SUMMARY OF THE REMEDIATION TECHNOLOGIES DEVELOPMENT FORUM
PHYTOREMEDIATION OF ORGANICS ACTION TEAM
ALTERNATIVE COVER SUBGROUP
CONFERENCE CALL



3:00 p.m.­5:00 p.m.
June 3, 1998

On Wednesday, June 3, 1998, the following members of the Phytoremediation of Organics Action Team, Alternative Cover Subgroup, met in a conference call:

Tom Wong, Union Carbide Corporation (Subgroup Co-chair)
Steven Rock, U.S. Environmental Protection Agency (EPA) (Subgroup Co-chair)
William Albright, Desert Research Institute (DRI)
Michael Bolen, Science Applications International Corporation
Paul Schroeder, U.S. Army Engineer Waterways Experiment Station

Also present was Christine Hartnett of Eastern Research Group, Inc. (ERG).


SITE UPDATE

William Albright said that DRI distributed a questionnaire to identify current and proposed alternative covers. Albright agreed to send a draft of the questionnaire to Michael Bolen, Steven Rock, and Tom Wong. Albright noted that Bolen sent him comments on a draft version but that he received some of the comments after the questionnaire was released. According to Albright, representatives from three states (Maryland, Nebraska, and Utah) have filled out the questionnaire and three or four other state representatives have called expressing interest.

Over the past few months, DRI has received numerous calls from site owners and regulators who are interested in learning more about the Alternative Covers Assessment Program (ACAP). Recently, Albright noted, a representative from a Montana site called asking for additional information. This site, Albright reported, does not currently have a cover and the site owner is interested in testing a variety of alternative cover designs. Albright was enthusiastic about including the Montana site because its climate differs markedly from the majority of sites that are being proposed to use alternative covers, namely sites in the arid southwest.

Rock and Bolen asked for a list of current and proposed alternative cover sites. Albright agreed to distribute the list be June 5, 1998. Albright noted that the list will become outdated quickly because he is still receiving questionnaire responses. Albright agreed to update the list on a periodic basis.


ACAP PROPOSAL AND SPECIFICATIONS ON THE FIELD PROGRAM

Prior to the June 3, 1998 conference call, Albright, Glenn Wilson, and Craig Benson agreed to compile a detailed outline of the ACAP design plan. The design plan, Albright explained, will be presented as an appendix to the revised ACAP proposal. Not surprisingly, Albright said, the team has encountered many challenges while drafting the specifications for the design plan. Albright stressed that it is very difficult to understand all of the components of the hydrological budget, in part because precipitation, evapotranspiration, and recharge are so difficult to measure. Albright has been conducting a thorough literature review to identify the best way to quantify some of these parameters. He said that the design team has been working diligently to complete the proposal and that a draft should be completed by June 12, 1998.

According to Albright, the design plan will describe methods used to measure infiltration and recharge and will discuss errors and difficulties encountered with different techniques. Albright said the design plan will recommend using a pan lysimeter and soil instruments to collect required data. The former, he said, provides estimates for infiltration and the latter provide information required for computer modeling.

Cover Design

Bolen asked whether the design plan will include recommendations for cover design. Bolen realized that cover design will be highly site-specific but asked whether it was possible to recommend a list of specific cover designs for different site categories and different regions of the country. Albright said it is too early to make such recommendations. Ideally, he said, recommendations of this kind will be possible after information is gathered under the ACAP program. At this point, Albright continued, the ACAP is not planning to propose actual cover designs because (1) insufficient data are available and (2) the ACAP does not want to force site owners to use a specific type of prescribed cover. Albright said cover design will be addressed individually at each site, based on site-specific soil data that is generated in the laboratory. (Albright noted that one soil parameter, hydraulic conductivity, can range by 10 orders of magnitude across different sites.)

Albright said covers can be designed by site owners, consulting engineering groups, or ACAP members. Regardless of who develops them, Albright stressed, all of the covers must be reviewed by the ACAP team before a site is officially accepted into the program. Evaluating the covers should help ensure that the team does not test gross design failures. Albright said that he and Benson have already been asked to evaluate the cover design at one landfill: Keifer Landfill. At this landfill, a cover design was drafted without any supporting soils data. According to Albright, he and Benson have refused to evaluate the cover until soils data are presented.

Pan Lysimeters

Albright said that the design plan will recommend using a 10-meter-wide and 20-meter-long pan lysimeter to measure infiltration. Bolen asked whether pan lysimeters differ from drainage lysimeters. Albright said that pan lysimeters, drainage lysimeters, and basin lysimeters are very similar but that suction lysimeters are much different.

Rock asked how many pan lysimeters will be required per site. Albright said that one lysimeter should be installed for a given cover design. If multiple cover designs are tested at a site, he said, multiple lysimeters will be required. Otherwise, only one lysimeter will be required, even for large (e.g., 40-acre) covers. Albright noted that using additional lysimeters would provide more information about spatial variability across a given cover but did not think the added insight would outweigh the additional cost.

According to Albright, Benson estimated that installing a test facility would cost about $75,000. Albright stressed that this price quote includes (1) excavation costs, (2) purchase and installation of three lysimeters, other instruments (e.g., telemetry and soil moisture probes), and a meteorological station, (3) the cost of replacing excavated soil back after instrumentation is installed. In addition, Albright said that the estimate covered some of the quality assurance, networking, and troubleshooting activities that would be required for test facilities. Albright said that Benson's estimate was submitted as a lump sum but Albright agreed to ask Benson for a more detailed breakout and to send it to Bolen.

Albright said that Benson's estimate assumes that the lysimeter will be covered with native material and does not include costs associated with purchasing and bringing in off-site soils. Albright noted that the estimate assumes that three lysimeters will be installed. He guessed that the cost of a test facility would decrease to about $40,000 to $50,000 if only one lysimeter was going to be used. Albright stressed that he was hesitant to give cost estimates because costs will fluctuate based on site-specific conditions. For example, he said, costs would differ between a privately-owned site and a high-security radioactive DOE site.

In response to a question asked by Bolen, Albright said that each test facility would encompass about a 20-meter by 30-meter area, large enough for the lysimeter, the meteorological station, and other instrumentation.

The conference call participants talked at great length about the depth at which the lysimeter should be installed and whether a root penetration barrier is required. Wong warned that installing a lysimeter too deep can limit the amount of useful information that is yielded. As an example, he described a hypothetical system in which 4 feet of cover material are placed over a lysimeter. If no infiltration is detected, he noted, investigators can assume that the cover worked but they have no idea whether 2 feet of cover material or 4 feet of cover material are required. Albright acknowledged Wong's point, noting that the ACAP team does not want to test gross overdesigns. He said that modeling efforts will help determine how many feet of cover are required at a site and that testing multiple covers per site could help identify an optimal cover (i.e., an efficient cover that uses minimal materials). Paul Schroeder said that investigators will likely get a good idea of how much cover is required by comparing the results collected from a variety of sites across the ACAP.

Schroeder said that the lysimeter should be installed beyond a depth where water is drawn upward. He estimated that 6 feet would be an appropriate depth. The participants noted that it is crucially important to ensure that plant roots cannot tap into water that builds up in the lysimeter's liner. Rock said the lysimeter's liner is not a "swimming pool" and will not accumulate large quantities of water. Albright acknowledged Rock's point but argued that the water buildup could be fairly significant. Conference call participants noted two ways to prevent roots from interacting with the lysimeter's liner:

Schroeder asked Albright to explain how water is drained from the pan lysimeter and whether any capillary suction is exerted during collection. Albright said that no capillary suction is exerted. He explained that the water collected on the liner passes through woven synthetic fabrics, is then shuttled laterally, and eventually passes down the trough-shaped center line of the lysimeter. From there, the water passes through an opening at the bottom of the lysimeter and drains into a tipping-bucket-type rain gauge.

Schroeder suspected that the drainage lysimeter will underestimate the actual drainage through a system. He noted that soils surrounding the lysimeter will sustain a higher moisture content than surrounding soils. Because of this, the gradient for water to flow into the lysimeter will be reduced. (Schroeder said that water is drawn more readily to dry soils than to wet soils.) Schroeder likened installing a lysimeter into a system to changing a system's water table. When the water table is 100 feet below the ground, Schroeder noted, capillary suction is exerted over 100 feet. Changing the table to 6 feet, he continued, reduces the capillary suction to be exerted over only 6 feet. Albright pointed out that soils reach a point at which they have relatively constant moisture content and are unigradient. Schroeder agreed, noting that the capillary suction at 100 feet is not very different from that recorded at 110 feet. He warned, however, that the differences in suction may be very different when comparing 6 feet to 100 feet. Albright acknowledged that this was true. Schroeder suggested calculating the unsaturated hydraulic conductivity at a soil suction of 6 feet and 30 feet to get an idea of how suction changes with depth through a system. Albright agreed that performing this calculation would be straightforward and informative.


THE JUNE 1998 IBC CONFERENCE IN HOUSTON, TX

Rock told conference call participants that the RTDF Phytoremediation of Organics Action Team will meet on June 23, 1998, following the IBC conference. Rock said team members will gather as an entire group between 6:00 and 6:30 p.m. Later in the evening, the Alternative Cover Subgroup will meet and discuss issues. Before June 23, Rock would like Albright to complete the ACAP proposal and Rock would like to identify a list of expectations that are required from RTDF participants.


EXPECTATIONS OUTLINED FOR RTDF PARTICIPANTS

Rock said that RTDF participants will be asked to give a 3- to 5-year commitment. He also noted that they will be required to contribute a certain amount of money or in-kind service. Initially Rock planned to ask participants to contribute $30,000 to $50,000 but realized that this quantity was low based on Benson's test facility cost estimate ($75,000 for 3 lysimeters). In addition, Albright noted, reviewing a site's cover design and test facility design could require an additional $5,000 to $20,000.

Based on this information, Rock surmised that each site would require about $100,000 in startup costs and about $20,000 a year for followup activities. (Albright said that part of the followup activities would include paying for an ACAP team member to perform a biannual site visit to troubleshoot and calibrate the instruments.)

With the assistance of the conference call participants, Rock made a list of advantages that RTDF participants gain from becoming involved:


MISCELLANEOUS

Wong said it is unlikely that Union Carbide will be able to install a lysimeter at their test site. Wong said that one problem at his site is defining where the cap starts and ends.

Rock noted that regulators in Region VIII define a leaky cap as a failed cap. He said the ACAP team will have to decide what criteria they want to use to determine whether a cap has passed or failed.

Albright said that the Spring 1998 issue of EPA Region IX Solid Waste Program's Garbage Gazette offers an informative article on alternative covers. Bolen asked for a copy and Albright advised him to contact Steve Wall.

Albright said that he would send Bolen a copy of the revised timeline for the Phase I portion of the ACAP project. Albright noted that Rock agreed to extend the Phase I deadline. Under the new schedule, DRI will complete a draft summarizing Phase I activities by the end of September 1998. Albright agreed to send copies of the draft to Rock, Bolen, and three designated reviewers (i.e., Schroeder, Mark Ankeny, and Benson) as soon as the draft is complete. Ideally, he said the report will be finalized by the end of the calendar year.


ACTION ITEMS

Albright said that he will distribute a(n):