Horizontal wells are gaining ground as an alternative to vertical wells for assessing, monitoring and remediating soil and groundwater.
The drawbacks of vertical wells include installation methods that may penetrate, and possibly compromise, landfill liners or clay caps. In contrast, installing horizontal wells, or "directional drilling," penetrates the surface at a remote point, travels thousands of feet in any direction and installs the wells in any configuration (usually horizontal or parallel to the surface).
In the past year, many vertical well drilling companies and newly-formed specialized companies have moved toward directional drilling. As a result, the availability of well drilling services has skyrocketed while prices have plummeted.
A few years ago, vertical drilling could cost hundreds of dollars per installed well-foot. Today, horizontal drilling costs range from $30 to $40 a foot (for wells which have both ends open to the surface) to $80 to $90 a foot (for wells with only one open end).
Horizontal wells can be used for passive or active applications; are usually four to six inches wide; are constructed of PVC, HDPE or steel; and vary in length. Wells are slotted in areas where groundwater recovery, air sparging or soil vapor extraction is needed; samples may be taken during well installation.
Horizontal wells originated in the oil and gas industry and have re-cently been used by the utilities and cable television industries. In the late 1980s, a United States De-partment of Energy program at the Savannah River Laboratory, Aiken, S.C., developed horizontal well ap-plications. This project prompted manufacturers to develop new, less costly equipment and installation methods.
In 1990, owners of a private Mid-western landfill installed horizontal wells at their site. Wells were in-stalled halfway between and parallel to the surface and the water ta-ble in order to extract soil samples without drilling from above. The wells were then fitted with air blowers to create an in-situ aerobic bio-degradation barrier between the surface and water table. This passive barrier to contaminant migration eliminated the need for barrier membranes, allowed the landfill to continue operating and alleviated the need to remove contaminated soil to a lined installation. Using horizontal wells at the landfill re-portedly was more cost-efficient than closing the landfill or in-stalling a liner system.
Perhaps this technology's greatest benefit is the cost savings. For example, installing four horizontal wells to address a pipeline leak at an Oklahoma site took three weeks and reportedly cost $160,000. In-stalling a vertical well system re-portedly would have required 200 wells, taken six months and cost $1.1 million.
Although real savings have been made at some industry sites, many of today's environmental consulting and remediation firms lack the ex-perience and necessary tools to en-sure project success. This will change as the industry becomes more experienced.