For at least 60 years, a man-made ditch at the Sparrows Point steel mill carried stormwater and polluted discharge from steelmaking operations across the vast property.
Known as the Tin Mill Canal, it was once filled with murky water that deposited contaminants in the soil around it.
The canal represents one of the biggest environmental challenges for Tradepoint Atlantic, the company that bought the old mill and is turning the site into an industrial campus. Company officials say the canal will flow through a new retail center on the property.
Since January, contractors have been gradually removing the contaminated soil and re-lining the canal bed. On Wednesday, Tradepoint officials showed off their progress to government regulators and the news media.
"We have a lot of work to do, no doubt," said Eric Gilbert, Tradepoint Atlantic's chief development officer. But he said the cleanup of Tin Mill Canal marks a "major milestone" in the company's effort to undo a century of environmental damage to the Sparrows Point peninsula.
Tin Mill Canal was dug in the 1950s and expanded in the 1960s to carry stormwater to a wastewater treatment plant.
But more than just stormwater flowed through it. The canal also picked up discharge from manufacturing facilities at the steel mill. Contaminants that eventually settled to the canal bottom included oil, grease, arsenic, benzene and polychlorinated biphenyls — also known as PCBs — according to a consultant's report on file with state regulators.
To clean the canal, contractors working for Tradepoint Atlantic dammed off sections, drained the water, excavated steel slag and contaminated soil, deposited clean fill dirt and lined it with large white rocks called riprap. Since January, the process has been repeated section-by-section along the 1.4-mile-long canal.
The work is 55 percent done and is expected to cost $9 million by the time it's completed next year.
"There's real progress being made here," said Ben Grumbles, Maryland's secretary of the environment. "It's gratifying to see the progress Tradepoint is making."
Some environmentalists have questions about the work. Two advocacy groups — the Chesapeake Bay Foundation and Blue Water Baltimore — have raised concerns that the cleanup of the canal doesn't address groundwater that may be contaminated via seepage from the canal over the years. That groundwater eventually filters out to nearby Bear Creek.
Paul Smail, an attorney with the bay foundation, said his group has been pressing the U.S. Environmental Protection Agency to require a thorough evaluation of possible polluted groundwater, but has "hit a brick wall" on that front.
"You need to do this now because the remediation and construction is happening apace," Smail said in an interview.
Cecil Rodrigues, deputy regional administrator for the EPA, said a groundwater study is being planned, and said that if groundwater needs to be cleaned up, it can still happen even as more of the property gets paved and covered with buildings.
Rodrigues said the EPA's priority is for Tradepoint to fix sources of pollution, "then we can work on historical contamination that exists."
The demonstration of the Tin Mill Canal cleanup comes as Tradepoint prepares to officially ask Baltimore County to authorize a public financing plan to pay for additional roads, water pipes and sewer lines at the 5-square-mile property.
Tradepoint, which bought the property in 2014, has demolished most of the steel mill buildings and is transforming the property into an industrial campus with port, logistics and manufacturing uses. The company has landed tenants including FedEx, Amazon and Under Armour, which have built distribution warehouses.
But company officials say they need help in building out the infrastructure in order to lure manufacturers to the site.
If approved by the Baltimore County Council, the state would issue up to $150 million in bonds to pay for the infrastructure work. Tradepoint would pay the bonds back through future property taxes that otherwise would be paid to the county. Tradepoint's property value, and therefore its property taxes, are expected to increase as development continues.
The arrangement, called tax-increment financing, is rarely used in Baltimore County and can be controversial, because the county would lose out on a portion of the property taxes it would receive.
The Baltimore County Council could start considering the tax-increment financing proposal as soon as next month.