Nyanza cleanup a long haul
Federal environmental regulators thought they knew how to clean up the hazardous wastes at the site of the former Nyanza dye plant in Ashland. But the project has taken unexpected twists and turns, with ground-water contamination emerging in recent years as a major issue.
``It's a problem we didn't recognize as a serious one a while back, and now we do, but we're here," said the Environmental Protection Agency's Jim Murphy , the cleanup project's community involvement coordinator. ``We're not going anywhere, and we're trying to address it as quickly as we can."
The Nyanza plant closed in 1978, the last in a series of companies that made clothing dyes and related chemicals on the site beginning in 1917. Over the years, waste chemicals including mercury, arsenic, benzene, lead, and acetone were dumped onto a nearby hill. The chemicals ran back down the hill in colorful streams that local children played in, an activity that state officials believe led to an increase in cancer rates in town.
Five years after the plant closed, the EPA began its battle to clean up the hill, making Nyanza one of the first Superfund sites in the country. Over the next two decades, workers dredged contaminated soil out of nearby wetlands, and the hilltop dump site was sealed off with a 13-acre multilayered cap and a 50-foot-deep trench.
The EPA then focused its efforts on cleaning up the soil and water around a former underground storage vault on the plant grounds, in which chemicals were temporarily stored before being dumped on the hill. In 1994, the agency installed pumps to pull out what was believed to be mildly contaminated ground water, but it discovered something worse: Dense nonaqueous-phase liquid (DNAPL), a concentrated oily soup of chemicals that had leaked out of the concrete vault over the years and settled into an 800-foot-wide, six-foot-deep pool, beginning about 50 feet below the surface and extending 20 feet or more into the underlying bedrock.
``We were totally unprepared for that," said Jim DiLorenzo, EPA cleanup project manager . ``It degraded the seals around the pumps and the pumps froze. So we had to shut the system down and reevaluate."
During that reevaluation, the EPA discovered that the pool was directly in the path of ground water that flows under the town. Directly above the pool, and for part of the ground water's slow trip toward the Sudbury River, the cracks in the bedrock are deep enough, and numerous enough, that little contamination makes its way to the surface.
But those cracks decrease in depth and number north and east of the pool, so that when the contaminated ground water reaches an area roughly bounded by Tilton Avenue, Cherry Street, Water Street, and the river, its toxic vapors, most notably the carcinogen trichloroethene (TCE), seep out of the soil into the basements of about 40 buildings.
While the drinking-water supply is safe -- DiLorenzo says that no one in the area of concern uses ground water for drinking -- the agency is taking a conservative approach to the vapor intrusion.
Even though the federal standard for TCE toxicity is 134 parts per billion, the federal cleanup project is using a stricter standard of 2 to 43 parts per billion in the cleanup. (In previous testing in 1998 and 2004, TCE levels ranged from 1.3 to 7.3 parts per billion.)
Beginning next spring, workers will install vapor mitigation systems, which DiLorenzo described as heavy-duty versions of systems commonly used to disperse radon gas. The systems, which cost about $10,000 each, will be installed at no cost to property owners in the 40 homes and businesses where TCE intrusion has been identified or is believed to be a risk.
Additionally, DiLorenzo said that a new round of testing will be conducted beginning next month, both in the previously identified area and in several other homes and businesses outside it.
The cleanup is expected to go on for many more years. DiLorenzo said that the EPA is weighing a couple of different approaches to removing the pool of DNAPL. Digging it out is risky because it could fracture the bedrock and disperse the toxins even further, he said, while readily admitting that the other option under consideration -- conveyor-belt-like machines that dip down into the DNAPL and pull it out a few drops at a time -- might not work.
Also, no one really knows how much DNAPL is down there; they'll know they're done, he said, when they stop pulling it out of the ground.
Ground water moves very slowly, so even if the source of contamination is shut off, it will be years before what's already moving through the ground will dissipate.
DiLorenzo and Murphy will update residents on the Nyanza cleanup at a community meeting on Thursday at 7 p.m. at the Ashland High School auditorium on East Union Street. EPA project manager Cheryl Sprague will also be on hand to detail plans for cleaning up contamination of the Sudbury River.
