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Home My WebLink About06.26.2024 Board Correspondence - FW_ Part 12 Consultant Safety Inspection Reports submitted in FERC P-619-000 by Pacific Gas and Electric Company,et al.From:Clerk of the Board To:Bennett, Robin; Clerk of the Board; Connelly, Bill; Cook, Holly; Cook, Robin; Durfee, Peter; Jessee, Meegan; Kimmelshue, Tod; Kitts, Melissa; Lee, Lewis; Pickett, Andy; Ritter, Tami; Stephens, Brad J.; Sweeney, Kathleen; Teeter, Doug; Zepeda, Elizabeth; Loeser, Kamie Cc:Nevers, Dawn Subject:Board Correspondence - FW: Part 12 Consultant Safety Inspection Reports submitted in FERC P-619-000 by Pacific Gas and Electric Company,et al. Date:Thursday, June 27, 2024 11:08:18 AM Please see Board Correspondence - -----Original Message----- From: 'FERC eSubscription' <eSubscription@ferc.gov> Sent: Wednesday, June 26, 2024 5:46 AM Subject: Part 12 Consultant Safety Inspection Reports submitted in FERC P-619-000 by Pacific Gas and Electric Company,et al. .ATTENTION: This message originated from outside Butte County. Please exercise judgment before opening attachments, clicking on links, or replying.. On 6/26/2024, the following Filing was submitted to the Federal Energy Regulatory Commission (FERC), Washington D.C.: Filer: Pacific Gas and Electric Company Pacific Gas & Electric Company (as Agent) Docket(s): P-619-000 Lead Applicant: Pacific Gas and Electric Company Filing Type: Part 12 Consultant Safety Inspection Reports Description: Pacific Gas and Electric Company submits Summary and Conclusion for Recommendation 3a from the Eleventh Part 12D Safety Inspection Report re the Grizzly Forebay Dam of the Bucks Creek Hydroelectric Project under P-619. To view the document for this Filing, click here https://urldefense.com/v3/__https://elibrary.ferc.gov/eLibrary/filelist?accession_num=20240626- 5023__;!!KNMwiTCp4spf!FdYWeTrSpzMiNXAyCs8RP0AGc4TPc9p4VAPRyHt3b7MiL-RsO0N6K9sc4dxOUo58vOmvyVsWmrqpG3qwvfd- Tp9n5Gtq60jIdnNo$ To modify your subscriptions, click here: RsO0N6K9sc4dxOUo58vOmvyVsWmrqpG3qwvfd-Tp9n5Gtq6-c3wSZP$ ------------------------------------------------------------------------ Please do not respond to this email. Online help is available here: https://urldefense.com/v3/__http://www.ferc.gov/efiling-help.asp__;!!KNMwiTCp4spf!FdYWeTrSpzMiNXAyCs8RP0AGc4TPc9p4VAPRyHt3b7MiL- RsO0N6K9sc4dxOUo58vOmvyVsWmrqpG3qwvfd-Tp9n5Gtq68CgZ4l1$ or for phone support, call 866-208-3676. Power Generation 300 Lakeside Drive Oakland, CA 94612 Mailing Address: P.O. Box 28209 Oakland, CA 94604 June 25, 2024 Via Electronic Submittal (E-File) Frank L. Blackett, P.E., Regional Engineer Federal Energy Regulatory Commission Division of Dam Safety and Inspections 100 First Street, Suite 2300 San Francisco, CA 94105-3084 RE: Bucks Creek Hydroelectric Project, FERC No. 619-CA Grizzly Forebay Dam, NATDAM No. CA00333 11th Part 12D Inspection – Summary and Conclusion for Recommendation 3a ENCLOSURE CONTAINS CUI//CEII – DO NOT RELEASE Dear Frank L. Blackett: This letter reports on the completion of Pacific Gas and Electric Company’s (PG&E) efforts to address Recommendation 3 (R-3) from the 11th 5-year Part 12D safety inspection report (dated January 2021) for Grizzly Forebay Dam, which is part of PG&E’s Bucks Creek Hydroelectric Project, Federal Energy Regulatory Commission (FERC) No. 619. PG&E provided its most recent update and request for extension of time regarding R-3 on November 10, 2023. For tracking purposes, PG&E has broken R-3 into to two individual items, R-3a and R-3b. A summary and conclusion of PG&E’s efforts to complete R-3a is provided in Enclosure 1 of this letter. PG&E provided its plan and schedule to address R-3b in a letter to FERC dated November 10, 2023. A scour assessment report is provided in Enclosure 2. PG&E has reviewed the consultant’s report and concurs with the information presented therein. Should you have technical questions concerning this matter, please contact Ben Fontana, senior dam safety engineer for PG&E, at (530) 762-9459. For general questions, please contact Andrew Garcia, license coordinator for PG&E, at (530) 228-8990. Sincerely, Robert O. Ellis, P.E., G.E. Deputy Chief Dam Safety Engineer Enclosures: 1. Summary and Conclusion for Recommendation 3a from the 11th Part 12D Safety Inspection Report 2. Grizzly Forebay Dam Scour Evaluation, Scour Assessment Report, prepared by HDR Engineering and dated May 29, 2024 - CUI//CEII – DO NOT RELEASE Document Accession #: 20240626-5023 Filed Date: 06/26/2024 ENCLOSURE 1 Document Accession #: 20240626-5023 Filed Date: 06/26/2024 Enclosure 1 1 Bucks Creek Hydroelectric Project, FERC No. 619-CA Grizzly Forebay Dam, NATDAM No. CA00333 Summary and Conclusion for Recommendation 3a from the 11th Part 12D Safety Inspection Report Recommendation 3 (R-3) was provided in the 11th 5-year Part 12D safety inspection report (dated January 2021) for Grizzly Forebay Dam, which is part of Pacific Gas and Electric Company’s (PG&E) Bucks Creek Hydroelectric Project, Federal Energy Regulatory Commission (FERC) No. 619. For tracking purposes, PG&E has broken R-3 into two individual items as shown below. For reference, R-3a and R-3b are copied below, followed by a summary and conclusion regarding PG&E's efforts to address the recommendations. R-3a: Perform an erodibility and scour assessment of the downstream foundation and abutment rock subject to overtopping (PFM No. 1) for various flood levels up to the PMF including but not necessarily limited to 50% of the PMF and the PMF. Following completion and FERC review and acceptance. R-3b: PG&E should update Section 5.0 of the STID to include results. (PFM Nos. 1 – 3) PG&E retained HDR Engineering (HDR) to assess the scour potential from dam overtopping for Grizzly Forebay Dam. Results of the scour assessment are presented in a report titled Grizzly Forebay Dam Scour Evaluation, Scour Assessment Report, prepared by HDR, and dated May 29, 2024, which is enclosed with this letter for FERC review. PG&E has reviewed the report prepared by our consultant and concur s with the findings and conclusions therein. HDR used the semi-empirical Annandale’s Erodibility Index Method to evaluate the scour potential of the dam abutments, downstream dam toe , and in the channel downstream of the dam. HDR developed computational fluid dynamic (CFD) models of the Grizzly Forebay Dam and ran the models for four flow scenarios, including 10, 47, 75, and 100 percent of the probable maximum flood (PMF) peak outflow. HDR used the CFD results estimate stream power values, which they compared against the threshold stream power values of the foundation rock to determine the potential for and extent of scour. HDR based the quality of the foundation rock on information collected during an on-site geologic assessment and review of historical information. Table 3-1 of the report provides the erodibility index values used in the assessment based on the observable surface condition of the rock mass. The following tables (Tables 1 through 3) show the calculated stream power values and anticipated ultimate scour depth for an infinite duration of constant peak flows of each scenario. As shown in Figure 5-1 of the report, the following potential scour for the plunge pool is anticipated for the four flow scenarios modeled. The jet trajectory impacts the plunge pool approximately 25 to 30 feet downstream of the toe of the dam, and that scour will be directed predominantly away from the toe of the dam, based on the CFD results. Document Accession #: 20240626-5023 Filed Date: 06/26/2024 Enclosure 1 2 Table 1. Plunge Pool Anticipated Stream Power and Scour Depth Results Flow Scenario Stream Power (kW/m2) Anticipated Scour Depth (feet) Full PMF 3,125 32 75% PMF 3,234 35 47% PMF 2,898 31 10% PMF 225 No Scour Notes: kW/m2 = kilowatts per meter squared; PMF = probably maximum flood As shown in Figure 5-2 and 5-3 of the report, the following scour potential is anticipated along the dam toe and abutments due to dam overtopping flows during the full PMF and 75-percent PMF. The CFD models shows approximately 3 feet of overtopping at the full PMF and 1.5 feet for the 75-percent PMF scenarios, while the other two flow scenarios do not produce overtopping. Table 2. Full PMF Right Abutment Anticipated Stream Power and Scour Depth Results Flow Scenario (Full PMF) Stream Power (kW/m2) Anticipated Scour Depth (feet) Site 1 (right side) 316 30-40 Site 2 (right side) 316 10 Site 3 (left side) 186 15 Notes: kW/m2 = kilowatts per meter squared; PMF = probably maximum flood Table 3. 75% PMF Right Abutment Anticipated Stream Power and Scour Depth Results Flow Scenario (75% PMF) Stream Power (kW/m2) Anticipated Scour Depth (feet) Site 1 (right side) 316 5–10 Site 2 (right side) 316 10 Site 3 (left side) 186 10–15 Notes: kW/m2 = kilowatts per meter squared; PMF = probably maximum flood A general limitation of this scour assessment is that no time-duration component is associated with the flow scenarios for the employed methodology. This approach determined erosive capacity (i.e. stream power) for a given flow scenario, which was held constant and then compared to the erosion resistance of the foundation materials to determine the potential for scour initiation and anticipated progression. As is discussed in the report, the dam experienced flood flows in 1964 that were similar to the flows modeled at 47 percent of the PMF, but without experiencing the predicted plunge pool erosion. A possible explanation of that observation is the limited duration of the event being insufficient to initiate erosion. To address the scour potential identified above, PG&E plans to present and discuss the findings and suggested mitigation measures of this assessment during the upcoming FERC Part 12D comprehensive assessment (CA) for Grizzly Forebay Dam. As part of the CA, PG&E will conduct a formal risk assessment to evaluate the risks associated with scour potential from dam overtopping. PG&E plans to submit the findings from the CA to FERC by November 1, 2025. Document Accession #: 20240626-5023 Filed Date: 06/26/2024 Enclosure 1 3 PG&E believes that the information included with this filing satisfactorily addresses the intent of R-3a and that no further action is required at this time. PG&E provided its plan and schedule to address R-3b in a letter to FERC dated November 10, 2023. Document Accession #: 20240626-5023 Filed Date: 06/26/2024 Document Content(s) PGE20240625_619_Grizzly_R3_Closure_Ltr.pdf................................1 PGE20240625_619_Grizzly_R3_Closure_Enc1.pdf...............................2 Document Accession #: 20240626-5023 Filed Date: 06/26/2024