Landfill Tracer Tests (SEAtrace^TM)

Description

Sandia National Laboratories (SNL) and Science and Engineering Associates, Inc., (SEA) have developed a subsurface barrier assessment system called SEAtrace^TM. It works by injecting a non-toxic tracer gas into the barrier. The gas diffuses through the barrier and through any breach into the soil (vadose zone) surrounding the barrier. A vapor sampling system outside the barrier is used to detect the tracer gas. Measured concentration histories from the various sampling points are used in a model to find the probable location and size of the breach.

Traditional monitoring techniques rely on groundwater monitoring, requiring the contamination of groundwater to indicate containment failure. The SEAtrace^TM System uses a low-cost, early detection method both to verify subsurface containment emplacement and to monitor long-term performance. The system is non-destructive and minimally intrusive. It can sample up to 64 ports and analyze barrier integrity within 30 minutes. The system is robust, and unattended, it can monitor a site for months.

Limitations and Concerns

During the installation phase, port locations and depths should be surveyed immediately after the installation of ports.

Prediction of leak sizes may be inaccurate, as it is a function of many of the assumptions made in creating the model.

The accuracy of the results is a function of the model used and the monitoring point locations.

Identifying multiple leaks close to a single port needs to be improved.

Applicability

SEAtrace^TM is a monitoring tool designed to verify the integrity of subsurface barriers in soil, mostly around landfills.. Underground barriers are installed around leaking landfills, underground storage tanks, and other types of hazardous waste sites to prevent the movement of contaminants in either the liquid or vapor phase. These barriers often give project proponents time until a decision can be made about a permanent remedial strategy. However, conventional monitoring techniques do not provide the degree of resolution required to assess the continuity and integrity of an in-situ barrier.

Technology Development Status

This technology is commercial.

Web Links

http://costperformance.org/monitoring/pdf/seatrace_2.pdf

http://www.sandia.gov/Subsurface/factshts/ert/bvms1.pdf

Other Resources and Demonstrations

Three field demonstrations have been conducted: at the Dover Air Force Base, Jet-Grouted Barrier Demonstration; Brookhaven National Laboratories, Viscous Liquid Barrier Permeation Grouting Demonstration; and the Brunswick Naval Air Station. At Brunswick, the technology was used to validate a section of a 3-foot thick, 2,300-linear-foot soil-bentonite slurry wall placed around a landfill. Field tests have demonstrated that the SEAtrace^TM system is able to identify multiple leaks, locate leaks to within 0.5 meters, and to size leaks to within 0.15 meters.