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PRIVILEGED&CONFIDENTIAL 6.2 Utility Clearance Prior to destroying the monitoring wells, Building Analytics will contact the regional utility notification center 48 hours in advance of the field work. 6.3 Monitoring Well Abandonment 6.3.1 Over Drill Method Because TPH and BTEX was reported in Monitoring Well Nos. MW-2 and MW-4, Building Analytics proposes to destroy these two wells by over drilling the wells. The wells have a total depth of approximately 80 feet bgs. The two wells will be over drilled using a Mobile B-61 drill-rig equipped with 12-inch o.d. hollow-stem augers. The well casing, screen, grout and sand pack material will be over drilled, by using an auger that has a larger diameter than the auger that was originally used (10-inch O.D.) to install the wells. The cuttings (i.e., grout and sand pack material) will be placed in 55- gallon drums. Subsequent to the removal of the casing, screen and sand pack, the borings will be filled with Portland cement grout. A tremy hose will be placed near the bottom of the borings and grout will be pumped into the borings from the bottom. The hose will be +v removed slowly as the boring fills with grout. Once the borings are filled with grout, the grout will be allowed to settle. Once the grout has settled, the grout in the borings will be topped-off to within approximately two feet of the ground surface. A concrete cap of low approximately two feet thick will be placed on top of the grout and the surface refinished to match the existing ground surface. 6.3.2 Pressure Grouting Method Because TPH and BTEX were not reported in Monitoring Well Nos. MW-1 and MW-3, Building Analytics proposes to destroy these two wells by the pressure grouting method. The wells have a depth of approximately 80 feet bgs. The two wells will be pressure grouted using a Mobile B-61 drill-rig mounted or trailer mounted grout pump. ~' Prior to grouting, a mechanical or pneumatic packer will be placed near the top of the well casing. Portland cement grout will then be pumped into the borings under pressure through the packer. The borings will be filled with grout and then held under ... approximately 30 to 40 pounds of pressure for approximately five minutes, or until grout is observed seeping from around the exterior of the well casing. The packer will then be removed and the grout allowed to settle. Once the grout has settled, the upper five feet of well casing will be drilled out. The grout in the boring will then be topped-off to within approximately two feet of the ground surface. A concrete cap of approximately two feet thick will be placed on top of the grout, and the surface refinished to match the existing ground surface. V 7.0 DECONTAMINATION ,r The hollow-stem augers will be steam-cleaned prior to their use in the two monitoring wells that will be over drilled. Any equipment which will come into contact with TPH or BTEX impacted well construction materials will be decontaminated, using a bristle brush and a trisodium phosphate (TSP) solution, which will then be followed by two tapwater rinses. ,r 6 199164—WFB,Stockton Well Abandonment Work Plan V