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Odyssey Landscape—Nitrate Loading Section Page 12 of 14 Our Project Number: NA157000 March 17, 2015 Table 4. Typical Quantity of Effluent. Category Total People Average Quantity per Average Daily Flow per Parcel per Day Person Permanent 20 *13 gal/day/employee (20 employees* 13 gpd) = 260 gpd Employees 260 gpd 5/7 = 185.7 gpd Occasional 8 *5 gal/day/visitor (Maximum 8 Visitors* 5 gpd) = 40 gpd Visitors 40 gpd 1/7 = 5.7 gpd Average Daily Flow from Existing Septic 191.4 gallons per day Note: gpd is gallons per day. *Value cited from Crites, R. &Tchobanoglous, G., Small and Decentralized Wastewater Management Systems, 1998. Table 4-2: Typical Wastewater Flowrates from Commercial Sources. For the existing septic on the site, the total daily wastewater quantity for permanent employees is 260 gallons per day. A five-sevenths conversion was used for the permanent employees to account for a five day work week. Five-sevenths of 260 is 185.7 gallons per day. There will be a maximum of 8 occasional visitors per week, equaling 5.7 gallons per day using a one-seventh conversion to average the 8 visitors Ov I entire week. The total waste water quantity for the existing septic system is therefor 191.4 ga ons per day. The average total nitrogen concentration of domestic wastewater is normally considered to be 20-85 mg/L-N with 35 to 45 mg/L-N being typical (Crites and Tchobanoglous, 1998). It is estimated that commercial use will have higher concentrations of total nitrogen when compared to residential use. It is estimated that he erage concentration for total nitrogen in wastewater for the project is approximatel 85 mg/ N over the long term. 2.3.4.2 Denitrification Estimate Denitrification is an important process which occurs within the leach field whereby certain bacteria utilize the oxygen in the nitrate (NO3) and release nitrogen gas (N2) to the atmosphere. Denitrification is expressed as a percentage, and the normally accepted range is 10 percent to 35 percent. Soils with higher clay content, moist soil conditions, high pH, and organic material denitrify by about 35 percent, and soils with high sand content and fast percolation rates are estimated to denitrify at a lower rate, about 10 percent to 15 percent. A denitrification factor of 25 percent was selected for the site because of the silty sand soil at 3.25 feet bgs with a rapid percolation rate. 2.3.5 Nitrate Loading Scenario A nitrate loading scenario was performed to determine the impact from the proposed project. The scenario utilizes the variables discussed previously which represent the estimated conditions and uses associated with this project. The following table presents a summary of the nitrate loading calculation for the site, as presented in Plate 8. ©2015 Neil O.Anderson&Associates,Inc. A Terracon Company