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'Vr/ to/,iVVtl VC:Y4 hRF ^ Im 00y/0z8 t 9. 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 (NO,) and 10 mg/1 as Nitrogen (N) in groundwater. In 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. 1 (i+R) The selection of parameters used in the equation was based on previous studies and investigations performed by our firm and others, San Joaquin County Sewage ' Standards, previous communications with Mr. Mike Huggins and Mr. Rodney Estrata with SJCEHD, and information provided in a report dated March 19, 1997 prepared by the Questa Engineering Corporation and authored by Mr. Hantzsche for a ' development in the Stockton area. Nc = Average calculated nitrate-nitrogen in groundwater resulting from leach field source and precipitation - mg/1, as N. ' i - Volume rate of waste water entering the soil averaged over the gross developed area = 2.76 Inches per year (calculated as follows: (8,400 gal/week x 52 weeks/year x 0.1337 cubic ft/gal)/(5.83 acres x 43,560 sq ' ft/acre) x 1 ft/12 inches)) NW = Nitrate concentration of nitrified leach-field effluent (mg/1) = 45 mg/I (The ' Hantzsche and Finnemore (1992) technical paper indicates that the average total nitrogen concentration in septic tank effluent ranges form 35 to 45 mg/I, This range was also reported in the 1996 Dames and Moore technical ' - memorandum. Accordingly, our assumed value is considered conservative.) D _ Fraction of nitrate-nitrogen loss due to dentrification of leach field effluent = 0.2 percent (Per Hantzsche and Finnemore (1992), 0.10 to 0,35 is typical). ' The 0.2 value was selected given that groundwater in the project area is relatively shallow and the subsurface soils are fine grained and will not easily allow infiltration of effluent to the groundwater 1 R = Average recharge rate of rainfall = 9.2 inches per year (representing 80 percent of the average annual rainfall of approximately 11.5 inches. The ' remaining 20 percent of rainfall is assumed to drain off-site into natural or manmade drainages or be lost to evapotranspiration.) 1 ' 71,124.G01/ST06117511 July 13.2006 CemyTighl 2000 Kleinfo.1dor,inf•. Page 5 of B