SUMMARY OF THE REMEDIATION TECHNOLOGIES DEVELOPMENT FORUM
PHYTOREMEDIATION ACTION TEAM
CHLORINATED SOLVENTS SUBGROUP
CONFERENCE CALL

March 15, 2000
1:30 p.m.–3:00 p.m.

On March 15, 2000, the following members of the Remediation Technologies Development Forum’s (RTDF’s) Phytoremediation Action Team, Chlorinated Solvents Subgroup, met in a conference call:

Milton Gordon, University of Washington (Subgroup Co-chair)
Keith Rose, U.S. Environmental Protection Agency (Subgroup Co-chair)
Bob Tossell, GeoSyntec Consultants (Subgroup Co-chair)

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

THE SUBGROUP’S PROTOCOL

During previous conference calls, the Chlorinated Solvents Subgroup decided to develop a protocol for a field study program. Robert Tossell, who had agreed to generate an outline for the protocol, distributed a first draft to Subgroup members on March 13, 2000. This draft, entitled A Guide for the Evaluation of Phytoremediation of Chlorinated Solvents in Ground Water, contained the following sections: (1) Foreword, (2) Acknowledgments, (3) Introduction, (4) Background, (3) Evaluating Phytoremediation, (4) Methods for Assessment, (5) Summary and Conclusions, (6) References, and (7) Appendices.

Tossell asked Milton Gordon and Keith Rose for comments on the outline. Gordon had none, saying that he received the outline just minutes before the discussion began. Rose, however, did have several comments, and this generated discussion on the following topics:

Title

Rose recommended changing the protocol’s title to reflect the fact that the Subgroup plans to evaluate soil as well as ground water.

Inserting a New Section: "Potential Applications"

Rose noted that Tossell’s draft outline provides information on phytoremediation’s applications under the "Evaluating Phytoremediation" section. Rose recommended making some modifications to the information provided and inserting it immediately after the "Background" section, under a stand-alone "Potential Applications" heading. Rose suggested listing four categories under this new section: (1) hydraulic control in the shallow subsurface, (2) treating solvents in the shallow vadose zone, (3) water management, and (4) innovative and potential new applications.

Tests Addressed in the Protocol

Rose, Tossell, and Gordon agreed that greenhouse studies and pilot studies should both be addressed in the Subgroup’s protocol. Upon Rose’s request, Tossell clarified what he means by the term "pilot tests": tests that are performed outside, in the field. All of the conference call participants agreed that pilot tests should be performed prior to full-scale implementation. In many cases, they agreed, it is also beneficial to perform greenhouse tests. Tossell said that these tests are particularly important if investigators are unsure whether a site’s conditions or contaminants will have a deleterious effect on plant health or growth. Performing these tests helps investigators decide which plants are best to use at a site. For example, Tossell said, greenhouse tests were used to determine whether to use poplar, eucalyptus, and/or tamarisk trees at a site in Palo Alto, California, that had high (>2,000 milligrams per liter) sodium concentrations. By subjecting these plants to the site’s ground water, it became clear that poplars would not survive in such a saline environment; thus, the other two plant species, which were more salt tolerant, were chosen. (As an aside, Tossell noted an interesting feature about tamarisk: this tree contains a dehalogenation enzyme.)

Restructuring the "Methods for Assessment" Section

Rose said that Tossell’s outline lists three subsections under the "Methods for Assessment" section: (1) screening-level assessments, (2) detailed evaluation, and (3) research evaluations. Rose referred to these three subheadings as tiers 1, 2, and 3. He recommended rearranging some of the topics that will be addressed under the first two tiers.

• Changes recommended for Tier 1. Rose recommended including the following as the first three subcategories under Tier 1: (1) review available site data, (2) visit the site, and (3) collect agronomic soil and plant information. Tossell’s draft outline included the last two topics under Tier 2; Rose said they should be moved to Tier 1, because this information is essential to have when trying to determine whether phytoremediation is feasible at a given site. Rose recommended listing the final category under Tier 1 as "Evaluating Feasibility of Phytoremediation." Under this subheading, he said, the protocol should advise (1) using the Subgroup’s flow chart and other screening criteria, (2) determining whether greenhouse studies are necessary, and (3) deciding whether phytoremediation should be used as a stand-alone technology. Rose said that it should be made clear that greenhouse studies are optional. He and Tossell agreed that there may be instances when greenhouse studies can be bypassed. For example, if enough information has been published about a plant’s performance under different site conditions, investigators may be able to predict whether a plant will thrive at a given site just by reviewing the literature.

• Changes recommended for Tier 2. By the time that investigators reach Tier 2, Rose said, they should have already decided whether to implement a full-scale project. Therefore, he recommended changing the title for Tier 2 to "Full-Scale Field Assessment." When investigators reach this tier, he said, they must determine which technology design and monitoring scheme is needed to meet cleanup goals and regulatory compliance standards. Tossell’s outline contained 10 steps under Tier 2, but Rose recommended including only 6: (1) review available site data, (2) collect additional data, (3) refine the site conceptual model, (4) conduct a pilot test (field demonstration), (5) design and implement a full-scale remedy, and (6) conduct full-scale monitoring. Expanding on the latter step, Rose advised providing information on how to sample and analyze air (if necessary), plant tissue, soil, and ground water.

Tossell agreed to give Rose’s suggested changes for Tiers 1 and 2 much thought, noting that he thought that Rose had made several good recommendations. However, Tossell said, he wants to collect feedback from other Subgroup members before finalizing the organizational approach for the "Methods for Assessment" section. Tossell said that it might be useful to limit Tier 1 activities to those that involve reviewing reports, rather than including extensive data collection and greenhouse testing. In some cases, he said, investigators will be able to determine that a site is not a potential candidate for phytoremediation just by reviewing information that has been collected in previous reports. For example, he said, a site would probably be automatically eliminated from consideration if its ground-water table were located 60 feet below ground surface.

Rose noted that Tier 3, "Research Assessment," does not yet contain any information. Tossell said that he is depending on Gordon and Lee Newman to fill in this section. Gordon asked for some guidance on what the section should cover. Tossell said that it should provide guidance to clients who are interested in taking a field study to the research stage, and perhaps publishing papers. He said that these clients will need information on how many samples to collect, how many replicates to include, and how to design their studies so that they provide information that is defensible from a research perspective. Rose said that the section should not focus solely on field study research efforts. For example, he said, it would also be useful to provide some guidance to those who plan to write research papers on new plant species that are tested in the laboratory. Basically, Rose said, this section should explain what must be done to evaluate efficacy and a contaminant’s fate and transport processes.

ACTION ITEMS

• Tossell distributed a draft outline of the Subgroup’s protocol on March 13, 2000. Subgroup members should review this draft and send Tossell comments by March 29, 2000. (Rose agreed to submit his comments in the form of a revised outline, which he will send to all Subgroup members.)

• By March 29, 2000, Gordon will send Tossell information to use for the "Research Assessment" subsection that is listed under the outline’s "Methods for Assessment."

• Tossell said that he will review all the comments he receives, incorporate them, and distribute a revised version of the outline on March 31, 2000. He said that Subgroup members should review the revised version and be prepared to discuss it during the next Subgroup conference call.

• ERG agreed to set up the next conference call for April 5, 2000, between 1:30 and 3:00 Eastern Standard Time.