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Values and Assumptions: <br /> I=450 gpd x 365 d/v= 164,250 eals/y=21,959 cu ft =7.57 in/yr <br /> 0.80 Ac x 43,560 sq ft/Ac x (I ft/12 in) <br /> Nw= 35 mg N/L <br /> d = Assume 20%N reduction in both septic tanks(Ref. 8)and 60%denitrification due to high clay content soil <br /> R = 2.21 in/yr. <br /> Nb= Assumed to be 0.1 ppm NO3-N <br /> 7.57 in/yr(35 mg N/L x(1-0.20))=211.96 x 0 -0.60)=84.78+(2.21 in/vr x 0.1 ms/L)=8.7 ppm <br /> Nr = (7.57 in/yr+2.21 in/yr) <br /> Nr =8.7 ppm as nitrate-nitrogen (NO3-N) or 39 ppm as nitrate (NO3) <br /> IV. WASTEWATER TREATMENT SYSTEM - OPERATIONAL CRITERIA <br /> SSS§3.7. Discussions on the efficient operation of the effluent disposal methods,disposal field <br /> longevity,and environmental protection are based upon the parameters discussed within this report. The <br /> onsite wastewater treatment system(OWTS)for the existing 4 bedroom structure,and constructed for the <br /> proposed 3 bedroom structure, is as follows: <br /> A. SEPTIC TANK <br /> Septic tanks store the accumulated sludge,scum and effluent(clear zone)volumes,which in turn affect <br /> treatment of Total Nitrogen(TN)within the tank. Total Nitrogen is the summation of ammonia-nitrogen <br /> (NH4)and organic nitrogen(proteins, amino acids, enzymes). Since the septic tank is predominately <br /> anaerobic,nitrogen cannot exist in its oxidized state as nitrate(within the septic effluent)for any length of <br /> time and is rapidly reduced to NO or NO2. <br /> The following calculation illustrates that a 2,000 gallon septic tank will be ample size for sufficient <br /> hydraulic residence time(HRT)of influent for the proposed 3 bedroom modular home. A septic tank <br /> effluent filter must be installed on the outlet tee of this tank,as noted on the Site Plans. <br /> Detention Time: <br /> Detention Time=2,000¢al total tank capacity x 0.70(30%volume lost to sludge/scum accumulation) <br /> 1.5 (Peaking Factor)x 420 gals/day <br /> Detention Time=2.2 days. The minimum acceptable detention time is 1.0 day. The calculated detention <br /> time is based on using an exorbitant flow volume of 420 gpd(70 gpdpc x 2 people/bedroom= 140 x 3 <br /> bedrooms=420 gpd). A reasonable flow volume of 210 gpd yields a detention time of 4.4 days. The <br /> 2,000 gallon septic tank is suitable for greater detention time and will allow for greater nitrogen retention <br /> and decomposition. <br /> 7 <br /> Chesney Consulting <br />