Pierce Mills powerhouse

Pierce Mills Powerhouse

The Pierce Mills Project is the most upstream of the four Projects, located at river mile 15.2.  It was built in 1917-1919 by the Twin State Gas & Electric Company. The powerhouse was completely destroyed in the flood of 1927, although the concrete dam was largely undamaged. The plant was rebuilt in 1928 utilizing portions of the earlier substructure.

Project Name Pierce Mills
LIHI Certificate Number 92
LIHI Effective and
Expiration Dates
February 6, 2012
February 6, 2017
(extended to September 30, 2018)
Owner Green Mountain Power Corporation
State Vermont
Location Located at river mile 15.2 on the Passumpsic River, a tributary of the Connecticut River; the most upstream of the Passumpsic River Projects.
Installed Capacity 250 kW
Average Annual Generation 1,133 MWh
Facility Type Run-of-river
FERC No. 2396

The Project impounds a 24.7-acre reservoir that extends 1.25 miles upstream to the Great Falls Dam with a water surface elevation at 605.0 feet msl and 24.7 acre-feet of usable storage. The concrete gravity dam is 93 feet long by18 feet high, with a crest elevation of 603.5 feet mean sea level (msl). The dam is topped with 18-inch flashboards. A 37-foot-long intake structure forms the left abutment, with a manually operated bulkhead gate and rashrack.

A 6-foot diameter, 246 foot-long wood stave conveys flows from the dam to the powerhouse with a drop in elevation of 18 feet. The powerhouse contains one vertical shaft turbine rated at 271 kilowatts (kW) and a generator rated at 250 kW, along with appurtenant equipment.

The Project also includes a substation, and a downstream fish passage facility located in the spillway adjacent to the intake. The bypassed reach at Pierce Mills is about 330 feet long. The Project has a hydraulic range of 90 to 200 cubic feet per second (cfs) and an average annual generation of about 1,337 megawatt-hours (MWh).

Certification History

July 12, 2018: The Low Impact Hydropower Institute (LIHI) preliminarily approved the Pierce Mills Hydroelectric Project for a new 8-year term of Low Impact Certification.

This decision is preliminary pending the 30-day appeal window. Only those who commented in the initial application during the 60-day comment period are eligible to file an appeal. Such appeal needs to include an explanation as to how the projects do not meet the LIHI criteria. Appeal requests can be submitted by email to comments@lowimpacthydro.org with “Pierce Mills Hydroelectric Project” in the subject line, or by mail addressed to the Low Impact Hydropower Institute, 329 Massachusetts Ave, Suite 2, Lexington, MA 02420. All requests will be posted to the website and the applicant will have an opportunity to respond and any response will also be posted. Requests must be received by 5 pm Eastern time on August 11, 2018.  The full application and reviewer’s report are available below.

If no appeal requests are received and the decision becomes final, the new term for the Pierce Mills Project will be February 6, 2017 through February 5, 2025.

June 11, 2018: The Pierce Mills certification term has been extended again to September 30, 2018.

April 3, 2018: The Pierce Mills certification term has been extended again to June 30, 2018.

November 28, 2017: The Pierce Mills certification term has been extended to March 31, 2018.

December 30, 2016: The Low Impact Hydropower Institute has received a complete application for a new term of Low Impact Certification for the Pierce Mills Hydroelectric project. The application materials can be found in the Files section below.

LIHI is seeking public comment on this application.  Specifically, we are interested in knowing whether you think the Pierce Mills project meets the LIHI Low Impact Certification Criteria, as revised in the 2nd Edition Handbook released in March 2016.  Please review the program and criteria in LIHI’s revised Handbook and then review the Project’s 2016 application materials posted below.

Comments that are directly tied to specific LIHI criteria (flows, water quality, fish passage, etc.) will be most helpful, but all comments will be considered.  Comments may be submitted to the Institute by e-mail at comments@lowimpacthydro.org with “Pierce Mills Project Comments” in the subject line, or by mail addressed to the Low Impact Hydropower Institute, PO Box 194, Harrington Park, New Jersey 07640.  Comments must be received at the Institute on or before 5 pm Eastern time on March 4, 2017 to be considered.  All comments will be posted to the web site and the applicant will have an opportunity to respond.  Any response will also be posted.

December 16, 2016: The Pierce Mills Hydroelectric project has been granted an extension of the current certificate term. The new expiration date is May 6, 2017. See extension letter for explanation below.

September 9, 2012: The Pierce Mills project has been certified as low impact for a five year term, effective February 6, 2012 and expiring February 6, 2017.

April 6, 2012: Public comment period on application has closed.

February 6, 2012: The Central Vermont Public Service Corporation has submitted an application for the certification of the Pierce Mills project. Public comment period on application has opened.


2017 Re-certification

2012 Certification