In situ -- 2001 and beyond

The 1990s saw unparalleled development in innovative in situ treatment technologies for remediating groundwater contamination. Have these new technologies met the challenge of remediating groundwater more efficiently and cost-effectively than conventional methods? How can we assure their continued progress? This article examines the development and use of innovative groundwater treatment methods and examines how our industry can continue to apply these methods successfully. This article also identifies the sources of information for both potential users and regulators to make informed decisions regarding innovative groundwater remediation technologies.

A historical perspective

The term "innovative technology" is applied to many new categories of technologies if their widespread use is considered limited because inadequate performance and cost data, such as bioremediation, permeable reactive barriers, surfactant flushing and in situ chemical oxidation. Innovative technologies can become "conventional" or "developed" when their design, performance and cost is well understood for most possible applications.

For instance, soil vapor extraction was considered innovative as recently as 19961. Before the 1990s, common remediation practice, after performing what typically was a limited site characterization, was to implement a "pump and treat" strategy for "cleaning" affected groundwater. This method was used for many chemicals-of-concern (COCs) in groundwater, was relatively straight forward to design and construct, was not terribly complicated to operate and routinely gained regulatory acceptance. What soon became apparent, however, was that although the hydraulic control provided by pump and treat could slow or even reverse the plume migration, it typically could not reduce the concentrations of target chemicals to water quality goals (i.e., drinking water limits). Many of these sites were forced to operate their systems for much longer than estimated. Remediation costs skyrocketed, regulatory closure was not attained and economic use of such sites was forestalled.

In the 1980s and early 1990s (before the widespread use of risk assessment and monitored natural attenuation strategies), the environmental community recognized a need to develop new technologies that could better address the complexities of reducing chemical mass in the subsurface. Additionally, there was increasing pressure from the public sector to remediate sites quickly. University, government and industry researchers began developing and testing, often in a collaborative effort, a variety of destruction, containment and enhanced mobilization methods (Table 1).

Table 1: Examples of innovative technologies for in situ groundwater treatment

Containment/

Immobilization

Treatment / Destruction

Solubility control /

Enhanced removal

Physical and Chemical Barriers

Intrinsic and Engineered Bioremediation

Cosolvent Flooding

pH Control

Permeable reactive barrier

Electrokinetics

Cryogenics

Chemical oxidation

Steam injection

In situ Vitrification

Reduction/Oxidation Control

Vapor stripping / Extraction


Phytoremediation

Phytoremediation

Note: This is not intended to be a comprehensive list.

As new technologies were developed, consortiums among academia, industry and government were created to promote and share their development with the public. Tests of innovative technologies were administered for practical uses. Consortiums and working groups included the University of Waterloo (Ontario, Canada) Solvents in Groundwater program, the Remediation Technology Development Forum (RTDF), the U.S. Department of Energy's (USDOE) In Situ Remediation Integrated Program, and the USEPA's Superfund Innovative Technology Evaluation (SITE) program.

Similarly, the Interstate Technology Regulatory Cooperation (ITRC) was created by state regulatory agencies to develop uniform guidance standards for regulatory evaluation of innovative technologies. Beginning in the mid-1990s, technical conferences and short-courses focusing on innovative remediation technologies became common. Professional papers on the subject were being published in nearly every environmental journal, and as Internet use became practical and commonplace, detailed information on innovative technologies, including case histories, became readily available.

Successful remediation technology

The success of an in situ remediation technology for a given site depends on the four C's: coverage, chemistry, completeness and cost.

The application of a technology must provide coverage of the volume of groundwater requiring treatment before that water arrives at a sensitive receptor. Assuring coverage relies on developing a sound conceptual model of the distribution of the COCs, stratigraphy and hydraulic conditions. Because subsurface hydrogeologic systems are inherently heterogeneous, the technology must be sufficiently engineered to compensate for uncertainty and variability. For example, in a paper describing considerations for applying in situ chemical oxidation, Oberle and Schroeder2 note how chemical destruction of target compounds from the oxidation process is greater in more permeable sediments than in low permeability sediments because of contact limitations.

The chemistry of a treatment process must work within the site's hydrogeochemical environment. Development of a treatment method typically begins in the laboratory, where the process can be evaluated under controlled conditions, but development must not ignore the unique inorganic and organic conditions of each site. Bench tests performed before implementing a pilot-test or full field remedy may not accurately simulate field conditions or provide fully accurate information on treatment longevity under site conditions.

For example, the presence of sulfate (e.g., from anthropogenic sources, or natural gypsum) in groundwater can limit the effectiveness of enhanced bioremediation in degrading chlorinated hydrocarbon compounds. Careful consideration must also be given for treatments that radically alter the ambient geochemical condition of the aqueous system, such as using in situ oxidation within a naturally reduced system.

A treatment process must be complete. That is, it must meet the regulatory objectives at designated locations, and it must not create byproducts or conditions less favorable than the initial condition. Some byproducts (e.g., vinyl chloride) that have stricter cleanup criteria than the parent compound (e.g., trichloroethylene) can accumulate from incomplete treatment. A treatment train may treat the complete mix of COCs, but the combined treatment process can not be internally competitive. For example, an upgradient treatment process that increases the pH of the groundwater system may inhibit performance of an oxygen-releasing constituent designed to stimulate aerobic microbiological activity.

The cost of treatment must warrant its application. Although the cost to design and implement a remedial technology can be substantial, it may be acceptable if the remedy can significantly decrease treatment time and is less expensive than operating and maintaining a conventional technology, even if the innovative technology has a greater capital cost. Although the innovative technology may require occasional replenishing or replacing, if designed properly, the cumulative costs should remain less then costs for the conventional technology it replaces.

Successes and failures

There are many documented cases in which innovative remediation technologies have been successful. Examples include the use of a patented bioremediation process to degrade COCs and attain regulatory closure in the San Francisco Bay area3, and a program that enhanced the biodestruction of chlorinated hydrocarbon compounds using injection of methane to stimulate anaerobic microbiologic activity at the Savannah River Site in South Carolina4. Many examples of bioremediation projects also are included in widely distributed proceedings from conferences sponsored by Battelle Memorial Institute5. Cases in which innovative technologies have been less successful than projected are less well documented although they often provide useful information. In one such case described by Roberts and Bauer7.

Approval and acceptance of innovative remediation technologies

There is no one recipe for gaining approval from regulatory agencies, although regulators appear to be more open today to considering and permitting innovative technologies. Although some inconsistency exists with regard to permitting (e.g., underground injection control permits and waste discharge reports are jurisdiction-specific), there appears to be a growing tendency among regulators to allow limited testing of new technologies for demonstrating a process and evaluating potential impacts to the site. Training opportunities for regulators (as developed by the ITRC, for example) have increased in the past decade - a trend that is expected to continue through 2001.

Most projects that receive regulatory approval for an innovative technology have at least one commonality: open dialogue between project personnel and regulators that began early in the design process and continues throughout the project. Another critical element for approval is that the technology does not create conditions worse than what preceded its implementation.

Information sources

The information available on innovative groundwater remediation technologies genereally falls into one of three categories:

  • Detailed information - research studies, pilot tests, descriptions of technologies, some construction information
  • Summary information - most construction information, remedial strategies, some performance monitoring, some cost data, success stories
  • Limited or no information - most cost and performance information, failures

This summary suggests that information on conceptual ideas and basic research is readily available, but the critical information required for decision-making is less available. Although cost and performance data is becoming more available, there are no standards by which cost data is compiled and evaluated, and cost comparisons among sites may not be helpful because of the site-specific nature of each project. Performance data is becoming more available, thanks in part to detailed studies by the U.S. Environmental Protection Agency and others. However, long-term performance data for most innovative technologies is generally not available because the methods are so new.

What we can expect in the future

As the cliché goes, one way to predict the future is to learn from the past. Another way is to ask your colleagues what they foresee. We can apply both methods. For the former, the hundreds of case studies in public domain provide ample information for assisting site owners, consultants and regulators in implementing appropriate remedies for their sites.

For the latter, I asked approximately 100 colleagues from industry, consulting, academia and regulatory agencies questions regarding their use of innovative groundwater remediation technologies compared to five years ago. A summary of the approximately 40 responses received follow:

  • 60 percent are more likely to use an innovative technology; 20 percent foresee about the same rate of use; 20 percent are more likely to use a conventional technology.
  • 70 percent believe that gaining regulatory approval for an innovative approach is more likely now.
  • 50 percent believe that overcoming legal hurdles to implementing some innovative technologies is more likely today.
  • 75 percent believe sufficient cost and performance information is not available.
  • 67 percent believe a sufficient number of "unbiased" technical documents are not available.
  • Industry site owners generally said that although some consultants are well-qualified, most do not have enough experience.
  • Most industrial representatives and consultants stated that regulators in general do not have enough experience assessing innovative technologies, but that this is changing.
  • Respondents generally preferred getting information on technologies from colleagues and internal resources. Information from technical journals, seminars, short courses and Internet resources were relied on about equally.

When asked to identify the most critical issues implementing an innovative remediation technology at their site, respondents most often suggested that compiling more information on cost and performance from different sites under diverse conditions should be a priority. By what the survey suggests, an attempt should be made to lessen the perceived bias of touted "success stories."

As we head into the next year and decade, innovative technologies will continue to play an important role in how we remediate affected sites. Today's innovative technologies will become tomorrow's conventional technologies if they continue to be used wisely and meet project and regulatory objectives, are designed for site-specific conditions by experienced professionals and their successes and failures are well documented in the literature. Consortiums among industry, academia, engineering and regulatory groups should and will continue to provide opportunities for developing practical approaches to solving groundwater issues. Training in design and application of innovative remediation methods must continue, and critical, thorough evaluations of the performance of these methods are vital to assuring that affected groundwater is remedied by technical and financially-effective methods.

References

1 U.S. EPA. Treatment Technologies for Site Cleanup: Annual Status Report, Eighth Edition, Technology Innovation Office, Office of Solid Waste and Emergency Response, EPA 542-R-99-001, August 1998.

2 Oberle, D.W. and D.L. Schroeder, 2000. "Design Considerations for In-Situ Chemical Oxidation, in Wickramanayake, G.B. Gavaskar, A.R., and A.S.C. Chen, Chemical Oxidation and Reactive Barriers: Remediation of Chlorinated and Recalcitrant Compounds." Battelle Memorial Institute, pp. 91-99.

3 Delfino, T. and J. Honniball. "Food for Thought", Environmental Protection, Nov. 2000, Page 33.

4 U.S. EPA. "Engineered Approaches to In Situ Bioremediation of Chlorinated Solvents: Fundamentals and Field Applications." Office of Solid Waste and Emergency Response, EPA-542-R-00-008, July 1998.

5 Wickramanayake, G.B. and R.E. Hinchee. Bioremediation and Phytoremediation, Chlorinated and Recalcitrant Compounds. Battelle Press, Columbus, Ohio, 1998.

7 Warner, S.D., Yamane, C.L. Bice, N.T., Szerdy, F.S., Vogan, J., Major, D.W., and D.A. Hankins. "Technical Update: The First Commercial Subsurface Permeable Reactive Treatment Zone Composed of Zero-Valent Iron, in. Wickramanayake, G.B. and R.E. Hinchee, 1998." Bioremediation and Phytoremediation, Chlorinated and Recalcitrant Compounds. Battelle Press, Columbus, Ohio, pp.

8 Roberts, E.P. and N Baurer, 2000. In-Situ Chemical Oxidation Limited by Site Conditions - A Case Study, in, Wickramanayake, G.B. Gavaskar, A.R., and A.S.C. Chen, Chemical Oxidation and Reactive Barriers: Remediation of Chlorinated and Recalcitrant Compounds. Battelle Memorial Institute, pp. 169-180.

This article originally appeared in Environmental Protection magazine, January 2001, Vol. 12, No. 1, page 26

This article originally appeared in the 01/01/2001 issue of Environmental Protection.

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