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Stantec Addendum to Work Plan for Vapor Probe Destruction, Well Destruction, and Well Installation ARCO Service Station No. 2186 January 26, 2009 advanced to a depth of 65 ft bgs, using a drill-rig equipped with a 15-inch diameter, continuous flight, hollow-stem auger centered on the eight-inch pilot hole. An eight and 518 inch diameter, flush-threaded, steel conductor casing will be set within the annulus of the a g. The--annular space between the inner diameter of the auger and the outer diame#er of the conductor casing will be filled with neat cement and/or grout via tremie pipe from total depth to 12-inches from the — surface. The grout will be given at least 24-hours to cure, after which the soil boring will be continuously cored beginning at 65 ft bgs to the total depth using a drill rig equipped with an eight-inch diameter, continuous flight, hollow-stem au er insi r casing. _ The deep we tie constructed of two diameter, flush-threaded, schedule 0 PVC well casing with20 of 0.020-inch factory-slotted well screen set at depths o 70 to 8 bgs, nstead of 65 o 85 ft bgs. A sand filter pack will be placed in the annular space surrounding the ` entire screened interval, and will extend approximately one to two ft above the screen interval. A two to three-foot thick bentonite annular seal will be placed above the filter pack and will be �S hydrated. The remainder of the annular space will be filled with neat cement and/or grout from the top of the bentonite seal to within 12 inches of the surface. The well will be secured with a locking well cap, and completed with a watertight traffic-rated well box installed at grade. A detail of the well completion is presented in Figure 2. OTHER CONCERNS Groundwater Monitoring and Sampling Vapor wells VW-1 B through VW-3B and VW-4 are included in the quarterly groundwater monitoring and sampling program as required by SJCEHD. During the second quarter 2008, groundwater from vapor wells VW-1B through VW-36 and VW-4 were not monitored nor sampled due to health and safety reasons associated with the field activities. Efforts will be made in future groundwater monitoring and sampling events to prevent this from happening. In addition, SJCEHD will be notified at least seventy-two hours prior to future groundwater monitoring and sampling events. Remediation System Status Since data show the SVE system has reached asymptotic recovery levels, the soil vapor extraction system has been shutdown per SJCEHD letter dated August 22, 2008. Stantec proposes for vapor wells VW-1A through VW-3A to be taken out of the groundwater monitoring and sampling program. These wells have been mostly dry in past monitoring and sampling events. Vapor wells VW-1 B through VW-3B will still be part of the program. A work plan addressing the remaining petroleum hydrocarbon mass from the groundwater will be submitted separate from the well installation report for the new wells. 2186 Addendum to Work Plan for Vapor Probe Destruction, Well Destruction, and Well Installation.doc 3