Since 2014, McMillen has been providing a comprehensive range of engineering services for PG&E. Our dedication to delivering innovative design solutions resulted in the establishment of a Master Services Agreement (MSA) in 2018. By leveraging PG&E's Hydro Design Guide and dam safety standards, we have successfully provided technical support for multiple facilities.
Under the MSA, our work encompasses various aspects such as cost estimation, conceptual design, alternative development and analysis, technical design reviews, field surveying, constructability assessments, and procurement support for specialized equipment. Our team of experts covers diverse engineering disciplines including civil/structural, hydraulic, geotechnical, electrical, and mechanical engineering. We also provide ongoing engineering assistance during construction, including start-up testing and as-built documentation.
In addition to our technical expertise, we regularly meet with federal and state government agencies such as the FERC, USFWS, California Department of Safety of Dams, and California Department of Fish and Game. These interactions are pivotal for obtaining necessary approvals and permits.
Example projects with PG&E include hydraulic modeling, alternatives analysis, and design of spillway gates, the preliminary design of a debris boom, and inspections and design for miles of penstock. Additional projects are described below.
Helms Pumped Storage Improvements.
In 2020, we began work on task orders for improvements at the Helms Pumped Storage Facility. Due to aging infrastructure, PG&E has several areas of the plant that need to be repaired including tunnels and the powerhouse. The tunnels and penstocks (approximately 12’ in diameter) have experienced leakage and other issues that have received temporary fixes, such as grouting, drainage, and lining system measures. However, PG&E is now considering long-term solutions. Issues include longitudinal, radial, and oblique cracks in the concrete liner. The steel reinforcement is also exposed at severely damaged locations. Nearly 30 cracks, seepage, or offset within the liner were detected.
McMillen conducted tunnel inspections at the site, utilizing a remote operational vehicle. We also performed a dye and tracer study and held a risk, vulnerability, and failure review workshop. Based on our findings, potential mitigation efforts were identified and incorporated into the final tunnel design. McMillen completed an alternatives analysis to determine the necessary repairs that can be accomplished within the limited timeframe. The repairs prioritize addressing cracks and spalling concrete in the concrete tunnels and implementing a detailed contact grouting program for the steel and concrete sections of Penstock 1.
The project also involves the final design of liner repairs and treatment for areas with defective concrete lining to maintain reliability and durability. The repairs aim to limit exposure of the groundmass to variable pressurized water conditions and prevent potential loss of ground into the tunnels. McMillen identified repairs could involve removing defective concrete, adding additional rebar and doweling, and retaining repair materials in place. These types of repairs have been commonly performed in overhead repair areas and areas with high pressure and flow velocities.
In addition to the repairs, McMillen identified the need for grouting treatment in select locations to improve lining performance by enhancing rock mass confinement. Geologic mapping and observed liner damage patterns suggest that low lateral confinement in shear zones may be causing a shortened useful life of the tunnel liner in the penstock and manifold areas. McMillen proposed performing a three-dimensional model of the tunnel, surrounding rock mass, and shear zone using finite element modeling software to better understand and mitigate these distressed conditions. This analysis would help determine shear zone properties and inform future work on lining repairs.
Haas and Kerckhoff Powerhouse Generator CO2 Fire Suppression System Replacement.
As Engineer-of-Record, McMillen provided engineered drawings and specifications for replacing legacy CO2 fire suppression systems within two hydroelectric generators in an underground powerhouse with new hybrid water mist/nitrogen fire suppression systems (Victaulic Vortex). Design work included modifications to existing PG&E record drawings with new detailed electrical schematics for generator unit control interfaces. We also provided engineering support during construction. All work was performed in accordance with NFPA 850, NFPA 70, NFPA 72, NFPA 101, NFPA 770, and PG&E Hydro Design Guide.
Bucks Creek Turbine Shaft Replacements.
Bucks Creek powerhouse has two double-overhung 32 MW Peltontype generating units operating at 2,000' of head. McMillen performed engineering support of PG&E’s efforts to replace the unit #2 generator shaft, bearings, and bearing cooling system. We also provided technical support with reviews and assessments and advised PG&E on the construction and design of components, fixtures, and procedures.
FERC Part 12D Inspection and Reports.
McMillen provided Independent Consultant (IC) services to lead FERC Part 12D Safety Inspections, Potential Failure Mode Analysis (PFMA) Workshops, reviews and updates to the Supporting Technical Information Document (STID), and preparation of PFMA and Part 12D Reports for five PG&E dams (Pit 3, Pit 4, Pit 5 Open Conduit, North Battle Creek, and Macumber) and appurtenant structures
