$1 million project reduces Mirror Lake pollution
The environmental problems at Dover's Mirror Lake were once so severe that the water was tainted and the bottom sediment was polluted by mercury, polychlorinated biphenyls dioxin and other pollutants. The banks were eroding, invasive plants were taking over and you couldn't eat the fish.
But a year into an innovative state project to reduce pollution and restore habitat, even the scientists who worked on the project are surprised by the outcome. Pollution levels — in the water, fish tissue and sediment — are down dramatically.
"We are seeing a 60 percent baseline improvement after the first year, which is significant," said Rick Greene, of the state Division of Watershed Stewardship.
The experimental restoration project cost $1 million. The tidal lake flows to the St. Jones River and then to Delaware Bay. Canada geese and ducks use the waterway as a resting area and bald eagles are common.
The pollution came from industrial waste and storm water runoff, and is typical of pollution concerns in urban areas, Greene said.
Before the project started, pollution levels were decreasing, but the rate was so slow that state environmental officials estimated it would take years for a natural breakdown, Greene said.
"We wanted to speed that up," said John Cargill, with the state's site investigation and remediation branch.
"It was going to take several decades before we could lift the fish advisory," Greene said. "We knew that the sediments had to be addressed."
So Cargill and Greene went looking for alternatives. They looked at de-watering sections of the lake and removing the most polluted sediment. They looked at capping it in place. And then they looked at research on treating pollution in place.
Crews and volunteers in fall 2013 spread 79 tons of activated carbon granules, pelleted with a sand and clay blend to make them heavy enough to sink into the sediment, in the lake. They stabilized the eroding shoreline with coconut fiber logs and created a wetland planted with native species.
But the big idea was to see if pollution could be treated in place. At Mirror Lake, the theory was that the sand and clay would wash away from the pellets and the activated carbon would absorb and detoxify the toxins in the sediments — the most serious of the pollution concerns.
State scientists settled on SediMite —activated carbon pellets similar to the contents of tap water carbon filters. They also explored a $1.5 million excavation project. Disposing of the sediment would have added even more to the cost.
The SediMite treatment, developed by cleanup researcher Upal Ghosh and his team at the University of Maryland, Baltimore County, was used on a smaller project at Aberdeen Proving Grounds and other federal facilities. But it had never been used in a state-funded cleanup until the project at Mirror Lake.
Sediment, water and fish samples were taken just prior to the application of the pellets. Then officials returned a year later and ran the same series of tests. On the retest, they found the 60 percent reduction in baseline pollution.
At this rate, there could be at 70-90 percent less pollution in three to five years, Greene said.
"We're well on our way to meeting our goal," he said.
But state officials had another aim in mind.
"We wanted to do this project and we wanted to learn from this project," Cargill said.
The two scientists now know that is is possible to treat serious urban water pollution in place and they are considering other locations where it might be possible. Among the possibilities: a wetland restoration project in Wilmington, at a site in Little Mill Creek, and perhaps along Red Lion Creek. Whether the same type of treatment will be used has yet to be decided.
There are many sites throughout the state that are tainted with legacy pollutants, Greene said.
"Things are getting better ... but it's going to take a long time," he said. "For all these legacy toxins ... it's going to take decades. We're looking to speed that process."
The results at Mirror Lake were so good, Greene said, "we changed the trajectory from 30, 40, 50 years to three to five years."
Reach Molly Murray at 463-3334 or mmurray@delawareonline.com. Follow her on Twitter @MollyMurraytnj.
Mirror Lake project
THE PROBLEM: Mirror Lake in Dover had become polluted with mercury and other pollutants over the years.
WHAT WAS DONE: Crews in 2013 added 79 tons of activated carbon granules and improved the shoreline.
THE RESULT: Pollution levels have decreased about 60 percent; the technique is being explored for other polluted areas.