INVESTIGATING SPORADIC ELEVATED METAL CONCENTRATIONS IN MONITORING WELLS AT THE SAVANNAH RIVER SITE, SOUTH CAROLINA

Monitoring wells listed in the RCRA Corrective Action Plan for the Mixed Waste Management Facility Southwest Plume Area have sporadic elevated metal concentrations identified as Potential Constituents of Concern which may be the result of inadequate well development, improper sampling techniques and possibly corrosion of pump hardware rather than the geochemistry of formation water. To evaluate the presence of metals contamination in the groundwater, five wells were selected for redevelopment based on persistent detection of metals contamination, little or no purge volumes, and high turbidity.

The wells were sampled three times, once before redevelopment, once immediately following redevelopment and again one month after redevelopment. Redevelopment methodology consisted of treating the well with a deflocculant to remove silt and clay size particles and a regiment of pumping and swabbing to clean the well and well screen filter pack. Older single-speed pumps were replaced with low flow pumps.

After redevelopment, there was a notable decrease in concentration of total metals, specifically Pb and Al concentrations. Purge rates, which were not sustainable before redevelopment, produced 1.3 to 2 gpm and turbidity was reduced to below 15 NTUs after redevelopment. The results indicate that proper sampling techniques, adequate well development and maintenance and utilization of correct pump hardware are essential to support groundwater monitoring programs and sound regulatory decisions.