(Certified Best Practice by BMPCOE)
Mason & Hanger Corporation, Pantex Plant - Amarillo, TX
Results from drilling test wells showed that past practices of flushing contaminates into drainage ditches at the facility had contaminated only perched aquifers and underlying flats and not the main drinking water aquifers used by many states in the southwest. This prompted the need for a study on groundwater treatment.
The treatability study was tasked to:
- Demonstrate that the groundwater level could be lowered sufficiently to expose the capillary fringe zone for volatile contaminant removal by vacuum;
- Assess the ability of the system as designed to expose the capillary fringe zone and remove volatiles by directing air from passive vent wells through the groundwater extraction wells;
- Determine optimum well spacing and the radius of influence for additional or future groundwater and or vapor extraction wells;
- Assess the ability of the dual phase groundwater/vapor extraction to be operated over an extended period of time in which to obtain reliable design parameters and other performance data for refinements to the existing system or a full scale treatment system;
- Assess the effectiveness of the carbon absorption system for removing HE components from the groundwater; and develop field proven design criteria and equipment specifications for future remedial activities at Pantex.
The study showed that HE contaminations of groundwater could be removed and remediated by dual phase extraction of unsaturated and saturated zones. The modified design calls for the same drilling of dualphase wells along with the strategic location and drilling of injection wells to reuse the decontaminated water. Geological survey data and computer modeling provides needed information to maximize the treatability area and optimize well placement.
Test wells were drilled to locate and define the flume of contamination. From the test well data, Pantex engineers determined where to drill the required dual phase wells to begin decontamination. After installing the system, data and analysis revealed that the treated groundwater was of sufficient purity to allow its reuse, thereby avoiding pumping it to the wastewater treatment facility for further treatment and disposal. These findings allowed Pantex engineers to modify the process design. By successfully applying the results from the treatability study on high explosive (HE) contaminated soil and groundwater, Battelle Pantex has been able to treat the soil without the risk of lowering the water table in treated or downstream areas.