About Beach Monitoring in Michigan
Many county health departments routinely collect water samples at beaches to determine if the water is safe for swimming. Samples are generally taken one foot below the surface in water that is between three and six feet in depth. A laboratory using standard methods performs the analysis. The method for analyzing water samples for Escherichia coli (E. coli) can be found in the document entitled, "Improved Enumeration Methods for the Recreational Water Quality Indicators: Enterococci and Escherichia coli" (PDF format, 394 KB). Results of the analysis are available after approximately 28 hours, so water-testing results are reported the following afternoon. E. coli bacteria are counted and judged against standards established by state rules.
County health departments need to take a minimum of three samples each time a beach area is monitored. The daily geometric mean calculated from these samples must be below 300 E. coli per 100 milliliters for the water to be considered safe for swimming. Sometimes one or two of the samples may be above 300, but if the daily geometric mean is below 300, the beach is not in violation of the water quality standard. The county health departments frequently sample more than once a month. A minimum of five sampling events (consisting of at least three samples per event) must be collected within a 30-day period for the results to be considered a reliable indication of water quality. After 30 days, a geometric mean is calculated for all the individual samples collected within that time frame. This 30-day geometric mean must be below 130 E. coli per 100 ml for the water to be considered safe for swimming.
A beach is closed if monitoring conducted by the county health department determined that levels of bacteria exceed the limits established by the Michigan Public Health Code and Rule 323.1062(1) of the Part 4. Water Quality Standards (Promulgated pursuant to Part 31 of the Natural Resources and Environmental Protection Act, 1997 PA 451, as amended). A beach is closed if either the single-day or 30-day average bacteria count exceeds the established limit. If a beach is closed due to bacterial contamination, county healthy departments will continue to monitor the water quality at the beach and will permit the beach to re-open when bacteria levels fall back within acceptable levels. It is possible that a beach could be closed for swimming but other recreational activities at the beach may still be available.
Private Beach Monitoring
If you are conducting some sampling of your own, you will need to know the E. coli limits and the sampling schedule. It is important to understand that random, individual samples are not reliable indicators of water quality. County health departments are required by law to take a minimum of three samples each time a beach area is monitored. The daily geometric mean of these three samples must be below 300 E. coli per 100 milliliters (ml) of water for the water to be considered safe for swimming. Sometimes one or two of the samples may be above 300, but the daily geometric average is below 300, so the water is not in violation of the water quality standard. Also, if you want to get an accurate idea of your beach's overall water quality, you can sample on more than one occasion. The law requires a minimum of five sampling events (consisting of at least three samples per event) within a 30-day period to be considered a valid and reliable study of the water quality. After thirty days you need to calculate a seasonal geometric average for all your individual samples within that time frame. This seasonal geometric average must be below 130 E. coli per 100 ml of water to be considered safe for swimming.
Bacteria in the Environment
Escherichia coli (E. coli) bacteria live in the digestive systems of humans and other warm-blooded animals. Most strains of the E. coli bacteria are not dangerous, but they can indicate the presence of other disease-causing bacteria. There are a variety of sources that contribute bacteria and other pathogens to the surface water. These sources include illicit waste connections to storm sewers or roadside ditches, septic systems, combined and sanitary sewer overflows, storm (rain) runoff, wild domestic animal waste, and agriculture runoff.
E. coli bacteria do not survive long in water. Factors such as wind and wave action, as well as ultraviolet light from the sun help to reduce the level of bacteria. The amount of time needed to reduce bacteria levels can be unpredictable, however it usually takes less than 48 hours.
It is a popular misconception that if one area of the lake is contaminated, then the whole lake is contaminated. Bacteria contamination originates from conditions or factors present on or near the shore. Two beaches on opposite ends of a lake that have different on-shore conditions will not have the same bacteria levels. This is why it is important for private homeowners who swim near their house to periodically take samples from where they swim and not rely on results from a beach located on a different part of the lake. Since contamination originates near the shore, it is generally considered safer to swim in deeper water away from the shoreline.
Water quality standards for surface waters in Michigan
Epidemiological studies of fresh water bathing beaches have established a direct relationship between the density of Escherichia coli (E. coli) in water and the occurrence of swimming-associated gastroenteritis. Recognition of this relationship has led to the development of criteria that can be used to establish recreational water quality standards. The basis for these criteria can be found in the United States Environmental Protection Agency (EPA) documents entitled, "Ambient Water Quality Criteria for Bacteria - 1986" and "Implementation Guidance for Ambient Water Quality Criteria for Bacteria -1986."
The Michigan Department of Community Health and the Michigan Department of Environmental Quality used guidance provided by the EPA to develop ambient standards for E. coli. E. coli standards for water used for total body contact recreation are provided in the Michigan Public Health Code and Rule 323.1062(1) of the Part 4. Water Quality Standards (Promulgated pursuant to Part 31 of the Natural Resources and Environmental Protection Act, 1997 PA 451, as amended). R 323.1062(1) states, "All waters of the state protected for total body contact recreation shall not contain more than 130 Escherichia coli (E. coli) per 100 milliliters (ml), as a 30-day geometric mean. Compliance shall be based on the geometric mean of all individual samples taken during five or more sampling events representatively spread over a 30-day period. Each sampling event shall consist of three or more samples taken at representative locations within a defined sampling area. At no time shall the water of the state protected for total body contact recreation contain more than a maximum of 300 E. coli per 100 ml. Compliance shall be based on the geometric mean of three or more samples taken during the same sampling event at representative locations within a defined sampling area."