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August 16, 2004 <br /> NOA Project Number: LE03-120 <br /> Page 2 <br /> of septic system effluent. It is my understanding from discussions with EHD staff that water <br /> wells which have high nitrates are often old and"screened" into these impacted aquifers. <br /> Drilling a deeper well often results in better water quality independent of gradient of direction of <br /> shallow ground water. If a well is sufficiently deep, there are normally several to many <br /> significant clay layers (eg: aquiclude or aquitard) to protect water quality from downward <br /> percolating nitrates from the surface. <br /> 5.2: Based on the Nitrate Loading Study, our objective is to keep the nitrates under 10 mg/L-N <br /> which is equivalent to 45 mg/L as N031 the drinking water standard. The use of a modified filter <br /> bed septic system with 3 to 4 inches of peat on the bottom of the bed should go a long way to <br /> improve treatment and slow the rapid percolation of effluent. Our proposed design would also <br /> enlarge tank size to obtain a daily retention ratio of about 3.0. If these modifications (to standard <br /> filter bed systems) could be permitted through the normal EHD permitting process, we would not <br /> require them to be engineered. We believe that this approach could reduce nitrates by <br /> approximately 40 percent [16.7 mg/L-N (Nc) * (1-0.40) = 10 mg/L-N] which is at the limit for <br /> the site. <br /> Address numbers were reviewed between 16500 and 17856 North Ripon Road. Three septic <br /> system permit copies were identified and are attached. These addresses also contain numerous <br /> well repair permits. <br /> 6.6: 1 am in responsible charge for all the work conducted as part of this study. I certify the <br /> percolation tests were performed to the EHD standards. <br /> We appreciate your recommendations for this project and your continued interest in our work. <br /> Be gards, <br /> p FOC <br /> David Welch, M.S v�p 3 1'V�c� O�� <br /> CEG-2151, CHG-653, GP-1049 <br /> � 15 <br /> �� S � <br /> Environmental Department Manager Cr No. 21CERTIFIED <br /> ENGINEERING <br /> att: three (3)permits GEOLOGIST �Q <br /> �TFOF CAL\FOP <br /> CC: Mr. John Glick <br /> Quartaroli &Associates <br /> 310 Sun West Place, Suite A <br /> Manteca, CA 95337-4347 <br /> (209) 239-4908 <br />