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Nucleal Metals Site Update-May 2017

EPA Settlement Ensures Groundwater Cleanup

Water District Press Release

EPA 1,4 Dioxane sheet on W.R. Grace

Nuclear Metals Site Update

WR Grace Community Update 

Site plan for 1,4-dioxane 

MassDEP Fact Sheet

 AWD 1,4 Dioxane Results for 
South Acton Water Treatment Plant

*Running Annual Average for last 4 Quarterly Samples Taken
0.21 ppb
August 14, 2023 0.218 ppb
May 10, 2023 0.227 ppb
February 21, 2023 0.231 ppb
October 26, 2022 0.175 ppb
July 5, 2022 non-detect <0.150 ppb
June 8, 2022 0.217 ppb
February 8, 2022 0.16 ppb
December 6, 2021 0.165 ppb
August 10, 2021 0.17 ppb
May 13, 2021 0.12 ppb
January 20, 2021 0.18 ppb
November 2, 2020 0.161 ppb
August 24, 2020 0.14 ppb
May 11, 2020 non-detect <0.150 ppb
March 2, 2020 non-detect <0.144 ppb
December 11, 2019 non-detect <0.132 ppb
September 16, 2019 non-detect <0.144 ppb
May 14, 2019 non-detect <0.153 ppb
March 26, 2019 0.210 ppb
December 10, 2018 0.206 ppb
September 19, 2018 0.136 ppb
June 11, 2018 0.204 ppb
March 14, 2018 0.235 ppb
December 11, 2017 0.211 ppb
August 31, 2017 0.182 ppb
May 3, 2017 0.201 ppb
February 1, 2017 0.257 ppb
November 17, 2016 0.285 ppb
September 7, 2016  0.256 ppb 
June 6, 2016 0.238 ppb
February 10, 2016 0.291 ppb
November 16, 2015 0.258 ppb
August 17, 2015 0.219 ppb
June 25, 2015 0.218 ppb

*Running Annual Average – The highest level of a contaminant as determined by an average of the prior four quarterly samples taken at the South Acton Water Treatment Plant (SAWTP).

MassDEP Guideline for 1,4-dioxane in drinking water is 0.3 ppb


The Acton Water District has been monitoring our sources of supply in South Acton for 1,4-dioxane since 2006, when it was first identified as a potential concern at the WR Grace Superfund site.  Since that time we have learned a great deal about 1,4-dioxane, how it may be regulated in drinking water, where we believe it is coming from, and how it may be treated in the future.  A few points that are important to understand:

  • The District is monitoring both raw and treated water to understand the concentrations.
  • The South Acton Water Treatment Plant (SAWTP) is designed for future treatment technology that may destroy 1,4-dioxane and other emerging contaminants.
  • Efforts to assess the threat of 1,4-dioxane to our sources of supply, minimize these threats, and prevent increased concentrations from being introduced to our wells are ongoing.
  • We have worked closely with State and Federal regulators to understand and adapt to the concerns related to 1,4-dioxane and the ongoing Superfund cleanups in South Acton.
  • In addition to our own staff resources, we have retained legal, engineering, hydrogeological, and risk assessing professionals to assist in our work.

Following the change in the drinking water guideline value for 1,4-dioxane by the Massachusetts Department of Environmental Protection (MassDEP) in 2011, we began our quest to understand what the guideline would mean for us.  This was important, as MassDEP has applied guidance values to various other compounds in different ways.  More information on how contaminants are evaluated for drinking water suitability can be found at

The first step was to determine against which data point(s) the guideline would be measured.  It was determined that compliance with the guideline would be based on the treated water concentrations from the SAWTP on a running annual average (four most recent quarterly samples).  This data is presented in the graph above.  Next, we wanted to know what would happen if we exceed that guideline.  Working with our team of advisors, MassDEP informed us that a site specific risk characterization would be completed.  At our urging, this assessment was completed proactively, as we felt it was prudent in our planning and resource allocation to understand the longer term impacts of what the guideline would mean.  The good news is unacceptable health risks for 1,4-dioxane are associated with much higher levels than those we have historically seen in our treated water. 

It is our understanding that when the guideline was set, it was to be protective of non-cancerous and cancerous risks occurring.  This takes into consideration excess lifetime cancer risks (ELCRs) at both one in a million and one in one hundred thousand chance of increasing an individual getting cancer if exposed for 70 years to consuming two liters of water daily.  What this means is that one person in one million or one hundred thousand could attribute a cancer to the drinking water.  Therefore people that do not consume 2 liters per day of drinking water or do not spend 70 years doing so, will be at a lower risk.

The difference between the guideline and the level at which unacceptable risk occurs is due to the risk assessment process itself.  The guideline, in effect, is a screening value to determine what, if any, additional steps need to be taken to understand the safety of the water.  This includes a safety factor between the two ELCRs noted above.  Many of the steps we have been taking would be considered next steps should our concentration of 1,4-dioxane exceed the guideline.

To summarize the findings, MassDEP provided concise guidance that current levels in both the untreated groundwater and treated drinking water do not pose an unacceptable risk to our customers.  Given the concentrations of 1,4-dioxane observed in the aquifer surrounding our wells, an unacceptable risk could be present if these elevated concentrations reach our production wells.  For perspective, these concentrations would be almost six times the highest concentration currently observed in a single production well.  Therefore continued monitoring and reporting of 1,4-dioxane concentrations in our raw and treated water is required.  MassDEP also called for effective steps to intercept the plume and/or steps to ensure blending and treatment can maintain acceptable levels of 1,4-dioxane going forward.    

Please continue to check this website for new information.  This site is updated with the results of our quarterly monitoring data and contains other helpful background information.  You can also speak with or email our Environmental Manager if you have questions or concerns.  She can be reached at 978-263-9107 or Alexandra Wahlstrom.