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Mr. Ron Rowe Project 20C42-001.026 <br /> June 25, 1998 <br /> Page 2 <br /> cause water in the upper 55 feet to be confined to that specific zone in which it originally <br /> occurred. <br /> At the time of well abandonment, it was observed that the well casing was loose in the <br /> borehole. A downhole video of the well casing, conducted prior to abandonment activities, <br /> indicated that the casing was corroded from a depth of 52 to 54 feet below ground surface <br /> (bgs), suggesting the integrity of the casing was in question. Based on the conditions <br /> observed in the field, it was determined that any attempt to perforate the casing could <br /> jeopardize (collapse) the entire casing. A collapse of the well casing would have prevented <br /> proper sealing of the well. Therefore, a decision was made to abandon the well using these <br /> methods: <br /> 1. Pump neat cement into the well casing using a tremie pipe, filling the casing with grout. <br /> 2. Extract the well casing allowing the grout to fill the entire borehole from the bottom <br /> UP. <br /> 3. Place additional grout using a tremie pipe and bring the top of the grout to ground <br /> level. <br /> The cement grout was placed prior to removal of the casing in order to ensure that the <br /> borehole could not collapse as the broken casing was removed. The cement placed was a <br /> type II Portland. The material weight was approximately 15.6 lbs./gal. Specific gravity was <br /> approximately 3.14. Note that the cement is significantly denser than water in the borehole <br /> and, thus, would displace and occupy any spaces, including voids, formerly filled with <br /> water. In addition, the vertical hydrostatic pressure of the grout is great enough to maintain <br /> borehole stability, preventing collapse, and will infiltrate the borehole walls providing an <br /> adequate seal to prevent water movement either up or down the borehole wall. <br /> The removal of well casing allows for the proper sealing of the borehole. By removing the <br /> well casing, the sealing of the upper 55 feet prevents the migration or percolation of waters <br /> through or along the outside of the casing. Pressure grouting through the well casing on <br /> 3-foot centers may or may not seal the entire length of the outside of the casing. Therefore, <br /> introduction of the grout into the bottom of the well (using a tremie pipe) and pumped <br /> progressively upwards to the top of the well, followed by subsequent removal of the well <br /> casing, avoids segregation and dilution of the seal and reduces the potential for annular <br /> voids in the seal. The grout is in contact with the borehole wall and eliminates potential <br /> pathways along any casing left in place. This method is recommended by the <br /> Environmental Protection Agency (Manual of Water Well Construction Practices, EPA- <br /> SAM:\PJMC42DGJ20012.6AG-9Nba s:I <br />