Total Coliform Rule & Monitoring
Bacteriological Sample Results
The graph below shows monthly results for all bacteriological samples. Heavy bacteria and total coliform are not a health threat by themselves since coliforms are naturally present in the environment. Samples with heavy bacteria and total coliform are used to indicate whether other potentially harmful bacteria may be present. Any sample with total coliform present must be re-tested at the same site and both upstream and downstream of the site. While there is not a legal requirement to retest locations where heavy bacteria has been identified, we voluntarily retest those locations also to ensure our water is safe. Fecal coliforms and E. coli are a health threat since these pathogens only come from human and animal fecal waste. Samples positive for fecal coliforms or E. coli result in corrective actions and possibly public notification.
Total Coliform Positive Samples
If a routine bacteria sample tests positive for total
coliform, the sample is then tested for E. coli. Three repeat samples are required
after a positive total coliform sample occurs: 1) sample from the original
location, 2) sample within five houses upstream and 3) sample within five
houses downstream. If any of the repeat samples test positive for total
coliform, then the sample must be tested for E. coli. If any of the repeat
samples test positive for E. coli, another set of repeat sampling is required,
unless an assessment is triggered. For more information on assessments, refer
to the quick reference guide.
The table below lists the City of Plano's positive total coliform samples from
July 2011 to present. All positive total coliform samples are available
through TCEQ's Drinking Water Watch