SUMMARY OF THE REMEDIATION TECHNOLOGIES DEVELOPMENT FORUM
SEDIMENTS REMEDIATION ACTION TEAM
GROUND WATER-SURFACE WATER INTERACTIONS WORKGROUP
CONFERENCE CALL

2:00 p.m.–3:00 p.m.
June 12, 2003

On June 12, 2003, the following members of the Remediation Technologies Development Forum's (RTDF's) Sediments Remediation Action Team, Ground Water-Surface Water Interactions Workgroup, met in a conference call:

Nancy Grosso, DuPont Corporate Remediation (Action Team Co-chair)
Peter Adriaens, University of Michigan
Bruce Duncan, U.S. Environmental Protection Agency (EPA), Region 10
Erin Mack, DuPont Corporate Remediation
Bob Maxey, U.S. EPA, Office of Solid Waste
Farukh Mohsen, Gannett Fleming
Bernie Zavala, U.S. EPA, Region 10

Christine Hartnett of ERG was also present.

BACKGROUND INFORMATION

The Sediments Remediation Action Team held a meeting in Seattle, Washington, in October 2002. During the meeting, there was much discussion about ground water (GW) and surface water (SW) interactions in the transition zone. By the end of the meeting, some attendees had volunteered to write a summary paper on that topic. This conference call was held to initiate the writing process. (Once completed, the summary paper will be posted on the RTDF Web site. If the authors want the paper peer reviewed and published, this possibility will be explored as well.)

DISCUSSION

Prior to the call, Nancy Grosso distributed a list of nine GW-SW interaction topics that were identified during the October 2002 meeting. She proposed addressing all nine topics in the summary paper. While the first six topics enjoyed a fair degree of consensus, Grosso said, the last three were still being debated when the October meeting came to a close. She asked call participants to decide whether enough information is available to address these last three topics. This was the focus of the entire call.

Question #1: How does one approach evaluation of a site where no apparent impact is evident and the only data available are site ground-water plume concentrations and flow direction?

Grosso initiated discussion on this topic, noting that DuPont uses screening values to determine whether contaminant concentrations in ground water are high enough to pose concern if the contaminants are discharged to a surface-water body. She said that ambient water quality criteria (AWQC) or state standards are used to perform the screening exercise. Bob Maxey said that he thought it would be useful to write up some information on the screening technique, noting that the only difficult questions that emerge with such a technique are (1) How should dilution be accommodated for? and (2) What should investigators do if a particular contaminant does not have an AWQC screening value? Bruce Duncan said that this latter issue--the lack of an available screening criterion--is not unique to GW-SW interaction assessments. Thus, he did not think it required detailed analysis in the summary paper.

Peter Adriaens said that it might be useful to provide information about techniques, such as conservative tracer tests, that can be used to predict where ground-water seeps are likely to emerge. He also recommended including information about scenario testing, a technique that involves exploring a series of "what if" scenarios to gain an understanding of how contaminated ground water could impact a receiving surface water body. This type of analysis involves analyzing a range of parameters, including infiltration rates, pumping rates, tidal action influences, seasonal effects, and geological information. Sensitivity analyses are performed, he said, to gain information about which parameters have the most dramatic effect on outcomes.

Farukh Mohsen said that he appreciated Adriaens' ideas, and that he does think it is useful to invest effort in determining how large an impact, in terms of contaminant and water flux, ground water could have on receiving surface-water bodies. Such information, however, is not enough to allow one to determine whether the impacts will pose unacceptable risks. When trying to determine this, Mohsen said, the real question is: What will the contaminant concentrations be after the ground water has entered the larger receiving water body and been diluted? Grosso, who agreed that this was an important question, said that people want to know how quickly a plume mixes with surface water and how much surface water is needed to dilute contaminants to a point where they pose little concern. Maxey contributed to the discussion, providing information about dilution and mixing numbers. He said that a draft EPA guidance document cites 10 percent river volume as an acceptable quantity for plume dilution. This number is still up for debate, Maxey said; the draft document that cites it has not been circulated for review yet. Maxey also noted a general rule of thumb that some people refer to: concentrations in the mixing zones must be below acute AWQC values, but concentrations in the larger portions of receiving water bodies just have to be below chronic AWQC values. In general, Maxey said, acute values are usually about 10 times higher than chronic values. (He advised referring to Figure 5-1 of EPA's Water Quality Standards Handbook for more information on the relationship between acute and chronic values.)

Question #2: How does one approach evaluation of ground-water contamination input to an urban river where multiple inputs to the system are likely (e.g., outfalls, historical spills)? How can one readily assess the incremental risk presented by ground water?

Maxey said that EPA's Water Quality Standards Handbook can help answer this question. The handbook, he said, devotes an entire chapter to the concept of waste load analysis. The methodology it presents, though, has attracted some criticism. Call participants agreed to review the handbook to become better acquainted with EPA's recommended approach. After doing so, they will revisit this question.

Adriaens discussed "fingerprinting" tools that have been developed to provide information about different sources' specific contributions to receiving water bodies. He said that several papers have been written on the topic. Grosso said that tools like this would probably be very helpful to people who work on Total Maximum Daily Load issues.

Question #3: How does one go about finding and assessing ground-water discharge area in large tidal and estuarine settings where the scale of the sediment issues may occur on a watershed scale?

Adriaens said that an American Geophysical Union publication might provide useful information for this question. Maxey said that Duncan might have information to provide on Question #3. (Duncan had to leave the call before Question #3 was discussed; Grosso will follow up with him.)

ACTION ITEMS

• Mohsen agreed to help rephrase Question #1 and to provide some information that might help address the question.



• Adriaens agreed to write up a summary of scenario testing techniques that can be used to predict the impact ground water could have on surface water bodies. His summary will refer to specific models that have been used to perform this type of exercise.



• Adriaens agreed to provide a writeup on fingerprinting tools that are used to provide information about the different sources' specific contributions to receiving water bodies.



• Adriaens agreed to distribute and/or summarize an article that appeared in an American Geophysical Union publication.



• Maxey said that he would try to find the source of the 10 percent value that is frequently cited as an acceptable dilution rate.



• Maxey will e-mail call participants the Web link for EPA's Water Quality Standards Handbook.



• Grosso agreed to distribute information about some of the techniques that DuPont uses internally to address GW-SW interaction issues.



• Grosso will follow up with Duncan about an unpublished EPA document that might provide information on Question #3.



• ERG will set up the next conference call for August 5, 2003, between 2:00 p.m. and 3:00 p.m. Eastern Daylight Time.