Sandia LabNews

Basic excavation of chemical waste landfill completed

Ponder this. Two thousand intact chemical containers with unknown contents. Three hundred and fifty corroded, banged-up compressed-gas cylinders. Nine hundred thermal batteries. Three dozen aging munitions components. Several hundred cubic yards of scrap metal, wood, paper, concrete, and plastics. Rocks, in all sizes, amounting to a thousand cubic yards. And 43,000 cubic yards of soil, some of it — about 25,000 yards — stained with chemicals and other contaminants.

In a nutshell, you now know what a dedicated team of environmental workers has been doing for the past two and a half years at Sandia’s Chemical Waste Landfill in the southeast corner of Technical Area 3. The basic landfill excavation, to a depth of 12 feet, was completed this summer without any serious injury to team members.

"Our team is going to be happy when we can take off these plastic suits and hard hats," says Sharissa Young (6134), Environmental Restoration (ER) Team Leader for the project. "But we’ll all breathe a sigh of relief when this landfill project is completed."

All workers at the site were specially trained in health and safety issues, and those working on the landfill surface wore "Level B" protective equipment, which includes synthetic coveralls, hard hats, safety glasses, and self-contained breathing systems. Chemical-vapor monitors and radiation-detecting instruments are also part of the safety gear.

There is still work to do, Sharissa says. But the excavation of the buried contents of the landfill marks a major milestone.

The 1.9-acre Chemical Waste Landfill site was Sandia’s main dump for laboratory-generated wastes and other chemical trash from 1962 until 1985. About half of the landfill contents were documented with disposal records, but no written records were kept for the site until 1975, making the job even more difficult.

"Although the landfill was intended only for chemicals, we’ve found radioactive materials, which we were prepared for, and a huge variety of other things in this landfill," says Don Schofield (6134), the project’s assistant task leader. "That’s why I started calling it the ‘A to Z’ landfill."

During operations, the rule of the day was to use unlined pits or trenches for various chemicals, relying on the depth to groundwater — almost 500 feet — and the remoteness of the location — four miles from the Albuquerque city limits — to create natural barriers to protect human health. That concept failed in part because some of the chemicals dumped at the site moved in a vapor state through the soil to reach the groundwater underlying the site.

Environmental professionals discovered solvents (TCE) in the groundwater below the landfill in 1989 and initiated a number of measures that culminated with the present excavation. Beginning in September 1998, workers used a labor-intensive approach to landfill excavation. Each bucket of excavated material was picked through by hand after dumping on a two-inch mesh screen top. By July of 1999, the process was reengineered using a mechanized screen table and a conveyor belt to improve productivity while maintaining safety. By last summer the landfill was 50 percent excavated (Lab News, June 16, 2000).

"By excavating the main body of debris from the landfill, we’ve removed the source for potential future groundwater contamination," says David R. Miller, Manager of Landfills and Test Areas Dept. 6134. Earlier projects, extracting chemical vapors from the soil between the landfill and the groundwater table, combined with the excavation, eliminate the potential for significant future contamination of the regional aquifer. Groundwater monitoring results during the past year for the site appear to confirm that result.

Some of the soils from the landfill will be returned as fill after sampling is completed to confirm that this is safe. Other soils will be stored, treated, and contained at a site adjacent to the landfill, called the Corrective Action Management Unit (CAMU). More concentrated chemicals, gas cylinders, batteries, and other items will be sent off-site to regulator-approved disposal facilities. Investigations are under way to determine if some of the precious metals recovered from the landfill can be recycled.

In some places soil contamination reaches deeper than the 12 feet excavated, Sharissa says. Sampling will help define several areas that can be safely excavated to deeper depths. In some cases, however, complete excavation of all contaminated soils will not be possible.

"Long-term monitoring will be needed at the site, but I believe we are going to have a successful closure," Sharissa says.

After the clean portion of soils from the landfill is returned to the excavation, backfilling will be completed with clean soil and an engineered cover will be put in place as part of the long-term maintenance. .