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Performa Inc. • • <br /> May 7,2003 <br /> Page 15 <br /> ' The range of nitrate concentration found in the ground water suggest that the water quality is <br /> variable with respect to nitrates. No published water quality information was found regarding <br /> the aquifer which underlies the site. <br /> According to the EHD and our experience, elevated nitrate contamination of shallow ground <br /> water occurs in many parts of the county. It is believed that higher concentrations of nitrate area <br /> ' caused by leaching agricultural fertilizers, leaching dairy animal waste, and leaching septic <br /> system waste. <br /> ' The nitrate loading study,based largely on a method by Hantzshe &Finnemore, has found that a <br /> build up of nitrates above 10 mg/L-N(MCL for drinking water),would occur if the proposed <br /> development were t proceed utilizing a standard septics stem. This is mainly due to the large <br /> ' estimated flows, low denitrification factor of san y soils, and the relatively small site w erT n` <br /> compared to the flow. <br /> ' Two other nitrate loading scenarios were performed to estimate the build up of nitrates in the �Qc <br /> aquifer utilizing available waste water treatment technology. Our office has evaluated several J <br /> treatment systems and believes that nitrogen reduction of treated effluent typically ranges <br /> between 50 to 75 percent prior to discharge to the disposal field. <br /> With less concentrated waste water from a treatment system, the Nc value in the nitrate balance <br /> was found to be 7.5 mg/L-N when a treatment system is operating at 50% efficiency with respect <br /> to nitrate removal. A Ne =4.0 mg/L-N was estimated for effluent treatment system treated at <br /> ' 75% efficiency with respect to nitrate removal. <br /> Based on the assumptions of the Hantzshe &Finnemore equation, we believe the proposed <br /> ' project will not cause a long term buildup of nitrates above 10 mg/L-N in the ground water <br /> utilizing a waste water treatment system that is capable of removing at least 50% of the total <br /> nitrogen of the waste water prior to disposal to ground. <br /> ' Short term build-ups are not considered by the Hantzshe &Finnemore equation and are possible <br /> due to the rapid percolation rate measured and the shallow depth to ground water. The use of a <br /> ' waste water treatment system will greatly reduce these impacts when compared to a standard <br /> septic system. <br /> According the Sewage Standards of San Joaquin County EHD, a qualified engineer will be <br /> required to design the sewage treatment system. Our office is experienced in designing these <br /> systems and can provide additional details regarding waste water treatment options and costs. <br /> • 'E A'. <br /> p't c <br /> 1 <br />