Information and Frequently Asked Questions about Disinfection Byproducts
West Parish Filters Water Treatment Plant Upgrades

Raw drinking water from Cobble Mountain Reservoir is filtered, treated, and disinfected at West Parish Filters Water Treatment Plant in Westfield, MA. The plant was originally built in 1909 and last underwent significant upgrades in 1974.

Springfield Water and Sewer Commission's West Parish Filters Water Treatment Plant in Westfield, MA

With systems, equipment, and machinery at West Parish Filters nearing the end of their useful life, the Commission recognized the need to modernize the facility to provide reliable drinking water service and comply with present and future drinking water regulations.

In 2015 the Commission initiated the West Parish Filters Facilities Plan for comprehensive modernization upgrades to the plant, including to the treatment process. Planning and design for this type of large-scale project takes many years and requires many layers of regulatory approval.  

The West Parish Filters Facilities Plan includes planning for:

  • Dissolved Air Floatation (DAF) Clarification Process – to more effectively remove suspended particles and dissolved natural organic matter (NOM) prior to filtration
  • Rapid Sand Filter Upgrades – to more effectively capture and filter out dissolved NOM
  • New Electrical System – to support new treatment processes
  • New Chemical Storage and Feed Building – to support new treatment processes

The addition of a DAF clarification process will improve water quality and compliance with drinking water standards, including standards for haloacetic acid 5 (HAA5). HAA5 is a disinfection by-product that forms when chlorine reacts with dissolved natural organic matter (NOM) found in surface water supplies, such as Cobble Mountain Reservoir. The new DAF clarification process will remove more NOM from the raw water, thereby permanently resolving any future issues with elevated HAA5.

Planning Process

Water treatment plants are carefully calibrated to the specific chemistry of the water source and must receive multiple regulatory approvals. Before any construction of a new treatment process can begin, different potential alternatives are tested at increasing scales to ensure their efficacy at filtering and treating safe drinking water.

Pilot Plant

As part of the planning process the Commission launched a pilot testing site on the grounds of West Parish Filters in the fall of 2019.  The pilot site, or “pilot plant,” was separate and isolated from the drinking water plant but used raw water from Cobble Mountain Reservoir to test the effectiveness of various types of treatment methods during different seasons and environmental conditions. These alternatives were chosen based on previous bench-scale (or laboratory-scale) testing conducted in coordination with the UMass Department of Civil and Environmental Engineering and other consultants.

The pilot plant was completed in November 2020. The pilot plant results were analyzed by a Commission team including a panel of national experts. Results of the pilot plant identified DAF as the most effective treatment alternative.

An exterior view of the pilot plant installed at West Parish Filters, Fall 2019.

An interior view of the pilot plant installed at West Parish Filters, Fall 2019.

Half-Plant Trial

The pilot plant identified a different coagulant that is effective at removing more dissolved natural organic matter (NOM), one of the main causes of elevated HAA5, from the raw water. Though the coagulant is new to the Commission, it is approved by the American Water Works Association (AWWA) and is regularly used by water systems around the country. MassDEP approved a trial of the new coagulant in half of the West Parish Filters Water Treatment Plant. The trial took place in January 2021.


The design phase for the treatment plant upgrades, including the dissolved air floatation clarification process, is scheduled to begin in 2021-2022.


Upon approval by MassDEP, construction is expected to begin in FY24.

The total estimated cost of the upgrades is $123 million.