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t Soil Suitability&Nitrate Loading Study Page 11 St. Patrick's Church,Escalon, CA t Project No. 607.1 j October 14, 2009 =d 7.0 NITRATE LOADING The maximum allowable nitrate as nitrogen concentration in drinking water is 10 mg/L. Measured as total nitrate, the allowable concentration is 45 mg/L. The introduction of human or animal wastes to the soil introduces nitrate 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 Finnemoreublished a simple mass-balance P P method of estimating the amount of nitrate that can be expected to reach groundwater i 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 F1neglecting 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. l . The actual Hantzsche-Finnemore equation is shown on the calculation sheets in Fill Appendix E. 7.1 Input Data to the Model The following points summarize key factors input to the nitrate loading model: urate in Effluent ^"" According to Rosen, et. al., (2006), the nitrate-CORO nitrate-Ctration of sep is—ta`nk effluent is variable, but the average is about 44 mg/L. For non-residentia systems, the nitrate concentration is nerally gre ue to a lower usage of ; non-sewage water uses, such as Ing. buildings where the wastewater consists mostly of sewage, up t S0 mg/L f nitrate may be present. The l lowing table summarizes the ni to.con trations assumed to be present. 2937 Veneman Ave.,#B240 Geo-Phase Environmental'I-nc -P-•hone--.209}.569=0293 Modesto, CA 95356 Fax: (209) 569-0295 F i