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h <br /> 7 GEOTECHNICAL i <br /> NEIL O. ANDERSON ENVIRONMENTAL <br /> A N D A S S O C I A T E S ! INSPECTIONS a TESTING <br /> E ' <br /> LABORATORY SERVICES <br /> POOL ENGINEERING <br /> 1 n s POST TENSION DESIGN <br /> April 3, 2006 Lf tf illi <br /> NOA Project Number:E05144B <br /> ENV1.hl0 NME{VT yEA LIN <br /> Rodney Estrada PER!417/SERV1C6S <br /> San Joaquin County Environmental Health Department <br /> 304 E. Weber Avenue <br /> Stockton, CA 95212 r <br /> Re: Addendum Letter for the Segura Property -SSS/NLS <br /> 24195 South Cabe Road, Tracy, Calfornia <br /> Dear Rodney, <br /> I Based on your recent comments, please note the changes in the following sections of the above <br /> report. <br /> I <br /> 4.0 DISCUSSION OF NITRATE LOADING RESULTS <br /> 4.1 Total Nitrate Impact <br /> 4 <br /> According to the Hantzsche and Fennemore equation and approach there is a potential for a <br /> buildup of nitrates in the ground water above 10 mg/L-N over the long term for both Nitrate <br /> Loading scenarios. The Hantzsche and Fennemore equation and variables used tend to be <br /> conservative and may over estimate the actual uses on the subject property. It is our opinion that the <br /> Hantzsche and Fennemore equation approach over estimates the potential nitrate impact to the <br /> aquifer. <br /> We realize the shallow aquifer within parts of the Tracy area is susceptible to Nitrate impacts due to <br /> _the shallow depth of water and permeable soils. There are some simple and cost effective <br /> _. _ - .. -�.- - -- Y -. .�- e_:-W- c.- n—o <br /> - - improvements to a standard septic system which couldprovid'e some adchhonal denitrification of <br /> percolating effluent from a septic system. <br /> 4.2 Methods of Mitigation <br /> To mitigate potential buildup of nitrate in the aquifer, some simple and cost effective measures <br /> should be utilized to improve digestion within the septic tank and improve the conditions in the <br /> leach field.We would recommend installing a double septic tank in addition to the utilization of a <br /> modified filter bed septic system.We recommend using EHD criteria for sizing the septic disposal <br /> field. The bottom of the modified filter bed septic system should maintain five feet of separation <br /> from first groundwater. Approximately four inches of loose compost or peat should be added to the <br /> filter bed to provide a carbon source and slow the percolation rate. We recommend the following <br /> septic tank size based on the proposed use as follows: <br /> LODI ■ SACRAMENTO ■ MODESTO <br /> ENVIRONMENTAL DIVISION 902 industrial Way,Lodi,California 95240 ■209.367.3701 ■ 209.369.4228 fax ■www.noandeison.com <br />