Directional Drilling Experts Install 3 Horizontal Remediation Wells in Cobble

The Issue

An active retail gas station next to a wetland area had benzene and trimethylbenzene plumes in a water table aquifer containing sand, gravel, and cobbles. Rock fragments and boulders, several feet in diameter, lie in the vadose zone, between the ground surface and the water table. Business at the gas station would slow down or stop for an extended period of time, if vertical air sparge and soil vapor extraction wells had to be drilled through the rock, because the wells would surround the pump island, block the driveways, and even interfere with access to the store itself. Also, the vertical wells would have to be spaced closely because of their limited zone of influence.

The Solution – Directional Drilling

As a national directional drilling company with many years of directional drilling experience in the soils of New England, Directional Technologies, Inc. has the experience to complete projects that would confound other companies. New England is known for its tough subsurface conditions and Directional Technologies has been installing conduits and horizontal wells in gravel, cobbles and rock since 1992. Directional Technologies installed three blind wells—two horizontal air sparge wells and one horizontal soil vapor extraction well under the pump island, driveways, and under the retail store—within a week. Horizontal blind wells have only one wellhead, avoiding the need to exit through the wetland area, and limiting the amount of directional drilling through boulders in the vadose zone to three riser sections (one for each well). Cars pumped gas while the directional wellbore was advanced beneath the pump island and driveways. Customers roamed the store aisles and paid at the cash register even as the directional drillers were locating the advancing drill bit 20 feet beneath the floor. The project was completed on time and without a change order request, despite the need to adjust well entry points, paths, screen depths, and completion details.

Directional Drilling – The Technology

Directional Technologies brought a variety of directional excavation and drilling equipment to the site in preparation of any obstacles to directional drilling that could be encountered. Limited excavation around the wellheads allowed the directional driller to coax the drill rod through the rock-strewn vadose zone layers. The horizontal well screens were directionally drilled beneath the layer of boulders, and the specialized drill bit navigated through cobbles and rock fragments in the target zone. Placement accuracy was achieved with the use of a walkover locating device, which allowed the experienced operators to narrow down the location of the drill bit in the midst of interfering subsurface utilities, tanks, and the foundations and flooring of the retail store. Directional Technologies customizes the drilling fluid for subsurface conditions at every job site. The wellbore remained stable during directional drilling and reaming through the cobbles and rock fragments, and Directional Technologies successfully installed up to 230 feet of completion pipe in each of the three blind horizontal wells.