LIHI Certificate #92 - Pierce Mills Project, Vermont

Project Name Pierce Mills
LIHI Certificate No. 92
LIHI Certificate Term February 6, 2017 – February 5, 2030
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. P-2396 issued 1994, expires 2034

The Pierce Mills Project is located in northeastern Vermont near St. Johnsbury, in Caledonia County, on the Passumpsic River. 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.

The Passumpsic River is host to several dams of which the project is the fifth on the river. The river is 22.7 miles long and a tributary to the Connecticut River, entering just downstream of Comerford Dam (part of LIHI #39). The project is owned by Green Mountain Power (GMP), the first energy utility certified as a B-Corporation.

The project includes: a dam, flashboards, intake structure, powerhouse, one vertical turbine, substation, spillway, and bypassed reach.

The concrete gravity dam is 93-feet-long by18-feet-high, topped with 18-inch flashboards. A 37-foot-long intake structure forms the left abutment, with a manually operated bulkhead gate and trashrack. A 6-foot diameter, 246-foot-long wood stave penstock conveys flows from the dam to the powerhouse. The powerhouse contains one vertical shaft turbine and generator with an installed capacity of 0.25 MW, along with appurtenant equipment.

The project operates in a run-of-river mode and impounds a 24.7-acre reservoir. The project provides a minimum flow of 20 cfs from April 1 through June 15 and from September 15 through November 15. Additionally, downstream fish passage is facilitated by an 88 cfs or inflow, whichever is less, passage flow. An aesthetic flow of 7 cfs is spilled over the flashboards from June 1 through October 31. These flow prescriptions were developed in consultation with the Vermont Agency of Natural Resources (VANR) and United States Fish and Wildlife Service.

Waters within the project reach are designated Class B and impaired for E. coli contamination due to the St. Johnsbury wastewater treatment plant passing combined sewer overflows. VANR has confirmed that the project does not adversely impact water quality and is not the source of river impairments. Class B waters are managed to support aquatic biota, wildlife, and aquatic habitat, public water supply, irrigation, primary contact recreation, and aesthetics.

While the Connecticut River Basin historically hosted naturally occurring Atlantic salmon runs, the species was extirpated from the river system due to the construction of dams. These downstream dams create a barrier to upstream passage at the project. Downstream passage is facilitated year-round via a transition box located in the spillway with an 88 cfs passage flow which leads to a plunge pool. Trashracks with 1-inch spacing mitigate the potential for entrainment.

The project lands consist of 2.8 acres. The lands surrounding the project are primarily mixed industrial and commercial buildings, rural residential housing, and farmland, with no lands of significant ecological value in the project area.

Threatened or endangered species potentially present in the project vicinity include the Northern Long-eared Bat, Spikemoss, and Shining Lady’s Tresses. Significant habitat does exist in the project vicinity but consultation with VANR determined that these habitats would not be adversely impacted by project operations.

Cultural resources in the project area include the project infrastructure which is eligible for listing on the National Register of Historic Places. The project owner submits annual reports to the Vermont Division for Historic Preservation and conducts shoreline monitoring every three years to ensure that no known or potential archaeological sites are threatened by erosion events.

Recreational resources at the project include a canoe portage, fishing access, a camping area, and a picnic area. Public access is provided free of charge.

PLUS-Standard: Criterion for LIHI certification include a PLUS standard for facilities that demonstrate substantial extra efforts in environmental and social mitigation, enhancement, or restoration. This project has achieved a PLUS standard by voluntarily making significant revisions to the Passumpsic River Canoeing and Recreation Guide which provides the public with enhanced knowledge of recreation opportunities both on and off project lands and waters. The collaborative effort of the multi-party interest groups established that the public needed better information to enhance their recreational experiences.

Compliance Status

There are no facility-specific conditions in the current Certificate.

2022: No material chances or compliance issues were identified. The project remains in compliance based on the annual review. Of note, the next upstream hydro project (Great Falls, P-2839) received a new FERC license in 2020 that increased its minimum bypass flow from 10 to 62 cfs.

2021: There were no report changes or compliance issues. The project remains in compliance based on the annual review.

2020: There were no report changes or compliance issues. The project remains in compliance based on the annual review.

2019: There were no report changes or compliance issues. The project remains in compliance based on the annual review.

2018: The project reported relocation of public parking, pedestrian access, and signage from the powerhouse area to 1/4 mile north at Highway 15 due to vandalism at the original site. A revised recreation plan was approved by FERC in 2017. The project remains in compliance based on the annual review.

2017: Annual reporting for the current Certificate has not yet taken effect.

Certification History

January 1, 2022: The LIHI Certificate term has been extended in accordance with Revision 2.05 of the LIHI 2nd Edition Certification Handbook issued January 1, 2022. Refer to the facility table above for the new term.

August 15, 2018: The decision to recertify the Pierce Mills Hydroelectric Project is final. No appeals were received during the appeal period which closed on August 11, 2018.  The new term for the Pierce Mills Project is from February 6, 2017 through February 5, 2025.

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, having earned a PLUS Standard in the Recreation Criteria.

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 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 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 Recertification

2012 Certification