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Disinfectant Byproducts Are the Most Common Water System Violations


In 2016, there were 2,733 public water supply systems in Missouri. In the previous post, I reported that 94.7% of the population received water from suppliers that had no violations of safe drinking water standards during the year (it has decreased from 95.7% in 2012). This means that 5.3% of the population was served by systems that did have a violation. As Missouri’s population in 2016 was 2,093,000, that means that almost 111,000 people were served water systems that had a violation during the year. This post looks into the nature of the violations.

In 2007 and 2010 there was an increase in the population affected by a violation. The cause in 2007 was an error in backwashing a filter at the Missouri American Water Company South Plant in St. Louis County. The error caused a spike in turbidity that lasted four minutes. During that time the water reached an estimated 24,578 customers, though no reports of illness were associated with this event. Even though only some customers were affected, federal documentation rules require that the entire service population be reported as exposed. In 2010, “the same phenomenon happened again.” (2012 Annual Compliance Report of Missouri Public Drinking Water, p. 4)

A violation does not indicate that public health was affected, but it creates the potential for a public health impact to occur. For this reason, violations are important administrative markers. The DNR monitors two broad kinds of violations. Water contaminants (chemicals and bacteria) can exceed their respective maximum concentration levels (health-based standards), or a water system can fail to meet adequate administrative standards (most often not performing and reporting the water quality tests required by law).

Figure 1 at right shows the percentage of the population served by community water systems that had different types of health-based violations in 2016. Violations of the Stage 1 & 2 DBP Rule were by far the most common, affecting about 3% of the population. (In the chart, Excel has rounded to the nearest full percent.) Figure 2 compares the data for 2013 and 2016.

(For larger view, click on figure.)

Figure 1. Data source: Missouri Department of Natural Resources, 2016.

Figure 2. Data source: Missouri Department of Natural Resources, 2016.











In previous years, the most common type of violation had to due with coliform bacteria. The text of the report indicates that in 2016 coliform contamination continued to represent the most common kind of violation. However, as shown in Figures 1 and 2, violations of the Stage 1 & 2 DBP Rule affected more of the population than did coliform contamination. Let me explain what this means.

Coliform bacteria are a family of bacteria that live naturally in the soil, and which also live naturally in the guts of many animals, including humans. Consequently, it is not uncommon for some coliform bacteria to get into water supplies. Most coliform bacteria are safe, but a few species of coliform bacteria (including some E. coli) can cause illness in humans. In addition, because they live in great numbers in the guts of humans and animals, their presence in large numbers serves as a sign of fecal contamination. Human and animal feces contain many species of harmful bacteria, and the presence of too many coliform bacteria serves as a marker that these other bacteria might be present, too.

Over the years, the EPA has lowered the maximum allowable level of coliform bacteria concentration in drinking water, and water systems have had to increase their treatment of the water to kill the bacteria. The treatment usually occurs in stages. Unfortunately water often contains organic matter, such as algae or dissolved plant material. If the water treatment is not done properly, the chemicals used to kill the bacteria react with the contaminants to form byproducts that can also be harmful. The Stage 1 & 2 DBP (Disinfectants and Disinfection ByProducts) Rule requires water systems to monitor the level of such byproducts in their water. Thus, it may be because water systems are using additional treatment to kill bacteria that decreasing coliform contamination and increasing violations of the Stage 1 & 2 DBP rule are occurring.

The presence of E. Coli or of other species of coliform bacteria remains the most serious violation, in the Department’s opinion. Thus, the presence of either results in a boil order. All water systems in Missouri are required to test for E. Coli. Nineteen systems received boil orders in 2016. That number has been moving mostly sideways since 2012, but represents a decrease from 32 in 2011. Most lasted for a few days up to two weeks, but some lasted for several months.

Seventy-four systems had chemical violations, almost all for trihalomethanes . Trihalomethanes are water treatment byproducts. They form if disinfectants used to treat the water (chlorine or bromine) react with matter that may be present in the water (e.g. decaying vegetation).

Eleven systems had violations involving excess radiological contaminants (down from 14 systems in 2012 and 16 systems in 2011). The problems came from several radiological elements, see the report for full details.

In 2016, 7 water systems had Surface Water Rule violations, the same as in 2013. All of the violations were for combined filter effluent turbidity. Systems must filter surface water to remove cryptosporidium, a parasite that causes diarrhea, and a violation of the turbidity rule means the filtering may not be adequate to remove the parasite.

As noted above, some of violations can be quite brief, and the threat they represent to public health can be small. However, the DNR puts a special focus on water systems that repeatedly fail to meet monitoring standards, and on those with a routine sample that tests positive for coliform, but which fail to submit follow-up or repeat samples as required.

As reported in the previous post, 38 water systems were listed as having had three or more major monitoring violations in 2016 (up from 27 systems in 2013). Many of them were in violation for many months. Figure 3 shows the list. Only 6 water systems had water that tested positive for excess coliform bacteria, but failed to provide the required follow-up samples for testing. This represents a decrease from 47 systems in 2013. Figure 4 shows the list.

Figure 3. Source: Missouri Department of Natural Resources, 2016.

Figure 4. Source: Missouri Department of Natural Resources, 2016.














Missouri Department of Natural Resources. 2013 Annual Compliance Report of Missouri Public Drinking Water Systems. https://dnr.mo.gov/env/wpp/fyreports/index.html. Published 2014-11-18.

Missouri Department of Natural Resources. 2016. Annual Compliance Report of Missouri Public Water Systems. Downloaded 5/11/2018 from https://dnr.mo.gov/env/wpp/fyreports/index.html.
Missouri Census Data Center. Population Estimates for Missouri. Viewed online 6/28/2018 at http://mcdc.missouri.edu/trends/estimates.shtml.
Wikipedia contributors. (2018, May 15). Trihalomethane. In Wikipedia, The Free Encyclopedia. Retrieved 22:26, July 5, 2018, from https://en.wikipedia.org/w/index.php?title=Trihalomethane&oldid=841446641

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