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Total Trihalomethanes (TTHMs)
Public Notice: September 2025 TTHM Exceedance
This notice is to advise our customers that our water system is in noncompliance with the drinking water standards for Total Trihalomethanes (TTHMs). Although this is not an emergency, as our customers, you have a right to know what happened, what you should do, and what we are doing to correct this situation.
This notice applies to customers served by the Maynard Water Division, located in Maynard, Massachusetts and those consumers directly served by our system in Acton, Stow and Sudbury. This notice does not apply to consumers who receive their water from a private well. We are required to monitor the drinking water for TTHM levels on a quarterly basis (once every three months) at four specific locations in the distribution system. The results of last quarters’ samples show that our system exceeded the standard or maximum contaminant level (MCL) for TTHMs at one out of four locations during the July through September 2025 compliance period. The standard for TTHMs is 80 parts per billion (ppb), and compliance is determined on a quarterly basis by averaging all samples collected at each location for the last 12 months (Locational Running Annual Average). The locations and those averages are as follows (averages above the MCL have been highlighted).
TTHM Locational Running Annual Average (LRAA) (ppb)
| April - June 2025 Running Average | July - September 2025 Running Average | TTHM MCL | |
|---|---|---|---|
| DBP1: 86 Power Mill Road – Village Plaza | 61 | 62 | 80 |
| DBP2: 3 Powder Mill Road -Jiffy Lube | 50 | 43 | 80 |
| DBP3: 195 Main Street – Town Hall | 69 | 66 | 80 |
| DBP4: Winter Street – DPW HWY Garage | 82 |
87 |
80 |
What does this mean?
This is not an emergency. If it had been, you would have been notified right away. However, young children (including infants), pregnant women, or those who may become pregnant may be potentially more susceptible to risks from exposures to chemicals, such as TTHMs, and should seek advice from their health care providers if they have any concerns. Some people who drink water containing (TTHMs) trihalomethanes in excess of the MCL over many years may experience problems with their liver, kidneys, or central nervous system, and may have an increased risk of getting cancer.
What happened?
TTHMs are a byproduct of chlorine disinfection which forms when chlorine combines with natural organic matter commonly found in surface water supplies and sometimes in groundwater sources. TTHM levels can vary depending on a number of factors including the amount of chlorine used, amount of organic plant material in water sources, temperature, water age and seasons. TTHM levels must be controlled while also maintaining appropriate levels of disinfectant in the water necessary to avoid bacterial issues.
What is being done?
The Town is working to minimize the formation of Total Trihalomethanes (TTHMs) while ensuring that we maintain an adequate level of disinfection. We are working with MassDEP regulators and have hired engineers to evaluate and implement treatment processes that will help to improve organic matter removal from our groundwater sources and minimize TTHMs in our drinking water. These processes include potassium permanganate as a pre-oxidant at Green Meadow Treatment Plant, adding mixers at both storage tanks and developing a comprehensive flushing program.What can you do to reduce exposure?
- You can choose to limit the amount of tap water used if you are pregnant, may become pregnant or are giving water to young children. For example, you can use water from another source, such as bottled water for drinking, preparing formula, beverages, or food that retains water (e.g., hot cereals, rice, or pasta).- You can let water sit in a pitcher overnight to allow the TTHM chemicals to leave the water. Most TTHM are volatile and will easily evaporate from the water at room temperature.
- While breast milk can be a source of TTHM exposure for infants, Please contact your healthcare provider for guidance.
- You can use home water filters that remove or lower chlorine and TTHM levels to reduce exposures.
Public Notice: August 2025 TTHM Exceedance
This notice is to advise our customers that our water system is in noncompliance with the drinking water standards for Total Trihalomethanes (TTHMs). Although this is not an emergency, as our customers, you have a right to know what happened, what you should do, and what we are doing to correct this situation.
This notice applies to customers served by the Maynard Water Division, located in Maynard, Massachusetts and those consumers directly served by our system in Acton, Stow and Sudbury. This notice does not apply to consumers who receive their water from a private well. We are required to monitor the drinking water for TTHM levels on a quarterly basis (once every three months) at four specific locations in the distribution system. The results of last quarters’ samples show that our system exceeded the standard or maximum contaminant level (MCL) for TTHMs at one out of four locations during the April through June 2025 compliance period. The standard for TTHMs is 80 parts per billion (ppb), and compliance is determined on a quarterly basis by averaging all samples collected at each location for the last 12 months (Locational Running Annual Average). The locations and those averages are as follows (averages above the MCL have been highlighted).
- This notice informs residents that during the July–September 2025 compliance period, the Maynard public water system experienced an exceedance of the EPA’s standard for Total Trihalomethanes (TTHMs) at one of the monitored locations in the distribution system.
-Although this is not considered a public health emergency, the Town is required to notify customers, explain the causes and risks, and provide guidance.
- The U.S. Environmental Protection Agency (EPA) and the Massachusetts Department of Environmental Protection (MassDEP) has a Maximum Contaminant Level (MCL) of 80 parts per billion (ppb) for TTHMs (running annual average at each monitoring location).
- Compliance is evaluated using the Locational Running Annual Average (LRAA), which averages quarterly samples at each location over the most recent 12 months.
- TTHM stands for total trihalomethanes, and are a group of byproducts that can form when chlorine (used to disinfect drinking water) reacts with natural organic matter (e.g. decayed plant material) in the water.
- The four most common ones are chloroform, bromodichloromethane, dibromochloromethane, and bromoform.
- Because they form in the distribution system (after treatment and while water is in pipes/storage tanks), their levels can vary across the town and with time.
- No, this is not an emergency. If it were, the Town would provide instructions to stop using water.
- The exceedance pertains to long-term exposure, not an acute toxin event. However, the MassDEP notes that young children (including infants), pregnant women, or people who may become pregnant might be more sensitive to chemical exposures and may wish to consult with their healthcare provider if they have concerns.
- For general population in the short term, water is still considered safe to use for drinking, cooking, bathing, etc.
- Water age / contact time: The longer water sits in pipes or storage tanks, the more opportunity for TTHM formation.
- Organic matter in source water: Elevated levels of natural organic compounds (e.g. from decaying vegetation or runoff) raise the precursors that react with chlorine.
- Chlorine dosage / distribution: Adjustments of chlorine for disinfection may inadvertently increase byproduct formation.
- Seasonal or temperature effects: Higher temperature can accelerate chemical reactions.
- System hydraulics, mixing, and tank stratification: Uneven flow or mixing in storage reservoirs can cause localized zones where reactions continue.
As Maynard’s public notice states, the Town is balancing the need to maintain effective disinfection (to control microbial risks) while trying to reduce byproduct formation.
- Continue to work with MassDEP regulators and engaging engineers to assess and implement improved treatment approaches.
- Engineer and design a system to utilize potassium permanganate as a pre-oxidant at the Green Meadow Treatment Plant to reduce organic precursors.
- Install mixers in storage tanks to reduce stratification and dead zones where reactions can continue unchecked.
- Continue to implement a comprehensive flushing program to reduce water age and move stagnant water out of the system.
These are interim or operational fixes; over time, additional or upgraded infrastructure or treatment systems may be needed.
- Here are steps households can take if they wish to reduce TTHM intake voluntarily:
- Let water run (flush) the tap for 30–60 seconds, especially if the tap has not been used for a few hours. This helps purge water that has been stagnant in your service lines.
- Use a pitcher and allow water to sit (e.g. uncovered in the refrigerator or on a countertop) overnight—because many TTHMs are volatile, some will evaporate out.
- For drinking and cooking, you may consider point-of-use filters certified to remove TTHMs (e.g. activated carbon, reverse osmosis).
- If you are pregnant, may become pregnant, or are serving water to infants and are concerned, you should consult with your health provider.
- Continue to use water for bathing, washing, etc.—the risk is primarily ingestion over long periods, not short-term use.
- The Town will continue quarterly monitoring of TTHMs as required by state and federal law.
- Results and compliance or noncompliance status will be publicly reported (e.g. via public notices, the Town website).
- The engineering evaluation and design of improved treatment or operational upgrades are underway.
- Implementation of new systems may take months or longer, depending on permitting, funding, and construction constraints.