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May 25,2001 Job Number:LGOI-115 Page 9 VII. NITRATE LOADING STUDY A build up of nitrates in ground water can cause a temporary blood disorder in infants called methemoglobinemia(blue baby syndrome). Serious and occasionally fatal poisonings of infants have occurred following the ingestion of water containing nitrate concentrations greater than 10 mg/I 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 required 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 from the proposed residences constructed on each of the proposed parcels, agriculture, and deep percolation of rain water containing nitrate. The method utilized in this analysis is based on a simple mass balance formula discussed in a published article by Hantzsche and Finnemore7 that provides a convenient and simplified method to estimate long-tern 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 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 Fennemore' 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 ' Hantzshe N.N.,Finnemore,E.J. 1992,Predicating Ground-Water Nitrate-Nitrogen Impacts. Ground Water,Vol.30,No.4. _ Soo _ o,j o