Background/ History
The SunEdison Semiconductor LTD site, formerly MEMC Electronic Materials Inc., is located on 185 acres at 501 Pearl Drive in St. Peters. In 1959, Monsanto Electronic Materials Corp. began manufacturing silicon wafers at the site for electronic products. MEMC Electronic Materials Co., a separate company, purchased the facility assets in April 1989 and continued the same operations. Operations included research, growing semi-conducting silicon crystals and producing polysilicon materials. Currently the facility cuts, polishes, etches, washes, and packages the silicon wafers. In May 2013, MEMC changed its name to SunEdison to reflect the company's new focus on solar energy. SunEdison is an international company in semiconductor and solar technology fields with headquarters and facilities in St. Peters.
Monsanto, and later MEMC used two surface impoundments to receive process wastes, including waste waters containing 1,1,1-trichloroethane, methylene chloride, trichloroethylene and Freon. The use of trichloroethylene at the plant has been discontinued, along with changes to the method of wastewater treatment. There were also several tanks and hazardous waste storage areas used to store arsenic-contaminated materials, spent solvents, waste oils, and empty drums. Monsanto and MEMC operated these hazardous waste management units under the “interim status” portions of the federal Resource Conservation and Recovery Act (RCRA). The other surface impoundments, or lagoons, currently used at the site are mainly used for holding storm water run-off.
Cleanup Summary
According to applicable state and federal hazardous waste laws and regulations, all hazardous waste treatment, storage and disposal facilities are required to investigate and clean up releases of hazardous waste and hazardous constituents to the environment at their facility resulting from present and past hazardous waste handling practices. Initial investigations identified soil and groundwater contamination and several areas that required further investigation. In 1985, a groundwater pumping and treatment program was begun. From 1989 to 1996, MEMC investigated and performed a corrective measures study under a 3008(h) Corrective Action Administrative Order on Consent with the Environmental Protection Agency (EPA). The main contaminants of concern are volatile organic compounds, specifically 1,1-Dichloroethylene, 1,2-Dichloroethylene, Trichloroethylene, Trichlorotrifluoroethane (Freon-113) and Vinyl Chloride. A Deed Notice, signed by the St. Charles County Recorder of Deeds in 1992, was placed on the property in order to inform potential future buyers of the property that the surface impoundments had been used to manage hazardous wastes.
MEMC closed both surface impoundments in 1993. In August 1996, EPA replaced the 1989 order with a Corrective Measures Implementation Administrative Order on Consent, in order to implement the approved final remedy. MEMC also closed the remaining hazardous waste management units. The department accepted MEMC’s closure certifications for the units; however, MEMC is subject to the permitting requirements of the Missouri Hazardous Waste Management Law and federal Hazardous and Solid Waste Amendments for post-closure care because hazardous waste remained in place after closure. As of 2013, MEMC is conducting post-closure and corrective action activities under the 1996 Consent Order and related corrective measures implementation work plan. The interim status post-closure plan requiring inspection and maintenance of the cap for the closed surface impoundments is still in effect and being followed. The groundwater pump and treatment system is still operating.
