Mercury cuts on the ground not enough
MERCURY Reducing mercury in wastewater hasn't solved contamination in lakes and fish.
By John Myers
Duluth News Tribune
Published February 26, 2006
When you raise your face into that first spring rainfall, remember this:
The water splashing off your head is higher in mercury contamination than the treated sewage water leaving the Western Lake Superior Sanitary District.
And therein underscores an environmental conundrum.
The WLSSD, like all large Great Lakes wastewater plants, is under federal order to reduce mercury in its discharge to 1.8 parts per trillion. It's an effort to keep Lake Superior free from mercury that builds up in fish and makes them unsafe for humans to eat.
But that wastewater standard is so far below the level of mercury in rainwater that falls on the Northland -- now about 12 parts per trillion -- that many experts say it's impossible to meet.
The WLSSD receives untreated wastewater that averages about 100 parts per trillion mercury. Its treatment process reduces that to about 2.6 parts per trillion, on average, before it flows into the St. Louis River.
That 2.6 parts per trillion (2004 average) is down from 20.6 parts per million a decade ago and is among the lowest of any wastewater plant in the region. And it reflects more than a decade of efforts to get mercury out of the waste stream -- reducing mercury from the papermaking process, dental and medical offices, school labs, consumer products and more.
The level of mercury leaving the WLSSD pipe in Duluth's West End is lower than the level in the river upstream, now about 3.1 parts per trillion.
"We could cut our emissions to zero and it still wouldn't affect the river or the lake or the fish. It wouldn't make a difference," said Tim Tuominen, engineer for the WLSSD. "That doesn't mean we won't keep trying. We'll keep looking at options... But it does mean that it's going to take a local, state and global effort to cut mercury (emissions) or we're never going to get there."
Falling from the sky
Gary Glass, retired U.S. Environmental Protection Agency mercury researcher in Duluth, said it doesn't make sense to require mercury levels in wastewater to be lower than levels in the river or falling rain. Efforts should first be aimed at getting the mercury out of the rain, he said.
That would require cutting mercury in industrial air emissions, such as coal-burning power plants.
"The only way to reduce mercury in the river and lake is to get it out of the rain. But we aren't doing that yet," said Glass. "It's lunacy that our government has a (mercury) standard for lakes but then no standard for the rain that fills the lakes up."
Still, the federal mandate for sewage effluent remains. In just 12 months the standard will drop from 21 parts per trillion to 1.8 parts per trillion. Kurt Soderberg, WLSSD executive director, said it's not likely they'll meet the March 2007 deadline. The Hibbing wastewater plant, and Minnesota Power's Laskin Energy Center wastewater treatment facility, are the other Lake Superior basin plants expected to need a variance.
WLSSD officials already are working with the Minnesota Pollution Control Agency to seek a variance to the federal rule. Ohio and Michigan plants already have been granted a similar variance.
"We look at where they have gone and are going, whether there's been a good-faith effort to get there," said Gary Kimball of the PCA's standards unit. "WLSSD has been who everyone looks to for mercury reduction ideas. It's likely if they say they can't get there by the deadline it probably can't be done."
In the meantime, efforts to cut mercury from wastewater continue. The WLSSD is looking at chemicals that might bind up the mercury and allow it to be captured before it leaves the plant.
The district also is spending $4.1 million to upgrade several last-step holding tanks that capture suspended solids in the wastewater that sometimes flow out of the plant during storms. Most of the mercury in the wastewater is tied up in those solids.
WLSSD has contracted with the Natural Resources Research Institute's Coleraine Minerals Lab to investigate possible mercury filters. The WLSSD also is looking at test projects for end-of-pipe mercury reduction by the University of North Dakota and Ferrometrics Inc.
"It hasn't been practical at all in the past, but we're always looking," Soderberg said.
Minnesota has reduced mercury in products and garbage by 70 percent since 1990, from 8,881 pounds annually to 739. But airborne mercury emissions have increased, from 1,667 pounds to 1,923, mostly as the economy has required more electricity.
Soderberg and others welcomed word last week that Gov. Tim Pawlenty was changing course and now supports state legislation to curb mercury air pollution that originates within the state, especially from coal-fired power plants. The PCA previously backed a course that waited for stronger federal laws.
The state's goal is to make all fish in Minnesota's lakes safe for all people to eat. It's still not clear what steps will be taken to make that happen.
While state sources are only part of the total mercury that falls here -- as much or more mercury comes from regional, national and even global sources as far away as China -- environmental groups say Minnesota should be leading the way.
"The local sources are probably a bigger portion of the problem because the mercury is more active, closer to the source" of combustion, Glass said. "The notion that we can't make a difference by cleaning up our own sources is hogwash."
Mercury doesn't disappear
Thanks to efforts to get mercury out of consumer products, dental waste and industrial recipes, such as paper pulp processing, the amount of mercury coming into the WLSSD has declined rapidly in recent years, from 180 parts per trillion in 1995 to 100 parts per trillion in 2004.
But mercury -- from rainwater, schools, households and other sources -- continues to flow into the plant. Much of the mercury captured by the WLSSD leaves the plant inside a sewage sludge fertilizer product called biosolids. That treated sludge, which has been anaerobically digested to kill disease-carrying pathogens, contains a small amount of mercury per ton that does contribute to the ground mercury in the soil.
The level of mercury in the material spread by the WLSSD dropped from 1.3 parts-per-trillion in 1995 to 0.37 parts per trillion in 2004. It remains far below EPA standards.
While some opponents of sewage sludge fertilizer say the mercury levels are too high, WLSSD officials say it would take regular applications for 500 years to raise soil mercury levels to EPA limits.
Still, the PCA's Kimball noted, mercury is being reintroduced to the environment in the sludge, and some of that may end up moving into the atmosphere. It would be best, he noted, if mercury didn't flow into the plant to start.
"The only way to prevent having mercury to deal with is not have it going out to begin with," he said. "There's no magic way to get rid of it once in becomes part of your process."