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Coralville Reservoir Water Quality Monitoring Program - Beach Reports
The Coralville Reservoir beach monitoring program objectives are to protect the public health, and to inform the public of potential health risks associated with waterborne disease-causing microorganisms.
Table 1: Recent Sampling Results (E. coli; colony forming units per 100 mL)
Sampling Date |
Sandy Beach |
Sugar Bottom |
West Overlook |
Standard Violation |
Geometric Means |
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Report |
Comments |
| Sep 20, 2005 | <10 | <10 | <10 | no | na | Word | |
| Sep 12, 2005 | <10 | 20 | <10 | no | na | Word | |
| Sep 6, 2005 | 50 | 20 | 20 | no | na | Word | |
| Aug 29, 2005 | 10 | 40 | 10 | no | na | Word | |
| Aug 22, 2005 | 40 | <10 | <10 | no | na | Word | |
| Aug 15, 2005 | 36 | <10 | 40 | no | na | Word | |
| Aug 8, 2005 | <10 | <10 | <10 | no | na | Word | |
| Aug 1, 2005 | <10 | 20 | 10 | no | na | Word | |
| Jul 25, 2005 | <10 | <10 | <10 | no | na | Word | |
| Jul 18, 2005 | 10 | <10 | 10 | no | na | Word | |
| Jul 11, 2005 | 45 | 130 | 30 | no | na | Word | |
| Jul 5, 2005 | 91 | 100 | 82 | no | na | Word | |
| Jun 27, 2005 | 73 | 30 | <10 | no | na | Word | |
| Jun 20, 2005 | 30 | <10 | <10 | no | na | Word | |
| Jun 13, 2005 | 30 | 50 | <10 | no | na | Word | |
| Jun 6, 2005 | 70 | 90 | 20 | no | na | Word | |
| May 31, 2005 | 30 | 10 | 10 | no | na | Word | |
| May 23, 2005 | 130 | 50 | 91 | no | na | Word | |
| May 18, 2005 | 130 | 130 | 150 | no | na | Word | |
| May 16, 2005 | 590 | 300 | 340 | yes | na | Word | resample on May 18 |
The most recent bacterial standards set two types of limits for indicator organisms in recreational waters:
- a limit on the geometric mean of 5 samples in a 30-day period (must be less than 126 cfu/100 mL)
- and a one-time maximum value (235 cfu/100 mL)
Beaches that exceed Iowa’s proposed geometric mean water quality standard for bacteria (the geometric mean of 5 samples in a 30-day period exceeds 126 colony forming units of E. coli bacteria per 100 mL of water) will be posted with signs that state, “Swimming is Not Recommended.”
Geometric mean = 
,
where n is a single E. coli bacteria result.
If any of the values used to calculate the geometric mean is less than the detection limit (currently 10 cfu/100 mL), it is replaced with a value of one-half the detection limit. If an E. coli result exceeds the one time maximum of 235 organisms/100 mL or the geometric mean of 126 organisms/100 mL for five consecutive samples, reservoir operations personnel are notified immediately.
Sampling Season
The sampling season will extend from mid-May through mid-September. Sampling will commence two weeks prior to Memorial Day and extend to the second week following Labor Day each year. Each beach will be sampled once per week during the season, on a Monday or Tuesday. An additional sample will be collected during a week if resampling is required due to high bacteria concentrations..
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