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Bethel Mills Hydroelectric


Hydroelectric Facility Improvements
Bethel, Vermont

The  Bethel Mill hydro-electric plant underwent significant improvements to it’s historic facility and selected the Turner Group for upgrades design and construction administration.  The project involved a turbine replacement, a new inflatable dam,  redesign of the river intake and trashrack (for enhanced debris handling and management), and a fish by-pass.  A unique alignment and structural design for the trashrack system was used to make the racks “self-cleaning” for most of the typical river debris encountered on the site. 

A fish sluice/by-pass plunge chamber was designed to work integrally with the rack system in order that the debris and fish passage can be accomplished as the same time without impact to the rack operation and injury to the fish.



NH Historical Society


Energy & Environmental Upgrades
Concord, New Hampshire

The Historical Society Museum building, designed in 1909 by the renowned architect Guy Lowell, was suffering from excessive energy use and poor humidity control.  The project was seen as an opportunity to remove the inefficient, expensive steam heating system with a conversion to natural gas fired hot water.

The work included installation of a condensing boiler plant, replacement of refrigerant cooling systems with a new chiller and chilled water distribution, new air handling equipment, energy recovery ventilation, and a new automatic temperature control system.  Constraints within the building forced a change from distributed steam radiators for heating to an all air system.  All hot water distribution and most air components were designed to remain on the lowest level of the building.  This enabled the Museum to remain in operation virtually throughout the entire project.

Envelope upgrades incorporated into this project primarily consisted of skylight infill, coupled with LED lighting to maintain the look of the original skylights on the interior.  Following the building improvements, the NHHS has seen more than 90% savings in energy bills.

The historical grants that provided a portion of the funding for this project required the use of “reversible” installations, meaning that any new equipment, openings, louvers, and other components had to be capable of full removal and restoration to the original historic character of the building.



Town of Sanbornton


Evaluations & Facility Assessments
Sanbornton, New Hampshire

The Turner Group was selected to provide the Town of Sanbornton with needed expertise for the evaluation and assessment of Sanbornton’s Town Hall Office and Public Safety Building.  The assessments will determine overall as to whether or not they are structurally sound for expansion, and/or reconstruction, or whether new construction is the most feasible option. 

 Work will included field evaluations, visual assessments, existing conditions documentation, code assessment, and site assessment.



Jackson Mills


Reconstruction for Flood Mitigation
Nashua, New Hampshire

Located on the Nashua River in Nashua, NH, the Jackson Mills Dam project removed the top 8 feet of an existing concrete spillway, and replaced it with 8 feet high pneumatically controlled crest gates.  Prior to the project completion, a significant portion of the downtown area upstream of the dam was within the FEMA 100-year floodplain, with some areas flooding at much lower flows.  With the completion of the project, approximately 70 properties were removed from the FEMA 100-year floodplain, with flood flow elevations reduced by as much as 5 to 6 feet upstream.  The crest gates can be controlled automatically, remotely, or manually; gauges and sensors at the dam can start to lower the crest gates when flood flows reach a certain elevation, and raise when water surface elevations (WESLs) drop.


Supply Pond Dam


Repairs & Rehabilitation
Nashua/Merrimack, New Hampshire

This project included significant repairs and rehabilitation of the existing 25-foot high, gravity-type, stone masonry Supply Pond dam.  Design and construction administration included installation of a structural cofferdam, demolition of the existing crest and construction of a new "hydraulically" shaped reinforced concrete crest, installation of new stainless steel hinged flashboards, and a new steel pedestrian bridge across the 30-foot crest.

Work also included installation of low level, slide-type sluice gates, installation of upstream shotcrete facing on the dam, installation of filter soil and tow drains on the downstream embankment, and installation of rip rap for causeway slope protection.



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