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August 15,2003 Job Number:LG03-221 Page 8 wide basis. Hantzsche and Finnemore 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 approach for estimating potential ground water impacts 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 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"...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." 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 8 through 10. 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 Agricultural Fertilizer and Irrigation According to Madelyn Ripken,no nitrogen fertilizer has been applied to the vineyard. Legume orchard grass is planted between the rows which provide small amounts of nitrogen to the soil. Leaching losses of nitrate fertilizer occur when soils have more incoming water(rain or irrigation) than the soil can hold. As water moves through the soil, the nitrate(NOO that is in soil solution moves along with the water. Ammonium (NH4') forms of N have a positive charge and are held by the negative sites on the clay in the soil; therefore, NH4' forms of N leach very little. In sands where there is very little clay, ammonium forms of N can leach. Coarse-textured sands and some muck soils are the only soils where ammonium leaching may be significant. One way to minimize N leaching and denitrification is to minimize the time the N is in the soil before plant uptake. This cuts down on the time when conditions are favorable for losses (Vitosh and jpE RSO h s r z r �ssoc�