BLAINE MUNICIPAL WELLS
The Minnesota Pollution Control Agency (MPCA) requested that Minnesota Department of Health (MDH) staff review its public water supply database to identify any existing bedrock public water supply wells in the area and determine if any DCA has been detected in these wells. MPCA and the city of Blaine also requested that MDH review data collected from the MDH Dump Monitoring Program near the Blaine Municipal Wells.
The city of Blaine is a northern suburb of the Twin Cities Metropolitan area with a population of approximately 43,000. 1,2-Dichloroethane (DCA) has been consistently detected in Blaine Municipal Wells #3, #4 and #16 since at least 1993 (Figure 1 and Attachment 1). Currently the city of Blaine has voluntarily placed Municipal Wells # 3 and 4 off-line. Well #4 is being monitored periodically this year. If concentrations in Municipal Well #4 continue to remain around 1 µg/l the city may bring the well on-line again (MDH 1998a). Well #16 is currently the only municipal well contaminated with DCA that is on-line. DCA has always been detected in well #16 below the federal regulatory limit of 5 ug/l since at least 1993.
Blaine is experiencing rapid population growth and city officials are considering options on how to meet future demand for their municipal water system. This process is made more difficult with DCA contamination in three of the city's wells. Currently the source of the DCA contamination is unknown. MPCA, MDH and City of Blaine staff have had several meetings discussing currently available data on the site and what future site investigations are needed to help identify the source, the magnitude, and extent of the groundwater contamination.
DCA has been used in the manufacturing of vinyl chloride and insecticidal fumigants and is a constituent in tobacco flavoring, paints, varnish, finish removers, and metal degreasers. Its most common use today is for the production of vinyl chloride and other chemicals and to dissolve grease, glue, and dirt. In the past it was added to leaded gasoline to remove lead. (ATSDR 1994 and Verschueren 1983).
Concentrations of VOCs detected in Municipal Wells #3, 4 and 16 are listed in Attachment 1. DCA concentrations have been detected at concentrations as high as 11 µg/l in Well #3, 5.9 µg/l in Well #4, and 4.5 µg/l in Well #16.
The Maximum Contaminant Level (MCL) for DCA is 5 µg/l and the MDH Health Risk Limit (HRL) is 4 µg/l. The HRL is based solely on what the MDH believes to be the concentration of DCA in water that can be consumed for a lifetime and still result in a negligible risk of cancer for an individual. The HRLs are health based concentrations sometimes used by state regulatory programs to help derive regulatory numbers for drinking water. The MCL is a regulatory number which takes into health based information and other factors like the technical feasibility of detecting and treating DCA in drinking water as well as the economic and legal issues involved in the detection and cleanup of DCA contamination.
As part of its effort to identify the source of the DCA contamination, the MPCA is trying to identify bedrock wells in the area for sampling. Therefore, MPCA requested that MDH staff review its public water supply database to identify any existing bedrock public water supply wells in the area and determine if any DCA has been detected in these wells. After reviewing available data MDH has concluded that no wells, other than Blaine Wells #3, 4 and 16, appear to be impacted by DCA. Public well systems reviewed are listed in Attachment 2.
In addition to searching the MDH public water supply database, MPCA and the city of Blaine requested that MDH also review data collected from the MDH Dump Monitoring Program near the Blaine Municipal Wells. The Hendascran/Gallagher Dump is located nearby (Figure 1) and is considered a potential source of the DCA contamination found in the municipal wells. MDH has sampled several private wells in the area. No DCA was detected in any of the private wells sampled. Locations, water chemistry results and well depths for these wells are found in Attachment 3.
As part of an investigation involving a leaking underground storage tank (UST) near the municipal wells, several other private wells were sampled in the area by the city of Blaine's environmental consultant. No DCA contamination was detected in these wells. The leaking UST has been removed and currently is not thought to be the source of DCA found in the municipal wells.
Most of the private wells are either known or thought to be screened in the unconsolidated drift aquifer. The municipal wells have open intervals in bedrock formations at much deeper depths. A confining unit of clay is known to exist in this area between the surface and the lower bedrock aquifers used by the contaminated municipal wells.
Groundwater flow direction within the unconsolidated drift aquifer is thought to move in a west-southwesterly direction (DNR 1993). The groundwater flow in the lower bedrock aquifers is thought to move in a westerly direction toward the Mississippi River.
DCA has been detected in the bedrock wells near Municipal Wells #3, 4 and 16. No DCA has been detected in the drift wells sampled in the area. This suggest the source of the contamination may not be nearby and may be in an area that has a strong vertical hydraulic gradient. If the site is located a fair distance from the site it also suggests the magnitude of the contamination source is sizeable.
DCA may be related to a spill of leaded gasoline even though other contaminants associated with gasoline (benzene, toluene, ethylbenzene and xylenes) have not been detected in the municipal wells. It is worth noting that any residual petroleum contaminants from a large spill in the area would likely have been disposed of in the Hendascran/Gallagher dump when the dump was in operation (MDH 1998b). However, the dump appears to be the least likely source at the present time since other VOCs commonly associated with dumps have not been detected in the municipal wells and no DCA has been detected in shallow wells near the dump. Regardless, it is currently unknown whether the DCA is from a leaking UST, a solvent spill or from another source such as the dump.
Certain steps are currently being considered in order to identify the source of the DCA. The MPCA is currently considering having a consulting firm review the MPCA closed tanks and spills sites in the area to identify whether significant residual contamination was left on site.
MPCA staff are planning to request that the Blaine Municipal Well Field become a CERCLIS site in order to conduct further investigations. MPCA intends to identify and sample more wells in the Blaine area during the Summer of 1998.
Finally, city of Blaine staff believe a well may be present at a waste transfer station called United Waste located at 1691 91st Ave. North. This property is located where the Hendascran/Gallagher dump operated. MPCA and the city of Blaine requested help in trying to identify whether a well exists at this address, and if so, that it be sampled by MDH the dump monitoring program. Review of MDH databases indicates a well was located at this address; however, it was sealed in October 1996. The well was reported as being constructed in the 1950s. At the time of sealing the well was screened from a depth of 12 to 15 feet and was dry. The 1996 sealing report stated that no other unsealed wells or borings are known to exist on the property. MDH records also indicate a boring was drilled and sealed at this property in March 1997. The boring was sunk to a depth of 22 feet. The purpose of this boring is unknown but may be related to an unknown environmental investigation conducted at the site. Well Records on this property are found in Attachment 4.
Since Municipal Wells #3 and #4 are off-line, they do not represent a current exposure concern. Because Municipal Well #16 is being used, exposures to DCA are occurring to at least some of the users of the Blaine Municipal Water System, but the concentrations to which individuals are exposed is unknown since the water from well #16 enters the water distribution system and mixes in unknown ways with water from the system's clean wells. However, it is possible that some individuals using the system may obtain all their water from Well #16. The water in Well #16 has never been detected above the MCL of 5 µ/l. However, three samples for DCA were recorded above the HRL of 4 µg/l. The average concentration of DCA detected in Well #16 from 1995 to the present is 3 µg/l.
Significant exposures to DCA may occur from inhalation and dermal pathways (Andelman, 1985; McKone, 1987; McKone, 1989; Szejnwald-Brown et. al., 1984). The MCL and HRL are based on exposures through ingestion only. However, studies suggest that the ratio of inhalation uptake to ingestion uptake for VOCs is in the range of 6:1 (Andelman, 1985; McKone, 1987; McKone, 1989).
There is even less information for dermal absorption at low concentrations of VOCs in water. However, studies have suggested that if dermal exposures were included in the cancer risk estimate, the risk may be any where from 60% to 900% greater than the risk from ingestion alone (McKone 1989, Szejnwald, et. al., 1984). The U.S. EPA is currently working on a guidance document to address exposures to household water other than ingestion. The document is expected to be released for review in a few months (MDH 1998c). MDH will review this document when it becomes available and incorporate this information into future assessments.
It is unknown if any individuals are exposed to DCA at concentrations approaching the maximum of 4.5 µg/l in their drinking water since Well #16 water is mixed in unknown ways with clean well water within Blaine's municipal water distribution system. The HRL for DCA is 4 µg/l. This is the concentration of DCA in drinking water that MDH believes can be ingested over a lifetime with negligible risk of cancer. MDH defines negligible cancer risk as the incremental addition of less than 1 case of cancer in 100,000 individuals exposed to the contaminant (DCA) over a lifetime (70 years). However, it must be noted that if dermal and inhalation uptake are considered, the cancer risk from exposure to concentrations of 3 µg/l DCA (Well #16 average since 1995) in drinking water may exceed MDH's negligible cancer risk level.
ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and children demand special emphasis in communities faced with contamination of their water, soil, air, or food. Children are at greater risk than adults from certain kinds of exposures to hazardous substances like DCA. Children are smaller, resulting in higher doses of chemical exposure per body weight and their developing body systems can sustain permanent damage if toxic exposures occur during critical growth stages. In addition, children depend completely on adults for risk identification and management decisions, housing decisions, and access to medical care. Such factors need to be considered during decisions on future investigations and possible cleanup of this site.
- Since at least 1993 DCA has been detected in Municipal Well #16. Mixing in the Blaine Municipal Water System may, or may not, dilute the actual delivered DCA concentration to a fraction of its measured concentration at the wellhead (maximum of 4.5 µg/l). Therefore, it is not possible to determine the actual concentration of DCA in consumed water.
- The presumed maximal exposure to DCA (4.5 µg/l) from the Blaine Municipal Water System is below the federal regulatory limit of 5 µg/l. However, exposure may have exceeded the Minnesota HRL of 4 µg/l at different times during the past three years as demonstrated by the three detections (out of 14 samples) above 4 µg/l at the wellhead. While the HRL is a health-based limit, it is based solely on the ingestion route of exposure which may underestimate exposure by as much as one order of magnitude. Dilution of contaminant by water from other wells within the system may reduce an individual's expected level of exposure. Furthermore, temporary and slight exceedances of the HRL do not constitute a significant health risk because: the HRLs are conservative health standards; the cancer HRLs, based on an incremental increase in cancer of 1 in 100,000 exposed individuals, are not precise numbers; the HRL for carcinogens is based on a lifetime exposure.
- Based on the data evaluated, at this time Municipal Well #16 poses no apparent public health hazard.
- 1,2-Dichloroethane (DCA) has been consistently detected in Blaine Municipal Wells #3, 4 and 16 since at least 1993. Municipal Wells # 3 and 4 are currently off-line and well #16 is on-line. Currently the source of the DCA contamination is unknown. MPCA, MDH and City of Blaine staff are discussing available data on the site and what future site investigations are needed to help identify the source, the magnitude, and extent of the groundwater contamination.
- As part of a larger investigation, the MPCA requested that MDH staff review its public water supply database to identify any existing bedrock public water supply wells in the area and determine if any DCA has been detected in these wells. After reviewing available data, MDH has concluded that no municipal wells, other than Blaine Wells #3, 4 and 16, appear to be impacted by DCA.
- MPCA and the city of Blaine requested that MDH review data collected from the MDH Dump Monitoring Program near the Blaine Municipal Wells. The Hendascran/Gallagher Dump is located nearby and is considered a potential source of the DCA contamination found in the municipal wells. MDH has sampled several private wells in the area. No DCA was detected in any of the private wells sampled.
- DCA has been detected in only the deeper bedrock wells near Municipal Wells #3, 4 and 16 not the shallow drift wells. This suggest the source of the contamination may not be nearby and may be in an area that has a strong vertical hydraulic gradient. If the site is located a fair distance from the site it also suggests the magnitude of the contamination source is sizeable. Steps are currently being considered in order to identify the source of the DCA. The MPCA is considering having a consulting firm review closed tanks and spills sites in the area and determine if they may be a potential source. In addition, MPCA intends to identify and sample more wells in the Blaine area during the Summer of 1998.
- City of Blaine staff suspected a well may be present at a waste transfer station called United Waste located at 1691 91st Ave. North. This property is located where the Hendascran/Gallagher dump operated. Review of MDH databases indicates a well was located at this address; however, it was sealed in October 1996. MDH records also indicate at boring was drilled and sealed at this property in March 1997. The purpose of this boring is unknown, but may be related to an unknown environmental investigation conducted at the site.
- DCA concentrations in Well #16, as well as other potentially impacted wells, should be sampled frequently and closely monitored because:
- high levels (and possibly increasing concentrations) of DCA have been detected in Well #3
- the DCA concentration in Well #16 may be increasing
- MDH will review pertinent information on inhalation and dermal exposure to VOCs in household water following the anticipated release of a guidance document by EPA.
- As investigations to identify the source of DCA detected in Blaine Municipal Wells #3, 4 and 16 continue, MDH staff will assist MPCA and city of Blaine staff when necessary and appropriate.
- Any comprehensive investigation to identify the source of DCA in the municipal wells should include a review of any environmental data collected at United Waste.
Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for 1,2-Dichloroethane. May 1994.
Andelman, J. "Human Exposure to Volatile Halogenated Organic Chemicals in Indoor and Outdoor Air". Environmental Health Perspectives vol.62, pp.313-28. 1985.
Department of Natural Resources (DNR). Regional Hydrogeological Assessment Anoka Sand Plain. 1993.
McKone, T., "Human Exposure to Volatile Organic Compounds in Household Tap Water: The Indoor Inhalation Pathway". Environmental Science and Technology vol. 21 pp. 1194-1201. 1987.
McKone, T., "Household Exposure Models". Toxicology Letters, vol. 49 pp. 321-330. 1989.
Minnesota Department of Health (MDH). Personal conversation with Chuck Lenthe, City of Blaine. May 6, 1998a.
MDH. Personal Conversation with Jerry Stahnke, MPCA. April 1998b.
MDH. Personal Conversation with Nancy Chiu, U.S. EPA (tel:202-260-7587). March 20, 1998c.
Minnesota League of Cities. http://www.lmnc.org/cities/bi-bocities.htm#Blaine
Szejnwald-Brown, H.; Bishop, D.; and Rowan, C. "The Role of Skin Absorption as a Route of Exposure for Volatile Organic Compounds (VOCs) in Drinking Water". American Journal of Public Health vol. 74, pp.479-484. 1984.
Verschueren, K. Handbook of Environment Data on Organic Chemicals (2nd Edition), Van Nostrand Reinhold Inc., New York. 1983
Mark Staba, Health Assessor
Site Assessment and Consultation Unit
Minnesota Department of Health
The Blaine Municipal Wells Health Consultation was prepared by the Minnesota Department of Health under a cooperative agreement with the Agency for Toxic Substance and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health consultation was initiated.
Technical Project Officer, SPS, SSAB, DHAC
The Division of Health Assessment and Consultation (DHAC), ATSDR, has reviewed this health consultation and concurs with its findings.
Sven E. Rodenbeck (for Richard Gillig)
Chief, SPS, SSAB, DHAC, ATSDR
|Municipal Well||PWSID||DCA Detected|
|Andover||1020034||None Detected (N/D)|
|Spring Lake Park||1020029||N/D|
|Name||Address||Unique Well #||Well Depth||Aquifer||Sample date||Detections|
|PW 1||Mike Strater |
9454 Central Ave N.E.
|nitrate 7.1 mg/l |
|PW 2||Hartse Motors Truck Sales |
(Marv Hartse) 1600
91st Ave. N.E.
|PW 3||Cyril Yonke |
8833 Davenport St.
|PW 4||Arthur Phelps |
8770 Davenport St.
|PW 5||Todd Schneider/ |
8760 Davenport St.
|w20120||100 feet||Unconsolidated||(8/91) |
|PW 6||Joanne Smith |
8741 Hastings St.
|w20072||"shallow"||?||(4/89)||nitrate =2.2 mg/l|
? - unknown depth