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July 17,2002 Job Number:LG02-136 Page 9 In addition to the soil suitability study, a nitrate loading study was performed for the project. The nitrate loading study provides an estimate of the potential impact from nitrate to the ground water. 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 from septic system and other sources, a nitrate loading analysis was required by the SJC PHS-EHD. The nitrate loading balance is used to estimate the average annual 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 over the long term. The nitrate sources considered for this project are discussed in the report. The method utilized in this analysis is based on a simple mass balance formula discussed ` in a published article by Hantzsche and Finnemore'which provides a convenient and simplified 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. Hantzsche and Finnemore 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) fust 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 ' Hantzche N.N.,Finnemore,E.J. 1991,Predicating Ground-Water Nitrate-Nitrogen Impacts. Ground Water,Vol.30,No.4. r_ 'pSRSOM1 O 4 �SSO L ' L•