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STATE OF CALIFORNIA <br /> PETE WILSON. Governor <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— <br /> CENTRAL VALLEY REGION <br /> 3443 ROUTIER ROAD, SUITE A <br /> SACRAMENTO. CA <br /> 95827-3096 Vol <br /> PHONE: (916) 361-5600 cop <br /> FAX: (916) 361-5686 <br /> 25 September 1991 <br /> Mr. Fred Kaufman <br /> Environmental Health Division <br /> San Joaquin County Public Health Services <br /> Post Office Box 2009 <br /> Stockton, CA 95207 <br /> ABANDONMENT OF DRINKING WATER SUPPLY WELLS, LINCOLN VILLAGE SHOPPING CENTER, <br /> STOCKTON, SAN JOAQUIN COUNTY - CASE NO. 3002 <br /> We have reviewed the 1 August 1991 proposal by the San Joaquin County <br /> Department of Public Works to abandon Lincoln Village Maintenance District <br /> Wells 1, 2, 4 and 6. We have determined the proposed abandonment procedures <br /> will not prevent the perchloroethylene and its breakdown products <br /> contaminating the shallow and intermediate water-bearing zones from migrating <br /> to deeper zones. <br /> The boreholes will always remain as potential conduits between the shallow and <br /> deeper zones. Also, the water supply wells are screened in a deep, productive <br /> zone tapped by numerous other supply wells. Therefore, it is imperative that <br /> the inter-aquifer migration pathways created by the wells are eliminated. <br /> To interrupt the potential migration pathways, we require that the outer well <br /> casings are punctured and pressure-grouted for the entire depth of the wells. <br /> We request you ensure that the contractor who will perform the well <br /> abandonments considers the following concerns and recommendations. <br /> • The grouting procedure should minimize the excessive escape of <br /> grout into the highly transmissive water-bearing zones. We <br /> understand that increasing the grout's viscosity while plugging <br /> the borehole in the more transmissive zones of the aquifer is a <br /> means whereby the escape of grout can be controlled and confined <br /> to the annular zone surrounding the borehole. We also understand <br /> that this goal may also be achieved by pressure-grouting the <br /> boreholes in stages from the bottom. <br /> • To allow the abandonment procedures to be optimized before <br /> operating in the most sensitive areas, the contractor should first <br /> abandon the supply well farthest away the most highly polluted <br /> zone. <br /> We recognize that there are aspects of each well , such as the PVC liner and <br /> the double casing in one well and the caving of part of another, that may <br /> interfere with the desired goal of puncturing and pressure-grouting all the <br /> wells ' outer casings from top to bottom. It is essential that the maximum <br />