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6. .s r_ Mr. Steven Malcoun December 9,2003 Page 11 Hantzsche and Finmemore found that over a long period of time, water quality in the upper saturated ground-water zone closely approximates the quality of percolating recharge waters. They 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 L Water, 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-gradient 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., over years) on ground-water quality, and is not intended for prediction of seasonal changes" (Hantzsche and Finnemore, 1992). The method takes into account development area, soil denitrification factor,rainfall volume, ` rainfall nitrate concentration, the waste effluent quantity, and waste effluent nitrate concentration. The formula, assumptions and calculations used for the analysis are shown on Plates 2 through 4. The units of nitrate used in the mass balance equation are nitrate-N whose maximum drinking water contaminate level is 10 mg/L. ` 7.1 Quantity of Quality of Domestic Wastewater From Proposed Project The average total nitrogen concentration of the domestic waste water is normally considered to be 20-85 mg/L-N with a typical concentration of 45 mg/L-N(Crites and Tchobanoglous, 1998). We believe the long-term average concentration for total nitrogen in waste water is most likely 45 mg/L-N. r 7.2 Quantity and Quality of Deep Percolating Rain Water An estimate of the quantity and quality of rainfall was required for the analysis. The estimate of deep percolation of rain is based on the average monthly precipitation of rain fall and evapotranspiration for Lodi, California. The estimate first determines whether the average monthly precipitation exceeds average monthly potential ET. If so, then the difference is potential deep percolation. This method does not consider runoff. See Plate 8 for the data and calculation. L OF gip; ` Obi®~