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ITRC Permeable Barrier Wall Guidance Documents Used in the Review and Approval of Cleanup At U.S. Energy Department Site at Rocky Flats
How has Colorado utilized the PBW Guidance Document?
How was PBW technology implemented at this specific
In mid-1998 a subsurface groundwater collection system was installed south of South Walnut Creek to intercept the contaminant plume and minimize impacts to surface water. A collection trench was excavated by conventional excavation/trenching techniques. It consists of a trench from 15 to 20 feet deep, two to three feet thick, and 230 feet long, keyed into the underlying claystone. A perforated collection pipe was placed at the bottom of the trench. An impermeable geomembrane was emplaced along the downgradient side, and the trench was backfilled with filter pack. A two-foot thick impermeable cap was placed at the top of the trench to prevent infiltration. Contaminated groundwater flowing into the trench is conveyed by the collection pipe to a series of buried cells containing reactive iron filings. The iron degrades the chlorinated hydrocarbons and removes the radionuclides by reduction and/or absorption. Water is treated to meet surface water action levels and is discharged to South Walnut Creek. A series of piezometers and downgradient wells are monitored regularly for water quality and hydraulic head to measure system effectiveness. The first treatment cell of iron filings will remove radionuclide contamination. When the absorptive capacity is reached, the iron filings will be removed, managed, and disposed of appropriately. The second treatment cell of iron filings will degrade the chlorinated organics. When material in this cell is exhausted, it will be replaced. It is expected that the iron filings will require replacement every five to ten years.
What are the overall benefits of Colorado's use of the PBW
"My review of RFETS' Mound Site Plume Decision Document was enhanced and made more efficient by having the guidance documents provided by ITRC. My review of the draft decision document was actually concurrent with my review of the draft guidance document, but the ITRC materials proved useful mostly by providing background on a new technology not yet utilized at RFETS, and by raising issues that might not otherwise have been considered. Because of the concurrent nature of the reviews, the resulting time savings may not have been as great as otherwise. Still, several hours were probably saved - at least 10% of the total review time. Even greater efficiencies are expected when the ITRC documents are used during reviews of the several future PBW projects anticipated for Rocky Flats."
He also stated that the plume in this example is fairly small, but the next two PBW projects at Rocky Flats involve much larger plumes. These new projects are in the regulatory agency review stage at this time and are expected to proceed to implementation next year. The ITRC PBW Guidance Documents will be very useful to CDPHE in reviewing these remediation proposals in a thorough and timely manner.
The most significant benefit for Colorado, and also the U.S. Department of Energy (DOE), is that the Guidance Documents contributed to the CDPHE's ability to confidently approve the use of this innovative technology, which in turn resulted in significant cost savings to taxpayers. Two other alternatives were evaluated for remediation of the Mound Site Plume. Both were variations of the baseline technology that was previously used at the Mound Site Plume. These alternatives were based on trucking contaminated groundwater for treatment at an on-site treatment facility. The costs of treatment over the life of the project was estimated to be approximately $3 million plus the maintenance costs of the existing on-site treatment facility. The cost to construct the permeable barrier wall was $300,000 plus periodic maintenance and monitoring costs. The savings are estimated to be $2.7 million. Additionally, the permeable barrier wall is a less intrusive remedy that allows for site conversion at a significantly early time.
Who can I contact to learn more about this Example?
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