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7D. WASTEWATER FLOW CALCULATIONS AND CHARACTERISTICS Domestic wastewater flows have been studied for decades with variable data published in the scientific literature. Assuming wastewater flows are to be served by on-site septic systems, total daily water use is a combination of household and personal uses, as itemized: 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 The flow rate in gals/home/day 40gals/household/day+ 35gal/person/day x number ofpersons/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 residences will be built with water saving devices, the occupants will be of a higher income level. This normally translates into higher water usage for various reasons (e.g., indoor spas, increased entertaining, greater number of children, etc.). Therefore as a safgty factor in consideration of the t e of residential structure,s pro osed the total daily wastewater flow per house and averageda flow per resident,will be doubled to 360 gals/house and 90 gals/resident, re�spectivel w 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 showerlbath water. In most cases, and in particular with the proposed residential structures due to their size, peak flows are attenuated by the plumbing. The ratio of the peak day to the average day can vary from 1.5 to>5, depending upon the time of the year and usage. 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 such as effluent filter vaults within septic tanks and kitchen food-waste disposals. lei 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 ofN/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/capita/day. 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- See Reference 3), has average the means from 20 other studies to arrive at a concentration of 62 f 21 mg N/L in septic tank effluent. Page -11- Chesney Consulting