Sites and Substances in Minnesota
Township Groundwater Contamination Site
On this page:
What has occurred at the site since early 2002?
What do the cumulative sampling results tell us about the TCE plume?
Will sampling of residential and Lake Elmo airport hangar wells continue?
What does MDH conclude in the 2004 report?
What are MDH's recommendations in the 2004 report?
Where can I get more information?
This web site provides information about public health issues related to the Baytown Township Groundwater Contamination site in Washington County, Minnesota. Trichloroethene, also known as trichloroethylene or TCE, is a chemical solvent often used for degreasing metal parts. It was first found in the groundwater in the area in 1987, and the site is listed as a state and federal Superfund site. TCE is a potential human carcinogen.
Activity at the site increased dramatically in February 2002 when the Minnesota Department of Health (MDH) changed its health advice for TCE based on new information on its toxicity to an interim exposure limit of 5 micrograms of TCE per liter (from 30). Since that time, TCE has been detected in the Bayport municipal water supply, and in several private wells drilled in the previously unaffected Franconia groundwater aquifer.
In 2004, MDH completed a report on the site, known as a Public Health Assessment, that describes activities since 2002 and MDH's recommendations to protect public health. Please see the list at the end of this page for further contacts and for instructions on how to obtain a copy of the MDH report.
Since 2002, the Minnesota Pollution Control Agency (MPCA) and the MDH have sampled water from hundreds of wells (See Baytown Township Groundwater Contamination Site, October 2002) in Baytown and West Lakeland townships, the City of Bayport, and Lake Elmo. To date, 149 wells have TCE levels that exceed the interim exposure limit of 5 micrograms per liter (µg/L). All but a few of these wells have been fitted with a granular activated carbon (GAC) whole house filter. In the interim between sampling results and filter installation, the MPCA provides bottled water; over 25,000 gallons of bottled water have been delivered to area residents to date.
The MPCA provides whole house GAC filter systems to homes where the level of TCE equals or exceeds 5 µg/L, if the homes are on properties platted for development before April 9, 2002. For wells not eligible for the MPCA program, Baytown and West Lakeland Township passed ordinances in the fall of 2003 that provide for governmental supervision of GAC filters installed by individual homeowners. The ordinances mandate that the privately installed systems be regularly tested and maintained, and provide for the township to conduct the work, if necessary. Also in 2003, the Minnesota state legislature passed a law requiring homeowners within the Baytown Special Well Construction Area (SWCA) who have private wells to notify buyers at the time of sale that the property is within an SWCA.
In May of 2003, TCE was detected for the first time in private wells drawing water from the Franconia aquifer, which is located below the previously affected Prairie du Chien and Jordan aquifers. An aquifer is a natural underground layer of sediment or rock that contains water. TCE has been found at levels above the interim exposure limit of 5 µg/L in several Franconia wells located at the eastern edge of the SWCA. MDH had previously recommended that new wells be drilled into the Franconia because it is overlain by a less porous layer of bedrock (referred to as a "confining layer") and tests of Franconia wells located in the central and western part of the SWCA had not found TCE. Those wells continue to be free of TCE.
Also in May of 2003, one of three Bayport municipal wells showed TCE for the first time. Levels of TCE in this Franconia well have increased since it was first detected, at times slightly exceeding the federal Maximum Contaminant Limit (MCL) for TCE of 5 µg/L. The city's other two wells have also show low levels of TCE. A MCL is the regulatory standard for public water supplies developed by the U.S. Environmental Protection Agency based on health, economic and technological information. While the concentration of TCE in the overall city water supply has remained below the MCL, the City of Bayport and the MPCA are designing a treatment plant to remove the TCE from the most affected well. The plant should be operational sometime in 2006.
The MDH is monitoring the city wells and distribution system every six weeks. Washington County, MDH, and the MPCA are also working with the Minnesota Geological Society to understand what geological features may be allowing TCE to enter the Franconia.
The MPCA has also conducted additional field investigations at the Lake Elmo Airport, and at the site of a former metal working shop in Lake Elmo that is now believed to be the main source of the TCE contamination. Now that a probable source has been identified, a more efficient groundwater cleanup plan can be developed. The MCPA is currently evaluating several options to clean up the TCE at or near this source.
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Aside from the presence of TCE in the easternmost Franconia wells, well sampling results in the SWCA have not been surprising. Levels of TCE have increased in some wells, and decreased or stayed the same in others.
Updated maps of the TCE plume in the two main aquifers under the area, the Prairie du Chien and the Jordan are available. These maps illustrate several key points:
- Generally the plume is not expanding to the north. Expansion to the south was much less than observed in sampling information from 1999. Where some expansion did occur, it was very small (less than 250 feet).
- The southeastern section of the TCE plume in the Jordan aquifer may be expanding. This expansion may either be real, possibly caused by additional pumping of the aquifer by many new wells drilled as part of recent development, or it may only appear to be expansion as the result of having new wells from which to take samples. Future testing will help to clarify this.
- While individual wells vary in their concentration trends, generally, wells near the center of the TCE plume have the greatest rates of increase (about 0.5 µg/L per year), while those near the edge generally have lower rates of increase (about 0.1 µg/L per year). Exceptions exist; the rate of increase in the Bayport city well #2 has been quite rapid despite its location near the edge of the plume.
One thing to keep in mind when looking at the maps is that some of the irregularities in the shape of the TCE plume may be due to a lack of information. For example, there are few Prairie du Chien wells present in the southeastern portion of the SWCA. The 1 µg/L contour line may actually extend further into this area of the Prairie du Chien.
Comparison of the sampling results to previous information also reveals several things:
- The TCE plume shape in the Prairie du Chien aquifer is different than the shape of the plume in the Jordan aquifer. A larger area of the Prairie du Chien exceeds 5 µg/L TCE.
- The 5 µg/L TCE contour line is shown on the map of the Jordan aquifer as extending to the St. Croix River. Due to erosion, the two upper aquifers are not present in the river valley. Instead, the plume moves through sediments as it approaches the river. It is likely the plume is also present in the upper portion of the Franconia as it approaches the river.
- Neighboring wells that draw water from the same aquifer sometimes have very different TCE concentrations. This can happen when they draw water from different depths within the aquifer.
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Yes. The following sampling plan has been developed:
- Wells with TCE concentrations of 4.3 - 4.9 µg/L will be sampled every 3 months
- Wells with TCE concentrations of 3.0 - 4.2 µg/L will be sampled every 6 months
- Wells with TCE concentrations of 2.0 - 2.9 µg/L will be sampled each year
- Wells with TCE concentrations of 1.0 - 1.9 µg/L will be sampled every 2 years
- Wells with TCE concentrations of 0.1 - 0.9 µg/L will be sampled every 4 years
- Selected "sentry" wells inside of and along the edges of the plume will continue to be sampled annually (a "sentry" well is one that is sampled regularly to alert us to changes along the edges and in the center of the plume). Currently there are 40 sentry wells.
- Newly installed Jordan and Franconia wells without a GAC filter and within the plume will be re-sampled within one year of construction (this will be approximately 5 -10 wells).
- All wells within the plume, plus a "buffer zone" around the edges of the plume and the unfiltered water of wells with carbon filters, will be sampled at least once every five years.
Not all wells within the Special Well Construction Area will be sampled. The SWCA includes a generous border area outside of the plume. Many wells within the SWCA are too far from the plume to be affected. We will also look at individual wells with low concentrations of TCE that are located in areas of generally high TCE concentration on a case-by-case basis to determine if additional monitoring is required.
The MPCA will maintain GAC filters installed through their program based on reported water usage. Individual homeowners who installed GAC filter systems under the Baytown and West Lakeland Township ordinances are responsible for monitoring, maintenance and sampling at least every two years.
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The MDH concludes that there is no apparent public health hazard at this time because exposure to TCE above health-based criteria is currently being prevented by use of whole-house GAC filtration units on private wells, and because overall levels of TCE in the Bayport municipal system are below regulatory and health-based standards. However, potential uncertainties about the long-term maintenance of the many individual GAC filter systems in use at the site, tracking and monitoring of the plume, and possible development of the area are a concern. Past exposure to TCE and carbon tetrachloride ((CCl4), another contaminant that has been found at the site) in groundwater in private wells did represent a public health hazard because the individual or combined concentrations exceeded MDH's health-based criteria. At this time there is no direct evidence of an unusual incidence of adverse health effects as a result of this past exposure.
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A more detailed list of recommendations can be found in the Public Health Assessment.
- Any GAC filter systems installed on private wells should be supervised by a governmental entity to ensure regular monitoring and maintenance.
- MDH should finalize a new HRL for TCE through its rule making process. The current well sampling plan should be re-evaluated by all parties when a final HRL for TCE is adopted to ensure that it is still protective of public health.
- Additional permanent monitoring wells should be installed by the MPCA at or upgradient of the north hangar area at the Lake Elmo Airport, and to the west of the airport to clarify whether TCE sources are located in these areas.
- The confining rock layer between the upper aquifers and the Franconia should be studied to see how the TCE moves into the Franconia aquifer. The plume in the Franconia should also be studied and outlined.
- The city of Bayport and state agencies should continue to work together to minimize TCE concentrations in the public water supply and develop a contingency plan.
- The vulnerability of the currently unaffected Bayport city water supply wells should be evaluated and a plan developed to prevent further contamination of the water supply system.
- The feasibility of connecting homes within the city of Bayport that are currently served by private wells to the city's municipal water supply should be explored. When a connection is made, the existing wells should be properly sealed.
- As a precaution, Lake Elmo municipal well #1 should be monitored for VOCs on an annual basis by MDH.
- A comprehensive plan for long-term water supply options for the entire site that minimizes the number of new private wells should be developed. Alternate water supply options such as community wells, or connection to a municipal or other community water supply systems should be considered.
- Measures to control and prevent expansion of the contaminant plume should be evaluated and implemented. Finding the source(s) of the TCE would assist the remediation process.
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- Minnesota Pollution Control Agency:
- Baytown Township Groundwater Contamination Site
- Baytown Ground Water Contamination Superfund Site: Background Information (PDF: 179KB/1 page)
This information sheet was prepared in cooperation with the U.S. Agency for Toxic Substances and Disease Registry.