Jeff Koska, Director of Utilities City of Horseshoe Bay
The City recently received a letter from TCEQ informing us of a violation of total trihalomethanes (TTHM) levels in our drinking water in the fourth quarter of 2018. TTHMs are disinfection by-products created when organic compounds interact with Chlorine, what we use to ensure killing biological pathogens in our drinking water. This notice indicated we exceeded the 4-quarter running average maximum limit for this compound and in doing so we are required to provide a notice with mandatory EPA language of the violation to our customers. The City included the notice and supplemental information on TTHMs with each customer’s February utility billing. In addition, the notice will be posted at City Hall and on the City’s website.
In the notice the City provides an explanation of what caused the elevated levels in the November sample that was responsible for the violation. In short, the organic material washed in from the flood began to decay after it was deposited near the West Water Plant Intake. As this exceptionally large amount of decaying material increased the dissolved organics in the raw water it then reacted with the disinfection process (Chlorine) forming higher than normal TTHMs in our finished water. Unfortunately, the Water Plant Staff had increased the Chlorine to ensure enough disinfection during the flood event due to high levels of bacteriological contamination and did not know at the time of the sample the organic loads had risen to the highest levels seen in past flood events. TCEQ’s contract sampling firm takes sample for these once every quarter. The fourth-quarter (2018) sample was taken in November with results of the violation not sent to the City until January15th. The resulting sample made the four quarter total annual combined (2018) average exceed the limit (0.080 mg/L) by 0.002 mg/L.
Although it is over the limit, it was only slightly over, and additional analysis indicate the elevated levels were only for a short duration, about two weeks as subsequent rain events began to dilute the dissolved organic levels in the lake. These compounds also effected other water systems on Lake LBJ causing exceedance of their TTHM limits as well. Below is our TTHM yearly average, 2018 and 2015 had significant flood events.
The maximum contaminate level (MCL) for TTHM is based on EPA regulation and is based upon people drinking two liters (about half a gallon) of water daily for 70 years (approximate one lifetime). Maximum contaminant levels are set at levels that are expected to protect susceptible groups in our population, for example, children, pregnant women, the elderly, and people who may have existing health problems. For chemicals that may cause cancer, EPA also considers what amount of the chemical would cause an increased risk of one case in 1,000,000 people who are exposed over their lifetime.
The City believes that exceeding the maximum contaminate level (MCL) is a very serious issue. We do accept responsibility for the violation and sincerely regret the non-compliance. Plant Operations Staff, under direct management supervision, are developing operational plans to mitigate this issue during future flood events. The staff is training on TTHM formation to modify the treatment process and developing early detection procedures/testing going forwards. We have learned from this event and will be well prepared to do everything in our power to keep the TTHM levels in compliance going forwards.
If you have any question, to explain the event and actions we have in place to mitigate future issues, please contact Josh Hisey, Plant Operations Supervisor at (830) 598-9983 or by e-mail at jhisey@horseshoe-bay-tx.gov .
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