Mercury cleanup at Pena Blanca to start Oct. 6

Crews are scheduled to begin the draining of Pena Blanca Lake on Wednesday, Oct. 6, as part of a mercury-removal Superfund project.

Forest Service contractor Red J. Environmental from Joseph City, Ariz., will begin “setting up camp” to subsequently drain the 57-year-old artificial lake, said Maria McGaha, U.S. Forest Service regional environmental engineer.

It is estimated it will cost between $1.3 million and $2.9 million to remove the mercury and heavy metals that have entered the lake from old mining activity.

The Forest Service will tap into Comprehensive Environmental Response, Compensation and Liability Act program funding to clean a site that, at times, has had the highest concentration of mercury in fish in the United States.

McGaha cautioned area residents that roads leading into the 49-acre fishing lake that is about 15 miles northwest of Nogales and west of Rio Rico, will be congested with vehicles and heavy equipment. “The lake will be closed, but Ruby Road and White Rock Campground will remain open,” she said.

The contractor will bring in equipment and batteries to run the pumps to drain the lake into Pena Blanca Canyon and subsequently Agua Fria Wash west of Rio Rico.

Once the equipment and crew are ready, the weather will need to remain dry long enough to drain and scrape the lake and remove approximately 12 feet of contaminated sediment and, if possible, an additional layer of mud under the sediment from a catchment area that, when full, is around 22 feet deep in some areas.

Number of uncertainities,/b>

October weather is historically uncertain due to Pacific tropical storms. The project also faces a number of uncertainties based on money, said McGaha. “We have a little under $1.3 million approved for FY 2008. We’d like to get another $1.6 million for FY 2009 to complete the job, but I have no crystal ball to tell whether we will get it, so we will be working in phases.”

McGaha said, “Phase one, we drain 332 million gallons of water. Then we move about 100,000 cubic yards (roughly 100,000 tons) of contaminated sediment onto a 10-acre ‘consolidation cell’ (the old motel-resort site). If we do not have the FY 2009 funding available, then we place a red geo-membrane liner over the sediment so we know it is contaminated beneath that and place up to 12 inches of earth over it as a temporary cap.”

“Whenever the phase two funding is available — hopefully while the work goes on under phase one — we excavate another 155,000 cubic yards of soil from under the sediment, move it on top of the sediment and cap that. If we have to return later then we will remove the soil and natural materials cap and place the lake soil on top.”

And if the funding is unavailable for 2009 and they have to go back after the lake is partially or completely filled?

McGaha says that the contractor will have dug a sedimentation basin in the canyon entering the lake that would capture future mercury above the lake. “We think we removed the source of mercury in 2000 when we excavated old mine wastes upstream,” she said. “But it is possible that we could have to drain it again before the work is complete. Both weather and money are difficult to predict.”

Projects in New Mexico

She adds that heavy-metal remediation near the northern New Mexico Molycorps mine site has been somewhat similar and that work advances incrementally year by year with caps created and removed to capture more contaminated soil. McGaha pointed out that Bear Lake and Roberts Lake in the Gila National Forest in New Mexico, also once contaminated with mine wastes, as successful similar cleanup precedents. Arivaca and Parker Lake also have some mercury contamination problems in Southeast Arizona.

“Our goal is to be able to remove the danger signs surrounding the lake so fishermen can eat the fish — even if those fish are much smaller for a while after the remediation is complete,” McGaha said.

Monitoring of the consolidation cell where the mercury-laden sediment is deposited could be an important consideration. There is no way of knowing what the concentration of mercury at the site will be. When it is removed from the water it will be exposed, at least temporarily, to oxygen that increases toxicity of the element in the form of methyl mercury.

McGaha said that monitoring, at this time, “will consist of visual observation for five years of the condition of the cap, which will consist of earth and on-site natural materials.”

The Forest Service could put in monitoring wells up and down-gradient of the consolidation cell to see whether surrounding groundwater is and remains uncontaminated. The agency had not planned to do that.

Such wells can vary in costs from about $30,000-$50,000 presuming they are not extremely deep and they are analyzed for years afterward for the contaminants in question — mercury and heavy metals, in this case.

McGaha said, “We could always put in monitoring wells around the consolidation cell; we have done so at Red River (Molycorps in New Mexico). It is something to consider as the project unfolds and we think more about it.”

Dick Kamp is the Environmental Liaison for Wick Communications Co. Reach him at bepdick@att.net.