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FFDomestic WATER FLOW CALCULATIONS AND CHARACTERISTICS water flows managed by on-site septic systems have been studied for decades with blished in the scientific literature. Wastewater flows for the Las Palmas project will "future"basis whereby it will be assumed the existing household will have four persons per house(husband, wife and two children). The likelihood of second unit dwellings on any of the subject lots is highly unlikely due to area constraints, and would be prohibited by EHD due to the nitrate loading calculations for the subdivision, as illustrated below. If second unit dwellings were allowed,this would push the nitrate loading projection over the Maximum Contaminant Level (MCL) for drinking water. 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). 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. As a safety factor,the total daily wastewater flow per house and average daily flow per resident will be increased 1.5x to 270 gals/day and 68 gals/resident,respectively. 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,thus a 1.5 safety factor. The characteristics or composition of septic tank effluent is dependent upon several parameters due to idiosyncrasies within each household. Certain appurtenances change the characteristics of the wastewater effluent such as filter vaults within septic tanks and kitchen food-waste grinders. 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/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 N/L(milligrams total nitrogen per Liter of effluent). Unfortunately,these units superimpose wastewater flow variability onto nitrogen influent variability, thus creating even greater LL—the ability. One researcher, (Bauman),has averaged the means from 20 other studies to arrive at a entration of 62 f 21 mg N/L in septic tank effluent. If the above figure for wastewater discharge timated at 68 gals/resident/day(257 liters) and using the figure of 17 g N/cap/day excreted= 17 g 7 L=66 mg N/L/day estimated for the proposed Las Palmas project. This concentration will be stimated nitrogen loading in the effluent discharged from each of the dwellings. Page -9- Chesney Consulting