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Di Salvo Trw* ag-Rept <br /> ' October 31,1995 <br /> Page-Z. <br /> space from the total depth to 10 feet figs. Bentonite p llets were placed from 10 feet to 7.5 feet. A <br /> surface seal of neat cement containing five percent bentonite by weight was placed from the top of the <br /> bentonite seal to the ground surface. A water-tight traffic box was installed at the ground surface. <br /> DECOMNHSSIONING METHODS <br /> SICPHS,EHD indicated during telephone correspondence on October 27, 1995, that MW1 <br /> should be decommissioned by pressure grouting and not: over-drilled as presented in the work plan <br /> prepared by Condor. The volume of cement required to pressure grout MW 1 was estimated using the <br /> equation to determine the volume of a right circular der, V=nr2H, and then modifying the <br /> equation for the volume of the PVC casing and the porosity (n) of the filter pack. The resulting <br /> equation is: <br /> V= n[7C (r14— r22) t]+ 7U32H2 <br /> where r1 = radius of bore hole (0.33 ft) <br /> r2 =radius of outside diameter of PVC (0.09 ft) <br /> r3 = radius of inside diameter of PVC (0.08 ft) <br /> Ht = height of sand pack (8.5 ft). <br /> H2 = height of PVC casing in monitor well (15.5 ft). <br /> n = porosity of the filter pack (0.39)1 <br /> The estimated maximum volume of cement net ded to decommission MW 1 by pressure <br /> grouting was approximately 1.4 feet3 (10.5-gallons). <br /> MWl was decommissioned using a pressure grout system operated by Spectrum Exploration <br /> (C57 License #512268)under the supervision of a Condor geologist. Prior to decommissioning, the <br /> total depth of MW 1 was measured to confirm no down-hole obstructions were present in the well. The <br /> pressure grout system was then attached to the top of the open well casing and a cement slurry was <br /> pumped into the well casing. Following removal oft the pressure grout system, the cement slurry was <br /> allowed to settle. The elevation of the cement slurry ' iside the PVC casing dropped approximately 2- <br /> 3 feet below the top of the well casing due to settling. The monitor well was immediately topped off <br /> Driscoll. Fletcher G.. Groundwater and Wells, Second Ed., IS 86,p.3W <br /> n ' <br /> ti CONDOR <br />