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January 16,2004- Job 004Jab Number: LG03-304 Page 11 According to the Environmental Health Department, a double system willberequired with 100 percent repair/replacement.area: .Each.filte'r bed area is calculated to be 1,396 square feet'in size. The Site.plan shows one possible configuration of the raised filter beds and reserve area. The required septic tank size should be 1,394 gallons. One 1,600 gallon septic tank could provide this volume. In addition, a e uired. The location of the proposed new water well with-a 100-foot offset from.septic systems is shown in Plate 1. 7.0 NITRA'T'E LOADING ANALYSIS Because of the concern of nitrate leaching into ground "water from septic,systems, a nitrate loading analysis was required by the San Joaquin County P.ubIic Health Services;-Environmental Health Division.(PHS-EHD), for the proposed facility to measure the potential.concentration of percolating effluent combined rain fall.over the long term: The method utilized for the nitrate loading analysis is based on'a simple mass balanceformula, discussed in a published article by Hantzsche and Finnemore(1992)'which,provides a convenient and simplified method to estimate long-term-ground-water nitrate impacts on an area-wide basis. Hantzsche and Finnemore found that-over a long period`of time,water quality.in the upper saturated ground-water zone closely approximates'fhe quality of percolating recharge waters. Hantzsche and Finnemore believe that their method is a good planning tool and:provides useful information to planners and local officials but with'some real limitations. In their article published in Ground Watdr, Hantzsche and Finnemore mention that "...the equation ignores dispersion, lateral flow, and mixing'with ground water flow from up-gradient areas. These processes would-generally contribute to additional reduction of nitrate-nitrogen concentrations in ground water to the extent that the nitrate-nitrogen concentration of ground-water flow from up- rgradient'areas is lower." ,. —The Hantzsche and Fennemore approach-is ...a'conservative(worst case) first approximation of ground-water'nitrate-nitrogen concentration resulting from'the combined effect of on-site sewage .disposal systems and precipitation. This (the equation and approach) is.for estimation'of long.- term effect(i.e., oyer years) on.ground-water quality, and is not intended for,prediction of . r .seasonal changes" (Hantzsche and Finnemore, 1992). The method takes into account development area, soil denitrification factor,.rainfall.volume, , rr4 rainfall nitrate concentration, the waste effluent quantity, and waste effluent nitrate concentration. . i .'. . .The formula, assumptions and calculations used for the analysis are'shown on Plate 5. The units of nitrate used in the mass balance equation are nitrate-N whose maximum drinking water contaminate level is 10 mglL: P pE 4S0� I