Background:
The following example is intended to highlight how the State of Colorado's Department of Public Health and Environment (CDPHE) has used their participation in the ITRC to promote the use of innovative technologies in their state. More specifically, this example highlights the CDPHE's use of the Permeable Barrier Wall Guidance Document developed by the ITRC. The Permeable Barrier Wall Guidance Document (PBW) is a baseline set of technical regulatory requirements for demonstrating and/or approving the use of PBW technologies to remediate Chlorinated Solvents. In addition, the PBW Guidance Document also has a companion Design Guidance for the Application of Permeable Barriers to Remediate Dissolved Chlorinate Solvents which is intend to provide engineering guidance on the design, construction, and installation of a Permeable Barrier Wall. These documents blend the diverse state technical requirements for approving the use of a PBW remediation technology.

How has Colorado utilized the PBW Guidance Document?
During the development of the PBW Guidance Document, a near final draft version of the Guidance Document was provided to a CDPHE site manager who was currently reviewing a proposal to use a PBW at the Rocky Flats Environmental Technology Site (RFETS). This site manager proceeded to use the ITRC PBW Guidance Document to review RFETS' proposed remedial work plan. The PBW Guidance Document allowed a more efficient review of this new remedial technology by presenting background on technological and regulatory issues. The outcome of these discussions was captured in the "Decision Document for the Mound Site Plume.

How was PBW technology implemented at this specific site?
The Mound Site Plume contains chlorinated organic contamination, americium and uranium in excess of cleanup levels defined in the Rocky Flats Cleanup Agreement (1996). The plume is comprised primarily of volatile organic compound (VOC) contaminated groundwater. Most of the groundwater contamination is believed to be derived from the Mound Site where approximately 1,405 intact drums were stored on the ground surface, covered with soil, between April 1954 and September 1958. The drums contained uranium and beryllium-contaminated lathe coolant (a mixture of approximately 70 percent hydraulic oil and 30 percent carbon tetrachloride). Historical information also indicates that some of the coolant contained low levels of plutonium. In 1970, all drums along with some radiologically contaminated soil were removed from the Mound Site, thereby removing the primary source of the contamination. Approximately 10 percent of the drums were thought to be leaking at the time of removal.

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 Guidance Document?
The Mound Site Plume remediation presented in this example is actually the third application of PBW technology to be approved in Colorado by CDPHE. The Guidance Documents were helpful to the CDPHE site manager in improving his understanding of and comfort with the technology. Specifically he stated that:

"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?
Gary Baughman
Department of Health & Environment
4300 Cherry Creek Drive South
Denver, CO 80246-1530
Phone: 303-692-3338
Fax: 303-759-5355
e-mail: gary.baughman@state.co.us

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