Project Specifics

The groundwater at this former manufacturing facility had elevated levels of 1,4-dioxane, chlorinated volatile organic compounds, 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 (P&T) 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 operation and maintenance were anticipated to obtain site closure. Geosyntec was retained to identify and evaluate alternative remediation technologies and implement a more cost-effective and sustainable strategy that would obtain site closure quickly.

Geosyntec Scope of Services

Geosyntec refined the conceptual site model (CSM) by completing vertical geologic and groundwater profiling, pump testing, and groundwater flow modeling. Based on this CSM, Geosyntec designed a final remedy that included engineered phytoremediation using TreeWell technology to reduce contaminant concentrations and contain affected groundwater in conjunction with reclamation of an on-site, distressed wetland by using native tree species in the system’s plantings. TreeWell phytoremediation was selected for use rather than conventional phytoremediation approaches because it directly targeted the impacted aquifer, forcing tree roots to utilize only the groundwater of interest. This specialized phytoremediation technology enables tree roots to develop a hydraulic connection with groundwater at depths of 50 feet below ground surface or more, and overcomes the constraints and challenges typically encountered by conventional phytoremediation approaches.

Geosyntec used the groundwater flow model to identify the number and location of TreeWell units required to capture the affected groundwater. Within the second growing season, monitoring of the TreeWell system demonstrated hydraulic containment of the affected groundwater 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 P&T system. At the end of the fourth growing season, COCs within the source area had decreased to concentrations slightly above the groundwater cleanup target level, and the downgradient plumes were significantly reduced and shrinking. Therefore, Geosyntec prepared, and Florida DEP approved, a Proposal for No Further Action with Controls.

Notable Accomplishments

Geosyntec developed a viable, sustainable remediation approach using engineered phytoremediation to replace a P&T remedy, and successfully negotiated with Florida DEP to expedite site closure in under five years. By ceasing operation of the P&T system and its associated annual maintenance requirements, Geosyntec delivered substantial cost savings to the site owner. Notably, the cost to install the TreeWell system was approximately the same as just one year’s operation and maintenance costs for the P&T system.

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