Results from Field Sampling in Flint (Aug 17-19 2015): No Fecal Bacteria in water but Low chlorine residuals a problem

Last week, our team visited Flint to conduct extensive field sampling (Aug 17-19, 2015) and evaluate several water quality parameters at different sites within and outside the city (on Detroit water, for comparison). We will post a separate article on trip specifics and our experiences, but here are some preliminary results on what we know so far.

Report 1. Good News. Fecal Indicator Bacteria in Flint.

The most important goal of drinking water treatment is to make sure that fecal bacteria and viruses are removed or destroyed at the water treatment plant. We tested 18 samples collected from around the City of Flint, including 6 from consumer’s homes. We had the samples analyzed by the City. Importantly, we also submitted a POSITIVE CONTROL SAMPLE with high levels of fecal bacteria, labeled like every other sample we submitted. This sample let us know if the city’s testing could correctly tell us that a badly contaminated sample, was in fact, contaminated. This is a common approach used by researchers, to be sure that a test is working as expected, and that results are trustworthy.

Results: The River had detectable levels of fecal bacteria as is expected, but none of the samples collected from the Flint distribution system had any detection. The city also correctly reported that the POSITIVE CONTROL SAMPLE had high levels of fecal bacteria.

Conclusions: It appears that the treatment plant is achieving their most important goal, and that the city tests are accurate.

Report 2. Bad News. Chlorine measurements in Flint.

To keep the water safe as it is transported to consumer’s homes, it is necessary to maintain a Cl2 level of 0.2 mg/L or higher throughout the distribution system. In Flint, the Great Lakes-Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers, 2012 Edition, Recommended Standards for Waterworks (Ten States Standards) says that:

  • Minimum free chlorine residual in a water distribution system should be 0.2 mg/L.
  • Higher residuals may be required depending on pH, temperature and other characteristics of the water.

Results: While we were in Flint, we sampled a total of 17 locations for free chlorine in flushed cold water. Of those 17 samples, 7 samples (41%) did not have any detectable chlorine at all. At one location, Dr. Edwards flushed the tap for 8 hours and never obtained any detectable chlorine. This confirms our concern, that it might not be possible to treat the water to meet existing Federal standards given the high corrosivity of Flint water. In other words, no matter how good the people at the Flint treatment plant are at their jobs, it is possible that Flint residents cannot receive the minimum quality of water mandated by Federal regulations. We will be posting more on this problem in the future.

For comparison, we also took samples of water from a nearby city still using Detroit water, and 4 out of 4 had chlorine levels of 0.2 mg/L or higher. Significantly, these were also collected from hot water samples, which tend to have much lower chlorine than cold water.

Conclusions: It seems very hard to believe that standards for free chlorine residual were being met in the Flint distribution system from August 17-19, 2015.

Primary Author: Dr. Marc Edwards

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