| Community Surface Water Sampling Program |
Surface Water Sampling Interpretation
| Water Quality Standards |
| Geometric Mean |
| Sampling Methodology |
| Laboratory Facilities |
| Environmental Health |
| Community Surface Water Sampling Program |
The amount of rainfall that occurred in the week previous to the date of collection is recorded for each collection date (the previous Monday through Sunday). The rainfall data is collected from the Michigan Automated Weather Network (MAWN). MAWN provides a daily weather summary that includes such measures as air and soil temperature, average relative humidity, and total precipitation (in inches).
Escherichia coli (E. coli) bacteria, a fecal coliform species, are naturally occurring microorganisms in the intestinal tract of all warm-blooded animals, including humans. Most forms of the bacteria are harmless, however some strains can cause severe illness. The most common strain, E. coli 0157:H7, produces toxins that cause abdominal pain, fever, diarrhea, and vomiting. E. coli bacteria are an indicator of the presence of human or animal fecal material in the water. People may become infected with the bacteria by swimming in or drinking sewage-contaminated water.
Potential sources of E. coli bacteria that may contaminate our surface water resources:
Illicit waste connections to storm sewers or roadside ditches
Malfunctioning on-site sewage disposal systems (septic systems)
Sanitary sewer overflows and sewer line break discharges
Urban storm water runoff which may include rain and snow-melt
Polluted runoff from rural areas which may include roads, golf courses, agriculture, and lawns
Wild & domestic animal waste
Total Body Contact:
According to the Water Quality Standards and the provisions of Rule 323.1062, all surface waters of the State of Michigan are designated for, and shall be protected for total body contact recreation from May 1 to October 31. Surface water sample results are compared to the total body contact recreation standards contained in Part 4, Rule 323.1062 of the Water Quality Standards of the Michigan Department of Environmental Quality which state the following:
300 E. coli colonies per 100 milliliters, as a geometric mean of all samples collected at a beach during one sampling event
130 E. coli colonies per 100 milliliters, as a geometric mean of all samples collected over a 30-day period
Compliance shall be based on the geometric mean of three (3) or more samples taken during the same sampling event at representative locations within a defined sampling area. If either of the above standards is exceeded at a bathing beach, the beach operator is contacted and a public health advisory issued.
Partial Body Contact:
Partial body contact recreation is defined as any activities normally involving direct contact of some part of the body with water, but not normally involving immersion of the head or ingesting water, including fishing, wading, hunting, and dry boating.
≤ 1000 E.coli colonies per 100 milliliters, as a geometric mean of all samples collected during one sampling event.
A geometric mean is used to estimate the 30-day average from all individual samples. The geometric mean is another way to average a set of values and is commonly used with bacterial water assessment, which often show a great deal of variability. One benefit the geometric mean has over the arithmetic mean is that it (geometric mean) reduces the effect of an occasional high or low value on the average.
Most spreadsheet and database applications can automatically calculate the geometric mean. Two methods to calculate the geometric mean, both which achieve the same result, can be used with a scientific calculator and are illustrated in the following examples:
Procedure #1:
1. Multiply all the data values (sample results) together to
get the product.
2. Take the "nth" root of the product of the multiplication,
where "n" is the number of values multiplied. If you multiply
three (3) values together and get the result, take the 3rd root
of the product. If you multiply ten (10) values together and
get the result, take the 10th root of the product. This is the
geometric mean.
Example
Calculation #1:
With the following sample data results of 38, 95, and 52
colonies per 100 ml, calculate the geometric mean.
Multiply the three (3) data values together (38 * 95 * 52 = 187,720)
Take the 3rd root of 187,720 = 57.2580889011 colonies per 100 ml
Procedure #2:
1. Add together the base 10 logarithms for the data values.
2. Divide the sum by the number of values added.
3. Take the antilog of the result of step #2. This will again
be the geometric mean.
Example
Calculation #2:
With the following sample data results of 38, 95, and 52
colonies per 100 ml, calculate the geometric mean.
The base 10 logarithm of:
38 is 1.57978359662
95 is 1.97772360529
52 is 1.71600334363
5.27351054554 (sum)
Divide by the number of sample data values 5.27351054554 / 3 = 1.75783684851
Antilog of 1.75783684851 = 101.75783684851 = 57.2580889013 colonies per 100 ml
Surface water samples are collected once weekly at each sampling location in accordance to established procedures. Each weekly visit will consist of collecting a minimum of three (3) surface water samples: left, right, and center. The bacteriological results are entered and maintained in a computer database and then posted to the web page. If the result was recorded as <10 a 9 was recorded in the table for 2005. Starting in 2006 a 10 will be recorded in the table when the result is <10. These results will be highlighted in blue. Additional samples taken in response to combined sewer overflow events will be highlighted in purple. Starting in 2006 an additional column will be added for combined sewer overflow (CSO) events. River samples are collected by the Ingham County Health Department on Mondays and reported to the website by Friday of that week. Sampling is performed April through October. An alternative site was chosen for S-Web-B due to a crime scene investigation. Some sites are inactive due to lack of funding. Sites labeled 'A' are upstream, and sites labeled 'B' are located downstream.
Surface water samples are collected and delivered to the In-House Laboratory in Howell, Michigan.
Adapted from Kalamazoo County Health Department Surface Water Quality Monitoring Program
updated 8/9/2005 MDB