Hazardous Sites and Substances in Minnesota
Township Groundwater Contamination Site, October 2002
Note: This page provides information on the site's status in October 2002. For current information, please visit the Baytown Township Groundwater Contamination Site home page.
This web site provides updated information about public health issues related to the Baytown Township Groundwater Contamination site. Trichloroethylene (TCE), a chemical solvent often used for degreasing metal parts, was first found in the groundwater in the area in 1987. TCE is a potential human carcinogen. The highest concentrations of TCE are found underneath the Lake Elmo airport.
Activity at this site increased dramatically in February of 2002 when the Minnesota Department of Health changed its advice to an interim exposure limit of 5 micrograms per liter based on new information on the toxicity of TCE. There will be a new Health Risk Limit established during the next two years that may be different than the current recommended exposure limit.
More detailed information about this site can be obtained from the Minnesota Department of Health (MDH) and the Minnesota Pollution Control Agency (MPCA). Please see the list at the end of this sheet for contacts. Information is also available at the Bayport Public Library.
- What has been accomplished since this past winter?
- What do the 2002 sampling results tell us about the TCE plume?
- Will sampling of residential and airport hangar wells continue?
- What activities are planned for the future?
- Where can I get more information?
As of the first week of September, the MPCA has sampled water from about 320 wells in Baytown and West Lakeland townships, Bayport, and Lake Elmo. Laboratory results were reviewed by MDH staff and then sent with a brief explanation to the homeowner. Of the 320 wells sampled, 116 wells have trichloroethylene (TCE) levels that exceed the interim exposure limit of 5 µg/L (micrograms per liter).The sampling results have been mapped (pages 5 and 6) to give us a current picture of TCE in the affected aquifers.
When the water for a home exceeds the exposure limit, the MPCA provides home delivery of bottled water until a granular activated carbon (GAC) whole house filter can be installed. To date, over 25,000 gallons of bottled water have been delivered to area residents.
The Metropolitan Airports Commission (MAC) provides whole house GAC filter systems to homes where the level of TCE equals or exceeds 5 µg/L. To check filter performance, the MPCA collected post-filter samples from some of the first GAC filter systems installed. The testing results confirm that the systems completely remove the TCE from the water. Installation of the last few remaining GAC filter systems will be completed shortly.
Soon there will be additional investigation at the Lake Elmo Airport and to the west of the airport. This is to try to pinpoint the source (or sources) of the contamination. If a source can be identified, it will help us develop a more effective plan to clean up the groundwater.
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The results of the well sampling so far have not been surprising. Levels of TCE have increased in some wells, and decreased or stayed the same in others.
On pages 5 and 6 of this document are updated maps of the TCE plume in the two main aquifers under the area, the Prairie du Chien and the Jordan. (An aquifer is a geologic unit that is fully saturated with water). The maps show the outline of the Special Well Construction Area (SWCA) in a straight, heavy dashed line and the 1, 5, 10, 20 and 30 µg/L TCE concentration contours. The 1 µg/L contour is a dashed line, the 5 µg/L contour is solid and black, and the others are light gray. The contour lines represent the area within which the concentration of TCE exceeds the value noted on that contour.
These maps illustrate several key points:
- Not all of the wells within the SWCA have TCE contamination. (Likewise, not all of the wells within the plume have TCE contamination.)
- The TCE plume shape is different in the two aquifers. A much larger area of the Prairie du Chien, the upper aquifer, exceeds 5 µg/L TCE.
- The 5 µg/L TCE contour extends to the St. Croix River
- Wells located very close together and drawing water from the same aquifer may have very different TCE concentrations. Usually, this is because they are drawing water from different depths within the aquifer.
One thing to keep in mind when looking at the maps is that some of the irregularities in the shape of the TCE plume are mainly due to variations of fracture patterns, density, and groundwater flow rates within the aquifer. Some 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 this year’s sampling results to previous sampling data also reveals several things:
- The primary direction of movement of the TCE is to the east, towards the St. Croix River.
- Generally the plume is not expanding to the north and south. Where some expansion has occurred, it is very small (less than 250 feet).
- The southeastern section of the TCE plume in the Jordan aquifer does appear to be expanding. This is an area of recent development with many new Jordan wells. It includes Olene, Osprey, and Oriole, between 21st and 24th St. N.
- Some wells show increases in TCE concentration, but many wells are either stable or decreasing. Wells near the center of the TCE plume (in both aquifers) are experiencing the greatest average rate of increase (approximately 0.5 µg/L per year), while those near the edge generally have much lower rates of increase (approximately 0.1 µg/L per year). One major exception is several of the Jordan wells along 34th St. N, in which the TCE concentrations have remained low and stable despite their location near the center of the plume.
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Yes. The following sampling plan has been developed for 2003 based on what we have learned from this year’s sampling. This plan is only for wells with TCE concentrations high enough to require quarterly, semi-annual, or annual monitoring. Once a new Health Risk Limit for TCE has been adopted in state rules, a long-term sampling program will be developed. In the meantime, the sampling plan for the remainder of this year and for 2003 will be as follows:
- Wells with TCE concentrations of 4.3-4.9 µg/L will be sampled quarterly (approximately every 3 months; currently there are 12 wells in this category)
- Wells with TCE concentrations of 3.0 – 4.2 µg/L will be sampled semi-annually (approximately every 6 months; currently there are 22 wells in this category)
- Wells with TCE concentrations of 2.0 – 2.9 µg/L will be sampled annually (currently there are 24 wells in this category)
- Selected “sentry” wells inside of and along the edges of the plume will 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. New wells may be added or other wells chosen based on the 2002 sampling).
- 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).
Not all wells within the Special Well Construction Area will be sampled in 2003. Many are located too far away from the TCE plume to be affected. The 2002 sampling has confirmed that the contaminant plume is not expanding significantly to the north or south.
The only possible exception to this is the southeastern edge of the plume in the area of Olene Ave., Osprey Ave., Oriole Ave., and Oakgreen Ave., between 21st and 24th Streets. In this part of the plume, we will do more sampling to find the edge of the TCE plume (i.e. until we identify a “non-detection” buffer zone around the contamination).
We will look at wells with low concentrations of TCE located in areas of high TCE concentrations on a case-by-case basis to determine if additional monitoring is required beyond the sampling plan. Factors that help us decide when to do more sampling include a lack of previous samples or a history of fluctuating TCE concentrations, particularly when there is no information about the depth at which the well draws water, or where the well draws water at the same depth as nearby high TCE concentration wells.
No matter what long-term sampling program is developed, wells within the “area of concern” will be sampled every five years. The “area of concern” includes all wells with any past detection of TCE, plus a “buffer zone” of wells where TCE has not been detected around the edge of the TCE plume. Unfiltered water from wells with GAC filters will be included in the 5-year sampling, but some of these wells will also be sampled annually as “sentry” wells to track contaminant concentration trends within the center of the plume. The MAC will maintain the GAC filters on a regular basis.
This information was prepared in cooperation with the U.S. Agency for Toxic Substances and Disease Registry.
If sampling in 2003 shows unexpected changes in concentrations of TCE or the size of the plume, the sampling plan will be modified as needed to ensure adequate information to protect public health.
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In addition to the new source investigation and continued monitoring of wells, representatives of Baytown and West Lakeland townships, surrounding cities, Washington County, and the various state agencies are currently discussing options for long-term solutions. In November there will be an open house to answer questions about the 2002 sampling, the sampling schedule and any other questions you might have. We will also be seeking your input about options for clean up and potential long-term solutions. You will receive a postcard telling the date, time and location of the open house.
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Please continue to make every effort to work with the MPCA and MAC on the water sample collection and GAC filter installation. Remember, MPCA needs your permission to collect a well sample and MAC needs you to sign and return an agreement before they can install a GAC filter system.
For more information, please contact us.
Special Well Construction Area (includes general area where TCE was found in private Franconia wells.)
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