Total Trihalomethanes (TTHM) Maximum Contamination Level Tier 2 Violation

Important Information About Your Drinking Water

Our water system recently violated a drinking water standard. Although the elevated levels of TTHMs are of concern, this is not an emergency, and an alternative source of water is not necessary. If it had been, you would have been notified immediately. As our customers, you have a right to know what happened and what we are doing to correct this situation.

We routinely monitor for the presence of drinking water contaminants. The quarterly water samples taken on October 7th, show that our system exceeded the standard, or maximum contaminant level (MCL), for TTHM. The standard for TTHM is 80 parts per billion (ppb). The maximum contamination level for total trihalomethanes is calculated by the Locational Running Annual Average (LRAA) for both the MassDEP and the US Environmental Protection Agency, all of the quarterly sampling results from January 1, 2021, through December 31, 2021, contribute to the LRAA. The level of TTHM averaged at our sampling location that exceeded the MCL for the period from January 1, 2021, through October 7, 2021, was 83 ppb. The October 7, 2021 sample, would be considered the last quarter sample for the LRAA compilation of the TTHM exceedance. The following chart depicts the quarterly testing results for total trihalomethanes:

The following chart depicts the quarterly testing results for total trihalomethanes from January 5, 2021 (Quarter 1) through October 7, 2021 (Quarter 4):

Sample Location

Q1 (Jan – Mar)

Q2 (Apr – Jun) Q3 (Jul – Sep)

Q4 (Oct – Dec)



ppb Date ppb Date ppb Date


Dedham Medical Associates


40 4/6/2021 58 7/8/2021 89 10/7/2021 118


Getty Gas Station


45 4/6/2021 33 7/8/2021 46 10/7/2021 81


East Dedham Fire Station


55 4/6/2021 45 7/8/2021 64 10/7/2021 42


Far Reach Pump Station


74 4/6/2021 59 7/8/2021 89 10/7/2021 109


We are here to answer your questions, call our water quality hotline to speak with a live representative Monday through Friday between the hours of 8 AM and 5 PM at (800) 279-8810 or email us at is important to keep in mind that the above numbers will fluctuate on any given day based upon usage, seasonal changes in temperatures, inclement weather such as rain or snow, adjustments in water treatment methods, equipment, flushing techniques, etc. It is important to follow the guidance set forth in the Tier 2 Notification Total Trihalomethane (TTHM) Violation of MCL:

What should you do?

  • There is nothing you need to do. You do not need to boil your water or take other corrective actions. If a situation arises where the water is no longer safe to drink, you will be notified within 24 hours.
  • If you have a severely compromised immune system, have an infant, are pregnant, or are elderly, you may be at increased risk and should seek advice from your health care providers about drinking this water.

What does this mean?

This is not an emergency. If it had been an emergency, you would have been notified within 24 hours. TTHM are four volatile organic chemicals that form when disinfectants react with natural organic matter in the water.

People who drink water containing 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 is being done?

We immediately began measures to improve water quality and reduce the TTHMs in the public drinking water supply by:

  • Reducing the age of the water in the distribution system through flushing. (The age of the water within the tanks and distribution lines can impact the level of TTHM in the public drinking water supply)
  • Increased and blended supplemental water from the Massachusetts Water Resource Authority to reduce TTHM in the water supply.
  • Increased sampling, testing, and monitoring TTHM monthly to gauge our actions and to implement other necessary actions to reduce TTHMs in the water supply.

Monthly Total Trihalomethanes (TTHM) Testing Results

The Dedham – Westwood Water District has implemented monthly sampling at the Fox Hill Water Storage Tanks 1 & 2, and at the Far Reach Pump Station and Dedham Medical Associates (the two sampling locations that had the highest results for TTHMs in the final quarter of 2021) to measure the impact of our corrective actions and determine our next steps. Water storage tank sampling is not a compliance measure of a public drinking water supplier, however, sampling at the tanks can provide our team with a subsequent data set for comparative analysis and determine if modifications are needed in the treatment process.

The sampling results in the chart below are not an indication that we are no longer in violation of the maximum contamination level for TTHM. The Dedham – Westwood Water District is sharing this information with the public in the spirit of transparency.

Tank Samples

Distribution Samples

Date Fox Hill 1 Fox Hill 2 Sandy Valley Stoughton Road Far Reach Pump Station Dedham Medical Associates





86.4 86.8 43.6 109







46.4 98.2 72.6 63.7


These combined actions and the change of seasons will help abate the immediate impact; however, we are committed to providing a long-term solution and have also implemented the following:

  • We have engaged the services of Weston & Sampson, a recognized leader in the engineering field of water projects to analyze the total organic carbon sampling data and research the cause of the elevated levels of TTHMs.
  • We are investigating alternative ways to reduce the age of the water in our storage tanks without impacting the pressure in the system for fire flows.
  • We have also included additional equipment in the plants, tanks, and distribution system as well as implementing a unidirectional flushing program in our 2022 capital plan.

Please share this information with all the other people who drink this water, especially those who may not have received this notice directly (for example, people in apartments, nursing homes, schools, and businesses). You can do this by posting the Tier 2 Notification: Total Trihalomethanes (TTHM) MCL Violation pdf version of this notice below in a public place or distributing copies by hand or mail.

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