IDAHO FALLS, Idaho – Deep aquifer monitoring wells at the DOE’s Idaho Site, the first of which tested positive for an industrial solvent more than two years ago, will be rehabilitated this summer for use by the environmental restoration program of EM cleanup contractor Fluor Idaho.
The wells are important for understanding how deep site-generated contaminants are located within the aquifer and the speed at which they move in water.
Since detections of perchloroethylene (PCE) first surfaced in a specialized, multi-port well in November 2015, two more multi-port wells tested positive for the solvent. Because the wells are sealed and have multiple ports to retrieve groundwater samples, the contaminant was likely inadvertently introduced after they were constructed during a sampling event.
Engineers ruled out the aquifer as the source of the solvent because the wells, during their construction, were initially filled with clean water that later became contaminated. Water is added to the well casing (or shaft) to prevent its collapse by balancing out the external pressures. Water remains sealed in the well; therefore, PCE present in the wells is not a threat to the aquifer.
Over the last year and a half, engineers investigated one of the wells that provided the clean water during well construction and determined its water was free of PCE. They also investigated the sampling logs, locations where sampling equipment was stored, the equipment, and lubricants used for maintaining the equipment.
“Based on our research, we believe the introduction of this contaminant into the wells was likely a one-time occurrence,” Fluor Idaho groundwater expert Jeff Forbes said.
The third well was drilled after the previous two wells. Due to its much lower concentration of PCE, it likely was sampled with the same sampling equipment as the previous two wells on a later date, which could have cross-contaminated the previously clean water in the well.
“These wells are valuable to us and other agencies that sample them,” Forbes said.
Fluor Idaho environmental engineers are now drafting a proposal with possible alternatives for well rehabilitation, which would result in the removal of the PCE from the wells. Since the initial cost to install each well was as much as half a million dollars, rehabilitating them is preferred to drilling new wells. If accepted by the agencies, well rehabilitation could begin by this summer and could be completed this field season or next.