Keeping track of aquifer-threatening contaminants and methane gas beneath waste disposal sites is simpler and less expensive with an "inside-out" combination well.
The patented inside-out well design originates from the United States Department of Energy's Idaho National Engineering and Environmental Laboratory (INEEL) and accommodates simultaneous gas sampling and groundwater sampling as well as remediation in the same bore hole - a trick that until now required multiple wells or complex well-within-a-well solutions. The technology is used to monitor volatile organic compounds (VOCs) at INEEL, Sandia National Laboratory, Los Alamos National Laboratory, NASA White Sands, and Tucson Airport.
Conventional designs for combination groundwater and gas sampling wells place the gas sampling tubing inside the well casing, and sampling ports penetrate the casing at various depths. But this physically interferes with the placement of groundwater pumps and samplers lowered within the well and usually requires an inner casing. Turning the well inside out - attaching the gas sampling tubing and ports on the exterior of the casing - eliminates costly problems and streamlines implementation.
A Simpler, Quicker Alternative
The inside-out well is simple to construct, install, and operate. Groundwater and soil-gas sampling activities do not interfere with each other, so the well can be used simultaneously for monitoring and remediation, allowing direct comparison of data. The combination well is assembled easily in the field with a variety of materials suitable for sampling organic contaminants and methane before the casing is placed in the bore hole. Gas-port depths are precisely known, which reduces the potential for plugging the ports with grout after the casing is set. The inside-out well lowers overall costs compared to installing separate bore holes for groundwater sampling and vapor sampling.
Concept Proved at Several Sites
Design feasibility was proven at INEEL's Radioactive Waste Management Complex, a low-level radioactive and hazardous waste storage facility near Idaho Falls, ID, that overlies the Snake River Plain aquifer. Seven wells were constructed to depths of 587 ft. with three to nine gas ports per well to track chlorinated solvent vapors.
Sandia National Laboratory is using the INEEL technology in six vapor-extraction wells ranging from 140 to 486 ft. deep at a 2-ac. chemical-waste landfill. To reduce monitoring-system installation costs, each of the new vapor extraction wells was constructed with three to five subsurface soil-gas monitoring ports by Duke Engineering & Services in Albuquerque, NM, which installed the system. Compared to an alternate system requiring six separate bore holes for soil-gas monitoring, the combination wells saved about $60,000, according to Duke.
A total of 70 combination wells for monitoring and remediation of VOCs have been installed at three other locations in the southwestern US - Tucson Airport, Los Alamos National Laboratory, and NASA White Sands - by Daniel B. Stephens & Associates Inc. of Albuquerque. The INEEL technology reduced the cost of these continuing projects in which vapor sampling has proved superior to soil matrix sampling for VOCs. The approach worked equally well in angled bore holes to reach areas of interest without drilling through the waste site itself.
The Conventional Approach: Two Wells Needed
Efforts to characterize and monitor VOCs and methane often include analyzing the distribution and concentration of VOCs and methane in soil gas in deep vadose (unsaturated) zones beneath a contaminated site. These factors are integral to determining transport to the underlying aquifer and to evaluate potential remediation alternatives such as soil-gas venting.
Generally, both groundwater wells and soil-gas sampling ports are installed in separate wells. Permanent gas sampling ports are usually installed by drilling a bore hole, placing sampling ports at the desired depth, connecting the ports to land surface through small-diameter pipe or tubing, and backfilling the hole with layers of air-permeable material adjacent to the sampling ports and low-permeable material between ports. For deeper installations, flexible gas-sampling tubing can be attached to a guide pipe to provide rigidity and guide the tubing into the well.
Other well completion techniques include installation of well casing with subsequent perforation to allow for discrete sampling. Nested or clustered well construction also can be used to monitor the vertical distribution of VOCs and methane.
A New Approach: Less Cost, More Versatility
The INEEL inside-out well is simple and cost-effective because the gas-sampling tubes are attached to the exterior of the casing while constructing the well. The advantages of using the inside-out well compared to conventional approaches include cost savings, flexibility in sample port placement, versatility in material use, reduced material requirements, and simplified installation and operation.
The inside-out well designs have lower overall costs than installation of two conventional wells. Total savings for a 50-ft. well over its life span is about $2,000, the cost savings increasing with depth of installation. For example, the cost savings for inside-out wells installed at INEEL (more than 557-ft. depth) were more than $30,000 per well compared to drilling separate wells.
Gas-sampling port depth can be modified at any time until the casing is set in the well. A variety of materials, from all stainless steel to a combination of PVC and polyethylene, can be used in the casing and gas ports. Field installation of the soil-gas ports is faster and simpler because the tubing is on continuous rolls; it attaches to the exterior of the casing and doesn't have to penetrate the casing. Field use of the well is simplified because there are no tubes or fittings inside the casing to get in the way when positioning groundwater sampling devices inside the casing.
Extraction and Injection Well Designs
|Figure 4. VOC Concentrates|
|This graph represents the concentration of carbon tetrachloride in a soil-gas sampling well with six sampling ports at a depth of 587 ft. The distance from the source of the VOCs to the well site is approximately 1,500 ft.|
Many sites have contaminants in both the groundwater and the vadose zone, and inside-out wells would allow cleanup of the entire contaminated area. Use of the inside-out well is not limited to withdrawing samples for monitoring. It also can be used for removing gas by gas extraction or injection of gaseous materials for remediation activities. In addition, extraction or remediation can be performed concurrently with monitoring from the same well.
Thus, the inside-out well can be used either for monitoring or remediation, depending on its construction. For extraction and injection techniques, gas-sample tubing size is determined by how much air must be injected or withdrawn. Gas-sample tubing is commercially available in diameters from 3 to 250 mm.
Technology Ready for Commercialization
The combination-well technology is ready for commercialization. Field experience has demonstrated the value of vertical sampling where VOCs in the vadose zone might affect groundwater. We think this is an exciting opportunity with excellent market potential. Companies interested in licensing the combination well technology should contact Tom Harrison at INEEL's Technology Transfer Office at 208/526-1710 or via e-mail at firstname.lastname@example.org.
INEEL is a multiprogram, DOE national engineering laboratory with special expertise in nuclear technology development, systems engineering, and environmental innovation. The laboratory's mission is to provide solutions for engineering and environmental problems for DOE, other federal agencies, and private industry. Lockheed Martin Idaho Technologies Company manages and operates INEEL under an incentive-based contract that encourages technology transfer from the lab into the hands of commercial partners.
Author's Bio: Joel M. Hubbell is an advisory scientist with the Applied Geosciences Unit at Lockheed Martin Idaho Technologies Company.