The Wellesley Cancer Prevention Project is pleased to address the specific questions raised at the March 14th town-wide forum. We would also like to respond new questions that arise. Please forward your questions to We will make every attempt to respond via the website to every inquiry received.

We are grateful to Steve Johnson, Chief of Site Management for the Northeast Region Bureau of Waste Site Cleanup, Department of Environmental Protection, who provided answers for us as follows:

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Regarding the Needham plume contamination, Steve Johnson stated that 80% of the contamination is being removed by the Permeable Reactive Barrier.

Q: What danger does the remaining 20% in the drinking water represent to our (and our children’s) health?

A: There would be a health risk from the concentrations of trichloroethylene (TCE) in groundwater at Central Avenue if there was exposure to it. However, there is no current exposure to TCE from drinking Wellesley’s water. The Department of Environmental Protection (DEP) installed the Permeable Reactive Barrier (PRB) to help ensure that there would be no future exposure to the TCE either.

Q: If the 20% is not currently a health hazard, when will it be?

A: Our hope is that the residual TCE concentrations will never be a health risk, but we cannot guarantee that outcome. We will monitor the groundwater downgradient of the PRB to see if the reduction in TCE levels occurs as we expect it will.

Q: Given that the reactive barrier is still turning out water that has toxins like TCE at 3 times the acceptable level, is it safe to be drinking Wellesley water?

A: Yes, it is safe to drink Wellesley’s water. In order for there to be a health risk from a toxin, there needs to be exposure to it. The TCE plume has not reached the water supply wells to date, with the exception of one, unconfirmed detection of a trace amount of TCE (less than 1 part per billion). While there is no current exposure, the intent of the PRB was to try to prevent the TCE from getting to the wells in the future. Groundwater modeling by EPA’s Center for Subsurface Modeling Support in Ada, Oklahoma predicted that the TCE would eventually reach the water supply wells if no cleanup actions were taken. Due to the persistence of these kinds of chemicals in the environment, the TCE plume would represent a threat to Wellesley’s wells for decades, if the PRB was not installed.

Q: What will be done about the contaminated ground water that has already passed where the PRB now exists?

A: DEP continues to monitor the concentrations of TCE in groundwater between Central Avenue and the Town wells. Over time, we expect that the concentrations of TCE will diminish, because natural attenuation processes will slowly reduce the TCE, and further TCE will not migrate to that area because of the PRB.

Q: When is TCE plume due to reach water supply (what had already seeped through)?

A: The DEP hopes that the TCE plume will never reach the Wellesley water supply wells now that the PRB has been successfully installed.

Q: What is the “acceptable” level of contamination?

A: The drinking water standard for TCE is 5 ug/L, or parts per billion.

Q: What happens to resultant contamination? Not touched by clean-up? Who will clean it up? Will it be cleaned up?

A: The residual concentrations of TCE are expected to “naturally attenuate”, meaning that they will dissipate over time due to biodegradation, volitilization, and dilution/dispersion processes. By cutting off the plume at Central Avenue, there is a vast reduction in TCE levels in groundwater as it moves through the PRB and toward the Wellesley wells. Our hope is that by cutting off the plume, the natural attenuation of the residual levels of TCE will obviate the need for further cleanup actions to be taken. Up near the Microwave Development Laboratories (MDL) facility on Crescent Road, DEP is currently evaluating additional cleanup options to try to do more to address the source of the TCE to further protect the Hillside School and area homes.

Q: Why will the percentage of TCE trapped by the barrier increase over time?

A: The percentage of TCE broken down by the PRB will not necessarily increase over time; but the concentrations of TCE in downgradient groundwater is expected to decrease as natural attenuation processes degrade the TCE, and no more TCE migrates to that downgradient environment (because of the PRB).

Q: What happens to the TCE trapped by the barrier? Is it chemically altered?

A: Yes, the TCE is chemically altered. The TCE molecules are broken down by the PRB. Zero-valent iron in the PRB donates electrons to catalyze a reaction that cleaves chlorine ions off of the TCE molecule. This results in chloride ions and ethenes, which are simple sugars. Please contact the WCPP for more detailed information on this reaction.

Q: Does an additional below-ground barrier need to be built between the present Central Street barrier and the town wells in order to protect the drinking water from the Needham Plume?

A: There is no feasible location for an additional PRB between Central Avenue and the Town wells. The location of the PRB beneath Central Avenue was selected because it was the closest location to the Town wells where such a system could be installed. If the remaining TCE between Central Avenue and the Town wells does not dissipate as we hope it will, it is expected that the aeration at the Town’s water treatment plant is able to remove whatever TCE might reach the wells.

Q: Will the PRB shift the Needham Plume? Is the TCE trapped or diverted by the PRB? Will the barrier become saturated with TCE?

A: No, the PRB will not shift the TCE plume. The PRB was designed to be more permeable than the native soils, so that groundwater will continue to flow through it. One of the great features of this technology is that it uses natural gravity flow to carry the contaminants through the treatment materials in the PRB. The TCE is neither trapped nor diverted; it is destroyed, which is another of the great aspects of this technology. Therefore, the PRB will not become saturated with TCE. The long-term (i.e., beyond 10 years or so) effectiveness of the zero-valent iron to destroy the TCE is not fully known, as the first PRB with zero-valent iron was installed in 1992. However, the effectiveness of that original PRB was studied after 5 years of installation, and found to still be highly effective in destroying the contaminants (see “Long-Term Performance of an In-Situ ‘Iron Wall’ for Remediation of VOCs”, Groundwater, Vol. 36, No. 1, page 164).

Q: For many years there was an auto salvage business near the site of the Needham Plume PRB. The marsh behind the site was littered with auto parts and drums of chemicals. Has this been cleaned up? Did it cause a chemical pollution problem? Is it still a problem? Does the PRB remediate this pollution (if it is a problem)?

A: This question refers to the Central Auto Salvage site once located on Central Avenue in Needham. There was an extensive cleanup conducted at this site. Both the U.S. EPA and the Needham Board of Health were involved with overseeing this cleanup. The main contaminant of concern was polychlorinated biphenyls, or PCBs. This contamination did not result in groundwater contamination that represented a threat to Wellesley’s water supply.

Q: How close is the Needham Plume to Longfellow Pond, i.e. is the pond at risk?

A: Longfellow Pond is more than ½ mile from the furthest downgradient extent of the TCE plume. The Pond is not at risk from the TCE plume.

Q: Where do they put all the toxins from the cleanup sites or from industry?

A: The management of wastes generated from cleaning up sites is often problematic. There is a small number of hazardous waste landfills in the country where wastes can be disposed. There is also a small number of hazardous waste incinerators. As said above, one of the nice features of the PRB is that the TCE is destroyed when it passes through the wall, generating no wastes that then have to be further treated or disposed. At the Wellesley College cleanup, DEP approved the construction of a multi-layered “engineered barrier” under which the lead and chromium waste were disposed.

Q: When is the TCE plume due to reach our water supply (what has already seeped through)?

A: The Department of Environmental Protection (DEP) hopes that the trichloroethylene (TCE) plume will never reach the Wellesley water supply wells now that the Permeable Reactive Barrier (PRB) has been successfully installed.