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I I� Soil Suitability&Nitrate Loading Study Page 9 St.Patrick's Church, Escalon, CA �^ Project No. 607.1 �. August 31, 2009 -- 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. n. 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 F! could reach groundwater as a result of construction of the proposed septic system. F0# 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- J 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 flaw. 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-Finnemore 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: F1 Nitrate in Effluent According to Rosen, et. al., (2006), the e__co ntration se�tank F effluent is variable, but the average is ab t 44 mg/L. Meteoric Water Rainwater percolating through the soil is the primary leaching agent carrying M nitrates to the groundwater. The estimate of the amount of deep percolation is E 2937 Veneman Ave.,#B240 Geo-Phase Environmental Inc. Phone: (209) 569.0293 Modesto, CA 95356 Fax: (209) 569-0295 ' 1 r 4 I