April 2004 factsheet
EPA wants barrier included in water cleanup plan
U.S. Environmental Protection Agency wants to install a specially built wall into the ground near a drainage ditch on Clare,s southwest side in a continuing battle against contaminated underground water. The special barrier, called a permeable reactive wall, would be built between the U.S. 10 drainage ditch and the Mitchell factory site in Clare,s industrial park. The barrier is needed because contaminated water is seeping into the drainage ditch, and the ditch feeds into the well field that provides drinking water to 3,300 residents.
EPA conducted an investigation and performed a feasibility study on stopping the contaminated ground water. The feasibility study came up with two cleanup options, and EPA selected the special barrier as the most cost-effective plan that will still protect human health and the environment. The proposed plan along with site history and the criteria used to compare cleanup options are outlined in this fact sheet.
Area residents have 30 days to comment on EPA,s proposed plan. See the adjacent box to find out how your opinion can be heard. Based on your feedback, EPA may modify the selected cleanup plan or pick the other option. (see note) When EPA makes a final decision on the cleanup option, it will publish its findings in an official document called record of decision or ROD and publish an announcement in a local paper.
EPA discovered a sump pump located near the Mitchell facility was not intercepting all of the contaminated underground water flowing toward the drainage ditch. Supplies of underground water are known as "ground water" in environmental jargon. The ground water seeping into the ditch contains volatile organic compounds, which are toxic chemicals that evaporate quickly when exposed to air. The ditch feeds a wetland (marshy area) next to the field where four wells supply Clare's drinking water.
Site has history of tainted ground water
Government officials have been fighting water and soil contamination in southwest Clare since 1981. That was when tests revealed that two of the city's water supply wells were contaminated with volatile organic compounds. Soil and groundwater investigations revealed that the chemicals were coming from contaminated soil around various commercial facilities in the nearby industrial park. The hazardous chemicals had apparently leaked from storage tanks, waste piles, floor drains and exhaust fans used with vapor degreasing machines.
By 1991 the drinking water contamination had worsened to the point where it threatened the health of residents. EPA placed the area on its National Priorities List of Superfund sites. The Agency then installed a device called an air stripper to clean the drinking water. The air stripper is still operating and is removing 99 percent of the contaminants, enough to make the water more than safe for drinking. EPA also ordered the companies judged responsible for the pollution to install a water pumping and treatment system. This system intercepts the tainted ground water as it moves from the industrial park toward the city wells and removes the dangerous chemicals.
EPA also required the responsible parties to clean up contaminated soil around the Mitchell and Ex-Cell-O properties. Most of the dirt was dug up and treated in a special pit. But tainted soil deeper than 25 feet was left in place because of the difficulty reaching it. Instead, a sump pump on the Mitchell site was installed to intercept the chemicals as they moved with the underground water.
Several monitoring wells were installed in the area to keep track of how these cleanup procedures were working. In 2000, it was discovered the Mitchell sump wasn't doing a complete job. Tainted ground water was still flowing out of the industrial park and into the U.S. 10 drainage ditch. Environmental experts conducted another study and settled on two options to solve this latest problem.
EPA considered two alternatives for managing the contaminated ground water. The Agency, as required by law, evaluated each option against nine criteria (see a comparison chart of the two alternatives and an explanation of the criteria). The two options are explained below:
Alternative 1. Permeable reactive wall: This is the option
preferred by EPA. The special reactive barrier would be installed downhill from
the Mitchell sump and uphill from the drainage ditch. The reactive barrier
would be 175 feet long, 3 feet wide and 15 feet
deep. The reactive media allows water to penetrate through the barrier at the same time destroying toxic chemicals. Tests show that such a barrier can reduce the toxic nature of a chemical such as trichloroethylene by more than 90 percent. The performance of the new barrier would be checked by four new monitoring wells and an existing well. Estimated cost for this cleanup option is $299,025.
Alternative 2. Ground water extraction and treament uphill of the U.S. 10 draingage ditch: This alternative called "pump and treat" would involve removing contaminated ground water from the Mitchell sump, treating it to remove chemicals, and then discharging the water into the Clare sewage treatment plant. A pump would move the ground water to an underground vault where it would be treated. Before the water would be sent to the Clare treatment plant, it would be run through an air stripper. This alternative would be expected to remove 90 percent of the hazardous chemicals from the ground water. Estimated cost for this cleanup option is $611,000.
See the comparison table
Based on this comparison, Alternative 1 would be more effective than the 1992 record of decision remedy; it would be more implementable than Alternative 2, and it would be the most cost-effective alternative.
Explanation of evaluation criteria
- Overall protection of human health and the environment. Addresses whether an option protects both human health and the environment. This standard can be met by reducing or removing pollution or by reducing exposure to it.
- Compliance with applicable or relevant and appropriate requirements. This standard, known as ARARs, ensures that options comply with federal, state and local laws.
- Long-term effectiveness and permanence. This evaluates how well an option will work over the long-term, including how safely remaining contamination can be managed.
- Reduction of toxicity, mobility or volume through treatment. Addresses how well the option reduces the toxicity, movement and amount of pollution.
- Short-term effectiveness. How quickly can an option help the situation and how much risk will there be while the option is under construction.
- Implementability. Evaluates how feasible the option and whether materials and services are available in the area.
- Cost. Includes not only buildings, equipment, materials and labor but also the cost of maintaining the option for the life of the cleanup.
- State acceptance. Does the Michigan Department of Environmental Quality accept the option. EPA evaluates this criteria after receiving public comments.
- Community acceptance. How well do nearby residents accept the option. EPA evaluates this standard after a public hearing and comment period.