Merrimack Water Main Crossing & Intake

Project Highlights

  • 2020 ACEC/NH Silver Award for Engineering Excellence
  • Horizontal Directional Drilling
  • Water System Expansion
  • Groundwater Trust Fund
  • State, Federal, Muncipal & Private Coordination
  • River Crossing Design Alternatives

Due to PFAS contamination in groundwater supplies in the Town of Litchfield, New Hampshire, Pennichuck Water Works (PWW) is responding with a new potable water pipeline crossing the Merrimack River from their property on the west bank of the river in the Town of Merrimack to the Litchfield side. The $3.2 million project, became substantially complete as of October 2018 and includes a new intake and pump station. In preparation for this work, Tighe & Bond completed a bathymetric survey of the Merrimack River in the vicinity of the PWW existing river bank intake and a geotechnical investigation that included drilling a total of seventeen borings.

Normandeau Associates’ services were retained to assist with coordination and permitting between the Town of Litchfield, NH, Town of Merrimack, NH, NHDES, U.S. Fish & Game, Pan Am Railroad, and private landowners. New and revised land takings and easements with the various federal/state/private entity abutters, shoreland and wetland impact permits were obtained.

Tighe & Bond is also assisting PWW with a new raw water intake in the Merrimack River. After completing an alternatives analysis, Tighe & Bond developed final design drawings and specifications for installation of twin 30 MGD passive T-Screen intakes with a 48-inch steel intake pipe approximately 215 linear feet horizontally into the river connecting to a 10’ x 10’ (inside dimensions) pre-cast concrete wet well on the river bank. The pre-cast wet well connects with a 48-inch steel pipe approximately 35 linear feet to a 12’-4” x 15’-4” cast-in-place junction structure that is constructed around the two existing 36-inch reinforced concrete intake pipes. An airburst system constructed inside the existing pump house, designed for air scouring of the screens at regular intervals, connects to the screens with two 6-inch High-Density Polyethylene (HDPE) air pipes. The project is slated for completion in late 2019.

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