DTD recently completed the installation of two approximately 2,000’ long horizontal remediation wells at an Air Force Base in the Southeast to treat a long hydrocarbon plume moving with groundwater. The horizontal wells were installed in difficult subsurface conditions common within the Coastal Plain Physiographic Province. DTD was brought in after a utility HDD contractor failed to complete the wells in early 2017.
Subsurface conditions consisted of stiff clay near the surface followed by poorly graded sand with zones of loose and flowing sand. Due to the long horizontal well length, the screen depth of 65’ below entry, and subsurface conditions we mobilized our Maxi-Rig (American Augers DD-210) for the project. Drilling was complicated by the entry area being 30’ higher than the exit, leaving the start of the borehole unsupported by drilling fluid during the well installation. Therefore, the bore’s entry section was isolated by driving 80’ of 12” diameter wash-over casing at each well. Navigation was completed using a combination of wireline and walk-over due to bore depth, restricted areas, obstructions along the bore path, and potential interference.
The wells were designed as horizontal air sparge wells, with each well distributing air across over 1,000 feet of the contaminant plume. Well material consisted of HDPE with custom designed, pressure activated ADS screen (http://www.airdiffusion.com/) which can be used in for horizontal sparge and liquid injection wells. Drilling, installation, and development of both wells was completed in less than four weeks.