Division of Water
Wastewater Treatment Plant at City of Cumberland Disrupted by Presence of Mercury
FRANKFORT, Ky. (Nov. 2, 2005) – During a recent rehabilitation project at the city of Cumberland’s wastewater treatment plant, contractors discovered mercury had been released in one of the treatment units. As a result of the mercury contamination, plant rehabilitation is on hold, allowing partially treated sewage to flow into Poor Fork of the Cumberland River at an average rate of 200,000 gallons per day.
The city of Harlan’s drinking water plant, 20 miles downstream, is the closest water intake to the discharge point. No mercury has been detected in the water samples taken and analyzed by the Division of Water (DOW) at the intake.
Inspectors from the Divisions of Water and Waste Management have been investigating the source of the mercury since Oct. 19, following the city of Cumberland’s mandatory notification to the Department for Environmental Protection. It has been concluded that the likely source was an old mercury seal of a mechanical bearing and that the majority of the release was contained in the trickling filter unit of the plant. The DOW sampled effluent from the plant on Oct. 22. Analyses of the samples measured 0.003 milligrams per liter (mg/l). The water quality standard for protection of fish for human consumption is 0.000051 mg/l.
A separate contractor hired by the city of Cumberland to clean up the mercury recovered three pounds of the toxic metal. The contractor then quit, advising the city that this level of mercury work was beyond his capabilities. The total amount of mercury that needs to be removed is unknown.
The mercury was detected in the drain grate of a trickling filter, a basin 8 feet deep and 35 feet in diameter. A rotating arm sprays liquid over the filter, and it trickles through for microbial breakdown. Mercury was originally contained in the seal of a bearing on the rotating arm. That bearing was replaced at some time in the ’90s, but before its replacement it was refilled several times in the ’70s and ’80s, leading investigators to suspect that mercury was released into the filter over a considerable period of time.
Mercury was also detected in the two sludge-drying beds at excessively high levels. Sludge in one of those drying beds has been present at the site since 2003. Due to detected levels, an additional test is expected to classify the sludge as a hazardous waste. The mayor of Cumberland has said that the city does not have the funding for a cleanup and is looking for state and federal assistance.