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October 12,2004 Job Number.LGOO-312 Page 9 fatal poisonings of infants have occurred following the ingestion of water containing nitrate concentrations greater than 10 mg/l nitrate as N or 45 mg/l nitrate as NO3_ Because of the concern of nitrate leaching into ground water, a nitrate loading analysis was requested by the County to estimate the average nitrate concentration of percolating water for the subject parcel: if a site is contributing excess nitrogen to ground water, ground water quality can be impacted.The nitrate sources considered for this project are percolating septic effluent and the deep percolation of rain water. The nitrate concentration of the"treated" septic eluent mixed with the d ercol in rain water i:s estim t es.with.g ,underwater d' es. The nitrate balance method assumes 1000/0 rnixino with dee er over long periods of time beneath acreage of the subject parcel. The method utilized in this analysis is based on a simple mass balance formula discussed in a published article by Hantzsche and Finnemore7 which provides a convenient and simplified method to estimate long-term ground-water nitrate impacts on an area-wide basis. The approach takes into account development area, soil denitrification factor, rain fall volume, rain fall 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, 9, and 10. The units of nitrate used in the mass balance equation are nitrate-N whose maximum drinking water . contaminate level is 10 mg/l. Denitrification is an important process in septic systems that mostly occurs in the leach line whereby certain bacteria utilize the oxygen in the nitrate(NO,) and release nitrogen gas (N,) to the atmosphere. Denitrification is expressed as a percentage, and the normally accepted range is 10%to 35%, Soils with higher clay content,moist soil conditions,high pH, and organic material denitrify about 35% and soils with very high sand content and fast peculation rates are ; estimated to denitrify at a lower rate, about 10%to 15%. Due to the common occurrence o£dark C' colored clayey surface soils,the denitrification factor is estimated to be about 25 %. An estimate of the quantity and quality of effluent is required for the analysis therefore we used the following information for our calculation. The deep percolation of rain was estimated to be 5.79-i s and is shown on Plate 8. The average residence size was assumed to be a three(3) and four(4)bedroom homes. To estimate the quantilL of se tic eluent an assu�n tion 50- gallons per person p irnQ. The quantity for two (2)different sized homes was det ne and is summarized in the next table. 7 Hantzshe N.N.,Finnemore,E.J. 1991,Predicating Ground-Water Nitrate-Nitrogen Impacts. Ground Water,Vol. 30,No.4. r9 Rto r ti a �;so6�