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r <br /> KLEINFELDER <br /> control the performance of a leach field system at the site. Therefore, we feel it was P y) <br /> moee re evan o pe orm a perco a Ion es In a sl a e'4l-f6ofo6p1F— <br /> 9. NITRATE LOADING CALCULATIONS <br /> Per SJCEHD requirements, the following summarizes our nitrate loading calculations <br /> for the proposed leach field. The state drinking water standard for nitrate is 45 <br /> milligrams per liter (NO3) and 10 mg/I as Nitrogen (N) in groundwater. In our <br /> evaluation of nitrate loading, we have used the Hantzsche mass balance equation <br /> (source: Predicting Groundwater Nitrate-Nitrogen Impacts, Hantzsche and Finnemore <br /> (1992)), which is presented below. <br /> Nc = I(NW)(1-D) + R(Nb) <br /> (I+R) <br /> The selection of parameters used in the equation was based on previous studies and <br /> investigations performed by our firm and others, San Joaquin County Sewage <br /> Standards, previous communications with Mr. Mike Huggins and Mr. Rodney Estrata <br /> with SJCEHD, and information provided in a report dated March 19, 1997 prepared by <br /> the Questa Engineering Corporation and authored by Mr. Hantzsche for a <br /> development in the Stockton area. <br /> Nc = Average calculated nitrate-nitrogen in groundwater resulting from leach field <br /> source and precipitation — mg/I, as N. <br /> I = Volume rate of waste water entering the soil averaged over the gross <br /> developed area = 1.69 inches per year (calculated as follows: (7,580 <br /> gal/week x 52 weeks/year x 0.1337 gal/cubic ft)/(8.6 acres x 43,560 sq <br /> ft/acre) x 12 inches/ ft)) 52 X95 j V415'4g2 <br /> NW = Nitrate concentration of nitrified leach-field effluent (mg/1) 70 mg/) ((Based <br /> on conservations with Mr. Mike Huggins with SJCEHD. The Hantzsche and <br /> Finnemore (1992) technical paper indicates that the average total nitrogen <br /> concentration in septic tank effluent ranges form 35 to 45 mg/I. This range <br /> was also reported in the 1996 Dames and Moore technical memorandum. <br /> Accordingly, our assumed value is considered conservative.) <br /> D = Fraction of nitrate-nitrogen loss due to dentrification of leach field effluent = <br /> 0.20 (Per Hantzsche and Finnemore (1992), 0.10 to 0.35 is typical). The <br /> 0.20 value was selected given that groundwater in the project area is <br /> relatively deep and the subsurface soils are interbedded with silt and some <br /> clay strata that would inhibit or slow infiltration of effluent to the groundwater. <br /> R = Average recharge rate of rainfall = 12.4 inches per year (representing 80 <br /> 59149.G01/ST05R1062 August 30,2005 <br /> Copyright 2005 Kleinfelder, Inc. Page 5 of 7 <br /> r <br />