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Soil Suitability& Nitrate Loading Study Munoz Property, Escalon, CA Page 9 Project No. 605.1 June 18, 2009 ` 7.0 NITRATE LOADING T I ximum allowable nitrate as nitrogen concentration in drinking water is 0' m /L. The introduction of human or animal wastes to the soil introduces itr e and nitrate-forming compounds, which can be leached downward, enter the groundwater and possibly degrade drinking water- These concerns triggered a requirement by the EHD that an estimate be made of the amount of nitrate that could reach groundwater as a result of construction of the proposed septic system. In 1992, Hantzsche and Finnemore published a simple mass-balance method of ri estimating the amount of nitrate that can be expected to reach groundwater from a septic system, and this model has become commonly accepted as a "first- look" approach. The model takes into consideration the volume and nitrate concentration of the effluent, the de-nitrification effect of the soil, and the amount and annual rainfall. The original paper stipulated, however, that while the model is useful for planning purposes, it suffers from limitations. The ` limitation is due to the introduction of simplifying assumptions; especially in neglecting the effects of dispersion and diffusion in groundwater flow. The model estimates the long-term concentration of nitrate in the upper-most groundwater layer, but ignores the effect that the mixing with deeper groundwater will have on overall nitrate concentration. These assumptions will generally tend to result in an over-estimation of nitrate loading. The Hantzsche- Finnemore model is a conservative tool, useful as a "first approximation" for long-term effects of nitrate sources, but it may not accurately reflect actual groundwater conditions closely. The actual Hantzsche-Fmnemore equation is shown on the calculation sheets in Appendix E. 7.1 . Input Data to the Model The following points summarize key factors input to the nitrate loading model: FjNitrate in Efflicent According to Rosen et. al., (2006), the , itra e ncentration of septic tank effluent is variable, but the average is ab ut 44 mg/L. Meteoric Water Rainwater percolating through the soil is the primary leaching agent carrying nitrates to the groundwater. The estimate of the amount of deep percolation is based, in part of the long-term average annual precipitation and on the average 2937 Veneman Ave.,#$240 Geo-Phase Environmental Inc. Phone: (209) 569-0293 Modesto, CA 95356 Fax: (209)569-0295 f I M