Installing Monitoring Wells for Well Abandonments
Malcolm Drilling provided the sonic drilling method to abandon 62 wells from the Santa Clara Valley Water District (SCVWD) the field activities were conducted in accordance with SCVWD well abandonment requirements. Monitoring wells were installed at depths ranging from 5 to 90 feet below ground surface (bgs) and constructed with 2-inch-diameter Schedule 40 polyvinyl chloride (PVC) screen and casing. The wells were completed with metal vaults set in flush mount concrete pads or with above-grade steel protective casings. Well abandonments were conducted by over drilling the original borehole size of 8 inches in diameter to remove all the 2-inch PVC casing. Over drilled wells were abandoned by removing the well vault and PVC well casing using the drill rig. The Sonic drill rig was equipped with a six-inch outer diameter casing and used to over drill the well boring and evacuate the annular fill materials to the original borehole depth. The casing, screen, annular fill material, drill cuttings, and filter pack material were removed before sealing each borehole. The boreholes were plugged from the bottom up by pouring bentonite chips into the borehole as the drill casing was withdrawn.