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CALCULATED NITROGEN CONCENTRATION TO GROUNDWATER UNDER LEACFHHLD=13 grams/QAyg+ Qg,,, = 13 g/(2201+ 108) 3.78 x 1000= 11 mg/L NO3-N C. SEPTIC SYSTEM DESIGN/IMPACT MITIGATION The design of a future septic system for the facility is based upon the factors of operation, longevity, and environmental protection. Plumbing fixtures must consist of low volume fixtures as specified in the Uniform Plumbing Code (UPC). SEPTIC TANKS _ The design and performance of future septic tanks for the project are dependent upon the effluent disposal surface area, discharge rate and exit velocity. These parameters affect the sludge and scum volumes, and therefore,the nitrogen capacity of the tanks. Tanks with a greater surface _ area and shallower depth are preferred for surge storage capacity. Waste inflow volume creates a smaller rise in water depth and a slower discharge rate and exit velocity. These surges of flow through the tank are dampened as surface area increases. By using the projected average daily flow volume of 220 gallons,the effective tank capacity is as follows: The pump-out interval should he 3 yrs. After three years, a determination can be made as to sludge and scum formation and wastewater flows to possibly extend this pump-out interval. Required septic tank capacity: 2.4(QAvF) x Peaking Factor(PF) = 2.4(220) x 1.5 = 792 gal tank capacity needed. It is assumed the current tank capacity is at least 1000 gallons. Future septic tank design considerations are discussed under Impact Mitigation. ilV LEACBTULDS Y 'T 1z Base Tank Capacity (BTC)+Average Daily Flow(ADF) x Soil Factor(S;) 1,600 gal BTC +220 gal ADF x .200 SF =364 lineal feet of leachline 4 - 100 foot sections of leachline pipe=4,000 square foot leachfield-7' a In addition to the leachlines, there should be a minimum of one sump installed for future expansion. The leachlines should be placed at a depth of 20+ inches below final leachfield grade. Trench depth should be 36-42 inches. The leachfield trenches and sumps should consists of the following surface area: Each trench=4 ft'trench sidewalls +2 ft' bottom of trench x 100 ft length=600 ft' x 4-100 ft sections=2400 ft2. Sumps 4 ft wide x 8 ft deep x 10 ft long=200 ft'x 2 sumps=400 ft : 2400 ft' +400 ft' =2800 ft' surface area for effluent infiltration. Several scientific studies have demonstrated that the infiltration capacity of a soil absorption system is dependant primarily by the formation of the biomat and not by the permeability of the soil. The biomat is a biological, slimy substance which forms on the soil-effluent interface over _ time. Hydraulic loading rates range from a conservative criterion of 0.125 gal/ftZ/day to 0.5 gal/ftZ/day for a percolation rate of approximately 1 min/in. These application rates are based on trench side wall areas only. 5 Vaffey Ag Research