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September 3,2003 ` Job Number:LG03-226 Page 6 potential concentration of percolating effluent and rain fall over the long term. Percolating septic effluent from each parcel may impact ground water to some degree. The method utilized for the nitrate loading analysis is based on a simple mass balance formula, ` discussed in a published article by Hantzsche and Finnemore,'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 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 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 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. �3 5� The formula, assumptions and calculations used for the analysis are shown on Plates 8 through 9 hU-The units of nitrate used in the mass balance equation are nitrate-N whose maximum drinking water contaminate level is 10 mg/L. ` 7.2 Agricultural Fertilizer 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 3 Hantzshe N.N.,Finnemore,E.J. 1991,Predicating Ground-Water Nitrate-Nitrogen Impacts. Ground Water,Vol. 30,No.4. pERSp1 Z W O � ` 7SSO`�r