Permeable Reactive Barriers (PRBs)
- Three types of PRBs demonstrated - phosphate (PO4), zero valent iron (ZVI), and amorphous ferric oxyhydroxide (AFO)
- PRBs installed side-by-side and operated concurrently
- Funnel and gate design; each PRB was keyed, along with each of the impermeable funnels, into the bedrock (Cedar Mesa Sandstone formation) beneath the colluvial aquifer
- 1.5-foot layer of pea gravel on the upgradient side of the PRBs to facilitate uniform flow of groundwater into the PRBs
- "As built" volume of reactive material was: PO4 - 67.2 ft3; ZVI - 77.7 ft3, and AFO - 67.2 ft3
- Each PRB contains a total of 22 monitoring wells, configured in two parallel "rows" - Row 1 and Row 2
- Estimated range of groundwater velocity through PRBs - 0.2 - 2.5 ft/day
Ariel Rios Building
1200 Pennsylvania Avenue, N.W.
Washington, D.C. 20460
David Naftz, Ph.D.
U.S. Geological Survey
2329 West Orton Circle
West Valley City, UT 84119-2047
Radionuclides (uranium) and metals
- Uranium concentrations in groundwater found at levels as high as 16,300 ug/L
- Iron and manganese concentrations found in groundwater at 90 ug/l and 180 ug/L, respectively
Subsurface drainage from abandoned uranium ore mill ponds
Type/Quantity of Media Treated:
Groundwater - 33,000 cubic feet (about 200,000 gallons)
- Depth to groundwater - 8 feet bgs
- Colluvial aquifer ranges in depth from 2-5 feet
- Groundwater flow rate - 0.2-2.5 ft/day
- Transmissivity - 10-200 ft/day
- Hydraulic conductivity - 55-85 ft/day
Purpose/Significance of Application:
Field demonstration of three types of PRBs to treat uranium-contaminated groundwater
Regulatory Requirements/Cleanup Goals:
- The objective of the demonstration project is to evaluate the use of three types of PRBs in controlling the migration of uranium and metals in groundwater
- Performance data were available for the first year (September 1997 to September 1998) of this ongoing demonstration
- The ZVI PRB showed the best removal rate of the three PRBs tested, removing more than 99.9% of the uranium from the groundwater
- The PO4 PRB initially removed more than 99% of the uranium from the groundwater, with the removal rate decreasing to 60-70% in January 1998, then increasing to 92% as of September 1998. Available results from tracer tests indicated that there was no leakage from the ZVI PRB to the PO4 PRB; rather, the increased efficiency in the PO4 PRB is the result of anoxic conditions caused by the release of PO4
- The AFO PRB had the lowest removal rate, consistently removing less than 90% of the uranium from the groundwater; with removal rates as low as 37% observed
- The cost for the PRB demonstration included $280,000 for site selection, characterization, and PRB material testing; $148,000 for design of the PRBs; and $246,000 for the installation of the PRBs
- O&M costs were reported as being relatively expensive because of the extensive monitoring performed for the demonstration compared to full-scale operation. Projected costs for full-scale O&M for a comparable site were estimated to be $55,000-$60,000 per year
Fry Canyon, located in southeastern Utah (approximately 60 miles west of Blanding, Utah), is the site of an abandoned uranium ore milling operation and copper leach operation. From 1957 to 1960, COG Minerals Corporation conducted uranium upgrading (concentrating) operations at the site, and from 1962 to 1968, the Besinare Company conducted copper leach operations. Waste from these operation, including tailings, were stored and disposed of at the site. The Utah Department of Health, Bureaus of Radiation Control and Solid and Hazardous Waste, conducted site visits to Fry Canyon in 1984 and 1986. Elevated levels of uranium were found in water samples from Fry Creek. The site was selected by the U.S. Environmental Protection Agency (EPA) in cooperation with the U.S. Geological Survey (USGS), the U.S. Department of Energy (DOE), BLM, and the Utah Department of Environmental Quality, for a field demonstration of PRBs to assess their performance in removing uranium from groundwater.
Prior to constructing the PRBs, extensive laboratory investigations were conducted to evaluate the various reactive materials for each type of PRB and to select the specific reactive materials for the Fry Canyon demonstration. Three types of PRBs were demonstrated - phosphate (PO4), zero valent iron (ZVI), and amorphous ferric oxyhydroxide (AFO). The PRBs were constructed side-by-side to allow all three types of materials to be evaluated during the demonstration period. A funnel and gate design was used and each PRB was keyed into bedrock beneath the colluvial aquifer at the site. After one year of operation, the ZVI PRB showed the best performance, consistently removing more than 99% of the uranium from the groundwater. The next best performance was observed for the PO4 PRB. While the removal rate for the PO4 PRB varied throughout the year, decreasing to as low as 62%, as of September 1998, the uranium removal rate for the PO4 PRB at the end of one year of operation was greater than 92%. The AFO PRB initially removed greater than 90% of the uranium from the groundwater, but dropped to as low as 37% after the first year of operation.
Several problems were encountered during installation of the PRBs. For example, a large bedrock nose was encountered that caused the PRBs to be rotated such that groundwater entered into the gate structures at an oblique angle rather than perpendicular, as designed. To prevent this problem for other applications, a more detailed view of the bedrock topography would be needed during site characterization. Full-scale cost considerations include potential lower costs for design and operation compared to the demonstration costs, which included three PRBs and a more extensive monitoring system than would be needed for a non-research application.