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the casing with a volume of cement at least 4 x the volume of the casing itself, to form an effective outer seal. Then, the operation of pressure grouting below a packer inside the casing should be successful and not cause leakage from the annular space around the outside of the casing. Destruction of PVC Casing in Place Mechanical perforators generally do not work in PVC casing, and drilling out the PVC casing and accompanying seal is probably the most effective method of destruction. The drilling(using a reaming and long pilot bit) needs to be done slowly to avoid deflection and plugging of the bit with PVC chips. Alternative methods, as discussed previously, might involve use of explosives. The explosives are professionally set at selected intervals, the well is then filled with sealing material, and the explosives are set off. This process drives the sealing material into:the annulus and the borehole wall. Remnants of PVC casing left in place are not considered to be a hazard to water quality. Monitoring Wells Although much of the information contained in this Article is applicable to small-diameter (eg. 2- inch and 4-inch) monitoring wells, this well category is excluded from consideration, for the reason that much detailed information on well destruction exists elsewhere. Detailed standards for monitoring well construction and destruction are contained in Bulletin 74-90, which should be referred to. In addition, the ASTM Book of Standards, Designation D 5299-92, 1993, should be consulted (see References), as well as the California Department of Toxic Substances Control series of well guidance documents._ Large Diameter Hand-Dug Wells Open, large diameter hand-dug wells not only present a pathway for groundwater contamination, but provide a physical hazard to persons or animals that may fall in. These wells may involve large volumes of fill and sealing materials,'and may present other unusual problems in their destruction. Sometimes there are small-diameter"laterals" at the bottom of such wells as used in the radial collector type of construction, that must be dealt with for effective destruction. Occasionally, there is a drilled well extending from the bottom of the hand dug well, constructed when water levels dropped below the lift of a'shallow centrifugal pump, and this bored well at the bottom must be destroyed first. As much of the lining should be removed as possible, consistent with safety concerns, with particular attention paid to the upper 5 feet of"curbing", so as to assure to the extent possible good contact of the upper sealing material with native materials of the well. If the well is dry, or can be pumped dry, clean backfill materials as previously described, can be used to fill the well up to 20 feet below the surface (or a shallower depth as applicable) at which point, sealing material should be placed to the surface or just below the "plowing" depth, with an accompanying concrete cap. If the well contains water, then cement or bentonite grout should be placed from the bottom of the well to several feet above the water level, followed by fill material to 5 feet below the surface, and in turn covered by a concrete "cap" extending to the surface, or below"plowing"depth. SURFACE CONSIDERATIONS Excavation for"Mushroom" Cap Specifications for well destruction in urban areas nhay call for the removal of the top of the casing to a depth of 5 feet below the ground surface and construction of a concrete "mushrooan" cap. Old wells that have been "sand pumpers" may have a cavity surrounding the top of the well, and excavation for a ARTICLE 299—DESTRUCTION OF WATER WELLS —Page 5 of 8 (Revised 4/27/2013)