Typical Diagram of In Situ Air Stripping with Horizontal Wells
Drilling techniques are used to position wells horizontally, or at an
angle, to reach contaminants not accessible by direct vertical drilling. Directional
drilling may be used to enhance other in-situ or in-well technologies such as ground water
pumping, bioventing, SVE, soil flushing, and in-well air stripping.
Hardware used for
directional boring includes wireline coring rigs, hydraulic thrust systems, electric cone
penetrometers, steering tracking hardware, sonic drilling, and push coring systems.
Hydraulically activated thrust equipment capable of exerting more than 40 tons of thrust
is used to push the directional boring heads into the earth. Directional control is
obtained by proper positioning of the face of the nonsymmetric boring head. Slow rotation
of the boring head will cut and compact the geologic material into the borehole wall.
Thrusting a boring head that is not rotating will cause a directional change. The
machinery is capable of initiating a borehole, steering down to a desired horizontal
depth, continuing at that depth, and then steering back to the surface at a downrange
Testing was performed as part of the Mixed Waste Landfill Integrated
Demonstration at Sandia National Laboratories, Albuquerque, NM. Several directional holes
were drilled; a depth of 12 meters (40 feet) was achieved with a maximum horizontal extent
of 174 meters (570 feet).
A DOE field demonstration at the Savannah River site was
performed in FY90 for in situ air stripping (ISAS), a mass transfer process that uses
horizontal injection and vacuum extraction wells to remediate sites contaminated with VOCs
within the vadose zone and soil/ground water in the saturated zone. Air is injected into
the saturated zone through horizontal injection wells placed below the water table. As the
air passes through the contaminant plume, it volatilizes the chemical constituents. This
process performs best in homogeneous soil conditions, while heterogeneities such as
formations, fractures, clay layers, and partial clay lenses hinder performance. Clay
layers often have high contaminant concentrations, while stratigraphy can cause
preferential flow paths and limit the process efficiency. ISAS has been shown to be
effective when some interbedded, thin, and/or discontinuous clays are present. A
full-scale demonstration, including 4% methane enhancement as a bioremediation nutrient in
the injection well, was conducted during FY92, with results to be available in FY93.
Better underground transport modeling and bioremediation modeling are needed. The
technology was also used successfully in the DOE VOCs in the Non-Arid Soils Integrated
Demonstration in Savannah River, South Carolina. Testing of directional boring for
monitoring equipment installation was performed in an actual contamination zone during the
summer of 1992.
Technologies: Field Scale Demonstration Project in North America,
of Remediation Case Studies, Volume 4, June, 2000, EPA
DOE, 1991. Horizontal Hybrid Directional Boring,
FY92 Technical Task Plan, TTP Reference No.: AL-ZU23-J2.
Guide to Documenting and Managing Cost and Performance Information for
Remediation Projects - Revised Version, October, 1998, EPA 542-B-98-007
DOE, 1991. SRS
Integrated Demonstration: Directional Drilling, FY92 Technical Task Plan,
TTP Reference No.: SR-1211-01.
DOE, 1992. Directional Sonic Drilling, FY93 Technical Task
Plan, TTP Reference No.: AL-2311-05.
DOE, 1993. Directional Boring and Thrusting with Hybrid Underground Utility
Industry Equipment, ProTech Database, TTP References: AL2211-16 and
DOE, 1994. Technology Catalogue, First Edition. February.
DOE, 1993. Technology Name: Slant-Angle Sonic Drilling,
Technology Information Profile (Rev. 2), DOE ProTech Database, TTP Reference
EPA, 1994. Manual: Alternative Methods for Fluid Delivery and Recovery,
Prepared by: Murdoch, L., and Wilson, D.D. EPA/625/R-94/003.
EPA, 1997. Analysis
of Selected Enhancements for Soil Vapor Extraction, EPA OSWER,
Kaback, D., and Oakley, D. 1996. "Horizontal Environmental Wells in the
United States: A Catalogue," Colorado Center for Environmental Management
Wilson, D.D., and Kaback, D.S., 1993. "Industry Survey for Horizontal
Wells", Westinghouse Savannah River Company (DOE), Aiken, SC.
Wilson, D.D., 1996. "Use of Horizontal Drilling In Environmental
Remediation: A Horizontal Well Case Study", Water Well Journal, February.
Wilson, D.D., 1996, "Horizontal Well Development Made Easy",
Water Well Journal, October.