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KLEINFELDER 7. NITRATE LOADING CALCULATIONS LPer 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 L (NO3) and 10 mg/1 as Nitrogen (I) in groundwater. III our evaluation of nitrate loading, we have 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 fr studies and investigations performed by our firm and others, San Joaquin County Sewage Standards, communication with Mr. Mike Huggins with SJCEHD, and information provided in a report dated March 19, 1997 prepared by the Questa Engineering Corporation and authored by L Mr. Hantzsche for a development in the Stockton area. Current laws allow two homes on each parcel. Based on a conversation with Mr. Ray Borges of SJCEHD, we present these calculations L for a total of six single-family residences (two per proposed parcel) over the total 16.27-acre existing parcel. Ne=AWNw (I-D) + (Nb)R AW+ R Where: Ne = Average calculated nitrate-nitrogen in groundwater resulting from domestic sources and precipitation—mg/l, as N. LA = Number of equivalent dwelling units per acre on septic tanks (unit/acre) = 0.37 (based on six homes divided by 16.27 acres.) 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.) LNw = Nitrate concentration of nitrified leachfield effluent (mg/1) = 40 mg/1 ((Hantzsche and Finnemore (1992)based on residential uses.) LD = Percent dentrification of leachfield effluent = 0.1 percent (0.1 to 0.35 percent typical per Hantzsche and Finnemore (1992). 0.1 selected due to the sandy nature of the near-surface soils. V R = Annual deep percolation of precipitation (inches) = 8.4 inches (representing 70 percent of average annual rainfall of approximately 12 inches being collected into tr the proposed on-site drainage basin and percolating into the soil. The remaining 30 percent of rainfall is assumed to evapotranspirate and drain off site into natural or Lmanmade drainages.) Nb = Background nitrate nitrogen concentration of rainfall recharge at the water table = L0.5 mg/1 (per Technical Memorandum, Hydrologic and Soil Investigation for the L44419.GOI/ST04R785 June 8,2004 ©2004 Kleinfelder,Inc. Page 4 of 6 L