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Soil Suitability&Nitrate Loading Study Page 8 Proposed Stama W inerv.17521 Davis Rd,Lodi CA Pmjmt No. 670,IS Julv 22,2013 7.0 NITRATE LOADING The maximum allowable nitrate concentration in drinking water (MCLis 45 mg/L (or 10 mg/L when measured as nitrogen). The introduction of human or animaYwastes 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 Finnemore published a simple mass-balance method of 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 Hantrsche-Finnemore equation is shown on the calculation sheets in Appendix E. 7.1 Input Data to the Model According to Rosen, et. al., (2006), the nitrate concentration of septic tank effluent is variable, but the average is about 44 mg/L for residential use. For non-residential systems, the nitrate concentration is generally greater due to a lower usage of non-sewage water uses, such as washing. In buildings where the wastewater consists mostly of sewage, up to 80 mg/L, of nitrate may be present. In this case sanitary waste is likely to consist mostly of sewage and so the 80 mg/L concentration is selected as most representative. The following table summarizes the nitrate concentrations from the several sources expected to he present 2937 Veneman Ave.,#6240 Geo-Phase EnAronmmtal Inc. Phone: (209)569-0293 re ocace r.-... 11.1 c<o_rno<