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07/13/.2008 08:24 FAX � 11003/028 9. NITRATE LOADING CALCULATIONS Per S,ICEHD 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 (NQi) and 10 mg/l 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 NwID�� Ne, � I � (ISR) The selection of parameters used in the equation was based on previous studies and investigations performed by our firm and others, Sart 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 Mir. Hantzsche for a development in the Stockton area. NC w Average calculated nitrate-nitrogen in groundwater resulting from leach field source acidrn-asci itation /l, as N. p p 9 f 1 - Volume rate of waste water entering the soft averaged over the gross developed area W 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 scl t 't ft/acre) x 1 ft/12 inches)) N,N = 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 mel/l. 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 dentri#ication of leach fieid effluent =; 0.2 percent (Per Hantzsche and Finnemore (1992), 0.10 to 0,35 is typical). The 02 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 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 dram off-site into natural or manrnade drainages or be lost to evapotranspiration.) a 7Ks2/,.r0INTOGR75a July 13.2006 f;[ yric�llt;?p(3(i Kl�intrlp�r,tr1C. P'tqu 5 of 8