The problem began decades ago, when the Onondaga Lake and its tributaries were used as dumping grounds by various industries. This ultimately led to around 165,000 pounds of mercury residing in the lake, leaving Onondaga considered to be one of America’s most polluted lakes until the government ordered a cleanup effort. One main goal of this three year clean up project was to reduce the amounts of mercury in the water and fish.
Other major parts of the cleanup included ongoing dredging of over 2 million cubic yards of lake muck, along with sealing the lake bottom by layering-on three feet of sand and dirt. This was initiated to reduce the rising mercury from the lake bottom that usually occurs every fall. Adding wildlife and building a retaining wall to prevent contaminated groundwater from entering the lake were additional tactics used throughout the project. The real highlight of the project, however, was the experimental solution to decrease mercury levels in the parts of the lake that were too deep to dredge and cap.
The resolution to reducing the mercury levels was using an agricultural fertilizer – calcium nitrate – which contained a specific type of bacteria and injecting it into the water. This fertilizer locks the mercury in the sediment at the bottom of the lake and doesn’t allow it to spread into the water, thus getting in the food chain. Scientists figured out that the nitrate would crowd out the bacteria that makes methylmercury, and it would also help the mercury bind to iron in the lake-bottom muck. This discovery was crucial to the project because it provided a solution to cleaning up parts of the lake that were too deep to dredge and cap.
The experiment involved years of research with scientists trying to figure out a way to cover several miles of lake bottom with enough nitrate to stay in place long enough to get the job done. The scientists at Parsons Corp. and Atlantic Testing Laboratories had to convince Honeywell, who heavily funded the project, and the state Department of Environmental Conservation that it had potential before the project could be funded. Once funded, Atlantic Testing Laboratories created metal diffusers which were attached to the end of large hoses. The diffusers had one-inch holes drilled into them, so that when they were lowered into the water the nitrates could seep through the holes and mix in with the lake water. In 2011, the hoses were lowered into the lake by a crane attached to a barge, which was motored out once a week for three months, dispersing 4,800 gallons of calcium nitrate. This was repeated in 2012 and this year’s round of treatments just ended in early October.
The experiment has turned out to be one of the major environmental engineering successes of the year, and some scientists say it could be a future model for mercury cleanup in lakes around the country. The success rates for the project were dramatic, with mercury rates dropping by 94% when tested in Fall 2011. It’s still too early to tell how much this project will cut the amount of mercury in fish, and when they will be safe to eat again, but the scientists involved remain optimistic. The fact still remains that this was a huge win for the environmental engineering industry, Honeywell, and the people affected by the mercury problem in Onondaga Lake.