Cleaning Polluted Groundwater

The Schoolcraft Project

Significance: Hazardous Waste Removal

Carbon tetrachloride is toxic stuff. So toxic, in fact, that if Michigan's Department of Environmental Quality (MDEQ) finds a concentration of five parts per billion in a water source, it condemns the polluted water as unsafe to drink and requires the polluting industry to treat the problem. The maximum allowable contamination level is set by the U.S. Environmental Protection Agency (EPA).

Prior to its regulation in 1989, carbon tetrachloride was commonly used in many industrial processes--in chemicals for refrigeration, dry cleaning, insecticides, and so on. Some of these uses are now outlawed by the EPA, and its usage overall is declining. However, contamination from past releases of the chemical into industrial and agricultural wastewater persists, and continues to pollute groundwater sources nationwide. The EPA estimates that as much as 10 percent of U.S. groundwater may be contaminated at levels near or above quality standards.

Current methods of remediation are expensive, time consuming, and unsatisfactory. Air-stripping, the conventional cleanup practice, uses activated charcoal filters to strip out the carbon tetrachloride. This does not reduce the pollution; it merely transfers the problem to the atmosphere. Even worse, the process also produces chloroform, which is hazardous in itself and is one of the most common contaminants of U.S. groundwater.

Context: Schoolcraft and the St. Joseph Aquifer

Schoolcraft is a small town in southwestern Michigan that lies above a section of the St. Joseph Aquifer (an aquifer is an underground bed of earth, sane, gravel, and/or other materials that carries water). In the 1960s about 15-25 gallons of carbon tetrachloride were dumped into the aquifer below Schoolcraft. By the early 1990s a toxic plume (or leakage pattern) had penetrated a mile long, a tenth of a mile wide, and 80 feet deep into the aquifer, with a concentration of 5 to 150 parts per billion of carbon tetrachloride--far above the maximum level permitted by the EPA.

The plume had begun to threaten lakes and drinking water sources southeast of the aquifer, in the direction of its flow. Detoxifying the site using conventional technology would have involved more than 25 years of work and five to six million dollars.

Researchers Craig Criddle (MSU and Stanford University), Mike Dybas (MSU), and a team of engineers, geologists, and microbiologists have developed a better plan.

Scholarship: Using Bioaugmentation to Remediate Carbon Tetrachloride Pollution

Serendipitous Discovery: Pseudomonas stutzeri Strain KC

In 1988, about the same time as federal regulation took effect, a microbe that could transform carbon tetrachloride into carbon dioxide and other inert compounds, without producing chloroform, was discovered.

Dr. Craig Criddle, who was then a graduate student and is now an associate professor of civil and environmental engineering at Stanford University, was looking for organisms that could dechlorinate carbon tetrachloride. As he remembers it:

The source of organisms was aquifer materials from several DOE sites, with one exception. As an afterthought, I remembered some old aquifer material sitting in a bucket at the back of a cooler. Since it was no extra work, I set up an enrichment [growing medium] using that material as well. Within two days a surprising thing occurred.... Pearly white balls formed, and there was no detectable carbon tetrachloride. Best of all, there was no detectable chloroform, the normal dechlorination product.... At the time, I thought it was unlikely that we had isolated anything unique.

But the phenomenon was interesting all the same, and Dr. Criddle was still tinkering with the microbe (Pseudomonas stutzeri strain KC) when he came to Michigan State University in 1991. Meanwhile Greg Tatara, a Ph.D. student in MSU's Microbiology Department, and Mike Dybas, the current project Principal Investigator, had joined Criddle's lab. The group continued to explore P. Stutzeri KC's idiosyncrasies. Did the transforming effect have something to do with the pH balance? Trace metals in the growing medium? They discovered that the bacterium liked an environment with a bit of copper and a very limited iron supply in order to "turn on" the ability to break down carbon tetrachloride. They also discovered that these precise growth conditions could easily be achieved by adjusting the pH of the environment--a finding that Dr. Dybas refers to as "the heart of the technology."

The field testing of the bacterium began when Tim Mayotte, a Civil and Environmental Engineering graduate student, took a course on biological processes that Criddle was teaching. Mayotte, who had worked for six years as the lead hydrogeologist on the plume at Schoolcraft, told Criddle about the project. Dybas obtained groundwater and aquifer sediment from Schoolcraft, spiked it with acetate and carbon tetrachloride, adjusted the pH, inoculated it with KC, and observed the transformation. The question then became, would KC be able to colonize itself onsite well enough to make long-term continuous transformation possible? A pilot study was quickly devised and the project was on.

Non-Technical Challenges

The initial challenges to the project were non-technical. Permission had to be obtained from Michigan's Department of Environmental Quality. Residents of the Schoolcraft community had to be informed about risks and benefits. Contractors and consultants had to be hired to design, build, install, and maintain the equipment. And, of course, funding had to be found.

About working with the Schoolcraft community, Dybas says,

We wanted to be preemptive--to anticipate problems and share information up front so people had ownership and didn't spin any nightmare scenarios, like 'The Andromeda Strain is coming.' Extension's help was invaluable. They made the contacts for us. We held community meetings. We talked to Kalamazoo Public Health and had articles in the Kalamazoo Gazette. At the beginning, industries felt they were targeted but they ended up feeling that MSU carried its own weight.

He adds,

It's good for scientists to have to pay attention to community interaction issues. People will sense it very quickly if you disdain the public. The meetings helped. We also studied potential effects of the project on corn, soybeans, minnows--we did other ecosystem evaluations in order to be able to assure the public it was OK. The lesson is to do it before problems occur.

Technical and Logistic Issues

A monumental list of technical and logistic issues also had to be addressed. First, the physical, geological, chemical, and other characteristics of the aquifer were studied. Next, modeling and cost analysis confirmed that a biocurtain, or system of closely spaced wells to span the plume and deliver the P. stutzeri KC solution, was technically feasible and economical. A pilot biocurtain system was then designed and constructed--delivery and monitoring wells were built, tracers were used to record the flow of materials inoculated into the groundwater, and the KC culture was adjusted as its performance was monitored.

Lessons learned from the pilot study were used to fine-tune the design of the full-scale system for remediating the plume. For example, the pH balance was tweaked again to more fully eliminate chloroform production, and a plan to funnel the aquifer into a more concentrated area for inoculation was discarded due to technical difficulties. Dybas calls this "a scaling-up process, checking the interplay among the various factors at each step of the way. It's a cost-effective design principle."

Conclusion: Bioremediation is More Effective, Less Expensive, and Faster

The scientific findings were dramatic: P. stutzeri KC was able to integrate into the aquifer community long-term, and the biocurtain proved to be a highly cost-effective, long-term solution capable of removing the carbon tetrachloride to levels well below the regulatory limits, with little chloroform production. Unlike existing "pump-and-treat" systems, it is ecologically sustainable. The technology also shows promise for generalizing to other situations. At the request of MDEQ, the team is beginning to address the issues of other, larger and more complex plumes within the aquifer.

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Impacts

Community Impacts

• This technology, including its research, development, construction, testing, and refinement, cost no more than a cleanup using current/conventional methods would have.
• It has the potential to be faster--again, including the time spent in research and development--and more effective at dealing with the problem.
• The technology is now available for other cleanup projects that will receive the financial benefit of its low cost and high level of effectiveness.
• MDEQ is funding a full scale remediation to clean the entire aquifer using this technology.

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Scholarly Impacts

• Research
  • Funding received from Michigan Department of Environmental Quality ($7.5 million), National Science Foundation ($200 thousand), and U.S. Environmental Protection Agency ($200 thousand)
  • Numerous publications and presentations
• Teaching
  • Dissertations (9 so far), Master's theses (15 so far)
  • Asset for recruitment of top students
  • Field lab in support of existing courses
  • Hands-on experience with technology
  • Technical certification in hazardous waste operations (40 hour OSHA training)
  • Interface with prospective employers (consultants, engineers)
• Technology transfer
  • Development of design principles
  • Full-scale treatment system as technology demonstration
• Outreach products
  • Private sector partnership serving design, construction, and operation
  • Project's multi-level Web site serves interests ranging from basic/casual all the way up to links that lead to full-text scientific journal articles (the graduate student who designed it has an interest in education)
• Awards
  • National Groundwater Association 2002 Outstanding Project in Groundwater Remediation (to MSU)

For a full description of this project, along with lists of partners, publications, and links to more information about bioremediation, see http://www.egr.msu.edu/schoolcraft .

Sources: Schoolcraft Project Web site, Powerpoint presentation, and conversations with Michael J. Dybas. Story written by Linda Chapel Jackson, Editor, University Outreach and Engagement.

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