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k'g KLEINFELDER also easily satisfy the required percolation rate of 30 minutes per inch or faster, as shown in the table above. NITRATE LOADING CALCULATIONS For new developments,the San Joaquin County Public Health Services Department (SJCPHS) of the Environmental Health Division requires a study to evaluate if discharge from an on-site sewage disposal system at the property could load or increase the nitrate levels in groundwater above the state drinking water MCL standard. As you may be aware, the drinking water MCL standard for nitrate as NO3 is 45 mg/1 and for nitrate-nitrogen as N is 10 mg/1. For the purpose of our evaluation, we have relied upon the application of an equation intended to predict the level of nitrate in groundwater often referred to as the Hantzsche mass balance equation' that is presented below with an explanation for each factor and the values used in our study. Nc=AWN,,, 0-D) + (Nb)r AW+r Where: NC = Average calculated nitrate-nitrogen in groundwater resulting from domestic sources and precipitation—mg/1, as N A = Number of dwelling units per acre on septic tanks (unit/acre) = 0.18 (estimated based on an estimated peak water usage of 900 gal./day for 60 employees at 15 gal./day for an industrial building without a food cafeteria divided by 150 gal./day/dwelling unit to determine the equivalent number of dwelling units and a 33 acre site) W = Annual wastewater loading per equivalent dwelling unit per acre (inches) = 2.0 inches (per year per equivalent dwelling unit assuming a flow of 150 gal./day/dwelling unit) NW, = Nitrate concentration of nitrified leachfield effluent (mg/1) = 35 mg/l typical (Hantzsche and Finnemore (1992)) D = Percent dentrification of leachfield effluent = 0.35 percent (0.1 to 0.35 percent typical per Hantzsche and Finnemore (1992). 0.35 selected given the large depth to groundwater (>75 feet)) R = Annual deep percolation of precipitation (inches) = 8.78 inches (representing 65 percent of average annual rainfall of 13.5 inches in project area. Remaining 35 percent of rainfall is assumed to drain off-site into natural or manmade drainages) Nb = Background nitrate nitrogen concentration of rainfall recharge at the water table = 0.5 mg/l (per Technical Memorandum, Hydrologic and Soil Investigation for the Han=sche N.,Finnemore J. (1992), Predicting Ground-Water Nitrate Nitrogen Impacts, Ground Water, Vo1.30,No 4 20-2080-19.G01/2002R083 February 4,2002 ©2002 Kleinfelder,Inc. Page 3 of 4