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APPLICATIONS SPECIFIC SITUATIONS Cable Tool or Other Casing Driven Wells Typically, wells drilled by the cable tool method do not have a concrete annular seal, but may have an outer casing seated in an "impervious" layer, with a telescoped smaller diameter inner casing with no gravel pack extending into the production zone(s). In the case of old agricultural wells, perforations may extend nearly to the surface, serving as a potential pathway for entry of near-surface contamination. Considering the above, the best method of destruction is extracting the casing(s) and at same time introducing the sealing material from the bottom of the well to the top. If not possible, or the casing fails during extraction, then perforating and sealing operations should be completed as described under the section Casing Destruction, with special attention to placing openings for sealing opposite "impervious" layers. Considerations in sealing"flowing"artesian cable-tool drilled wells are discussed below. Hard-Rock ells With Surface Casing Only In some wells, surface casing may only extend to a shallow depth, with open hole to total depth. After confirming that the well has and effective surface annular seal, it is recommended that the well should be filled with clean materials as defined previously in this Article up to a depth of 10 feet in native formation below the bottom of the existing casing(60 feet in this example). Appropriate sealing materials should then be placed from the top of the till material to the surface. In no case should there be less than 20 feet of sealing material, starting in native formation 10 feet below the bottom of an existing casing. If the well has no surface annular seal, it may be necessary to overbore the casing and tremie in a seal, or to extract the casing entirely while a seal is tremied into,place. Multi-Aquifer Wells The overriding concern in sealing wells that contain multiple aquifers is to permanently prevent the exchange of water from one aquifer to another, particularly in areas where wells penetrate aquifers containing differing water quality, or where one aquifer may be contaminated. Generally, sealing material is introduced into the well bore through perforations opposite "impervious" layers as interpreted from examination of driller's logs, geologist's logs, and geophysical logs, such as natural gamma-ray and video surveys that can be run in a cased hole where formation and well construction information is lacking. More detailed pre-destruction evaluation may be needed than normally employed for other types of wells. Focal regulatory agencies may dictate exact procedures for the sealing of certain aquitards or "impervious'' layers in well destruction, and for example, may require pressure grouting through existing perforations, or mechanical perforating of the blank casing. Flowing Wells Effective sealing of flowing wells, particularly those having relatively high flows from a large diameter casing, may be difficult to accomplish. One of the main problems is to reduce or eliminate the flow to the extent possible before destruction operations begin. For low flow from small wells, pumping the well, or extending the casing upward may eliminate the flow, allowing sealing to proceed. An inflatable packer may be installed in a larger diameter well, and cement grout pumped in below it with"accelerators" used to facilitate a rapid"set". However, particularly in old cable-tool wells, or in larger diameter rotary-drilled wells where the surface seal is not particularly effective, setting a casing packer may only add to the problem, as water flow is now diverted to the outside of the casing. In this situation, one remedy is to pressure grout the outside of ARTICLE 299—DESTRUCTION OF WATER WELLS —Page 4 of 8 (Revised 4/27/2013)