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1 � October 12 I ' 2006 - Job Number.LG00-312 . Page 9 fatal poisonipgs,of infants have occurred following the ingestion of water containing nitrate concentrations greater than 10 mg/l nitrate as N.or 45 mg/1-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, effiuent and the deep'percolation of rain water.,;,The nitrate conemiration of the``treated"se tic effluent mixed with the deep percol ' 2 rain water is estima ound water : d dyte The nitrate alance method assumes 100%MMM-with de2E Rer 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-Finnemore'whichprovides a convenient and simpiified t. 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 inthee mass balance equation are nitrate=N whose maximum-drinking water contaminate level is 10 mg/l. i Denitrification is an important process in`septicsystems that mostly occurs in the leach i line whereby certain bacteria utilize the oxygen i.n the nitrate(NO3) and release as nitrogen g g (N2) + 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 dower rate; about 10%.to-15%. Due to the common occurrence of dark 1 colored-clayey surface soils,the_ denitrification'factor is.estimated.to be about 25 %. i An estimate of the quantity andquality of effluent is required,for the analysis therefore we i used the following information for,our calculation. The deep percolation of rain was estimated to be 6.79-i d is shown on Plate 8: The average residence size was assumed to be a three.(3) and.four(4)bedroom homes. To`estimate theuanti f se tic eluent an assum tion of 50- gallons per person day med. The quantity for-two (2)different sized homes was dete une and is summarized in the table: Hantzshe N;N,;Finnetaore,EJ:1991,Predicating Ground-Water Nitrate-Nitrogen Impacts. Ground Water,Vol.30,No. 4.. _ Q