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Decrepit Dunstable Water System Threatens Swallow/Union School

by Russell Harris


   The School Committee has voted to reduce Dunstable’s school assessment by $92,000 and Groton’s by a proportional $308,000 [a 23%/77% split] by tapping funds from the District’s E&D account [Excess and Deficiency]. The motivation for taking this unusual step was to free-up funds for Dunstable to address their town operating budget this year and--it is hoped--to make a debt exclusion vote for repairs to the Dunstable Water System more likely to pass. Dunstable’s water system is largely dedicated to serving the Swallow/Union School building complex in the Center of the town. If the system were to fail, this school with about 364 students and faculty would be unusable. Consequently, it is in the School District’s and Dunstable’s long-term best interests to avoid such a catastrophic result.

   The District is looking to add an elementary wing onto the existing Middle School South with substantial savings over demolition and rebuilding an entirely new school on the Florence Roche site. But this plan requires that only Groton elementary students attend the new school wing. And so keeping Swallow/Union safe, viable and open for Dunstable children is essential for the plan to work.

   Dunstable’s public water system uses a pressurized storage tank system drawing from two, buried, 5,000-gallon tanks with well pumps maintaining pressure in the distribution system to deliver water to users. The tanks are more than 100-years old, and the system has long passed its expected useful life.  A pressurized tank system is uncommon as most water systems are fed by gravity, as is the Groton system which has large storage tanks located on Gibbet and Brown Loaf hills. 

   According to a report written by Dunstable Town  engineer Wright Pierce, system reliability and water quality cannot be guaranteed, and public health and safety would be threatened if the century-old tanks or the related corrosion system fails. 

   Dunstable’s water system serves a population of approximately 364 students and school personnel at the Swallow/Union school complex and 234 other non-school persons for a total of approximately 598 persons dependent on the water system.  The service area has 101 service connections, which consist of 90 residential, 7 municipal, and 4 commercial/industrial users.

   This is the only potable water storage facility in the water distribution system and it lacks redundancy or an emergency interconnection with any neighboring water systems, so a failure of the tanks or the corrosion system would impact everybody depending on the Dunstable water system. For this and other reasons, it is also no longer in compliance with MassDEP’s Guidelines for Public Water Systems.

   In their Sanitary Survey of the Dunstable Water system completed in 2017, MassDEP pointed to several issues with the existing tanks. First, it is unknown when was the last time the tanks were cleaned or inspected. Second, leaks have been observed in numerous locations on one tank. Third, the site glass on one tank is full of iron and manganese deposits, which have the potential to cause bacteria contamination. Fourth, the valves have not been tested for a number of years so if one tank has a problem and operators need to close the valve and operate off one tank, it is unknown if the valve will close.

   In addition, the system has been experiencing inconsistent pH readings in the water supplied by the system. In July 2017, Dunstable Water Department received a Notice of Noncompliance from the Massachusetts Department of Environmental Protection (MassDEP) based on the findings during their Sanitary Survey. MassDEP subsequently issued an Administrative Consent Order with Penalty (ACOP-CE-18-5D00004407) in May 2018. The ACOP identified concerns with inconsistent pH leaving the well site as well as issues with the existing tanks. As part of the ACOP, MassDEP is requiring Dunstable to submit a plan for the design of a new elevated 75,000-gallon water storage tank and water main replacement along Pleasant Street for improved hydraulics in the system. 

   The new water storage tank would replace the existing system. In addition, MassDEP has requested the corrosion control treatment process be optimized to ensure that the pH of the water entering the system is at least 7.0 or greater.

   The existing water main on Pleasant Street between Pond Street and the US Post Office (#170) is four-inch, asbestos cement pipe. This stretch of pipe was previously determined to be undersized for connection of a new water storage tank and needs to be upgraded to 12-inch diameter ductile iron pipe. In addition to being undersized, the existing pipe is prone to leaks/breaks. Replacing this section of pipe will improve hydraulics in the system and provide a more reliable pipeline.

     In addition to the current ACOP that the town needs to comply with, the condition of the existing hydro-pneumatic tanks and the inconsistent pH of the finished water is a

potential serious threat to the public and for future reliability of the supply. A failure of the tanks would impact all users of the system; therefore this project would be classified as Tier IV.

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