In November 2021, groundwater samples collected by Findett and Cadmus showed that cis-1,2-dichloroethene was detected in City drinking water wells CW-6 and CW-8. The concentration measured within these wells was below the MCL. Additional groundwater samples were collected by Ameren for laboratory analysis from drinking water well CW-6 in January 2022, which indicated that cis-1,2-dichloroethene and vinyl chloride were present in groundwater below the MCL.
In response to the ongoing threat of contamination to these wells, the City of St. Charles Public Works Department shut down well CW-6 in January 2022 and CW-8 in September 2022. In addition, the City of St. Charles contracted hired environmental experts to collect independent groundwater samples and evaluate the risks to the Elm Point Wellfield. Samples collected in March and June 2022 from the drinking water wells indicated that cis-1,2-dichloroethene and vinyl chloride were present in groundwater at concentrations that were below the MCL. But, in September 2022, the concentration of vinyl chloride measured in groundwater from drinking water well CW-6 exceeded the MCL.
Analysis of the data collected by the City of St. Charles and their environmental experts indicates that hazardous chemicals have moved from beneath the Ameren substation towards drinking water well CW-6 to the north and well CW-8 to the south. The concentrations of these hazardous chemicals, including cis-1,2-dichloroethene and vinyl chloride have been increasing over time and are being found further and further away from the Ameren Missouri substation.
While the drinking water is currently safe, the cost of purchasing additional drinking water from the City of St. Louis to meet current demand creates a burden on the City of St. Charles, its residents, and businesses. In addition, the cost of relocating the Elm Point Wellfield to an area free of contamination is estimated to cost more than $40 million. As a result, the City of St. Charles has renewed its demands that USEPA, Missouri DNR, and Ameren Missouri replace drinking water wells CS-6 and SW-8, as well as provide upgrades to the City water treatment plant to remove hazardous chemicals from the groundwater.
Piezometer Monitoring Well PZ-11 Contaminant Concentration Data Table
This table shows concentrations of contaminant cis-1,2-dichloroethene over time as measured by Ameren in their piezometer monitoring well PZ-11. The USEPA has established the maximum contaminant level (MCL) for cis-1,2-dichloroethene at 0.07 mg/L. Anything above this MCL is considered harmful to human health. The contaminant level measured prior to the Record of Decision was below the MCL which is the basis of the EPA filed Consent Decree being finalized. Since that time, the contaminant levels have continued to increase above the MCL. However, the EPA requirements of Ameren to protect the City’s nearby water supply wells have remained unchanged in the proposed Consent Decree.