DDT and several other organic chemicals were produced on BASF’s McIntosh, Alabama chemical production site from the 1950s to 1960s, resulting in contamination on the property in the surrounding soils, in the groundwater, and in the freshwater wetlands in the floodplain of the Tombigbee River. BASF needed a floodplain remediation approach that could be implemented rapidly, reduce ecological exposures to DDT, and maintain the integrity of the site’s bottomland hardwood forest. BASF also needed ongoing assistance with their soil and groundwater corrective measures implementation and effectiveness monitoring.
LimnoTech worked with BASF and regulatory agencies to understand the extent and nature of contamination and to develop remedy and management strategies for the site. We developed and refined a conceptual site model (CSM) for the floodplain through review of existing data, additional sediment characterization, and sediment fate and transport studies using clay sedimentation pads and turf mats. Because the CSM and supporting studies demonstrated the stability of impacted floodplain sediments, a sand cover with organic amendments was selected as the appropriate remedy. Geostatistical modeling of contaminant distribution and a simple cap diffusion model were used to determine the necessary extent and thickness of the cover. LimnoTech and BASF worked closely with US EPA and other stakeholders to gain approval of the remedy design. Post-remedial monitoring has confirmed the effectiveness of the cover.
Following the successful site remedy implementation for the floodplain, work on the site continues with annual monitoring and further investigation of site groundwater and identification and management of other potential source areas. This work includes streamlining operation and maintenance of an alluvial aquifer extraction system; characterizing the extent and distribution of impacts to two aquifers; developing cost-effective groundwater monitoring and reporting programs in accordance with RCRA permit requirements; identification, delineation and risk management of other potential source areas; and developing a Corrective Action Plan to address the potential for offsite migration of groundwater impacts.