FERC Part 12D Comprehensive Assessment High-Hazard Concrete-Faced Rockfill Dams
Client
Western United States Utility Company
Services Provided
FERC Part 12D Comprehensive Assessment Independent Consultant and IC Team; Potential Failure Mode Analysis (PFMA) and Level 2 Risk Analysis (L2RA) Facilitator and Facilitation Team; Supporting Technical Information Documents (STID)
Location
Western United States
Project Practice Areas
Geotechnical
Type of Facility
Concrete-Faced Rockfill Dams
Project Specifics
A utility company in the Western United States owns and operates two dams as part of a pumped storage project in a remote mountainous area. The pumped storage project consists of an upper reservoir, lower reservoir, and an underground powerhouse between the two reservoirs. The upper reservoir is impounded by a 315-foot-high concrete-faced rockfill dam with an ungated spillway, and the lower reservoir is impounded by a 260-foot-high concrete-faced rockfill dam with a spillway controlled by six radial gates. Both dams were constructed by the owner in the late 1950s. The pumped storage project has the unique ability to rapidly transfer water between the upper and lower reservoirs using the powerhouse, either in power generating mode (water flows from the upper reservoir through the powerhouse to the lower reservoir) or in pump-back mode (water is pumped uphill through the powerhouse from the lower reservoir to the upper reservoir). Both dams are classified as high hazard potential in accordance with the Federal Energy Regulatory Commission (FERC) Hazard Potential Classification guidelines.
On April 11, 2022, FERC established new requirements for Part 12D inspections. A notable change to the guidelines is the development of two types of Part 12D inspections: periodic inspections and comprehensive assessments(CA)s, where the latter includes a Potential Failure Mode Analysis (PFMA) and Level 2 Risk Analysis (L2RA) workshop. The owner retained Geosyntec to conduct the 2024 FERC Part 12D CAs and facilitate the PFMA/L2RA workshops for both dams.
Geosyntec Scope of Services
As the independent consultant, Geosyntec provided subject matter experts (SMEs) in geotechnical engineering, structural engineering, seismic hazards, and consequences. We also coordinated support from external SMEs. In addition, Geosyntec provided the PFMA/L2RA facilitator and facilitation team. The comprehensive assessments include detailed review and evaluation of analyses, design basis, reference documents, instrumentation and performance data, and dam safety program elements. They also include a field inspection and PFMA/L2RA workshops.
Our primary tasks include preparing of Part 12D inspection plans, pre-inspection preparation reports, PFMA/L2RA reports, and comprehensive assessment reports (CARs). Once completed, the CARs will comment on the safety and reliability of the project based on the document review, field inspection, and findings from the PFMA/L2RA. The CARs will recommend actions to reduce risk and enhance the safety of the facilities. We will update the supporting technical information documents to be consistent with the requirements of the new FERC guidelines and to include information developed over the previous five years since the last Part 12D safety review.
Notable Accomplishments
The comprehensive assessments submitted to FERC in early 2025 were the first for these dams and among the first performed for the owner.
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