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3/1/92 <br /> APPROPRIATE TECHNIQUES TO DECOMMISSION (ABANDON) <br /> WELLS AND BOREHOLES <br /> --------------------------------------- <br /> --------------------------------------- <br /> Richard D. McJunkin, CEG, Chief <br /> Geologic Support Unit <br /> Department of Toxic Substances Control - Region 1 <br /> California Environmental Protection Agency <br /> INTRODUCTION <br /> Wells and boreholes that are no longer needed or lost drive casing <br /> in an open borehole from drilling operations should always be <br /> Properly sealed with impervious material. More importantly, in <br /> addition to the well, borehole, or lost drill casing being <br /> phys..cally sealed, the hydraulic integrity of subsurface geologic <br /> materials should be restored to a pre-drilling condition. The <br /> restoration of subsurface hydraulic integrity is almost always a <br /> complex endeavor. <br /> Many terms such as "destruction, abandon, close, and decommission" <br /> have been used to describe the procedure of taking a well, <br /> borehole, or lost drive casing out of service. The common usage of <br /> a specific term to describe the procedures) for permanently taking <br /> subsurface installations out of service by destruction is not <br /> standardized among professionals working in the industry. Recently <br /> however, the term "decommission" has been used by members of the <br /> subcommittee on Monitoring Well Design and Construction of the <br /> American Society of Testing and Materials (ASTM) . Because of its <br /> uniqueness and to comply with ASTM recommendations, the term <br /> "decommission" is used in this paper. <br /> Techniques employed to "decommission" wells and boreholes are <br /> numerous. The focus of decommissioning activities should always be <br /> to effectively seal subsurface geologic materials and prevent cross <br /> contamination of aquifers or water-bearing zones. However, most <br /> decommissioning activities do not utilize appropriate technical <br /> specifications to achieve this condition. Depending on subsurface <br /> geology and well design or the position of lost drill casing in a <br /> borehole, subsurface placement of impervious materials may not <br /> provide for an adequate decommissioning effort and prevent cross <br /> contamination. <br /> 1 <br />