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Directional drilling for environmental remediation.

Compact directional boring systems are putting in new water distribution lines, replacing old water services to residences, and installing new underground electrical cable to replace falling power lines - all without cutting roads and sidewalks or trenching through landscaped yards. Surface damage is minimized and restoration time - and costs - are greatly reduced. Now environmental engineers are discovering that directional boring equipment can install horizontal wells for soil and groundwater characterization, for remediation, and to monitor for the presence and levels of underground contamination.

Directional boring brings the same advantages to environmental projects as it does for utility construction:

* Installations can be made beneath surface obstructions.

* Work does not require extensive excavations.

* Projects can be completed with little disruption of routine activities.

And for remediation, directional boring machines can reach areas of contamination that are inaccessible to other methods. Horizontal wells can access contamination plumes beneath landfills. Bioremediation procedures using horizontal wells can treat contamination caused by leaking fuel tanks without bringing contaminated soil or water to the surface for treatment.

Rick Plummer of R-H-S Engineering, Inc., an environmental engineering company in Monroe, Louisiana, points out that horizontal monitoring wells can identify contamination emanating from landfills sooner than the vertical wells now commonly used. By the time contaminants reach vertical monitoring wells, says Plummer, they often already have spread to outer portions of the landfill and perhaps into the groundwater.

Earlier Detection

Using horizontal wells under the landfill can provide earlier detection of contaminant seepage through the impermeable layer, Plummer says. A horizontal characterization or monitoring well can be converted to remediation use, providing substantial cost savings.

A horizontal well consists of underground screen - casing with patterns of slots that is positioned through contamination with a horizontal directional boring machine. At many locations, horizontal well applications can accomplish in situ remediation without removing contaminantes to the surface for treatment.

Because contamination plumes spread horizontally rather than vertically, horizontal wells provide greater surface contact with contaminants than is possible with vertical wells. Therefore, procedures using horizontal wells can be more efficient.

Horizontal wells can be used for bio-remediation, air sparging, and soil vapor extraction, all in situ methods. Searching for more efficient environmental cleanup methods, the U.S. Department of Energy's Department of Technology Development assigned Sandia National Laboratories (Albuquerque, New Mexico) to research and test the feasibility of using directional boring equipment for remediation.

The government contributed part of the funds necessary for the project. Charles Machine Works, Inc. (Perry, Oklahoma), serving as Sandia's industry partner, provided private capital, equipment, and personnel to conduct the tests. Various Ditch Witch directional boring systems, rod pushers, and pneumatic piercing tools from Charles were used at several test locations.

Sandia's preliminary report, issued in 1994, and its final report, published in January 1995, concluded that in many situations, wells installed with directional boring systems are superior to current vertical-methods "...because the process is technically superior, minimizes surface disturbance, and reduces the risk of contaminants being spread to deeper water tables."

Horizontal wells were found to influence a greater area within the contamination plume than vertical wells, so fewer horizontal wells are required. Because horizontal drilling systems launch bores from the surface, starting and receiving pits are unnecessary.

Typical Installation

A typical well installation begins with a bore that proceeds downward at an angle. When the necessary depth is attained, the bore path is leveled. As the bore progresses, sections of drill pipe are added. The bore is guided to its exit point where it surfaces. Bore head location and depth are monitored with tracking equipment, which also provides data needed to adjust steering.

After the initial bore is complete, screen is attached to the drill string and pulled back through the initial bore hole. Drilling fluid is used to assist the initial bore and to lubricate and treat the bore hole during pullback. A backreamer can be used to enlarge the diameter of the initial bore if necessary.

Another advantage of directional systems is that they produce less secondary waste than vertical drills. Limiting drilling fluid loss is extremely important at many remediation projects, especially if contaminants are toxic.

Directional boring machine capacity is measured in thrust and pull back - the amount of force available to make the initial bore and pull back material to be installed - and by spindle torque. The higher these numbers, the farther a machine can bore, the larger the diameter of its back reaming capabilities, and the more weight it call pull back. Boring and pull back also are affected by soil conditions.

Proponents of directional drilling equipment for remediation projects expect a rapid increase in the number of horizontal remediation wells. Many government sites are appropriate for horizontal well procedures, and public works staff members will be indirectly involved in other projects initiated by business and industry simply because they are located within the boundaries of their areas of responsibility.
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Publication:Public Works
Date:Sep 1, 1995
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