BANGOR, Maine — The smelly, dark and gooey coal tar that will be dredged from the Penobscot River in a couple of weeks, will be “dewatered” and mixed with cement at a temporary warehouse that has recently risen on the waterfront.
The dredging and cleanup of the polluting coal tar, which was deposited along the river’s shoreline years ago, is scheduled to begin Sept. 15 and cost about $7 million, said Eugene McLinn, consultant and geologist who has worked on finding a solution to Bangor’s coal tar problem for 11 years.
Once the coal tar is removed from the water it will be taken to the interim warehouse, which is being constructed behind the new Tim Hortons coffee shop on Main Street, for treatment before it is shipped to local landfills.
“We’ll pump the excess water off the dredged materials and that will be discharged to the sanitary sewer,” said McLinn, who works for Wisconsin consultant firm RMT Inc. “Then the materials will be mixed with a stability material. That will be either portland cement [a common cement] or a proprietary dewatering agent.
“That will turn the sediment from a runny, gooey material to a material much like a weak cement,” he said. “It will be much easier to handle.”
Keeping the odors at a minimum is one goal of moving the tar to the warehouse, which will be enclosed and have negative atmospheric pressure, McLinn said.
“We’ll be pumping the air out of the building, running it through a filter, and then it will be discharged into the atmosphere,” he said. That step should “make it so when we’re handling this very smelly material on land it won’t make as much of an odor imprint.”
Even with the containment efforts, city officials are telling people the project, which is expected to take 15 days, will produce a strong smell in the area.
Coal tar is a known carcinogen and was deposited along the Penobscot River’s bed by Bangor Gas Works, which operated from 1881 to 1963 on land where Shaw’s supermarket now sits. The dark substance is a byproduct of gas manufacturing and was deposited in the river through an old stone sewer that connected to the Main Street gas plant.
Work crews are constructing a containment curtain that will confine the work area to keep the contaminated sediments in the containment area and fish out of it.
Between 6,000 and 7,000 cubic yards of tainted sediment, approximately 10,000 tons, will be removed, treated and trucked to the Juniper Ridge landfill in Old Town or the Pine Tree landfill in Hampden, Tom Gilbert, environmental compliance manager for both landfills, said Friday.
“It will be treated just like any other special waste,” he said. “It will be dropped off and mixed with other waste and then covered daily” to encapsulate the material’s smell.
Because of the amount of waste expected to be delivered over a short period of time, the landfill operators have requested permission to use both landfills, Gilbert said. The permit for Juniper Ridge is in the process of being signed, he said.
“I have a blanket Maine DEP permit approval for both landfills for dredged spoils or sediments,” he said.
The application with the state would basically allow the landfills to take the waste without requiring testing for every 250 tons accepted.
“It’s not necessary,” Gilbert said. “It doesn’t display any hazardous characteristics according to Maine DEP regulations. Testing has verified that.”
The cost of the massive cleanup project will be paid using settlement funds from Citizens Communications Co., a group of third parties a federal judge ruled was responsible for a majority of the cleanup. Bangor tax increment financing district funds will cover any additional costs.
For most of the year, the coal tar deposit is not much of a problem. But when the water warms in August, the deposits rise to the surface in small blobs that stick to objects such as boats and animals. Coal tar, when absorbed through the skin, is known to cause cancer.
After the majority of the coal tar is removed, the polluted area will be capped to seal the unreachable tar along the edge of the river and also seal off the smell. The cap will be constructed of a layer of clay and an impermeable layer that allows gases through but not the remaining tar droplets. Those gases will be vented along the waterfront, and the top of the cap will be created with stones that will resemble a regular Maine shoreline, McLinn said.
“Won’t we be glad to get that stuff out of the river,” he said.