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blow 5.1 MONITORING WELL DESTRUCTION BY DRILLING • A hollow-stem rotary auger drill rig, set up with an 8-inch auger, is used to destroy a 2-inch or smaller diameter monitoring well or piezometer. Larger size wells require that the auger diameter match the original diameter of the well boring. The well cap and lock is removed, along with the protective well box, using either a jack- hammer or the drill rig winch cable. A centering device is placed inside the hollow-stem auger bit to insure that the augers follow the path of the original well boring. • The augers are used to drill out the well casing and well construction materials, which are handled similarly as investigation derived residuals. The augers are advanced to a depth of one foot below the original well boring depth. Neat cement or neat cement with 5% or less bentonite powder is utilized to backfill the destroyed well boring. In some instances, dependent on the permitting regulatory agency, a differing mixture of neat cement, bentonite powder, or bentonite grout is required for backfilling the boring. The grout is placed either utilizing the hollow-stem augers as a tremie (dependent on the height of the water column in the well, and the permitting agency requirements), or placing PVC tremie pipe inside the augers to one foot above the bottom of the boring. The augers are slowly removed as the grout is added to the bottom of the boring. The grout can be installed by free falling through the augers, gravity fed through the tremie pipe, or by being pumped, dependent upon the subsurface conditions and the requirements of the permitting agency. • The grout is brought to within 2 feet of the surface, and the surface is completed to match the surrounding ground surface (using concrete, black-dyed concrete, asphalt, or soil). 5.2 MONITORING WELL DESTRUCTION BY PRESSURE GROUTING Pressure grouting is utilized when allowed by the permitting agency, typically when drill rig access cannot be obtained to the wellhead. This methodology leaves the well casing and well construction materials in the subsurface, and instead blocks the potential for vertical contaminant migration by infusing the filter pack with cement and filling the well casing with cement. • The well cap and lock are removed, along with the protective well box, using either a jackhammer or the drill rig winch cable. • Neat cement is pumped into the well casing and maintained under pressure for a minimum of 10 minutes to ensure that the cement penetrates the well screen and fills the void space within the filter pack. The boring is topped off with additional cement as needed after the pressure is relieved. • The top five feet of the well boring is drilled out if possible, and backfilled with neat cement or neat cement with 5% bentonite powder to within 2 feet of the surface, and completed to match the surrounding ground surface (using concrete, black-dyed concrete, asphalt, or soil). 03009-10016-37140 2 of 2 October 2013