EPA and MDNR Announce Explanation of Significant Differences
Valley Park TCE Site, Operable Unit 2, Valley Park, Missouri
EPA Region 7 and the Missouri Department of Natural Resources (MDNR) announce an Explanation of Significant Differences (ESD) decision for the Valley Park TCE Site, Operable Unit 2 (OU2) in Valley Park, Mo.
The Valley Park TCE OU2 is located in Valley Park, Mo. and unincorporated areas to the east of the city. The site consists of soil and groundwater contaminated by chlorinated solvents within the Meramec River alluvial aquifer.
In 1982, MDNR detected volatile organic compounds (VOCs) including tetrachloroethene (PCE), trichloro-ethene (TCE) and 1,1,1-trichloroethane (TCA) in samples collected from three Valley Park municipal wells. In response to the contamination, the city of Valley Park installed equipment to remove VOCs from drinking water.
Since 1988, Valley Park residents have been connected to the St. Louis County public water system. Therefore, Valley Park residents are no longer using contaminated water for domestic purposes.
EPA and MDNR determined that the sources of contamination originated from a former Wainwright Industries (Wainwright) property and a current Valley Technologies, Inc. (Valley Technologies) property located in Valley Park. Wainwright and Valley Technologies both used chlorinated degreasers and solvents for cleaning purposes. Contamination located at the Wainwright property has been addressed in operable unit 1 (OU1).
The site was placed on the National Priorities List on June 10, 1986. MDNR conducted a Remedial Investigation/Feasibility Study (RI/FS) for OU2, which concluded with a Record of Decision (ROD) signed by EPA on September 26, 2001. The selected remedy is a combined groundwater and soil source remediation using an extraction and treatment system for the contaminated groundwater, and excavation with soil vapor extraction for the contaminated soils.
After the potentially responsible parties declined to conduct the remediation in 2002, EPA assumed the lead role in conducting the remedial design for OU2. The design consisted of two phases: 1) fieldwork to obtain the information necessary to complete a detailed design, and 2) the detailed design. After reviewing information collected during the fieldwork phase, EPA and MDNR identified the need to make several significant changes in the selected ROD remedy. The ESD presents the new information and recommends appropriate changes in the remedy for OU2.
The selected remedy for OU2 addresses the VOC contamination identified in the soil source on the Valley Technologies’ property and the VOC contamination identified in the aquifer. As defined in the 2001 ROD, the major components of the selected remedy for OU2 included:
- Ex-situ soil vapor extraction (ExSVE) will be conducted on excavated contaminated soil until VOCs are reduced to concentrations below the performance standards based on the threat to groundwater.
- In-situ soil vapor extraction (InSVE) will be conducted on contaminated soil below 16 feet until VOCs are reduced to concentrations below performance standards based on the threat to groundwater.
- Air withdrawn from the SVE systems will be discharged via properly designed stacks that will ensure acceptable ambient air concentrations of contaminants both on and off Valley Technologies’ property. Monitoring of emissions will occur and carbon adsorption equipment will be installed if deemed necessary.
- A groundwater extraction and treatment system, which will hydraulically control the impacted groundwater throughout the entire vertical section of the aquifer underneath Valley Technologies, will be implemented. Air stripping technology will be used to treat the extracted, contaminated groundwater. The treated water will be re-injected into the aquifer downgradient of the extraction well.
- The contaminated groundwater located off the Valley Technologies property will be addressed by installing air strippers connected to the production wells at Reichhold, Inc. and the former U.S. Cotton property.
- An institutional control will be placed on OU2 site property to prohibit the installation and operation of groundwater wells until the aquifer is remediated.
EXPLANATION OF SIGNIFICANT DIFFERENCES
The original remedy included ExSVE at a vacant lot owned by Valley Technologies. Subsequent to selection of the remedy, Valley Technologies sold the vacant lot. This was the only location where ExSVE could occur. Therefore, the soil remedy now involves excavation with off-site disposal and in-situ soil vapor extraction.
The groundwater remedy originally included installation of air strippers to treat production wells at Reichhold and the former U.S. Cotton property. Risk analysis of emissions from these production wells did not identify exceedances of risk-based levels of ambient air concentrations. Therefore, the installation of air strippers is no longer necessary.
The original remedy included injection of treated water from the Valley Technologies System downgradient into the aquifer. During fieldwork, a storm sewer was identified adjacent to the Valley Technologies property. Previously, this inactive sewer was unknown to local officials and residents. Use of the storm sewer for injection of treated water is preferable to re-injection downgradient in the aquifer. Therefore, the remedy will now discharge treated water into the storm sewer.
The changes described above conform with the scope and performance of the original remedy and the proposed changes do not increase costs significantly.
Detailed site information, including a copy of the ESD, is available at the following locations during normal business hours:
Valley Park Public Library
320 Benton Street
Valley Park, Mo.
EPA Records Center
901 N. 5th Street
Kansas City, Kan.
Questions about this fact sheet or the site can be addressed to:
Community Involvement Coordinator
Office of External Programs
EPA Region 7
901 N. Fifth St.
Kansas City, Kan. 66101
Toll free: 1-800-223-0425