Characterization Report to Support the Phytoremediation Efforts for Southern Sector, Savannah River Site, Aiken, South Carolina

In February, 1999, we conducted a small-scale characterization effort to support future remediation decisions for the Southern Sector of the upper Three Runs watershed. The study concentrated on groundwater adjacent to the seepline at Tim's Branch above and below Steed's Pond. the primary compounds of interest were the volatile organic contaminants (VOCs), trichlorethylene (TCE) and tetrachloroethylene (PCE). Due to the site topography and hydrogeology, samples collected north of Steed's Pond were from the M-Area (water table) aquifer; while those locations south of Steed's Pond provided samples from the Lost Lake aquifer. Results of the study suggest that the leading edge of the A/M Area plume in the Lost Lake aquifer may be approaching the seepline at Tim's Branch below Steed's Pond, south of Road 2. Neither TCE nor PCE were detected int he samples targeting the seepline of the water table aquifer. The concentrations found for both TCE and PCE associated with the Lost Lake aquifer outcrop region were slightly above the detection limit of the analytical instrument used. The findings of this study are consistent with the conceptual model for the organic contaminant plume in the A/M Area of the Savannah River Site (SRS) -- the plume in the Southern Sector is known to be depth discrete and primarily in the Lost lake Aquifer. The sites with detected VOCs are in the most upstream accessible reaches of Tim's Branch where water from the Lost Lake Aquifer crops out. Additional characterization efforts should be directed near this region to confirm the results and to support future planning for the dilute-distal portions of the A/M Area plume. These data, combined with existing groundwater plume data and future characterization results will provide key information to estimate potential contaminant flux to the seepline and to assess the effectiveness of potential clean-up activities such as phytoremediation