LANDFILLS: SEAMIST Monitors Landfills For Hazardous Wastes So, let 'eym at it!

William D. Siuru Jr.

SEAMIST (Science and Engineering Associates Membrane Instrumentation and Sampling Technique), an innovative technique for landfill monitoring and sampling of radioactive and hazardous wastes, has been developed over a four year period by Science and Engineering Associates Inc. of Santa Fe, N.M.

SEAMIST is a flexible well liner with an impermeable tubular membrane. The membrane, made of coated fabric or synthetic film, is deployed from a holding canister that uses air pressure to force the membrane into the landfilling borehole being sampled. The membrane then inverts and presses along the borehole sides as it is being pushed down the hole.

After monitoring, the membrane is manually reeled into the canister where it is inverted to its original shape for reuse. This process contains contaminants so they do not pose a threat to workers or contaminate other ground levels.

Eastman Cherrington Environmental, Santa Fe, N.M., current owner of the SEAMIST patent, is investing to develop the technology further and market it on a wide-scale basis. "SEAMIST has many applications beyond monitoring hazardous landfills," said Carl Keller, the inventor of SEAMIST, who now works with Eastman Cherrington.

Most arrangements or combinations of sensors and samplers can be attached to the membrane, according to Eastman Cherrington. The membrane's length can be tailored to the particular borehole length and sensing requirements. SEAMIST can be used for insitu sampling of subsurface environments and monitoring of hazardous and nonhazardous materials. Sensors include temperature and pressure devices, chemical detectors and vapor samplers. Samplers and sensors to detect contamination or measure soil pa rameters can be attached externally.

SEAMIST has been used as part of the Mixed Waste Landfill Integrated Demonstration (MWLID), which is sponsored by the Department of Environment's (DOE) Office of Technology Development and hosted by Sandia National Laboratories. MWLID is aimed at demonstrating cleanup technologies for mixed wastes (both radioactive and hazardous) in landfills, especially in arid areas. The MWLID demonstration site, Sandia's Chemical Waste Landfill, which closed in 1988, is a "real world" environment used to test new sampling and remediation methods. Sandia researchers used the system to tow cameras and tools in horizontal boreholes. Other tests included soil liquid and multipoint gas sampling plus air permeability measurements. In the testing, SEAMIST was used to line up 10-inch diameter by 110-foot long boreholes and 4-inch diameter by 400-foot horizontal bores.

SEAMIST systems also have been used at other DOE sites, including the Savannah River in Georgia, Los Alamos, N. M., Lawrence, Calif., and Hanford, Wash. It has been used by the U.S. Department of Agriculture in Utica, N.Y., Nebraska and by the city of Tucson, Ariz. Some of the measurements include volatile organic contamination distribution, tritium plume movement and sampling of gases in borehole sections.

SEAMIST offers advantages over other sampling and monitoring techniques for toxic and radioactive landfills, according to Keller. It eliminates lengthy, costly procedures for retrieving instruments for repair or at the end of the sampling and prevents problems with cross-contamination of samples. The system allows pinpointing samples to the exact location within the borehole. The many sampling ports improve the quality and quantity of the data. SEAMIST increases the speed of data results, which may take a few months with conventional methods, to a few days, according to Cecilia Williams, Sandia project manager.

On the other hand, different techniques may require drilling holes to identify the hazardous landfill boundaries and take samples, which may take weeks to analyze. Afterward, the boreholes must be sealed, an expensive and time-consuming operation, to prevent contamination of lower ground levels or workers.

The cost of SEAMIST varies depending on sensor/sampler sophistication, but typical costs are between $20 to $40 per linear foot. The canister unit costs approximately $2,000, but one canister can support multiple SEAMIST membranes.