Remediation efforts to prevent contaminated groundwater at Alcoa's Davenport Works from reaching the Mississippi River appear to be working, according to a five-year analysis issued recently (7/28) by the U.S. Environmental Protection Agency (EPA).
The report states the system of wells and pumps around the site are preventing contaminated groundwater from moving offsite. Once captured, the contaminated water is treated to remove the pollutants: polychlorinated biphenyls (PCB's), volatile organic compounds (VOC's), polynuclear aromatic hydrocarbons (PAH's) and metals.
The plant in Riverdale opened in 1948 and is the largest aluminum sheet and plate rolling mill in the world. In 2004, the EPA found plant manufacturing and waste management activities had resulted in the contamination of soil and groundwater at the plant site and in sediment along the shoreline of the Mississippi River.
According to the report, the primary groundwater extraction well is approximately 400 feet deep and has a 40-horsepower pump that delivers 220 gallons per minute to the "air stripper system" to remove the chemical contaminates.
"From October 2014 through March 2016, an average of 9.87 million gallons of groundwater were treated each month," the report states. "Approximately 9 percent of the treated water is discharged to the Mississippi River, and the remaining 91 percent is recycled for plant use." A total of 177.6 million gallons of groundwater was treated between October 2014 and March 2016, the report stated.
As part of the EPA Superfund site review, sampling of tissue from fish in Pool 15 of the Mississippi River has been done to "evaluate trends of PCB concentrations of fish, to compare fish tissue PCB concentrations from areas adjacent to the Alcoa facility and reference areas. . ."
"The analysis of data from the September 2016 sampling concluded that PCB concentrations in fish tissue collected at Mississippi River Pool 15 site were trending lower, were less than or equal to concentrations in reference area and were below performance standards," according to the EPA report.
The EPA human health risk assessment back in 2000 concluded there were no significant risks from the contaminated soils and groundwater to "shoreline trespassers," but there was "an unacceptable risk to recreational boat fisherman and recreational shoreline fisherman based on fish consumption." Consequently, the EPA has focused on comparing fish tissue samples to determine PCB concentrations.
"The selected remedy for the Mississippi River Pool 15 (contamination) is monitored natural recovery with management of on-site media on the Alcoa site property," the report states.
Because of high water on the Mississippi River during the latest site study, the EPA researchers were unable to analyze the shoreline sediment. That work was recommended for completion in the future.
The report also noted that a "vapor intrusion pathway" analysis of the plant must be completed over the next two years.
Alcoa split into two companies in November of last year, Alcoa Corp. and Arconic Inc. EPA is continuing to use the Alcoa name because it was the settling defendant when the superfund review began in 2016. Arconic, which operates the Riverdale facility, is the legal entity responsible for the remediation of the contaminated groundwater, according to EPA.
CLICK HERE to download the full EPA report. (The size of the report pdf file is more than 100 megabytes and may take a minute or more to download.)
