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February 27,2002 -- Job Number: LG02-048 Page 10 ... 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 have found that their approach is a good planning tool and provides useful information to planners and local officials but with some real limitations. In Hantzsche and Fennemore's article, published in Ground Water, they 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 �fS ground-water flow from up-gradient areas is lower." The Hantzsche and Fennemore equation'provides "...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 Hantzsche and Fennemore7 equation 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 9 through 16. The units of nitrate used in the mass balance equation are nitrate-N whose maximum drinking water contaminate level is 10 mg/1. Denitrification is an important process in septic systems that normally occurs in the leach line whereby certain bacteria utilize the oxygen in the nitrate(NO3) and release nitrogen gas (N2) to the atmosphere. Denitrification is expressed as a percentage, and the normally accepted range is 10 percent to 35 percent. Soils with higher clay content, moist soil conditions,high pH, and organic material denitrify about 35 percent and soils with very high sand content and fast percolation rates are estimated to denitrify at a lower rate, about 10 percent to 15 percent. Due to the occurrence of sandy soils, the denitrification factor is estimated to be about 10 percent. An estimate of the quantity and quality of effluent is required for the analysis. The deep percolation of rain was estimated to be 6.21 inches and the calculation is shown on Plate 8. The nitrate concentration of rain fall was estimated to be 0.17 mg/L-N.' PERS 1 f E 7'TSOL♦ r