 14 gal for bathing 16 gal for toilet flushing/sink washing FLOW RATE in gals/home/day= 40 gals/household/day+(35 gal/person/day x number of persons/home). Assuming the average household within the project will have 4 persons per house (husband, wife and two children), the daily wastewater flow rate can be estimated at: 40 gals + (35 gals x 4 people/home) = 180 gals/day for an average flow per resident of 45 gals. Although the residential structures must be built with water saving devises and fixtures, as a safety factor, the average flow per resident will be increased by 1.5x to 68 gals/resident/day. The peaking factor for individual residences on septic tanks will vary with the day of the week and usage. Peak hourly rates are normally associated with the discharge of clothes wash machines, dishwashers and shower/bath water. The ratio of the peak day to the average day can vary depending upon the time of the year and usage, but is usually around 1.5. The characteristics or composition of septic tank effluent is dependent upon several parameters because of idiosyncrasies within each household. Certain appurtenances change the characteristics of the wastewater effluent such as filter vaults within septic tanks and kitchen food-waste garbage disposals. In determining nitrogen concentrations of septic influent and effluent, per capita intake of nitrogen per day must be estimated. The average American consumes between 70 and 140 g of N/day. Since nitrogen comprises 16% of the weight of the average protein, 16% of 70 g N= 11 g N/capita/day and 16% of 140 g N = 22 g N/capitalday. The average of these two values is 17 g N/capita/day of theoretical influent. The concentration of nitrogen in septic system effluent is normally specified in the scientific literature as units of mg NIL. Unfortunately, these units superimpose wastewater flow variability onto nitrogen influent variability, thus creating even greater variability. One researcher, (Bauman - Reference 3), has averaged the means from 20 other studies to arrive at a concentration of 62 f 21 mg N/L in septic tank effluent. If the above figure for wastewater discharge is estimated at 68 gals/resident/day(257 liters) and using the figure of 17 g N/cap/day excreted= 17 g;257 L= 66 mg N/L/day estimated for the proposed project. This concentration will be the estimated nitrogen loading in the effluent discharged from the proposed project. 8 Chesney Consulting