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July 21,2003 Job Number:LG03-120 Page 8 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 (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 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,NH,' 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.' According to Angelo Stagnaro, approximately 20 units per acre of N are broadcast on the cherry orchard and 60 units per acre are applied to the vineyard. The vineyard is on a drip irrigation system. Walnuts take 60 units or more units Toacre. Irrigation is applied once per week during the summer for the orchard and none is appy d in the winter. With the development of residential home, ites,the size of vineyards, cherries, and walnuts may i r -5-ee 6 ' Vitosh,M.L.,J. W.Johnson and D.B.Mengel,July 1995.Tri-state Fertilizer Recommendations for Corn, Soybeans,Wheat and Alfalfa,Extension Bulletin E-2567. OE RSO f W i Iy.SOL♦ r