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CA ARNG Field Quality Assurance Project Plan • Casing sections adjacent to saturated, relatively low -permeability clayey zones, as inferred from the natural gamma logs and available well construction data, including the Corcoran Clay. 8.5.2 An average of four perforations per line foot (LF) of casing will be made. The perforations will be cut at 90 degree intervals around the casing circumference and will be at least one -quarter -inch wide and 2 inches long. The wells will then be abandoned by backfilling the casing with grout in lifts. The remainder of the casing will then be perforated and grouted in stages, as appropriate. 8.5.3 As previously noted, decommissioning techniques for wells with extensive filter packs and cable tool wells directed toward sealing aquitards should be the focus of the effort. As with filter packed wells, perforating cable tool wells adjacent to a permeable zone may severely limit efforts to achieve an adequate seal adjacent to aquitards because permeable geologic materials will more readily accept grout during the sealing operation. 8.5.4 The perforations will facilitate the flow of sealing material from the well casing into the annual space/gravel pack and aquitard. The grout should effectively seal the well casing and prevent it from serving as a pathway for contaminant migration from shallow to deeper zones. 8.6 Final Abandonment Procedures After the casing has been backfilled with grout, the protective casing will be removed and the well casing cut off at least 2 feet below grade and removed. Additional grout will continue to be added to the casing if any settlement occurs. Approximately 24 hours after the backfilling is completed, the grout will be topped off and any surface depression filled with soil material and slightly mounded to allow for settlement. All downhole equipment should be steam -cleaned between wells (see Section 9.3). -8.7 Regulatory Issues and Permits 8.7.1 Wells to be abandoned will be destroyed according to minimum requirements set forth in Bulletin 74-90, California Well Standards, prepared by the State of California Department of Water Resources (DWR). The DWR has responsibility for developing these standards under California Water Code Section 231. According to these standards, abandoned wells must be destroyed to ensure the quality of groundwater is protected and eliminate a possible physical hazard to humans and animals. 8.7.2 Each well must be investigated before it is destroyed to determine its condition and details of its construction prior to abandonment. All undesirable materials and obstructions that would interfere with well destruction must be removed (DWR, 1991). 8.7.3 If the presence of contaminants is known or suspected in a well to be destroyed, all applicable agencies overseeing the individual facilities shall be notified as soon as possible. The enforcing agency at CA ARNG facilities will vary at the different agencies. 8.7.4 Minimum well abandonment guidelines require that the well casing will be completely filled with sealing materials. If the hole is deeper than 30 feet, sealing materials must be placed under pressure and tremied to prevent separation of the grout components. Sealing materials must be placed continuously from bottom to top unless conditions in the well dictate that sealing operations be conducted in a staged manner. It must be verified that the volume of sealant equals or exceeds the volume of the casing to be filled and sealed. Suitable sealing materials include neat cement, sand cement, and bentonite (DWR, 1991). field QAPP.DOC 8-5 May 2000