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Lake by lake: Superior
Erie | Huron | Michigan | Ontario | Superior

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Not only is Lake Superior the largest of the Great Lakes, it also has the largest surface area of any freshwater lake in the world. It contains almost 3,000 cubic miles of water, an amount that could fill all the other Great Lakes plus three additional Lake Eries. With an average depth approaching 500 feet, Superior also is the coldest and deepest (1,332 feet) of the Great Lakes. The lake stretches approximately 350 miles from west to east, and 160 miles north to south, with a shoreline almost 2,800 miles long. The drainage basin, totaling 49,300 square miles, encompasses parts of Michigan, Minnesota, Wisconsin, and Ontario. Most of the Superior basin is sparsely populated, and heavily forested, with little agriculture because of a cool climate and poor soils.

Drinking water
Microbial contamination | Chemical contamination | Critical contaminants

Microbial contamination
In Minnesota, Wisconsin, Michigan, and Ontario, the communities that draw their drinking water directly from Lake Superior are the following:

  • Ashland
  • Baraga
  • Beaver Bay
  • Cloquet (as a backup water supply)
  • Duluth
  • Grand Portage
  • Grand Marais
  • L'Anse
  • Marquette
  • Rossport
  • Silver Bay
  • Sault Ste. Marie
  • Superior
  • Terrace Bay
  • Thunder Bay
  • Two Harbors

Thunder Bay has two treatment facilities, one drawing its water from Lake Superior (Bare Point Water Treatment Plant), and the other drawing its water from Loch Lomond, an inland lake. The remaining communities within the Lake Superior basin use inland lakes or rivers (surface water) and/or groundwater to supply drinking water. At present none of the eight Areas of Concern (AOCs) in the Lake Superior basin list restrictions on drinking water as a use impairment in their Remedial Action Plans (RAPs).

A variety of contaminants can adversely impact drinking water, including micro-organisms (for example, bacteria, viruses, and protozoa such as Cryptosporidium), chemical contaminants (including naturally occurring and synthetic chemicals), and radiological contaminants -- including naturally-occurring inorganic and radioactive materials.

Some individuals or groups, particularly children and the elderly, may be more sensitive to contaminants in drinking water than the average person. Although drinking water quality guidelines are for the general population, they are based on health effects observed in the most sensitive subgroup of the population (for example, lead and children).

A case in point. In October 1997, the Medical Officer of Health for the Thunder Bay District Health Unit issued a Boil Water Advisory to the residents of the south side of the city of Thunder Bay following the receipt of a laboratory report confirming the presence of Giardia in the water distribution system. The cyst was found on routine testing in the post-treated water supply in the south section of the city. In consultation with the Ministry of Health, Ministry of Environment, and city officials it was agreed that due to lack of a barrier filtration system, the advisory was made to inform the public who were supplied by the compromised system to a potential threat of water-borne disease.

During the 13 months of the Boil Water Advisory, the city undertook the installation of a temporary filtration plant to ensure that water from its Loch Lomond site was safe for its consumers. Once completed, and having met the minimum requirements of the Ministry of the Environment, the Boil Water Advisory was lifted on November 8, 1998. Plans by the city are underway to expand its water treatment facilities in the north end of the city to provide filtered treated water to the entire city from one source.

Boiling water is the best method for killing Cryptosporidium and bacteria in emergency situations. Boil water orders are generally the standard public health protection method when drinking water is found to be contaminated. The EPA has strengthened treatment requirements and standards for public water supplies using surface water. Health Canada, in collaboration with the provinces, is currently developing a drinking water guideline for Giardia and Cryptosporidium, is reviewing its turbidity guideline, and recently published a document titled Guidance for Issuing and Rescinding Boil Water Advisories (November 1998, revised March 1999) as a tool for health and environment authorities who must make the decisions concerning boil water advisories.

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Chemical contamination
Certain chemical contaminants are of concern in drinking water because of possible health concerns associated with exposure to these substances. These contaminants may be in the raw (untreated) water as a result of industrial and agricultural activities, or treated wastewater discharges. Some may also be present in the treated water as a result of chemicals used in the drinking water treatment process. A snapshot of some chemical contaminants of concern (including aluminum, chlorination disinfection by-products, and contaminants in groundwater) is presented below.

Food, including fish consumption, is the primary route of exposure to persistent bioaccumulative toxic (PBT) chemicals, including the nine chemicals designated as zero discharge contaminants for Lake Superior. Previous assessments for the Canadian Great Lakes basin show the intake of PBT chemicals via drinking water is negligible (less than 1 percent of total intake from all sources). They are well below the Maximum Acceptable Concentration (MAC) listed in the Ontario Drinking Water Objectives and the Guidelines for Canadian Drinking Water Quality. For the U.S. Great Lakes basin including Lake Superior, measured levels of these persistent toxic chemicals in drinking water are below the Maximum Contaminant Levels (MCLs) in Lake Superior, and therefore they are not considered to be a human health concern for drinking water.

Public water systems use various processes in order to treat raw water. One process involves the addition of alum, an aluminum compound that is used for the coagulation of suspended solids. Subsequently, the use of alum in the treatment process can raise the levels of aluminum in drinking water if the process is not optimized. If the quality of the raw water is poor, it may affect the amount of aluminum that needs to be added. There is much debate as to the role aluminum may play in the development of Alzheimer’s Disease and other dementias.

Currently, the U.S. EPA does not regulate aluminum under its drinking water program but has a secondary, non-enforceable standard of 50-200 micrograms/liter. The U.S. EPA is working to determine if aluminum is of health concern and has placed aluminum on its Contaminated Candidates List (CCL). This list is the source of priority contaminants for the Agency’s drinking water program. Priorities for drinking water research, occurrence monitoring, guidance development, including the development of health advisories will be drawn from the CCL. The CCL also serves as the list of contaminants from which the Agency will decide whether of not to regulate specific contaminants.

Other processes commonly used by water treatment plants include the addition of disinfectants such as chlorine to inactivate or kill micro-organisms in the distribution system. However, chlorine and other disinfectants can combine with naturally occurring organic matter in the raw water to produce disinfection byproducts. Of the chlorination disinfection byproducts, trihalomethanes (THMs) are present in the highest quantities. Evidence from toxicologic and epidemiologic studies suggests a possible link between byproducts of the chlorination process and increased risk of some cancers (e.g., bladder and colon) and adverse pregnancy outcomes (such as miscarriage, birth defects and low birth weight).

The amount of chlorination required and resulting levels of chlorination disinfection byproducts are dependent upon the quality of the raw water, including microbiological quality and organic content. Zebra mussel control at drinking water intakes can also result in increased levels of disinfectants and disinfection byproducts in finished drinking water. Nutrient enrichment in source waters can cause algal blooms which contribute to total organic carbon levels. In the U.S., EPA is developing standards to address the issue of disinfectants and disinfection-by-products. In Canada, Health Canada re-opened the THMs guideline in April 1998 and established a multi-stakeholder Task Group to oversee a comprehensive update of health risk information on THMs and to develop recommendations for controlling the risks.

Some materials in soils are naturally-present (for example, arsenic and/or mercury) and can become dissolved or suspended in groundwater. Groundwater can also pick up materials of human origin that have been spilled or buried in dumps and landfill sites, or that have resulted from agricultural activities (for example, nitrates and/or atrazine). Contamination can therefore occur both in urban and industrial areas, as well as in rural and agricultural areas.

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Recreational water
Beaches | Swimming | Critical contaminants

A determination of human health risk from swimming at Lake Superior beaches which exceed water quality standards has not been made. However, information on the bacteriologic condition of beaches and frequency of beach postings is available from a number of sources. At present three of the Lake Superior AOCs list beach closings as a beneficial use impairment in their Remedial Action Plans (RAPs). These AOCs are the St. Louis River, the St. Mary's River, and Thunder Bay.

Ontario Public Health Units, who are responsible for the monitoring of Ontario public beaches, collect, document and house detailed data on the beaches they monitor, including: a beach pollution survey or similar report, either historical, or done at the beginning of the bathing season, to include information on potential sources of contamination impacting on the bathing beach area; E. coli data; beach postings data; and additional information on beach conditions on the day of monitoring (rain, winds, temperature, visibility, etc.). The Ontario Ministry of Environment has a historic database that identifies total annual beach postings for public beaches in Ontario from 1988 onward.

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Chemical contaminants such as polycyclic aromatic hydrocarbons (PAHs) have been identified as a possible concern for dermal (skin) exposure in recreational waters. Dermal exposure to contaminants such as PAHs in sediment may occur when people swim in the water or come into contact with suspended sediment particulates in the water. PAHs adsorbed to these particulates would adhere to the skin. Research is ongoing to evaluate potential health effects of this route of exposure, including skin rashes and the potential to cause systemic effects, such as cancer.

A lifetime risk assessment from dermal exposure to PAHs in the St. Mary’s River (Ontario, Canada) indicates that a lifetime health risk of skin cancer was well below the negligible risk range at inshore locations, but that some upstream sites had risk values higher than the negligible risk range and this may be cause for some concern. Strategies to reduce risk were developed with communities where the risk of exposure to PAH from recreational water use was increased.

A key risk reduction recommendation was to take a bath or shower within 24 hours after a swim, thereby removing virtually all of the PAHs on the skin. Other sites in the Lake Superior basin where there are concerns about dermal contact with PAHs through swimming or wading include: two sites that are part of the St. Louis River Area of Concern (AOC) -- Stryker Bay (part of the Interlake Superfund site in Duluth, Minnesota) and Hog Island inlet of Superior Bay in Superior Wisconsin; and a section of the Ashland, Wisconsin waterfront -- due to contamination from the Ashland coal tar site.

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Fish consumption
Critical contaminants | Reducing exposure
Specific fish advisories: Michigan | Minnesota | Ontario | Wisconsin

Michigan Fish Consumption Advisories
Michigan Fish Advisory
A Family's Guide to Eating Fish from the Lake Erie Basin

Minnesota Fish Consumption Advisories
Fish Consumption Advisory
Fish Consumption Advisory General Guidelines
Fish Consumption Advisory Program
Eat Fish Often? A Minnesota Guide to Eating Fish (PDF)
Contaminants in Minnesota Fish

Eating Ontario Sport Fish
A Family's Guide to Eating Fish from the Lake Erie Basin
Mercury in Fish: A Special Advisory (PDF)
Mercury and Fish Consumption
Information on mercury levels in fish

Wisconsin Fish Consumption Advisories
Eating Fish from Wisconsin Waters
Fox River/Green Bay Fish Consumption Advisory (PDF)
Eating Safe Fish Information
Mercury in Wisconsin Fish

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