It has been determined a portion of the slurry wall surrounding the former Velsicol Chemical Co. plant is St. Louis is leaking contaminants into a nearby residential neighborhood.
An investigation by the U.S. Environmental Protection Agency began last fall after members of the Pine River Superfund Citizens Task force questioned a proposed plan to reuse a portion of the wall.
The new leak was discovered on the east side of the 52-acre parcel between the plant property and the residential area.
The two-foot thick slurry wall was installed in 1982 around the site where the plant, including buildings, storage tanks and piping, was demolished and buried.
The wall was put in place in an effort to contain contaminants that Velsicol and its predecessor Michigan Chemical Co, once manufactured, including such hazardous materials as fire retardants and DDT, among others.
The current leak was discovered after EPA contractor, Dallas-based Jacobs Engineering, conducted hydraulic conductivity testing, groundwater monitoring and a dye-tracer study.
“The dye test revealed the leak,” according to a task force press release.
A document published in 2012 stipulated a new sheet pile wall was to be erected outside the old slurry wall around the entire plant site.
However, after the EPA reviewed its data the agency determined that the “east portion of the wall was doing its job in containing contaminated groundwater and could be reused,” the release stated.
But that information has now been found to be inaccurate.
The new leak is suspected to be located where soil borings previously showed the slurry wall had not been “keyed into” the lower clay till of the site, according to the task force.
“Instead, the depth of the slurry wall had stopped in a sandy area that allowed groundwater to leak into the surrounding land,” the release stated.
The leak is “not a giant plume,” according the Jacobs Project Manager Scott Pratt.
But he did acknowledge some of the contaminated groundwater has leaked into the adjacent residential neighborhood.
However, monitoring wells in that area have found no evidence of contaminants in the drinking water, Pratt said.
The new data now supports the fact that the slurry wall “is not perfect,” he added.
The EPA and Jacobs now plan a second investigation.
Previous investigations on other portions of the wall were conducted in 1997, 2002 and 2006.
The first found the wall was leaking contaminants into the adjacent Pine River resulting in a multi-year, $100 million cleanup of the river near the plant site.