DTD completed installation of two HDD remediation wells at a leaking underground storage tank site in a Denver suburb. The wells entered the ground 16 feet below the pavement, from the bottom of a pit excavated to remove the tank. Since there were two HDD wells, this saved at least 100′ of horizontal well installation, and also allowed the drilling to start beneath an undrillable cobble and boulder layer.
The two wells included a deeper air sparge well at approximately 22 ft. below ground surface and a shallower soil vapor extraction well 12 ft. below the surface. Each well had 250′ of screen offering significant communication and treatment along the length of the contaminant plume.
Overall dimensions of the pit were approximately 30 ft x 30 ft x 16 ft deep. All four sides were vertical and supported by a shoring framework. With this configuration a crane was required to lower DTD’s Vermeer 24×40 drill rig to the bottom of the pit. Once the rig was lowered to the bottom drilling operations proceeded as normal. The mud mixing system and waste roll-offs remained at the top of the pit with pumps transferring fluids in and out of the pit.
In the end the both wells were successfully installed in seven days. By starting deep drilling did avoid most of the cobbles and rocks. Rocks encountered further out the bore path did necessitate double-ended installation on the the SVE well (single-ended installation for the air sparge well).