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s r? <br /> t 1 _ <br /> 7Nwtalnitrogen concentration of wastewater at 56 mg NIL based on average of three <br /> uent samples from residential units. Does not account for loss of nitrogen in septic <br /> tanks 10% or through biomat(10%+). <br /> d = Fraction (%) of nitrate-nitrogen loss due to denitrification in the soil (15%+) <br /> R = Average recharge rate of rainfall - 9 inches per yr <br /> Nb= Background nitrate-nitrogen concentration of rainfall recharge, exclusive of wastewater <br /> influences (ppm NO3-N) <br /> Values and Assumptions <br /> I= 3 942 .0 asptal WWI = 528,000 cu fl/ =0.33 in/yr <br /> 444 Ac x k4y,560 sq ft/Ac x (1 ft/12 in� <br /> Nw = 56 mg <br /> d = Assume 15%due to a fine-grained clay soil at soil/effluent interface. <br /> R = 9 in/yr. <br /> Nb= Assumed to be 0.1 ppm NO3-N <br /> 0.33 in/E(56 mgNj(1 - 0.15) +(9 in/yr x 0.1 m <br /> Nr = (0.33 in/yr+ 9 in/yr) <br /> Nr = 1.8 ppm as nitrate-nitrogen (NO3-N) or 7.9 ppm as nitrate (NO3) <br /> Nr is less than one- z th the Maximum Contaminant Level MCL for nitrate-nitrogen 10 m . <br /> VI. CONCLUSIONS AND RECOMMENDATIONS <br /> The perc test results for the 11 proposed parcels show acceptable percolation for the management <br /> of septic system effluent flows mostly from the deep percolation tests representative of sumps or <br /> limited depth seepage pits, and not the shallow test borings representative of leachlines. <br /> Potential septic system structures have been denoted in Table 1 based upon the test results <br /> obtained. For example, if acceptable perc test results were obtained from depths of approximately <br /> eight feet, both leachlines and sumps have been specified. If acceptable perc test results were <br /> obtained in depths deeper than eight feet,both leachlines and limited depth seepage pits were <br /> indicated. <br /> Only proposed parcel 8 was perc tested at the 25 foot depth. The soil profile included lean clay <br /> down to 23 feet in depth, where a silty sand material was encountered. This deep perc test reveals <br /> an exceptionally rapid perc test result, which EHD classifies as too rapid since it is under 2 min/in. <br /> As can be discerned, the volume of head water created the perc rate. In other words, if only six <br /> i <br /> inches of head water was applied at this depth, then the test boring would have had a passing rate <br /> (30 min�6 inches= 5 minlin). <br /> Page-9- <br /> Chesney Consulting <br />