Bonneville Power Administration Workshop Highlights

B O N N E V I L L E P O W E R A D M I N I S T R A T I O N RHWM Process Workshop BP-26 Rate Period Preliminary Outputs June 4, 2024 (Corrected) WebEx: Join Meeting Meeting Number: 2827 077 7222 Meeting Password: WPxDgmX*86

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N RHWM Process Workshop Agenda Topic Presenter Introductions and Purpose of the Workshop Liz Oberhausen Load Forecast Update Max St. Brown Tier 1 System Firm Critical Output (T1SFCO): Milli Chennell Hydro Study Results T1SFCO Study Results RHWM Augmentation Garth Beavon Next Steps Liz Oberhausen Predecisional. For discussion purposes only. 2

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N RHWM Process* *For more details about the Rate Period High Water Mark (RHWM) process and calculations, please refer to section 4.2.1 of the Tiered Rate Methodology (TRM) Predecisional. For discussion purposes only. 3

B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Load Forecast Update for BP-26 RHWM Process 4 Predecisional. For discussion purposes only.

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Load Forecast Agenda Review economic conditions Review current model performance Forecasted Agency Loads (Preference) Guidelines for Load Forecast Next steps Predecisional. For discussion purposes only. 5

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Current Economic Forecast 9.0 S&P Base Forecast U.S. GDP % Change S&P Optimisitc Forecast 7.0 S&P Pessimistic Forecast Historical GDP 5.0 3.0 1.0 2019:4 2020:1 2020:2 2020:3 2020:4 2021:1 2021:2 2021:3 2021:4 2022:1 2022:2 2022:3 2022:4 2023:1 2023:2 2023:3 2023:4 2024:1 2024:2 2024:3 2024:4 2025:1 2025:2 2025:3 2025:4 2026:1 -1.0 -3.0 -5.0 -7.0 -9.0 Positive GDP growth is expected for the nation World economic and geopolitical concerns continue Predecisional. For discussion purposes only. 6

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Current Economic Forecast 9.0 United States (S&P Base Forecast) Washington (S&P Base Forecast) Oregon (S&P Base Forecast) Idaho (S&P Base Forecast) Montana (S&P Base Forecast) Historical GDP U.S. GDP % Change 7.0 5.0 3.0 1.0 2019:4 2020:1 2020:2 2020:3 2020:4 2021:1 2021:2 2021:3 2021:4 2022:1 2022:2 2022:3 2022:4 2023:1 2023:2 2023:3 2023:4 2024:1 2024:2 2024:3 2024:4 2025:1 2025:2 2025:3 2025:4 2026:1 -1.0 -3.0 -5.0 -7.0 -9.0 All Pacific Northwest states are forecasted to grow faster than the U.S. Predecisional. For discussion purposes only. 7

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Current Models - Energy FY 2024 Forecasts vs Actuals 5,500,000 Total Tier 1 Energy (MWh) Load Following Customers 5,000,000 4,500,000 4,000,000 MWh 3,500,000 3,000,000 2,500,000 2,000,000 1,500,000 Oct-23 Nov-23 Dec-23 Jan-24 Feb-24 Mar-24 Apr-24 May-24 Jun-24 Jul-24 Aug-24 Sep-24 Rate Case Forecast Total T1 Energy Actuals Total T1 Energy Forecasted energy is performing well against Fiscal Year to date Actuals Predecisional. For discussion purposes only. 8

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Current Models - Peaks 9,000 FY 2024 Forecasts vs Actuals 8,000 7,000 6,000 Customer System Peak (MW) 5,000 MW 4,000 3,000 2,000 1,000 0 Oct-23 Nov-23 Dec-23 Jan-24 Feb-24 Mar-24 Apr-24 May-24 Jun-24 Jul-24 Aug-24 Sep-24 Rate Case Forecast CSP Actuals CSP Demand models are performing well after compensating for weather Predecisional. For discussion purposes only. 9

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Forecasted Agency Loads BP-24 RHWM_LORA_May 2022 BP-26 RHWM_LORA_May 2024 Fiscal Year (aMW) Preference Block Slice Block Slice (non-block) Load Following Tier 2 (Block) 2024 2025 2026 2027 2028 6,856 533 1,332 1,586 3,223 182 7,049 531 1,347 1,571 3,237 363 7,138 514 1,154 1,379 3,552 539 7,176 519 1,161 1,365 3,561 570 7,247 523 1,151 1,378 3,574 620 Increase in Preference Forecast between FY2025 & FY2026 Increase in Preference Forecast between FY2026 & FY2028 Increase in Tier 2 Load Three customers switched products between BP-24 and BP-26 10 Predecisional. For discussion purposes only.

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Load Forecast Next Steps Customers provide notice of additional changes - ASAP, please. Submit forecast change request (including cause and amount) on BPA.gov comment page by June 18, 2024. Forecaster to review and include necessary changes. Predecisional. For discussion purposes only. 11

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Guidelines for Load Forecast Guiding Principles for Revising Load Forecasts Avoid subjective bias in results Make changes with a clearly identifiable cause and effect Avoid making changes within the tolerance of model errors, i.e., changes less than 5% Rely on models and results put together when consequences are not immediately pending Avoid forcing the models to give specific answers Rely on statistics of models Rely on accuracy of models and improve when results are not within accuracy tolerance levels Avoid updating without sufficient new data Incorporate highly probably information Include new loads/projects that have higher than 70% probability of occurring Predecisional. For discussion purposes only. 12

B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Hydro and T1SFCO Study Results

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Hydro Study Typical Updates Pacific Northwest Coordination Agreement (PNCA) Project Data Updated based on 2023 Coulee pumping data from 2023 PNCA submittal, no other PNCA data changes since 2022 Canadian Operations Updated based on the 2024 Assured Operating Plan (AOP24) and Detailed Operating Plan (DOP24) completed under the Columbia River Treaty AOP24 provides the same Canadian Operation for FYs20 24, while DOP24 includes minor updates An updated AOP will be available at some point, but current timing is unknown. Bonneville expects changes to be minimal and would evaluate impacts to the RHWM process based on timing of the updated AOP and magnitude of change. Project Outages Updated based on 2023 vintage long term maintenance and capital program forecasts from the BPA Federal Hydro group. This will use the same methodology as the last rate case Flood Control Updated with Corps produced FRM for the 2020 Level Modified Flows Dataset, not reflective of CRT Article IV Reserves Updated FCRPS reserve assumptions consistent with Generation Inputs forecasts Loads Updated based on the latest forecasts produced by Load Forecasting and aggregated by Long Term Power Planning in LORA-LT Predecisional. For discussion purposes only. 14

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Spill Updated with 12/14 agreement (aka RCBA) Spring Spill Season 125% TDG spill at six projects 40% of outflow daytime spill and 125% TDG spill nighttime spill at John Day 40% outflow spill at The Dalles 24 hours a day Little Goose spill transitions from 125% TDG 24 hours a day to 16 hours a day, eight hours 30% outflow after adult criteria is met Summer Spill Season Like BP-24 RHWM, except transition to late summer spill shifted to August 1st Assumptions for surface weir flow slightly adjusted Fall/Winter Spill Season Increased to four hours a day for seven days a week September 1st through November 15th and March 1st through March 20th and 24 hours a day from March 21st through the beginning of spring spill Predecisional. For discussion purposes only. 15

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Firm Hydro Comparison to BP-24 RHWM 8000 7000 6000 5000 aMW 4000 3000 2000 1000 0 Oct Nov Dec Jan Feb Mar Apr1 Apr2 May Jun Jul Aug1 Aug2 Sep Avg BP26 RHWM (3-year average) 4764 6418 6932 7261 6535 6274 5243 4445 6467 7409 6306 6522 5699 5314 6219 BP24 RHWM (2-year average) 4790 6550 6834 7073 6524 6774 5572 5197 7047 7515 5920 5770 5729 5409 6297 BP26 RHWM minus BP24 RHWM -26 -132 98 188 12 -500 -330 -752 -580 -106 386 752 -30 -96 -78 The 78 aMW decrease in firm generation compared to BP-24 RHWM is attributable to: Net loss of 49 aMW of generation due to the 12.14 Agreement spill operations Net loss of approximately 28 aMW due to other modeling changes including: o Changes to Canadian outflows o Changes to Brownlee operations o Updates to FRM o Differences in the monthly p10 years Predecisional. For discussion purposes only. 16

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Firm Hydro Comparison to Recent Rate Case 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 Oct Nov Dec Jan Feb Mar Apr1 Apr16 May Jun Jul Aug1 Aug16 Sep Avg BP26 RHWM 4764 6418 6932 7261 6535 6274 5243 4445 6467 7409 6306 6522 5699 5314 6219 BP24 Initial Proposal 4842 6486 6922 6854 6749 6406 5600 5105 7088 7635 6387 6052 5801 5448 6339 BP24 RHWM 4790 6550 6834 7073 6524 6774 5572 5197 7047 7515 5920 5770 5729 5409 6297 Annual Avg. Hydro Gen (aMW) Delta from BP26 RHWM Study Vintage Firm Hydro Major changes from previous study BP-26 RHWM 6219 - New Spill Operations/DOP/Brownlee Operation/FRM BP-24 Initial Proposal 6339 +120 Updates to FRM/Flex spill modeling BP-24 RHWM 6297 +78 First 2020 Level Modified Flows/30-year subset study Predecisional. For discussion purposes only. 17

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Federal Tier 1 System Firm Critical Output Summary T1SFCO Projections Energy in aMW 2026 2027 2028 Average 1. 6,529 2. Total Federal System Hydro Generation (TRM Table 3.1) 6,525 6,594 6,549 1,119 3. Total Designated Non-Federally Owned Resources (TRM Table 3.2) 1,140 1,001 1,087 136 4. Total Designated BPA Contract Purchases (TRM Table 3.3) 136 136 136 -892 5. Total Designated System Obligations (TRM Table 3.4) -889 -889 -889.91 Federal Tier 1 System Firm Critical Output (sum of Lines 2-5) 6,892 6. 6,912 6,842 6,883 18 Predecisional. For discussion purposes only.

a B O N N E V T1SFCO Difference Between BP-26 RHWM Process and BP-24 Final RHWM I L L E P O W E R A D M I N I S T R A T I O N Federal Tier 1 System Firm Critical Output Projection - 3-Year Average RHWM Process for BP-26 Rate Period S253-RC-20240516-140109 T1SFCO Projections Energy in aMW 2026 2027 2028 Average Component Details Hydro gen decreased due to: - RCBA Spill Operations (-49aMW) - Willamette Injunction (-33 aMW) - Other model updates (-28 aMW) Total Federal System Hydro Generation (TRM Table 3.1) 6,525 6,594 6,529 6,549 Total Designated Non- Federally Owned Resources (TRM Table 3.2) Non-Fed resources increased due to: - Lower CGS Maintenance in the 3-year period (+20 aMW) - End of Stateline Wind Contract (-12 aMW) 1,140 1,001 1,119 1,087 Total Designated BPA Contract Purchases (TRM Table 3.3) 136 136 136 136 Total Designated System Obligations (TRM Table 3.4) Small changes in the obligations for the Bureau, Slice Transmission Losses and NTSA -889 -889 -892 -890 Federal Tier 1 System Firm Critical Output 6,912 6,842 6,892 6,883 Predecisional. For discussion purposes only. 19

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N T1SFCO Change Over Time Predecisional. For discussion purposes only. 20

B O N N E V I L L E P O W E R A D M I N I S T R A T I O N RHWM Augmentation

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N RHWM Augmentation Predecisional. For discussion purposes only. 22

B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Next Steps and BP-26 RHWM Timeline

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Next Steps RHWM preliminary outputs will be posted on the RHWM website following today s meeting: https://www.bpa.gov/energy-and-services/rate-and-tariff-proceedings/rate-period-high-water- mark-process o Public comment period June 5th June 18th, 2024 o Please submit comments (including load forecast change requests) on BPA s public comment page: https://publiccomments.bpa.gov/OpenCommentListing.aspx July 31st public workshop to present draft final RHWM outputs Predecisional. For discussion purposes only. 24

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N BP-26 RHWM Timeline Action FY 24 Timing Public workshop Present preliminary RHWM process forecast, augmentation and system size June 4th (Tuesday) June 4th (Tuesday) Publish preliminary RHWM process outputs June 5th 18th Public comment period Calculate draft final RHWM outputs Late July FORMAL PROCESS BEGINS Public workshop Present draft final forecast, augmentation and system size July 31st (Wednesday) Publish draft final RHWM process outputs July 31st (Wednesday) Public comment period August 1st-14th Deadline for written preservation of right to dispute August 5th (Monday) Republish RHWM Outputs (if changes made due to public comments) August 30th (Friday) Deadline for dispute notice September 10th (Tuesday) Publish final RWHM process outputs September 30th (Monday) 25 Predecisional. For discussion purposes only.

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Questions? Predecisional. For discussion purposes only. 26

B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Appendix

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Federal System Hydro Generation Used in T1SFCO Calculation Predecisional. For discussion purposes only. 28

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Federal System Hydro Generation Used in T1SFCO Calculation (cont.) 29 Predecisional. For discussion purposes only.

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Designated Non-Federally Owned Resources Used in T1SFCO Calculation Predecisional. For discussion purposes only. 30

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Designated BPA Contract Purchases Used in T1SFCO Calculation 31 Predecisional. For discussion purposes only.

a B O N N E V I L L E P O W E R A D M I N I S T R A T I O N Designated BPA System Obligations Used in T1SFCO Calculation - Corrected NO Changes to original June 4, 2024 Workshop numbers Designated BPA System Obligations for use in the T1SFCO Calculation RHWM Process for BP-26 Rate Period (3 year) TRM Table 3.4 (Negative numbers indicate obligations) S253-RC-20240516-140109 A B C D E 1. System Obligation Contract # 14-03-17506; 14-03-49151 Ibp-4512; 14-03-001-12160 14-03-73152 EW-78-Y-83-00019 14-03-49151 EW-78-Y-83-00019 14-03-49151 14-03-63656 14-03-32210 14-03-49151 10GS-75345 DE-MS79-88BP92591 99PB-22685 99EO-40003 12PG-10002 09PB-12126 09PB-12128 2026 2027 2028 Average 2. BPA to BRCJ Chief Joseph -8.6 -8.6 -8.6 -8.6 3. BPA to BRCB Columbia Basin Project -152.3 -152.3 -156.0 -153.5 4. 5. 6. 7. 8. 9. 10. BPA to BRTD The Dallas Reclamation Project 11. BPA to BRTV Tualatin Project 12. BPA to BRUB Umatilla Basin Project 13. BPA to BRYK Yakima Project 14. BPA to BCHP LCA (settled financially) 15. BPA to BCHA Can Ent 16. BPA to BCHA NTSA 18. BPA to PSE: Pwr S (Up. Baker 2) 20. BPAP to BPAT: Ops - IntrAgmt 21. Federal Power Transmisssion Losses 22. Slice Transmission Loss Return BPA to BRCR Crooked River Project BPA to BROP Owyhee Project BPA to BRRP Rathdrum Prairie Project BPA to BRSID Southern Idaho Projects BPA to BRSIN Spokane Indian Develop. BPA to BRSV Spokane Valley -0.6 -1.3 -0.8 -20.2 -0.3 -0.7 -2.1 -0.7 -2.7 -1.7 -0.6 -1.3 -0.8 -20.2 -0.3 -0.7 -2.1 -0.8 -2.7 -1.7 -0.6 -1.3 -0.8 -20.1 -0.3 -0.7 -2.1 -0.8 -2.7 -1.7 -0.6 -1.3 -0.8 -20.2 -0.3 -0.7 -2.1 -0.8 -2.7 -1.7 -454.3 -13.6 -1.3 -9.4 -246.3 28.2 -454.3 -13.7 -1.3 -9.4 -244.2 28.0 -454.3 -13.5 -1.3 -9.4 -245.7 28.1 -454.3 -13.6 -1.3 -9.4 -245.4 28.1 Predecisional. For discussion purposes only. 32 Total Designated System Obligations 23. -888.8 -887.2 -892.0 -889.3