Total Trihalomethanes (TTHM) result when chlorine disinfectants used to treat tap water combine with naturally-occurring organic and inorganic matter present in the water.  Known as a disinfection byproduct (DBP), TTHMs are among the substances the Public Utilities Department tests for in our water.  TTHMs are present at low levels in most chlorinated water supplies and can also be present in bottled waters.  

TTHM production is also a factor of water age…the older the water is, the more TTHMs / DBPs are produced.  The GA EPD approves the sample sites with the intent to represent the oldest water (worst-case scenario) in our distribution system.

Drinking water standards must meet a Maximum Contaminant Level (MCL) established by the EPA and GA EPD.  The MCLs limit risks to people from chemicals in drinking water. Some MCLs address the daily amount consumed (for chemicals that pose an immediate risk), and others address the amount averaged over a long period of time (for chemicals that pose a long‐term risk).

The MCL for TTHM is 0.080 mg/L, or 80 parts per million (ppm).  We determine the MCL by calculating the average of four quarterly samples collected at our eight testing locations.  If a sampling site is over 0.080 mg/L, a water system receives a permit violation.    

The PUD exceeded the MCL of 0.080 mg/L for TTHM with a rolling average of 0.082 mg/L at one of our eight sampling sites found on the southeast end of Barnett Shoals Road.

The PUD met the TTHM standards set forth by the GA Environmental Protection Division at all sampling sites except for the monitoring location on the southeast end of Barnett Shoals.  The site is one of eight sampling locations throughout Athens-Clarke County.  

The Georgia Rules for Safe Drinking Water and Title 40 CFR141.64(b) set the locational running annual average (LRAA) maximum contaminant level (MCL) at 0.080 mg/L.  The LRAA of four-quarters is used to determine if a water system violates the MCL. When a new quarterly sample is taken, the oldest results are removed from the LRAA.  Similar to how a poor grade has lasting effects on a GPA, the high 3Q2021 result, combined with the removal of the low 1Q2021 in the calculations, resulted in a violation for 1Q2022 despite the individual quarterly sample falling below the MCL. 

PUD sampling results for 2Q2022 find the LRAA below the MCL and return the utility to compliance.  The elevated 3Q2021 will drop from future calculations.  With this increased test result rolling off the LRAA and the actions the PUD has taken to address elevated TTHMs, we anticipate the TTHM LRAA to remain below the MCL, as was the case for the past thirteen years since the EPA's Stage 2 Disinfectants and Disinfection Byproducts monitoring requirements began.  The table below displays the quarterly results from this location.

Levels typically vary within a single water supply depending on the season, water temperature, amount of natural organic matter in the water, pH, amount of chlorine used, time in the distribution system, and other factors.  The Barnett Shoals Road sampling site is at the end of our water distribution system with minimal water usage, possibly contributing to the higher level found in the third quarter of 2020 (07/01/21 to 09/30/21).

Some people who drink water containing TTHM above the MCL over many years may experience problems with their liver, kidneys, or central nervous system and may have an increased risk of developing certain types of cancer.  Those with a severely compromised immune system, caring for an infant, pregnant, or elderly may be at increased risk.

Consumption of water with TTHM levels somewhat above the MCL for limited durations, as is the case with our water, while corrective actions are being taken to lower the levels, is not likely to significantly increase risks of adverse health effects for most people.  Cancer risks generally accrue over lifetimes and very long periods of exposure. For disinfectant byproducts like TTHM, risks are typically calculated with a daily average of drinking 2 liters of water over a lifetime of 70 years. Research on the connections between Total THM exposures and these health risks is underway.  

Water that meets the total THMs guideline is considered safe for all domestic uses, including drinking, bathing, showering, and food preparation.  The risk of illness from TTHM is much lower than that of drinking water that has not undergone disinfection. 

Regardless of the low risks associated with TTHM, the PUD has taken the following actions to address the elevated finding:

• Increased flushing along sections of our distribution system
• Installed automatic flushers at strategic points in the system
• Conducting a Water Quality Optimization Study to perform a holistic review of water quality from source to tap to evaluate additional methods to reduce the formation of disinfection byproducts such as TTHM

We are finding our efforts to address TTHM levels are effective.  The sampling results for the third quarter of 2021 and the first quarter of 2022 were 0.061 and 0.058 mg/L, respectively, below the maximum contaminant level (MCL) of 0.080 mg/L.  We anticipate these measures will prevent an exceedance in the future.

The EPA and GA EPD require public water systems to disinfect drinking water.  Disinfection is a necessary step in our treatment process to eliminate pathogens to prevent illness and protect public health.  The practice of disinfection in the United States has nearly eliminated most acute waterborne diseases, including cholera, typhoid fever, and many other illnesses.

The most widely used type of disinfection in the United States is chlorination.  The Public Utilities Department produces sodium hypochlorite, commonly known as bleach, at the J.G. Beacham Drinking Water Treatment Plant for this purpose.  The disinfectant is added at the end of the treatment process to prevent the growth of bacteria as it travels to homes and businesses across Athens.  

The PUD always welcomes the opportunity to answer your questions regarding the safety and quality of your drinking water.  Please reach out to our Drinking Water Superintendent, William Cottrell, at 706-613-3481 or email William.Cottrell@accgov.com.

Please complete our Report a Water Quality Concern form if you have water quality concerns regarding taste, odor, or color.  

For more information, we recommend the following websites:

• Center for Disease Control and Prevention, Disinfection By-Products
• Center for Disease Control and Prevention, Water Disinfection with Chlorine and Chloramine
• U.S. Environmental Protection Agency, Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules