Groundwater Testing & Monitoring
ExxonMobil has been sampling potable wells for MTBE in the vicinity of the former LaMountain service station for more than two decades.
The state’s standard for drinking water says MTBE may be present up to 70 parts per billion (ppb). This is a conservative standard and is designed to be protective for a lifetime consumption of 2 liters of water per day. This standard is also thousands of times lower than concentrations associated with adverse health effects in animal studies. Nonetheless, ExxonMobil’s procedure for LaMountain has been to provide bottled water to any residential households whose wells have any detectable levels of MTBE, and to install point-of-entry water filtration (POET) systems if MTBE levels are half – 35 parts per billion (ppb) – of the state’s water quality standard of 70 ppb.
In total, ExxonMobil originally tested 105 potable wells and MTBE was detected in 43 wells. Bottled water was provided to these homes; as of February 1, 2017, 33 homes continued to receive bottled water. Of the 33 homes, 11 were using water filtration systems installed by ExxonMobil, although in four cases the detections now are below 35 ppb.
Of the original 105 homes tested, ExxonMobil continues to sample and monitor 85 potable wells. The 11 homes with water filtration systems are tested monthly. ExxonMobil also tests some wells on a quarterly basis, chosen by their proximity to wells with POET systems. All 85 wells are tested at least annually.
ExxonMobil provides the routine potable well sampling results to the property owners via mail within 30 days of receiving the analytical results. ExxonMobil also provides written results to the MADEP and the Charlton Board of Health.
Expanded Testing Area
In order to sample all potable wells along and within the route of the proposed route of the waterline, in 2014 and 2016, the MADEP directed ExxonMobil to test more homes generally located along Morton Station Road and Muggett Hill Road, from Bond Road to Oxford Road. MADEP also directed ExxonMobil to test any potable wells located within 500 feet of wells that have a confirmed detection of MTBE.
- On May 19, 2014, MADEP directed ExxonMobil to test 53 homes, generally located along Morton Station Road and Muggett Hill Road, from Bond Road to Oxford Road.
- On January 29, 2016, MADEP directed ExxonMobil to test an additional 45 homes, generally located along Muggett Hill Road, from Main Street to Bond Road.
- On February 19, 2016, MADEP directed ExxonMobil to test four more properties in the vicinity of Heritage School and Charlton Middle School.
MADEP also directed ExxonMobil to test any potable wells located within 500 feet of wells that have a confirmed detection of MTBE.
As of February 1, 2017, test results of the expanded testing show 134 wells had “non-detect” levels of MTBE according to standard laboratory protocols; 17 properties detected MTBE, all were at levels below 5.5 ppb, which is well below the state’s standard for drinking water of 70 ppb.
Similar to the historic testing area, if any wells indicated MTBE levels at 35 ppb or above, ExxonMobil offered to install a filtration system. Bottled water was offered to residential property owners with confirmed detections of MTBE in their wells, regardless how low the detection levels were. To date, 13 homeowners in the expanded testing area asked to receive bottled water.
All homeowners in the expanded test areas were contacted within 48 hours – or sooner, if possible – of ExxonMobil receiving the analytical results; written notifications were provided within 30 days of receiving the results.
ExxonMobil provided weekly testing updates of this expanded area to the MADEP, the Charlton Administrator, the Charlton Board of Health and Charlton Water and Sewer Commission.
Testing Near Schools
In 2005, ExxonMobil sampled a well at Bay Path Regional Vocational Technical High School as part of its ongoing efforts to assess the scope of any contamination, regardless of source. It’s important to understand that this area has other potential sources of petroleum as well as naturally occurring groundwater contamination.
In 2008, ExxonMobil initiated monthly testing at Bay Path, although the MADEP has not named the LaMountain site release as responsible for any contamination at Bay Path. The most recent testing results from January 2017 showed MTBE levels of 1.5 parts per billion (ppb)– far below the state’s drinking water standard of 70 ppb. In May 2016, Bay Path decided to install a MTBE water filtration system. ExxonMobil helped pay the costs of the filtration system.
The Dudley-Charlton Regional School District also has been testing wells for Volatile Organic Compounds (VOCs), which includes MTBE, on an annual basis at Charlton Middle School and Heritage Elementary School. Starting in March 2016, the school district has increased the MTBE sampling frequency to monthly. The school district has reported that the last time MTBE was detected in the water at Charlton Middle School was in 2011 when it was 0.5 ppb. For Heritage School, MTBE was last detected in 2008 when it was at 0.83 ppb Dudley-Charlton MTBE Website.
ExxonMobil continues to closely monitor the groundwater situation in Charlton, and is taking actions to meet its responsibility – and will continue to do so.
Massachusetts’ Drinking Water Standards
For the Massachusetts drinking water standards, please visit the Massachusetts State Department of Environmental Protection.