In 1999, approximately 91,000 cubic yards of material were excavated from the site, and hauled away to licensed secure disposal sites outside of the area. The former disposal area was backfilled with clean fill, graded and capped with low permeability soils.
Despite having no known history of using 1,2-DCA and suspecting that others may have been the source of the compound, Rohm and Haas nevertheless responded by building two groundwater recovery systems to remove the 1,2-DCA from the groundwater. One is located at the former disposal area and the other is located towards the downgradient edge of the groundwater plume. The former disposal area system was redesigned and replaced with a new system to improve performance and to enhance capture of the on-site 1,2-DCA plume. This upgraded system became operational in February 2012. Since start-up, the systems have removed and cleaned over 300 million gallons of water through June 2016.
This removal action, combined with the active groundwater recovery systems, has reduced the levels of 1,2-DCA in groundwater. Investigations to identify the precise limits of the impacted groundwater were completed in 2007. Finally, Rohm and Haas submitted to TCEQ, and TCEQ approved in April 2011, a Final Response Action Plan, which presents the proposed response actions for dealing with 1,2-DCA in the groundwater. The main features of the plan include:
- Removal of significant amounts of 1,2-DCA through continued operation and optimization of the groundwater recovery (pump and treat) systems installed at the Site;
- Maintenance of groundwater recovery and treatment systems to limit the migration of the 1,2-DCA plume;
- Ongoing evaluation of other treatment options at the Site;
- Treatment of groundwater between the Site and the Subdivision, and between the Subdivision and the 13-Acre Tract, using injections of food-grade materials to enhance natural processes of 1,2-DCA removal; and
- Continued use of food-grade material treatment systems as needed to achieve remediation goals for the Site.
To address portions of the groundwater plume between the Site and the Subdivision, and between the Subdivision and the 13-Acre Tract, a process called enhanced anaerobic bioremediation (EAB) has been tested and approved for use at the Charlie Burch site by the TCEQ. The EAB application involves the injection of harmless organic materials, including vegetable and soybean oils, into the underlying groundwater to provide a long-term source of food that enables the microbial populations to more effectively decompose DCA. As groundwater flows through the treatment zones, microorganisms break them down converting them to harmless end products.
The EAB application is being implemented in a phased approach to facilitate optimization and incorporation of process improvements into subsequent phases. This phased approach allows for flexibility in treating areas predicted to take longest to clean up. The EAB application is designed to inject sufficient organic materials and amendments to persist in the groundwater for up to 4 years, requiring replenishment of those materials (re-injection) on an on-going basis until the groundwater is determined to be clean by the TCEQ. Injection activities associated with the implementation of Phases 1 and 2 of the EAB application were conducted between March and June 2012. Phase 5 EAB applications were completed in early 2014, and Phase 4 EAB applications were completed in November 2016. Phase 3 EAB applications remain pending. Performance monitoring is conducted periodically to measure application effectiveness.
Several treatments may be necessary to replenish the treatment materials before the EAB process is complete.