The groundwater at this former manufacturing facility contained elevated levels of chlorinated volatile organic compounds (CVOCs), 1,4-dioxane, and arsenic (constituents of concern [COCs]) resulting from historic facility activities. Conditions at the site were complex and included residual source areas and multiple plumes both on and off site. A pump-and-treat system was operated by others for 12 years. However, the system was not effectively reducing concentrations of COCs in groundwater, and a minimum of 25 additional years of costly operations and maintenance were anticipated to obtain site closure. Geosyntec was retained to evaluate alternative remediation technologies and implement a more cost-effective and sustainable strategy that would obtain site closure quickly.
Geosyntec reviewed reports provided by others to develop an understanding of the conceptual site model (CSM) and refined the CSM by completing vertical geologic and groundwater profiling, pump testing, and groundwater flow modeling. Geosyntec also conducted treatability testing, prepared a Focused Feasibility Study (FFS) that incorporated these data, and engaged the regulatory agency and other stakeholders on the decision making. Based on this approach, Geosyntec designed a final remedy for the site that included : (1) Isolation (containment) of the 1,4-dioxane source area (1,000 ft2); (2) Phytoremediation to reduce COC concentrations and capture the flow of affected groundwater in conjunction with reclamation of an on-site, distressed wetland using native tree species in an engineered planting (TreeWell® system); and (3) Long-term monitoring and monitored natural attenuation for the on- and off-site residual contaminant plumes.
Geosyntec designed an impermeable barrier to isolate the source of the 1,4-dioxane. In addition, Geosyntec used the groundwater flow model to identify the number and location of TreeWell® units required to capture the affected groundwater. As part of the phytoremediation approach, Geosyntec reclaimed a distressed wetland by removing solid waste and invasive species and installing TreeWell® units employing native species. Within the second growing season, monitoring of the TreeWell® system demonstrated complete capture of the affected groundwater flow and decrease in groundwater COC concentrations by up to two orders of magnitude. Based on these results, Geosyntec recommended, and the Florida Department of Environmental Protection (DEP) approved, shutdown and removal of the existing pump-and-treat system. At the end of the fourth growing season, 1,4-dioxane within the isolation area had decreased to concentrations slightly above the groundwater cleanup target level and other COC plumes were stable and/or shrinking. Therefore, Geosyntec prepared, and Florida DEP approved, a Proposal for No Further Action with Controls.
Geosyntec developed a viable, sustainable remediation approach using engineered phytoremediation to replace a pump-and-treat remedy, successfully negotiated with Florida DEP to expedite site closure in under five years.