June 22, 2010By Stephanie Choate Observer staff
Environmental Protection Agency staff is drilling deep below the surface of the ground near Commerce Street this week to learn more about Williston’s Superfund site.
A crew is carrying out a technique called vertical profiling, drilling down 30 or 40 feet to a layer of clay and taking groundwater samples. The samples are then processed at the EPA’s mobile lab to see where the most contaminated water is.
“It’s all going toward giving us a better understanding of the nature and extent of contamination of the site,” remedial project manager Karen Lumino said.
A plume containing high levels of compounds used to clean metals, including trichloroethylene and tetrachloroethylene, has contaminated groundwater beneath Commerce Street and South Brownell Road. The area became a federal Superfund site in 2005.
Buildings in the area use municipal water rather than wells, however, so there is little current health risk, according to the EPA.
The EPA, which has been drilling since last week, will wrap up the vertical profiling Friday after testing approximately 30 sites.
Earlier this summer, the EPA completed a geophysical survey of the area, where it determined the depth of the clay layer. The clay layer isn’t even, so finding depressions in the clay where the contamination might have “come to rest” will help characterize the plume, Lumino said.
Lumino said the results still need to be processed, validated and tested for quality control. EPA officials are also working to determine the exact parameters of the plume.
“The phase we’re in right now is remedial investigation,” she said.
Lumino said the clay seems to be acting as a barrier, stopping the contamination from getting into the bedrock. She also said the contamination seems to be settling deep underground, on top of the clay layer, which would reduce the risk of vapors causing any health risks.
The EPA plans to analyze the results from the survey and vertical profiling. In August, it plans to conduct soil borings, taking a cross-section of the soil in the area.
Later this fall, the agency also plans to dig more groundwater monitoring wells, since many of the existing ones are either unusable or were paved over.
By this time next year, Lumino hopes to have completed a risk assessment. Once she knows what the risks are, she will conduct a feasibility study to see what remedies, if any are needed, would be best. The feasibility study would likely take another year to complete.