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06/29/2006 13:49 FAX ^ I0o9/027 <br /> f � <br /> .F I N y. is €.a)T R <br /> (source: Predicting Groundwater Nitrate-Nitrogen Impacts, Hantzsche and Finnemore, <br /> (1992)), which is presented below. <br /> Ne <br /> R Nt,)... <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 /> N,; - Average calculated nitrate-nitrogen in groundwater resulting from leach field <br /> i source and precipitation—mg1l, as N. <br /> I - Volume rate of waste water entering tho soil averaged over the gross <br /> developed area = 2.76 Inches per year (calculated as follows: (8.400 <br /> gallweek x 52 weeks/year x 0.1337 cubic ft/gal)/(5.83 acres x 43,560 sq <br /> ft/acre) r. 411 1 t))1.1 <br /> � Z '� 4 ��+ v <br /> I L.E ti 6t.(�.s <br /> N, = Nitrate conce tration of nitrified leach-field effluent (mg/I 45 mg/# (The <br /> Hantzsche and Finnemore (1992) technical paper indicates that the average <br /> total nitrogen concentration in septic tank effluent ranges form 35 to 45 mg/#. <br /> This range was also reported in the 1996 Dames and Moore technical <br /> memorandum. Accordingly, our assumed value is considered conservative.) <br /> D - Fraction of nitrate-nitrogen loss due to dentrification of leach field effluent <br /> 0.2 percent (Per Hantzsche and Finnemore (1992), 0.10 to 0.35 is typical). <br /> The 0.2 value was selected given that groundwater in the project area is <br /> relatively shallow and the subsurface soils are fine grained and will not easily <br /> allow infiltration of effluent to the groundwater <br /> R - Average recharge rate of rainfall = 9.2 inches per year (representing 80 <br /> i 9 g <br /> percent of the average annual rainfall of approximately 11,5 inches. The <br /> remaining 20 percent of rainfall is assumed to drain off-site into natural or <br /> manmade drainages or be lost to evapotranspiration.) <br /> Nv rNr, Back round nitrate nitrogen concen#ration of rainfall recharge at the <br /> 9 9 gate 9 <br /> table = 0.5 mg11 (per Technical Memorandum, Hydrologi: and Soil <br /> Investigation for the Chico Urban Area, page 6, Dames and Moore. April <br /> 1996) r <br /> 71,124.47Y)1 f5TO6R 691 jkav,25� 2006 <br /> CopyrirUh`.M0 K10insOdOr,111C. rape 5 o9 P, <br />