Disinfection Byproducts Reduction

Hillsborough, New Hampshire

Client: Town of Hillsborough, New Hampshire


  • Bench-scale Treatment Testing
  • Bidding Administration
  • Construction Administration
  • Funding Assistance
  • Installation Contract Design
  • Pilot Testing
  • Treatment Alternatives Review
  • UV Equipment Request for Proposals

Project Summary

The Town of Hillsborough obtains its water supply from a reservoir – Loon Pond. The water receives slow sand filtration, chlorination and pH-adjustment with potassium hydroxide prior to discharge to the system.

In general, the water quality is very good except for chlorinated disinfection byproducts (DBPs) – total trihalomethanes (TTHM) and haloacetic acids (HAA5) – which have regularly exceeded state standards. In 2012, the Town entered into an Administrative Consent Order with NHDES to reduce the DBPs and selected Hoyle, Tanner to engineer a solution. Loon Pond Reservoir, Hillsborough, NH.

Working with the Town, available treatment alternatives and technologies were narrowed to two approaches for testing: post-filtration with granular activated carbon (GAC); and, UV disinfection followed by chloramination. These two approaches were selected, in part, to maintain two highly-valued existing system advantages:
• A completely gravity-fed system with virtually no pumping; and
• No daily or regular spent backwash or comparable waste product.

These advantages currently result in high energy-efficiency, very little waste product for disposal and reduced daily operator attention.

Hoyle, Tanner retained the University of New Hampshire to assist with the bench-scale testing and then performed GAC pilot-testing at the water treatment facility. The testing indicated that GAC would not be cost-effective so UV disinfection followed by chloramination was selected.

Hoyle, Tanner has engineered a direct-purchase procurement of the UV system equipment based on life-cycle costing and other considerations and is currently developing the installation construction bid package. Hoyle, Tanner assisted in obtaining SRF funding for the project which is expected to cost $904,000 and has worked closely with NHDES throughout the project. The expected completion is March 2014.

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