SUMMARY OF THE REMEDIATION TECHNOLOGIES DEVELOPMENT FORUM
PERMEABLE REACTIVE BARRIERS ACTION TEAM
STEERING COMMITTEE
CONFERENCE CALL

On Monday, November 20, 2000, the following members of the Remediation Technologies Development Forum’s (RTDF’s) Permeable Reactive Barriers (PRB) Action Team Steering Committee met in a conference call:

Bob Puls, U.S. Environmental Protection Agency (EPA) (Action Team Co-chair)
John Vidumsky, DuPont (Action Team Co-chair)
Neeraj Gupta, Battelle Memorial Institute
Liyuan Liang, Oak Ridge National Laboratory
Tim Sivavec, General Electric Corporate Remediation
Scott Warner, Geomatrix Consultants, Inc.

Christine Hartnett of Eastern Research Group, Inc. (ERG), also participated in the conference call.

Bob Puls opened the call by asking whether the PRB Action Team should meet in 2001. Call participants talked about this at great length. In the end, they decided to hold half-day sessions in conjunction with the following meetings:

• The April 2001 American Chemical Society (ACS) meeting. Scott Warner noted that ACS plans to hold a meeting in San Diego, California, during the week of April 1, 2001. During this conference, he said, technical presentations will be offered on PRB technologies and remedial approaches that can be used to address dense non-aqueous phase liquids. Warner said that he called the ACS meeting coordinator (Sue Henry) to ask if the PRB Action Team could hold a meeting in conjunction with the ACS meeting. Warner said that Henry was very receptive to the idea; in fact, she offered to arrange for meeting room space and to advertise the Action Team session. Warner said that the agenda for the ACS meeting has not been finalized yet. Thus, he could not be sure which days would be open for an RTDF session. Most likely, he said, the session will either be scheduled for April 4 or 5, 2001.

• The June 2001 International Containment meeting. Liyuan Liang said that many European representatives will be attending the International Containment meeting that is scheduled to take place in Florida on June 11 through 14, 2001. She listed the topics that will be covered during this conference: thermal and chemical remediation technology, biological remediation technology, modeling, PRBs, characterization, monitoring and verification, vadose zone issues, regulatory acceptance of technologies, multiagency remediation strategies, sediment remediation, and long-term stewardship. Liang said that she asked the meeting’s planners whether the Action Team could meet in conjunction with the conference; they expressed much interest. Liang said that there are two ways in which the Action Team could be involved: (1) it could meet immediately after the International Containment meeting or (2) it could make its meeting part of the International Containment meeting, claiming one of the latter’s session slots. Call participants liked the latter suggestion—incorporating the Action Team session into the larger meeting might boost its attendance. Before committing to this approach, however, they wanted to make sure they would have the freedom to choose their own meeting format. Liang agreed to talk to the meeting’s planners to make sure that they would be willing to let the Action Team use its own presentation format.

Liang did note one stumbling block associated with having the Action Team meeting in conjunction with other meetings: registration fees are required for the ACS and the International Containment conferences. She advised talking to EPA’s Technology Innovation Office to determine whether these registration fees could be waived for PRB Action Team members.

Call participants talked about the format they would like to use for their half-day sessions. They agreed that an informal roundtable discussion would be the ideal forum. They envisioned having five or six panelists summarizing major themes and then opening the session to general discussion. This might be a refreshing break, they agreed, from rigorous and formalized technical presentations. Call participants agreed that the different meetings should cover different topics. At the ACS meeting, they decided, discussion will revolve around performance monitoring. Subtopics under this umbrella will include: (1) improved monitoring methods, (2) changes observed over time in geochemical and microbiological activity within the reactive zones of PRBs, and (3) PRBs’ impacts on downgradient geochemistry and microbiology. At the International Containment meeting, discussion will revolve around what has been learned about best practices in the areas of design, characterization, monitoring, and emplacement. Neeraj Gupta asked if hydraulic issues should be discussed; call participants agreed that these issues will be captured under the discussions on PRB design.

Call participants talked about what needs to be done to plan the meetings and formalize an agenda. To accomplish these tasks, they decided to split into teams and to write draft scopes for each meeting. (See "Action Items" below for additional details.)

FUTURE PRB ACTION TEAM ACTIVITIES

During the Steering Committee’s last conference call, Puls said, two potential projects were identified for the Action Team to follow up on:

• Update an RTDF document. In September 1998, Puls said, the PRB Action Team released a document entitled Permeable Reactive Barrier Technologies For Contaminant Remediation. He said that some people have been asking whether a more updated volume is going to be compiled. He asked Steering Committee members to let him know if they are interested in updating the document.

• Update case studies. Puls said that it would be useful to add more case studies to the PRB Action Team’s Web page. In particular, he said, it would be useful to add some information on international sites. He agreed to talk to Carolyn Perroni about having the case studies updated and expanded.

UPDATES ON SITES WITH PRB INSTALLATIONS

Puls said that four funnel-and-gate systems have been installed at the Denver Federal Center. A failure has been detected in gate #2, Puls said: untreated contaminants are flowing through the gate. Massive accumulations of sulfide precipitants have been detected throughout the gate, as well as in the upgradient shallow portion of the gate. In addition, accumulation of microbial biomass has been detected in the upgradient areas. (The microbial activity rates at the Denver Federal Center, said Puls, are about an order of magnitude higher than the rates at the Elizabeth City site.) While blockage of pore space is clearly causing a problem at the site, Puls was not sure whether all of the problems can be attributed to this. It is possible, he said, that physical disruption of the cell is adding to the difficulties.

Puls noted that precipitant accumulation is to be expected at sites with PRB installations. What is surprising, he said, is that the accumulations happened so rapidly at the Denver Federal Center. He expects that the Elizabeth City site will exhibit such accumulation one day, but not until the system has been operating for about 10 years.

Puls said that it might be possible to use what has been learned at the Denver Federal Center to prevent such failures in the future. That is, it might be advisable to discourage scientists from installing PRBs in areas characterized by high sulfate concentrations, very fine-textured materials, and slow ground-water flow.

John Vidumsky said that a PRB is currently being installed at one of DuPont’s sites. The wall, which will be completed by December 2000, is being installed at a depth interval of 50 to 120 feet below ground surface. Vidumsky said that Golder Sierra is using its hydraulic fracturing technology to install the system.

Liang said that a wall is also being installed at a site in Paducah, Kentucky. This wall, which is being installed by FRX, is also being installed to a depth of 120 feet below ground surface.

Liang said that a multitracer test was performed at the Monticello site in July 2000. (Bromide and iodide were injected into the subsurface.) Data analysis is still ongoing. Liang said that the preliminary results suggest that there are preferential flow paths in the subsurface.

During the summer of 2000, Tim Sivavec said, a 900-foot full-scale installation was established at the Somersworth Landfill site. The PRB was installed using a biopolymer slurry, a technique that proved to be effective. Sivavec said that the PRB’s design was chosen with care. Before choosing a final design, remediators considered several options. For example, overlapping caissons and funnel-and-gate systems were identified as potential options, but the former option was eliminated because of the site’s heterogeneities and the latter was eliminated because it cost too much.

ACTION ITEMS

• Steering Committee members agreed that the RTDF Action Team should hold a half-day meeting session at the April 2001 ACS meeting. Puls, Vidumsky, and Warner agreed to work together to plan the Action Team meeting. Warner agreed to call the ACS meeting organizer (Sue Henry) to inform her of the Action Team’s decision. He also agreed to create a proposal for the meeting’s scope. (The scope will list topics for the meeting, describe the format that will be used, and identify panelists who will participate.) Warner agreed to send the draft proposal to Puls and Vidumsky for review by November 28, 2000. On December 1, after making revisions, the proposal will be distributed to Steering Committee members.

• Steering Committee members agreed that the RTDF Action Team should hold a half-day meeting session at the June 2001 International Containment meeting. Liang and Gupta agreed to work together to plan the Action Team meeting. Vidumsky said that Richard Landis would also be willing to help. Liang agreed to e-mail information to Gupta and Landis. Then the three will work together to create a proposal for the meeting’s scope. The scope—which will list topics, propose a format, and identify potential panelists—will be distributed to Steering Committee members by December 1, 2000.

• Call participants agreed that the Action Team’s September 1998 overview document should be updated. Puls asked Steering Committee members to let him (puls.robert@epamail.epa.gov) or Vidumsky (John.E.Vidumsky@usa.dupont.com) know if they are interested in contributing to the document.

• Puls agreed to talk to Perroni about identifying additional case studies for inclusion on the PRB Action Team’s Web page.