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California Regional Water Quality Control Board Central Valley Region Winston H.Hickox Robert Schneider,Chair Gray Davis Secretary for Sacramento Main Office Governor Environmental Internet Address: http://www.swrcb.ca.gov/rwqcb5 Protection 3443 Routier Road,Suite A,Sacramento,California 95827-3003 Phone(916)255-3000•FAX(916)255-3015 12 March 2003 MAR 13 2003 ENVIRONMENT HEALTH W. Michael Carroll PER County of San Joaquin Department of Public Works P.O. Box 1810 Stockton, CA 95201 GR 0 UND WA TER MONITORING WELLS, CORRAL HOLL 0 W LANDFILL, SAN JOA Q UIN COUNTY, Case No. This letter confirms the content of our conversation on March 6, 2003,regarding the proposed abandonment of three existing groundwater monitoring wells at the Corral Hollow Landfill. Two new wells are required at Corral Hollow because the groundwater elevation has decreased to below the bottom of the existing wells. Monitoring the deep aquifer is needed to comply with various requirements summarized in the Regional Board's letter of January 29, 2002 letter to the County. As discussed, we have received the plans and specifications for the installation of groundwater wells at the Corral Hollow and Foothill Landfills issued for bid February 11, 2003. We understand that the two wells planned at Corral Hollow(MW-6 and MW-7) are installed to monitor the deep aquifer in accordance with the Workplan for the Installation of Deep Groundwater Monitoring Wells and related comments by Board Staff on that workplan. A brief review of the bid documents indicates that the contract calls for the abandonment of three existing groundwater monitoring wells at Corral Hollow Landfill: MW-3 at the northern comer of the landfill, MW-1 at the eastern comer, and MW-2 at the Southwestern end of the site (Figure attached). We understand your desire to minimize potential contamination of the deep aquifer by monitoring well penetrations,but if the groundwater rises in the future and the existing wells can again monitor groundwater, then one or two of the existing wells could provide additional monitoring information. With this in mind,we ask that the County not decommission MW-1 because it is the only deep well on the southeastern comer of the landfill. Neither of the two new wells is located near this well. In addition, we ask that the county not decommission MW-2 until the geology and groundwater elevation at proposed new well MW-7 is determined during drilling. If the lithology at MW-7 is significantly different from that at MW-2, and if the deep aquifer is near the bottom of MW-2 (as determined by measurements at MW-7 when it is first,installed and developed), then we will ask that the County also not decommission MW-2. California Environmental Protection Agency_ co Recycled Paper The energy challenge facing California is real. Every Californian needs to take immediate action to reduce energy consumption. For a list of simple ways you can reduce demand and cut your energy costs,see our Web-site at http://www.swrcb.ca.gov/rwqcb5