Challenges in Planning for Groundwater Remedy Transition at a Complex Site
Presented on Tuesday, May 6, 2014
William N. O'Steen1 and Ralph O. Howard2, (1)Superfund Division, Technical Services Section, US EPA Region 4, Atlanta, GA, (2)Superfund Division, Superfund Remedial and Site Evaluation Branch, U.S. EPA Region 4, Atlanta, GA
Complex groundwater contamination sites require comprehensive, structured groundwater monitoring in planning for transition to a new groundwater remedy. An example is the Medley Farm Superfund Site, a former waste solvent dump located in South Carolina. Groundwater contaminants at the site are primarily tetrachloroethene, trichloroethene, and their degradation products. Groundwater remedial action began at Medley Farm in 1995, using a groundwater extraction and treatment system. In 2004, in response to declining efficiency, groundwater extraction was suspended. Enhanced reductive dechlorination (ERD) via injection of lactate solution into the groundwater was initiated as a remedial optimization measure. Between October 2004 and April 2012, lactate solution was injected on multiple occasions. Responses of the hydrogeochemistry and groundwater quality to lactate treatment have been positive. In August 2012, EPA issued an Amended Record of Decision, changing the groundwater remedy to ERD. Monitored natural attenuation (MNA) was selected as a contingency remedy with the anticipation that as cleanup progresses, ERD may transition to MNA.
The Medley Farm Site presents challenges to transitioning from ERD to MNA. Prior lactate injections have varied with respect to injection volumes, locations, and timing. Groundwater monitoring and data analysis during the injection period have been structured to evaluate responses to the individual, irregular injection events. These factors limit data interpretation and predictive analysis. Site geologic features create variable and complex groundwater flow patterns. The spatial and temporal extent of lactate influence and sustainability of favorable conditions without lactate treatments are incompletely understood but are apparently highly variable, consistent with Site complexities. Transition from ERD to MNA and evaluation of MNA as a potential final remedial action will require changing the current site monitoring and data evaluation paradigm. EPA is planning for restructuring the monitoring and data evaluation program to better discern treatment effects and facilitate MNA evaluation.
William N. O'Steen
Superfund Division, Technical Services Section, US EPA Region 4, Atlanta, GA
William O’Steen is a hydrogeologist in the EPA Region 4 Superfund Technical Services program. He provides technical consultation on investigation and remediation of groundwater contamination at Superfund sites in the region. He is a registered professional geologist in the state of Florida. O’Steen has worked as a hydrogeologist for 31 years, in both state and federal regulatory agencies and as a private consultant. He holds a B.A. in geology from the University of Tennessee (1978) and an M.S. in geology from West Virginia University (1982).
Ralph O. Howard
Superfund Division, Superfund Remedial and Site Evaluation Branch, U.S. EPA Region 4, Atlanta, GA
Ralph Howard Jr. is a geologist and Project Manager in U.S. EPA Region 4’s Superfund Program. He joined EPA in 1991 following four years with a consulting firm working on a variety of RCRA and UST sites. His current responsibilities include overseeing Superfund site evaluation activities by the Alabama and Mississippi state environmental agencies, and management of investigation and cleanup activities at Superfund sites in South Carolina. Howard is a registered Professional Geologist (Georgia) and holds B.S. (1981) and M.S. (1990) degrees in geology from the University of Alabama.
