Water Quality

PUBLIC NOTICE OF TOTAL TRIHALOMETHANE (TTHM) MCL VIOLATIONS

The Texas Commission on Environmental Quality (TCEQ) has notified the CITY OF HORSESHOE BAY TX1500015 that the drinking water being supplied to customers had exceeded the Maximum Contaminant Level (MCL) for total trihalomethanes. The U.S. Environment Protection Agency (U.S. EPA) has established the MCL for total trihalomethanes to be 0.080 milligrams per liter (mg/L) based on the locational running annual average (LRAA) and has determined that it is a health concern at levels above the MCL. Analysis of drinking water in your community for total trihalomethanes indicates a compliance value in quarter two of 2019 of 0.085 mg/L for DBP2-01. 

Trihalomethanes are a group of volatile organic compounds that are formed when chlorine, added to the water during the treatment process for disinfection, reacts with naturally occurring organic matter in the water. Some people who drink water containing trihalomethanes in excess of the MCL over many years may experience problems with their liver, kidney, or central nervous systems, and may have an increased risk of getting cancer. 

You do not need to use an alternative water supply. However, if you have health concerns, you may want to talk to a doctor to get more information about how this may affect you. The flood event in October 2018 brought with it large amounts of decaying organic material. The high levels of organic material increase the organic compounds in the lake water that interacted with the Chlorine disinfection used at the water plants consequently producing higher concentrations of Total Trihalomethanes in the  4th quarter of 2018  (0.082mg/L) and 1st quarter of 2019 (0.095 mg/L). These constituent samples increased the locational 4 quarter running annual averages (LRAA) to exceeded compliance level of TTHM of 0.080mg/L. Since being notified of the exceedance in late January the City Staff have lowered Chlorine levels and purchased in-house TTHM testing equipment and began operational modifications in an effort to lower the TTHM concentration to the lowest feasible levels while still ensuring biological disinfection is maintained.

The most recent samples taken for the 2019 2nd quarter resulted in levels at 0.018 mgL, more than the 4 times lower than the 0.080 mg/L compliance level.  Although the staff has successfully optimized the treatment process for reduced levels of TTHM, the Maximum Contaminate Level is based on a 4 quarter running average. Due to the high sample levels in November (.0153 mg/L) and again in January (114 mg/L) the 4 quarter running average levels, even with the lower TTHM levels of the 2nd Quarter, is just above the 0.080mg/L compliance level at .085mg/L. Since the City was notified of the violation, mitigating of this issue has been our highest priority. Continued monitoring and treatment optimization shows that the City’s water supply is safe based on our latest samples results more than four times lower than the 0.080 mg/L.

If you have questions regarding this matter, you may contact Josh Hisey at   830-598-9983. 


5_23_2019