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City of Bloomington Officials Report February 2017 Disinfection Byproduct Levels
Updated March 13, 2017 10:43 AM
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(BLOOMINGTON) - The monthly disinfection byproduct (DBP) test results for February have been released. For the first time in over a year, concentrations of one category of DBPs, haloacetic acids (HAA5), exceeded 50 ppb in the monthly measurement. However, annual average DBP concentrations for 2016-2017 remain less than in previous years.

Last spring, CBU changed the treatment process at the Monroe Plant to remove chlorine disinfectant from the sedimentation basins, adding it later in the process. However, in colder weather it has been necessary to add chlorine to the basins in order to achieve complete disinfection. With a very warm February, source water temperatures in the lake have been fluctuating over a large range. The warmer water increases the likelihood that DBPs will form. This is consistent with data from previous years, which often show higher HAA5 concentrations in the spring sample.

CBU Director Vic Kelson pointed out that the monthly sample is only part of the picture, saying, "the DBP regulations are based on the annual average concentration for four quarterly samples. Our annual average since last March is 39.2 ppb (parts per billion). At the same time of year in 2016 it was 52.5 ppb, and 59.0 ppb in 2015." Kelson added that CBU expects the HAA5 concentration to decrease as operators remove the chlorine addition from the basins in the coming weeks. "As spring arrives and the water warms we expect concentrations to decrease, and we will continue to optimize our process," he said.

For February 2017, the most recent month, samples revealed the concentration of haloacetic acid (HAA5) levels at the eight testing sites ranged from 56.4 ppb to 75.9 ppb and the total trihalomethane (TTHM) levels were between 47.2 ppb and 53.6 ppb. In January 2017, results indicated the concentration of HAA5 ranged from 32.0 ppb to 40.0 ppb, and the TTHM levels were between 31.0 ppb to 33.4 ppb.

Regarding the report, Mayor John Hamilton said, "This is a good example of why we have to be vigilant and continue to track DBPs monthly. We will continue to do everything in our power to provide this community with high-quality water."

Monthly water testing was initiated by Mayor Hamilton in January 2016, in an effort to better track water quality and specifically DBPs.

Four graphs are presented below. The first two show wintertime TTHM and HAA5 concentrations. The following two graphs below show quarterly systemwide 12-month average values for TTHM and HAA5 concentrations since 2014. The first graphs show the monthly increase in HAA5. The quarterly graphs show how the February results affect the regulatory trend values.

Testing of CBU water is conducted by a private, independent laboratory. All water quality test results are available online at under "Utilities."

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