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January 14,2003 Job Number:LG02-460 Page 7 6— 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 believe 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 L. estimation of long-term effect(i.e., over years) on ground-water quality,and is not intended for prediction of seasonal changes." L 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 analysis 6. are shown on Plates 4, 5 and 6. The units of nitrate used in the mass balance equation are nitrate- N whose maximum drinking water contaminate level is 10 mg/l. ORR 6.1 Quality and Quantity of Septic System Waste Water and Rain Water The total average nitrate concentration of the typical septic waste is normally considered to be 45 mg/L-N s (This concentration is not related to the maximum contaminate level for drinking water of 45 mg/L-NO3). The average daily flow of wastewater into a septic system on the site was determined by assigning a flow rate of seventy-five(75) gallons per day per person? If a primary residence on the property should ever be built, is estimated to be a three (3)bedroom NOR, home occupied by 4 people. In addition to the primary residence, a legal two (2)bedroom Otis,R.J.,Boyle,W.C., 1980,Design manual,onsite wastewater treatment and disposal systems: U.S. Environmental Protection Agency,EPA 625/1-80-012. (See page 100,table 6-1). 9 Crites,R and Tchobanoglous G., 1998,Small and Decentralized Wastewater Management Systems: McGraw-Hill Publishing Company,Boston. pF11S01 � A O �r50� 4..