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July 29, 2005 <br /> NOA Project Number: E05087A <br /> of 85 mg/L-N. Our report used an Nw value of 45 mg/L-N. <br /> 3) EHD staff would like to see a nitrate loading scenario using a six day work week <br /> instead of five days as was used in our report. Table 1 presents the flow rate <br /> calculation for a six day work week. <br /> (Please see the original report for a discussion of the methods and standard assumptions regarding the nitrate loading <br /> calculation <br /> Table 1. <br /> Typical Quantity of Effluent for Property. <br /> i <br /> Category Total People per Average Quantity per Average Daily Flow <br /> Days Person Per Parcel <br /> Business 6r� I 13 1/da /worker 65 workers* 13 gpd/worker*(6/7) <br /> (Office Worker) _? - Y = 724d <br /> z� <br /> Business 10 5 gal/day/worker 10 workers*5 gpd/worker*(6/7) <br /> (Truck Driver) =43 gpd <br /> Business 4 customers * 5 gpd/ customer*(6/7) <br /> (Customer) 4 5 gal/day/customer = 17d <br /> gP <br /> Total Daily Flow 784 gd,average daily flow <br /> Note —Gpd is gallons per day. <br /> —The 6/7 factor is to compensate for a 6 day work week <br />'t A new nitrate loading scenario has been prepared using the variables shown in Table 2. Please see <br /> r the following table for a summary of the results. The actual calculation is shown on Plate 1. <br /> Table 2. <br /> Suihmary of New Nitrate Mass Balance Scenario. <br /> Result Average Daily Effluent Acres Flow(Q) Concen- <br /> Leachfield Deep Percolation of <br /> Plate (Nc) * (A) (Table 3) tration(Nw) Denitrifi- Rainfall(R) <br /> (mg/L-N) (gPd) (rng/L-� cation(d) (Plate 9) (in.) <br /> 1 12.8 1 9.9 784 1 85 10% 5.76 <br /> * Maximum contaminant level(MCL) for nitrate in drinking water is 10 mg/L-N. <br /> The scenario requested by EHD using 85 .trig/L and a six day woxk week has resulted in an Nc value <br /> of 12.8 mg/L-N. The result of this scenario indicates that a buildup of nitrates in ground water <br /> over 10 mg/L-N may occur in the long term below the site. For planning purposes, it is desirable to <br /> have an Nc value below 10 mg/L-N, especially where sandy soils occur and ground water depth is <br /> not deep. This scenario was using standard septic system technology. <br /> Out office believes the Nw value of 85 mg/L-N requested by EHD is a conservative (and probably, <br /> worst case) especially given this method looks a long term impacts. We believe that actual onsite <br />