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i I � - Soil Suitability&Nitrate Loading Study Page 11 Munoz Property, Escalon, CA Project No. 605.1 June 18, 2009 Other Nitrate Sources Since the site is not in dairy or commercial agricultural use, dairy lagoons, corrals, and agricultural fertilizer is introducing no nitrates. A municipal sewage treatment plant lies nearby, but since it does not lie in an up-gradient # position, it also is unlikely to represent a source of nitrate. The two existing septic sewage systems on the property do, however, contribute to the nitrate load, and must be considered. 'I Flow Rates The average daily flow rates of each septic system on the site must be estimated based, in part, on guidance available from the tewater Standard (EHD, 2003). Residents are each assumed to produce GPD of sewage. The permanent residence is assumed to house 5 residents and the mobile home is assumed to house 3 residents. A table in the Wastewater Standard suggests that the proposed store will produce a total of 150 GPD of sewage- 7.2 Nitrate Loading Calculation The following table summarizes the nitrate total loading from the two existing i septic system and the proposed new system. The last column is the estimated total nitrate load as calculated from a simple mass-balance approach. The Hantzsche and Finnemore model is then used to estimate the nitrate concentration in groundwater. The calculation worksheets are in Appendix E. System Acres Daily Flow Effluent Denitrification Percolation N ` Cone. Nv Factor d R Loadin Perm Res. 1.27 250 GPD 44 m /L 25% 2.86 in. 35 lbs Mobil Res. 1.27 210 GPD 44 m /L 25% 2.86 in. 21 lbs Proposed 1.27 150 GPD 44 m /L 25% 2.86 in. 15 lbs The existing residential septic systems are producing a total of 56 pounds per year of nitrate leaching to groundwater. The proposed system will add a relatively modest additio 5 po ds. r, Each of the two exis ' g septic syste s and the proposed system will result in nitrate concentratio in excess of t e MCL limit at the uppermost layer of groundwater as sums ized below: em N as % of MCL F1 Perm Res. 191 Mobil Res. 1.50 Proposed 124 f , 1 2937 Veneman Ave.,#B240 Geo-Phase Environmental Inc. Phone: (209)569-0293 Modesto, CA 95356 Fax: (209) 569-0295 Fj