The Piscataqua River is a 12-mile long tidal estuary formed by the confluence of Salmon Falls and Cocheo River. The river runs along the border of New Hampshire and Maine emptying into the Atlantic Ocean. Spanning the Piscataqua River from Newington to Dover is the newly constructed New Hampshire Department of Transportation’s (NHDOT) Spaulding Turnpike, Little Bay Bridge (RT 4). Rather than attaching a vital Unitil (Granite State Gas) gas main to this new bridge the trenchless technology method of horizontal directional drilling (HDD) was selected to install the gas main under the Piscataqua River.

Unitil (AKA, Granite State Gas Transmission, Inc.) selected Carson Corporation as the preferred HDD contractor after a extensive prequalification and competitive bidding process.

Despite having to work through the harsh New Hampshire winter and drilling over 2,500 l.f. in 30,000 psi granite Carson Corporation completed this project on time as mandated by the New Hampshire Department of Fish and Game.

Guided by the latest gyroscope steering technology and a redundant traditional wire line, Carson Corporation drilled a “rifle barrel” of a bore hole that never deviated more than 2’ from the intended horizontal and vertical alignment.

In addition to the HDD, Carson Corporation was also responsible for welding, coating, x-raying, hydrostatically testing and pigging the pipeline in strict accordance with Unitil’s PLS-101 Pipeline Construction Specification.

Having drilled in New Hampshire previously, provided Carson Corporation with knowledge and expertise to successfully complete this challenging drill with ease.

Installation Details and Project Summary

Owner: Unitil, Hampton, New Hampshire
Consulting Engineer: JD Hair, Tulsa, Oklahoma
Pipeline Designer: BL Companies, Meridian, Connecticut
Project: NHDOT Relocation Spaulding Turnpike, Little Bay Bridge Gas Pipeline
Location: Newington to Dover, New Hampshire
HDD Contractor: Carson Corporation, Lafayette, New Jersey
Pipe Supplier: Pipe by Owner
Pipe Size/Length: Piscataqua River Crossing, 2,500′ 10″ steel gas pipe
Installation: Horizontal Directional Drill
Steering Contractor: Horizontal Technologies, Houston, TX

Carson Corporation Contact:

Bob Carson-VP of Business Development (201) 230-4686,
[email protected]