Saving Endangered Mussels in Missouri’s Big River

By Cody McLarty

When you want to spend a relaxing day outdoors in the Heartland, few places are more peaceful than Rockford Beach Park, just northwest of House Springs in east central Missouri. A low head dam, built in the late 1890s to power the now nonexistent Rockford/Bonacker Mill, still stretches partway across the Big River. This aging dam creates a tranquil waterfall that has enticed patrons of the Jefferson County Parks system for decades.

Photo of old Rockford/Bonacker Mill, near present location of Rockford Beach Park.

Photo of old Rockford/Bonacker Mill, near present location of Rockford Beach Park. (Courtesy of Jefferson County, Mo. Library, Northwest Branch, Special Collections)

Other patrons of the Big River also enjoy the benefits provided by the Rockford Beach dam: a vast, diverse community of freshwater mussels. Yet, unbeknownst to many, just below the babbling waters of the Big River, these abundant mussel species are becoming more endangered every day.

A visual inspection of the dam conducted by the Missouri Department of Natural Resources (MDNR) in January 2015 found that it had experienced heavy deterioration and was in a state of partial failure. Sections of the stone had washed away, leaving voids beneath the surficial concrete shell. Moreover, MDNR noted that if no action was taken, the dam would eventually experience a total breach.

EPA was placed in charge of this project because if the dam were to fail completely, it would result in the release of stored sediment behind the dam, which is contaminated with mining-related metals, and just 200 yards downstream from the Rockford Beach dam are three federally-listed, endangered mussel beds.

Eastern portion of Rockford Beach dam

Eastern portion of Rockford Beach dam

I’m a remedial project manager in the Special Emphasis branch of the Superfund program at EPA Region 7, and was assigned to the Rockford Beach dam project in September 2015. I had been working with the U.S. Army Corps of Engineers (USACE) on several other projects through interagency agreements, so I was familiar with the process and had pre-established contacts within the USACE in the St. Louis area.

A 2009 study of freshwater mussels throughout the Big River found a total of 2,198 living specimens representing 33 unionid species at 19 study reaches in the river. Nine species of state conservation concern were found, including three federally-listed species (Pink Mucket, Lampsilis abrupta; Scaleshell Mussel, Leptodea leptodon; and the recently listed Spectaclecase, Cumberlandia monodonta). The majority of the mussel population in the Big River occurs downstream from the Rockford Beach dam.

A breach or failure in the remaining section of the dam would release trace elements of lead, arsenic, barium, cadmium and zinc – all elements routinely found around older mining and industrial sites. As benthic, filter-feeding organisms, freshwater mussels are directly exposed to contaminants in sediment and surface water.

That kind of significant release would severely impact a large number of freshwater mussel species located downstream, and the Big River has an incredibly diverse mussel community.

Apart from biological impact to the endangered mussel beds, the failure of the Rockford Beach dam could present a myriad of other environmental and safety issues to the surrounding area. That contaminated sediment, if released, would be made available downstream to the floodplain and further into the Meramec River. Those deposits could disperse a concentrated volume of lead into the environment, making it a much larger problem to remediate in the future.

Construction to stabilize western portion of Rockford Beach dam

Construction to stabilize western portion of Rockford Beach dam

In January 2016, EPA entered into an Interagency Agreement (IAG) with USACE to conduct a removal action to stabilize the western portion of the dam. The eastern portion of the dam had already partially failed, which now allows for fish passage. This partial failure was not significant enough to cause the release of built-up contaminated sediment. Under the IAG, the USACE planned, designed, and constructed an interim solution to stabilize the western side of Rockford Beach dam.

Many other state and local agencies provided support to the project, including local fire and police departments, the U.S. Fish and Wildlife Service, Missouri Department of Conservation, and MDNR’s Dam and Reservoir Safety Program.

In Superfund, we often work on projects that can span a lifetime, so it’s nice to be able to start a project, see it run smoothly, and witness the completion. It’s not often that you get to work on a project that allows you to build strong and lasting relations with a community, and at the same time, protect and safeguard endangered species.

About the Author: Cody McLarty serves as a remedial project manager in EPA Region 7’s Superfund program. He mainly works in the southeast Missouri mining district. Cody has a bachelor’s degree in conservation biology from the University of Texas at Austin, and a master’s degree in engineering management from the University of Kansas.

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