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S GNET _.Vd STL Project No. 0010771 7z-,sil 1 Las Appendix D gbPage D.1 APPENDIX D ` NITRATE LOADING STUDY The principal concern with respect to the build-up of nitrates within the groundwater is methemoglobinemia, which is of particular concern with infant children. Methemoglobinemia, also known as "blue baby syndrome," occurs when bacteria in the digestive system transforms nitrate to nitrite and the nitrite oxidizes iron in hemoglobin of red blood cells to form methemoglobin. Methemoglobin lacks the capacity to carry oxygen and the resulting condition can ultimately lead to .. death if undetected. Therefore, the Environmental Protection Agency has set the maximum contaminant level(MCL)for drinking water of 10 mg/L or 10 parts per million for nitrate-nitrogen. Because of the concern for nitrate leaching into the groundwater system, a nitrate loading study was performed to estimate the average nitrate concentration of percolating water for the subject site. The sources included in our loading study included the percolation from the on-site sewage disposal system L and recharge due to rainfall. To this end, we utilized a simple mass balance formula, often referred to as the Hantzsche and Finnemore Equation. The equation is somewhat conservative and is often thought of as a worst-case approximation ` for the chronic effects of groundwater-laden nitrate-nitrogen resulting from the combined effect of rainwater and septic system percolations. The equation takes into consideration the development area and land use, soil chemistry, rainfall criteria and sewage system effluent characteristics. The Hantzsche ` equation and design parameters utilized herein are as follows: Nitrate-nitrogen (Nc)_(I Nw( 1-D)+R Nb)/(I+R) Where: I = Amount of wastewater entering subsurface for subject area in/year Nw= Nitrate-nitrogen concentration in wastewater (mg/L) D = denitrification as a percent of original concentration (%) R= Recharge due to precipitation (in/year) Nb = Background concentration of nitrate-nitrogen in rainfall (mg/L) The amount of wastewater that enters the subsurface was determined on the basis of the following criteria: The per capita flow to a septic tank is 80 gallons per day (US EPA Publication No. 625/1-80- ` 012, Design Manual for On-Site Wastewater Treatment and Disposal Systems, page 51, 1980; Kaplan O. Benjamin, Septic Systems Handbook, pages 147-148, 1988, Lewis Publishers). ` e have assumed 2.5 residents per household at 80 gpd, a working staff of 4 persons at 15 gpd, and 10 customers per day at 5 gpd, resultin i a net average of 19 gpd for 16.5 persons. The averse rate of discharge of nitrogen per person per da is 15 rams as N (Kaplan, O. 3' 8 g g P P P Y � g ( P ` Benjamin, Septic Systems Handbook, pages 147-149, 1998, Lewis Publishers; State Water Resources Control Board, Identification and Evaluation of Methods for Determining Sources of Nitrate Contamination of Groundwater, page 18, 1994). r 1417 No. Market Blvd., Suite 1 • Sacramento,CA 95834 . (916)568-5858 • Fax: (916)568-5813