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I � ? KLEINFELDER 7. NITRATE LOADING CALCULATIONS Per SJCEHD requirements, the following summarizes our nitrate loading calculations for the proposed leach field. The state drinking water standard for nitrate is 45 milligrams per liter (NO3) and 10 mg/l as Nitrogen (N) in groundwater. In our evaluation of nitrate loading, we have i � used the Hantzsche mass balance equation (source: Predicting Groundwater Nitrate-Nitrogen Impacts, Hantzsche and Finnemore (1992)), which is presented below with an explanation for each factor and the value used in our study. The selection of parameters was based on previous studies and investigations performed by our firm and others, San Joaquin County Sewage j Standards, communication with Mr. Mike Huggins with SJCEHD, and information provided in a F', report dated March 19, 1997 prepared by the Questa Engineering Corporation and authored by Mr. Hantzsche for a development in the Stockton area. F. N, = AWNW(I-D) + (Nb) R AW+R Where: Nc = Average calculated nitrate-nitrogen in groundwater resulting from domestic sources and precipitation—mg/l, as N. A = Number of dwelling units per acre on septic tanks (unit/acre) = 0.40 (We understand that there will be 3 to 4 em to ees at t _apr ximate1 8 hours per day, 5 days `f per week. In addition, there will be approximately 10 to em ovPPQ that I^k periodically will be at the site for brief periods of time. For the purposes of these calculations, we assumed an equivalent of 6 eml ,mss at the site 8 hours per day, 5 days per week, with each emp oyee using 15 gal/day, divided by 150 gal/dwelling F1 unit, divided by 1.08 acres.) l W = Annual wastewater loading per dwelling unit per acre (inches) =2.0 inches (per year - per dwelling unit assuming a flow of 150 gal/day/dwelling unit.) F1FkNW = Nitrate concentration of nitrified leachfield effluent (mg/1) = 70 mg/1 (Hantzsche and Finnemore (1992)). Percent denitrification selected based on past discussions with Mr. Mike Huggins of SJCEHD. D = Percent dentrification of leachfield effluent = 0.15 percent (0.1 to 0.35 percent typical per Hantzsche and Finnemore (1992)). 0:15 selected given the shallow depth to groundwater and clayey soil. R = Annual deep percolation of precipitation (inches) = 6.7 inches (representing 70 percent of the average annual rainfall of approximately 9.5 inches being collected into the on-site drainage basin and percolating into the soil. The remaining 30 percent of rainfall is assumed to evapotranspirate or drain off-site into natural or P, manmade drainages.) y! 38058 G0!/5T04R650 May 14,2004 ©2004 Kleinfelder,Inc. Page 4 of 6