1. potential failure mode analysis study … failure mode analysis study report m eld om~lle stid...

Jnofflclal FERC-Generated PDF of 20050401-0097 Received by FERC OSEC 03/29/2005 in Docket#: P-2100-000

1. POTENTIAL FAILURE MODE ANALYSIS STUDY REPORT

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POTENTIAL FAILURE MODES ANALYSIS %0 Int roduct ion and Background .................................................................................. 1-1

2.0 Descript ion of Project ............................................................................................... 2-1 2.1 General P r o j e c t Description ..................................................................................................... 2-1 2.2 Pertinent Data ........................................................................................................................... 2-1 2.3 Dam .......................................................................................................................................... 2-2 2.4 Spillway .................................................................................................................................... 2-3 2.5 Intakes ...................................................................................................................................... 2-3 2.6 Conveyance Systems ............................................................................................................... 2-3 2.7 Powerhouse .............................................................................................................................. 2-3 2.8 Outlets ...................................................................................................................................... 2-3 2.g VicJnity Map and Project Drawings ........................................................................................... 2-4 2.10 Standard Operating Procedures ............................................................................................. 2 - 4

3.0 Major Findings and Understandings ....................................................................... 3-1

4.0 Potential Failure Modes identif ied ........................................................................... 4-1

5.0 Likely Consequences of Each Potential Failure Mode ........................................... 5-1 5.1 Rood Related Potential Failure Modes .................................................................................... 5 . 1

5.2 Normel Operating Related Potentlel Failure Modes ................................................................. 5.1 5.3 Earthquake Related Potential Failure Modes ........................................................................... 5-1 5.4 Other Condition Potential Failure Modes ................................................................................. 5-1

6.0 Potential Risk Roduct ion Act ions ident i f ied ............................................................ 6 . 1

7.0 Other Considerat ions Related to S tudy ................................................................... 7-1

8.0 Summary of Potential Act ions Identl f iod In the PFMA wi th Respect to Performance Moni tor ing ................................................................................................. 8-1

9.0 Summary and Conclus ions ...................................................................................... 9-1

Append ix A - List o f Reference Reports ............................................................ .A-1

Append ix B - List of Reference Drawings/Figures ............................................... B-1

Append ix C - Photos Taken During Field Review ................................................. C-1

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1.0 Introduction and Background Beginning in 2003, the Federal Energy Regulatory Commission (FERC) implemented a new Dam Safety Performance Monitoring Program (DSPMP). The DSPMP requirements are included in Chapter 14 of FERC's Engineering Guidelines dated April 11, 2003. The new program consists of three parts:

1. Conduct a Potential Failure Modes Analysis (PFMA) and prepare a PFMA report. The PFMA is intended to broaden the scope of traditional dam safety evaluations. A Core Team consisting of the FERC inspector, Independent Consultants, Owner's representatives, and PFMA Facilitator participate in a workshop to identify potential failure modes under hydrologic, seismic, normak and operating conditions.

2. Prepare a Supporting Technical Information Document (STID) that includes the PFMA report. The STID is a summary of background information and analyses that do not change significantly between Part 12D safety inspection reports.

3. Prepare the Part 12D Safety Inspection report The Part 12D inspection and report will focus on the identified Potential Failure Modes (PFMs) and the information and findings presented in the PFMA report and will include an evaluation of the current performance monitoring and surveillance program as it relates to the identified potential failure modes.

This report is a summary of the PFMA workshop conducted for Oroville Dam on September 15, 2004. The workshop was conducted jointly by DWR, the Independent Consultants, and FERC with guidance from the Independent Facilitator. A list of the participants is presented in Table 1.

Table f : Orov~l[e Dam - PFMA Workshop ParfJclpant~

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Name Oriwnizzeon Pho~ ~ I P R ~ P,o~ I'IDR Co~ Team - In(bper, de~ ~

I . ~ Core Team- Indep~lerd ~ t

Corn Teem - FFMA Fl~li~or DWR-D~ (occupY) Corn T ~ DY~DSOD (Engineer) C m T ~ DWR-O4,M (Opam~5ons) Corn Team F'B~ (Englflee¢) Col~ Tw. DWR-DOE(£n~ Cont Team HDR ~ - Reomdv DWR-O&M ItQ Ps.,tidp~t OWR.OFDO&M P ~ DWR-OFD O&U

Par~ctpent

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Prior to the workshop, the Independent Consultants and DWR representatives gathered background documentation including previous safety inspection reports, stability analyses, hydrologic analyses, geologic and seismic information, construction history, and surveillance data for Oroville Dam. The Independent Consultants reviewed the information and prepared data summary sheets and the draft STID. Usts of the documents (reports and drawings) reviewed for the workshop are presented in Appendices A and B.

The core team met at the Oroville Field Division office at 7:30 am on Monday, September 13, 2004 and visited the dam to become familiar with the site conditions and relative location and relationship of the project components (See photos in Appendix C) and their general condition. On Tuesday, September 14, 2004, the core team met at the Joint Operations Center in Sacramento and read the available documentation for Oroville Dam. On Wednesday, September 15, 2004, the core team, other persons familiar with the project, and invited observers identified Potential Failure Modes (PFMs) for the dam. If the candidate mode was considered a credible potential failure mode it was carded forward and the team discussed factors that made it more or less likely to occur. Each PFM was then rated by category (see Table 2). If, after discussion the candidate mode was judged to be not a realistic, viable potential failure mode, R would be noted as an "other consi0eration" and the reasons why it was not a viable potential failure mode would be noted. FInal/y', the major findings and understandings ware developed by the Core Team.

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2.0 Description of Project

2.1 General Project Description Oroville Dam is part of the Oroville-Thermalito Complex, which aLso includes Hyatt Powerplant, Thermalito Diversion Dam and Powerplant. Fish Barrier Dam, the Feather River Hatchery. Thermalito Power Canal, Thermalito Forebay Dam, Thermalito Afterbay Dam, and the Thermalito Pumping-Generating Plant. In all, the Oroville-Thermalito Complex stores approximately 3.6 million acre-feat of water and can generate 841 MWs of power from releases through three powerplants.

Beginning at the upstream end of the Oroville-Thermalito Complex, water released from Lake Oroville is used to produce electricity at the Hyatt Powerplant, or may be directly released into the Diversion Dam Forebay. At the Thermalito Diversion Dam the water from Lake Omville then either is used to produce electricity at the Thermal/to Diversion Dam Powerplant, enters the Feather River directly, or is diverted into the Thermalito Power Canal which leads to the Thermalito Forebay. At the end of the Forebay, wate r either discharges directly into the Thermalito Afterbay or is used to generate power at the Thermalito Pumping-Generating Plant before entering the Afterbay. (See Figure 2-1.)

The Oroville portion of the complex consists of Oroville Dam, Edward Hyatt Powerplant, Hyatt Powerplant Intake, Bidwell Canyon Saddle Dam, Padsh Camp Saddle Dam, Flood Control and Emergency Spillways, the River outlet, and the Palermo outlet

2 . 2 P e r t i n e n t D a t a

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PMF/]DF Summary PMF (2003 study) based o~ HMR 59 - lnllo~ 725,000 cfs/outflow 671,000 ds atarting at E]ev. 901 It; Pt~ (1963 study) based on HMR 36 - inflow 1,167,000 ds/oulflow FJ6,000 ~kxJes f~um of 8ul/VaRey Dem upsttum; Pk(F (1~0 stuo~ baed o(1 ~ 36 - inflow 960,000 cls/oufflow no( mcotdecL PMF (1966 I~udy) breed on Hk~ 36 - nlow 71&000 ds/outflow 624.000 cls

Ma.~num PMF Water Sudace Eke. 917.5 It (2003 ~dy) ~mnnumPMFFmetJ~aM to ) based o~ 2003 PMF s~Jdy; no

TtaJnmeaoml PMF d~Bmtned f0¢ Om~h Confining Fault wld Peak Ground Aco~nel~on C:reve~Wld Hill- M 65 at 3 rni; 0.6g at file bese of the dam. (See STIO, Sec0on 5.}

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2.3 Dam

Oroville Dam is a zoned earth and rockfill embankment dam rising 770 feet above stmambed excavation with a crest length (incJuding the spillway) of 6,920 feet The dam axis is slightly curved into the reservoir. The embankment is approximately 5,420 feet in length and is comprised of 80,000,000 cubic yards of material. Specifically, the embankment is made up of an inc/ined impervious day core , with appropriate transitions and rock-filled shell zones on both sides; see Figure 2-15. The zone descriptions are given below:.

• Zones 1, 1A, 1B - Impervious core from the deposit adjacent to the pervious borrow areas consisting of a well-graded mixture of days, silts, sands, gravels, and cobbles to 3-inch rnammum size.

• Z o n e s 2, 2 A - Transition zones consisting of a well-graded mixture of silts, sands, gravels, cobbles, and boulders to 15-inch maximum size; 6% limit on minus No. 200 sieve material.

• Zone 3 - Shell zone of predominately sands, gravels, cobbles, and boulders to 24-inch maximum; 25% limit on minus No. 4 sieve material.

• Zone 4 - Impervious core from selected abutment stripping containing from 15% to 45% material passing No. 200 sieve, with a 8-inch maximum size.

• Zone 4A - Buffer zone designed to compress; with same grading as Zone 4 (but less stringent compaction requirements).

• Zones 5A, 5B - Drainage zones consisting of gravels, cobbles, and boulders with a maximum of 12% minus No. 4 sieve size permitted.

Bidwel! Canyon Saddle Dam and Parish Camp Saddle Dam are two small embankment dams that aid Oroville Dam in containing the 3,537,577-acre-foot Lake Oroville. They have maximum heights of 47 and 27 feet, respectively. Bidwell Canyon Saddle Dam consists of a zoned main embankment and a homogenous west embankment see Figure 2-32. The main embankment encompasses the former Miners' Ranch Dike built by the Orovllle- Wyandotte Irrigation Dislflct. Parish Camp Saddle Dam consists of one homogeneous embankment; see Figure 2-33.

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2.4 Sp i l lway

The spillway is located on the right abutment of the dam and has two components: a 140.7- foot long gated flood control outlet structure, and a 1,730-foot uncontrolled emergency overpour spillway with its crest set above normal maximum storage level (Elev. 900 feet). The flood control outlet consists of an unlined approach channel, a gated headwork, and a lined chute extending to just above the river channel. The ungated, concrete emergency spillway is an overpour weir located to the right of the flood control outJet; it is made up of an 800-foot broad-crested weir on a bench excavation on the right, and a 930- foot gravity ogea weir on the left that reaches a maximum height of 50 feet. Emergency spill flows to the river over natural terrain.

2.5 Intakes The intake for the Edward Hyatt Powerplant is a

2.6 Conveyance Systems The intake for the powerplant is a

. The intakes are protected by trashracks, covering a shutter system with settings determined by water temperature needs for agriculture and fishery puq)oses.

Discharges from the powerplant are conveyed to the Feather River by The facility has a

maximum release capability of 5,000 cfs,

2 .7 Powerhouse

The majority of the water released from Lake Orovtlle passes through Edward Hyatt Powerplant, . The plant is capable of 678.75-Megawatts of output due to three conventional generators rated at 123.2 MVA each, driven by Francts-tybe turbines, and three motor-generators rated at 115 MVA each, coupled to Francis-type reversible pump-turbines.

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2.9 V | d n i t y Map and Pro jec t Drawings

A vicinity map is presented in Figures 2-1 and 2-2. Pertinent project drawings are reproduced in Figures 2-10 through 2-36.

A list of operating criteria for regulating Lake Oroville has been established by the Department of Water Resources (DWR. The August 1 =, 1975 Orovil/e Earthquake Investigations, February, 1976), which is shown as Figure 4-1 in Section 4 of the STID.

Reservoir pool elevation fluctuates due to runoff, power production, flood control, and recreational demands. Historically, the reservoir level has varied 255 feet between El. 645 feet to El. 900 feet. Over the past four years, the reservoir has vaded on average 121 feet during the year, from El, 731 feet to El. 852 feel

The flood control outlet spillway has eight radial gates that have a top elevation of The gates are norrnally dosed, but are opened as necessary to pass flood flows.

Once a year they are load test by opening the gate approximately one foot. The emergency spillway, an ungated ogee weir, is located to the right of the flood control outlet spillway.

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3.0 Major Findings and Understandings 1. The most recent (2003 study) estimated PMF inflow, based on HMR 58/59 is

only slightly higher than the maximum project flood used for design of Orovilie Dam. The original maximum project flood based on a 72 hour storm was specified in 1968 and had a peak inflow of 718,000 cfs and a peak discharge of 624,000 cfs. Subsequently in 1983 a Probable Maximum Flood (PMF) was developed for the site which had a peak of inflow of 1,167,000 cfs and a peak discharge of 798,000 cfs. This study (because of the size of the flood) included the assumed failure of the upstream Butt Valley Dam. The most recent PMF, based on HMR 58/59, was developed in 2003 and has a peak inflow of 725,000 cfs and a peak discharge of 671,000 cfs (assuming an initial reservoir elevation of 901 ft). It is important to note that although the Oroville Dam can pass the PMF, the downstream channel capacity is considerably less than the PMF and the discharge capacity of the Thermalito Diversion Dam below Oroville Dam is considerable less that the PMFpeak discharge.

2. New PMF muting studies show that with all gates open and the initial reservoir pool at the emergency spillway crest elevation ( ), the PMF still passes with of freeboard to the nominal dam crest ( ).

3. Major floods up to PMF can be passed through Oroville spillway successfully without significant concern relative to debris blockage, power supply, some gate malfunctions or delays in releases due to City, State or Federal control of operations because of downstream impact concerns. These delays are related to the possibility that the inflow could be "held back" to avoid downstream damages rather than routed fully in acoordance with the spillway's capability and thus could ultimately create a higher reservoir elevation. However, review of the routings along with recognition that the emergency spillway will kick in once the reservoir elavation exceeds 901 obviated that conosm. Thus, it appeared clear to the PFMA team that even if some discharge delay may occur, such delay would not threaten overtopping of the main dam under the cun'ent understanding of the nature of major floods up to the PMF.

4. The latest survey shows that the Orovtlle Dam crest ranges from (

5. Crest

surveys are needed to verify actual crest elevations.

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7. The flood control outlet gates are reliable

8. There is substantial spillway capacity through the emergency spillway even if all gates are closed. The spillway rating curve shows that the emergency spillway has a capacity of 445,000 ds at Elev. 920 feel With zero freeboard to the nominal crest of the dam ( it is estimated that the emergency spillway can pass 520,000 ds.

9. Flood control rules would be superseded under PMF conditions and operation would be in "save the dam" mode.

10. It was recognized that City, State, or Federal concerns could affect flood operations and spillway rating assumptions. Any delay due to City, State or Federal concerns becomes moot after reservoir reaches approximately El. 901 feet since the emergency overflow spillway takes over.

11. Some spill control is available above El. 901 feat because the flood control gates can be shut to send the comparable flow over the emergency spilk~ray and to maintain control for later increase in spill at the gated spillway.

12. A shear zone in the foundation of the west dam of Bidwell Canyon Saddle Dam may be an extension of the Cleveland Hill fault which was responsible for the 1975 Oroville Earthquake. An evaluation of this situation had been made by the State of California (Bulletin 203-88) and was reviewed carefully by the PFMA team. Although this is a significant geologic feature, it was found that displacement on the shear zone should not cause a dam safety problem because the shear zone cuts obliquely across the dam and daylights above the maximum normal reservoir level El. 900 feat creating a long seepage path with a low enough gradient that even if an offset should occur, seepage erosion of the dam materials would be practically nil.

13. The 2003 stability analysis of Oroville Dam illustrated that the dam was stable and met all accepted minimum factor of safety requirements. Further, these analyses used original design strength estimates which subsequent evaluations have shown to be conservative. It is expected, based on understanding, that factors of safety would increase about 40% in reanalysis.

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15. Total seepage from Oroville Dam (under-seepage in the rod( as wall as seepage through the dam itself) is extremely low for this size of dam. Typical seepage is of the order of 25 to 30 gpm.

16. Steady-state seepage may not have yet developed in the dam due to the very impervious core and reservoir fluctuation.

17. The discussions during the PFMA led to a dear undemtending by the participants of the instrumentation in the dam, past problems with that instrumentelJon, and current procedures for monitoring the conditions and effects of the failed instrumentation. Many of the instruments have failed, especially piezometers, due to broken tubing bundles. Adequate data related to leakage and phreatic surface are still being collected. Much of the instrumentation was installed for construction monitoring and is not providing useful information.

18. Only one Potential Failure Mode (PFM) was identified for Oroville Dam. This potential mode of failure was related to

After discussion of this mode as a candidate potential failure mode it was recognized by the PFMA team that this potential failure mode was probably not credible but it was carried forward as a PFM because of the long history of discussion investigation and evaluation and the desire to fully document the issue using the likely and not likely factors. Further, it was agreed that of the several candidate potential failure modes that ware postulated relative to this PFM was, at the time, considered most plausible. During the discussion, of the likely and not likely factors for this potential failure mode, it

Omville - PFMA 3-3 November 2004


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would likely prectude deveJopment of a sustainable potential failure mode scenario. Subsequently this inference was reinforced

The PFM which was rated a Category II/IV at the session is now, based on this additional information considered to be a Category IV because

is not considered credible.

19. Encouraged to find that the team verified that are not a real safety problem in that their condition

does not appear to lead to a viable potential failure mode scenario.

20. DWR is currently redoing the deformation analyses using the higher strengths determined by U.C. Berkeley using large-scale tests. Expected results are seismic deformations of about 1 foot if updated strength properties are used.

21. The seismidty studies and re-evaluations made following the 1975 Oreville Earthquake appear to still be valid today and indicate the structures will withstand the predicted seismic loads.

22. A/though it was already well known that the foundation rock for these structures is strong, it was surprising to see the hundreds of shears shown on the detailed foundation geology maps (see Fig 2-34). As reported in the final design report, the structures were sited to avoid the shear zones.

23. Hyatt Power Plant could flood if the tail pond established by the Diversion Dam (and the Feather River) backs up / rises due to large spillway releases themselves, blockages at the diversion dam from the raised spillway gates and debris against the gate operators and guard rail and/or blockages in the pond due to debds from those releases. Preliminary estimates of tail pond elevations under successful operation of the Diversion Dam indicate that the power plant would not flood, however more refined backwater curves would be necessary to verify this and to evaluate the backwater under various blockage scenarios.

24. A large amount of soil, rock and trees will be washed into the Feather River if the emergency spillway is utilized. It is unknown if this debris will make it to Thermalito Diversion Dam and causes any adverse effects on flow passage or tailwater. From observations it appears that significant adverse effects are unlikely.

25. The main dam portion of Bidwall Canyon Saddle Dam was built on top of and tied into a pre-existing dam. The pre-existing dam had been constructed just a few years earlier with the anticipation of being raised.

26. Parish Camp Saddle Dam is almost entirely above elevation 900 and therefore will almost never store water.

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27. At Parish Camp Saddle Dam, the contact between two geologic units in the foundation may be a fault contact but future offset would not be a problem because the contact is above elevation 900 feeL

28. DSOD considered median earthquake ground motion parameters appropriate to use for Oroville Dam in combination with a conservatively estimated MCE. The re-analysis of the dam also considered an MCE (slightly less conservative) along with mean plus 1 standard deviation ground motion parameters.

29. No effective low level dewatering capacity exists at Oroville Dam. At reservoir elevations below feet (elevation of bottom of power plant intake stnJctum) normal inflows exceed outflow capacity.

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31.

32. Hydraulic fracturing of the core as a result of arching from the differential stress condition between the shell and the core) was not carded forward as a PFM since the core is filtered by the shell material. This filtering requirement was an appropriate design consideration because of the potential for arching and it fortunately covers the situation with the broken piezometers locally allowing reservoir pressure into the core.

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34. Seepage occurred through the downstream weir prior to filling at levels similar to present readings. The downstream weir elevation is 242 which is up to 76 feet higher than the lowest elevation of the bedrock beneath the dam. Records reportedly show that prior to filling, groundwater seepage and rainfall passing through the downstream face reached and spilled over this weir which exits at the outlet of an "underground dam built to capture and measure the seepage" at levels similar to seepage levels that have occur subsequent to filling.

35. The downstream pervious zone and seepage barrier dam result in and underground "lake'.

36.

37. Reverse seepage at the main dam at Bidwell Canyon Saddle Dam is probably not an issue. The main dam embankment has a reservoir (Miners Ranch) at its downstream toe. Soma minor seepage (roughly 5 gpm) probably originating in that reservoir has been observed at the upstream toe.

38. All significant landslides are mapped and monitored. Largest is Bloomer Hill which has been investigated and found to be stable. Okay to dismiss since it is highly unlikely that a preformed slide could move fast enough to generate a significant wave; furthen'nore Oroville Dam has of freeboard at normal maximum reservoir level,

39. The "green spot" located on the downstream sk:)pe existed pdor to reservoir impoundment. This fact is documented in photos and the reason for its existence was the dumping and non-removal of fines in the shell which was known (and witnessed by

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4.0 Potential Failure Modes Identified

During the workshop, the participants brainstormed candidate potential failure modes associated with hydrologic, seismic, static, and operating conditions. For each credible identified PFM, the group discussed factors and conditions that made the failure scenario more or less likely to occur. Possible risk reduction measures were identified for various candidate PFMs as well as the one Potential Failure Mode identified. The team members rated the identit'~:l PFM according to the criteria in Table 2 (below) based on the information available, the adverse and favorable conditions, and the likelihood that the PFM could lead to failure of the dam.

Only one potential failure mode was identified during the workshop for Orovilie Dam; it is listed in Table 3. The table includes a description of the failure mode, facts and data relevant to the failure mode, conditions considered adverse or favorable to its ocourTence. possible risk reduction measures, and finally the dassification arrived at by the session participants. Due to special interest in this issue based on past evaluations and discussions, and on the suggestion of the facilitator, the other candidate potential failure modes considered but not carried forward as credible potential failure modes

in order to facilitate understanding of the issue and illustrate the

comprehensive consideration of this topic by the PFMA team. The description of the candidate potential failure mode along with the primary rationale for not carrying these candidate modes forward is provided in each case.

Table 2: Potenffal FIIlum Mode Care ories Cat~ory De~rlpUo.

I H~hlighted Potor~al Failure Those potential failure modes of greatest significance conaldedng need Modes for awareness, potential for occurrence, magnitude of consequence and

like~lhood of adveme response (physical possib~y is evklent. fundamental Itaw or weakness is identified and corl~lJons and events leading to failure seemed reasonable and credible) am h~ghl'~hted.

II Potenl~ Fatlure Modes These aro j ~ e d to be of lesser s~nlfk~;)noo atwJ l~kallhood. Nots ~at Considered but not H~hDghled even though these potential faium mode~ are oonsldered less ~gniflcant

than Category I. Ihey are also described and included w~h masons for and against the occurrence of the potelYdal failure mode. The reason for the lesser ~dgnlfMance Is noted anti summarized in the ~ ~ o r no~.

Ill Morn Information ~ Analyses Needed in Order to ClasSy

IV Potim~ Failure Mode Ruled Out

These potentl~ failure modes to some clegme lacbecl ioformat~on t0 allow a confident judgment of algnlflcance and thus a dam safety inve~lgotN~ ec~,on or analyses can be reoommended. Because action is required before rosolu~on, the need for this action may also be h~OhlChted.

does not ~ ~ n came to I~M ~ ~ ~ concern

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Table 3: FMlum Mode Analysis - Orovllle Dam

STATIC I NORMAL OPERATION

PFM t Potentlai Failure Mode I)escdptlon - - Piping of Core Materisl leed]ng to hdlure of the dam.

Potential Failure Mode Scenario -

Piping progresses and I very large cavity forms at the upstream end of the core, the

maforisl above the mz~lty coilapsas Into the eavily during • high water pertod end aJl freeboard Is lost end the clmn breaches by overtopping ecealon.

Facfa/Condttlone: •

Adverse (likely) Conditions: •

•

F~voreble (Unlikely) Conditions: • It would be hard for the postulated

co~veyanco to can-/e~ugh mafadai to cauea a cavity large enough to cauea a dam failure condition upon colapse. Not e~o~gh gradient to move material (the Zone 1 is quite impermeable and it is unlikely that a prassudzed water flow coutd develop). Zone 3 may act as ~ner so mater;aJ may not move into abel. Hlatodcally had higher pressure monitored.

Possible RISk Reduction Measures: •

ConUnue monitoring seepage

quen~ and determine if core matedal is

: being transported. I • Obearve crest for a~f signs of

ealtiemant or dispisce~ne~t

•

• Localized zone where bundles cross core only a fow feat wide (would need a 700 fl wide zone to cmrse Insfal~lity I oolisl~).

) - •

• It la Ukely that e ealf fttedng zone *ould I

develop in front of the postulated entry point of the I~v

Clmlflcdfon - Cltlgory W- "Poter~ai failure mode is dearly so remote as to be non-cmdloie or not reasonable to postulate" --.-Ou~ng the PFMA, , the PFM was tenta~aiy rated Category ,/Category IV, primarUy on the basis of the llkaiihood of self fllfadng developing In front of the and on the belds of when it was learned

a Category IV seemed more appropriate.

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Candldldo Potential Fallur• Mode Description --Piping of Core Mated•l I•ading to • cavity I collapse I breach and failure of the dam.

Rational• for not carrying potential failure mode fo~vard - - th• Zone 3 sarve• as • flltm" for the core thus no unproteotKI exit exists at the terminus of the proposed path lind backward erosion the core material and cavity development thus can not take place. Facts/Conditions: •

~

Candidate mode not canted focwaN

Advers• (llk•ly) Conditions: •

Favombl• (Unlikely) Conditions: • Not enough gradient to establish a flow

path and move matedal to the d/s shell. (the Zone 1 is quite impermeable and It is unlikely that a pressurized water flow could devetop Zone 3 acts es •ter so backward erosio~ I p~plng can never Initiate even if tl'mn) is enough flow to reach the d/s shell.

No vislb~e water flow along outside of pipes .

Possible Risk Reduction Measures: • Considered grouting in past but

It was decided that grout would only get to first break and l~Jild up ~ from resenmk'. Prassum is be~g rol~eved

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Candidate 2 Potsnttel Failure Mode Dasc~ptlon. Hydraulic Fracturing duo to high reservoir pressure near extends an open crack or mmm In the core to the downstream shell, thus ~llow~ng core matilda/to be exposed, eroded and piped Into the Downstream Sh~ll

for no( cerrythg this candidate mode fonvlrd - - even ff hydraulic fractodng took place the Zone 3 still exists as I filter to prevent movement of core matedlll Into the shell (the primary defense Igelnxt hydraulic fracturing per Sherard was having • filter and thenl Is i very good thick one In this case). Therefore this candidate mode was not carded forward.

;Adverse (likely) Conditions: •

• Settkl~nent of corn could lead to

arching, decmmdng oved)unJen pressure.

• Fracturing could extend from upstream to downstream face of C O l e .

• Seepage pressures could be high e ~ g h to erode materials In the com.

Facts/Conditions: •

~

~ndidate mode not carded fo~vard.

Favorable (Unlikely) Conditions: • Filtering effect of tmnsl~on

zone would preve~ transfer of material through piping.

• Water pressure would need to be higher than confining pressure to cause hydraulic f r a ~ g

• There is cummb'y no Indication of 8 free water pocket at reservoir pmssura that could produce hydraulic fracturing

Posslbte Risk Reduction M s ~ l U r a l l :

• Watch for evidence of free wate~

- this would be a changed condition wodh noting.

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S~rATIC I NORMAL OPERATION

Cam~ldato 3 Pot~ntial Fat~um M~de De~r~t i~n ~ Hydr~u~ Fracturing du~ to ~gh ras~rv~r p~ssura leads to Piping FMlurl of Cam

Rationale for not cerrylng pofentisl failure mode forward - - Row could develop along this path, which follows the course of the and hydraulic fracturing could facilitate the flow and exacerbate the erosion of material. However

there Is no physical evidence of any free flow of wate~ at this time let alone any material movement - furthermore the project closely moctltors the opening on I weekly basis

Thus this potential failure mode Is not considered raasonlddy vfable at this time.

Facts/Conditions: •

Adverse (likely) Conditions: • Have water pressure from the

• Seffiement of core could lead to

arching, deoeastng overburden

Favorable (Unlikely) Condltfons: •

there Is no "free water" seepsge to travcl except by a weffing fronL The visual evlderce of no fee water I entering the k supports this concept.

•

• Water Wessum would need to be higher than confining preesum to cause hydraulic fractudng

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• Fracturing coutd extend from upstream to downstream face of Core.

• Seepage pressures could be high enough to erode materials in the com.

Candidate mode not carded forward.

' Posalble Risk Reductto~ Measures: • ConUnue to monitor seepage in

the . • Watch for evidence of flee water

(and for

any material in such water - this would be a ct~enged condi~on worth noting.

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Candldlte 4 Potlmtial FlllureMode Descrlption. t

RaUonsts foe not carrying potential failure mode forw•rd - The Zone 3 serves as • filler for the core thus no unwotscted exit exists at the terminus of the proposed path end b@ckwird erosion the core mst•rlat and cavity development thus can not take place. The cavity would have to be extremity large to effact • collapse failure st this depth, it does not seem reasonably posatbte. Facte/CondiUons: •

Adverse (likely) Conditions: ;)-

materials through core.

Candidate mode not carded forward.

Favorable (Unlikely) Conditions: ) , Filtering effect of b-ansltJon

zone would prevent transfer of rnatodal through piping.

•

t the water Is

~mp~y b e ~ absorbed by the embankment so~l sudl that there Is no "free water" seepage to bavel except by 8 watting front The vlsu~ evldetce of no free water entering the supports this concept.

Possible Risk Reduction M e l l U r e O :

• Continue to monitor seepage In the am•. Even blockage some evidence at

would likely exit.

) . Watch for evldenco of free water

and for any material in such water) - this would be a changed condition worth noting.

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5.0 Likely Consequences of Each Potential Failure Mode

5.1 Flood Related Potential Failure Modes No flood related potential failure modes were identif'md. Issues related to hydrologic loading at Oroville Dam are included in Section 7 - Other Considerations.

5.2 Normal Operating Related Potential Failure Modes A potential failure mode, PFM 1, related to the piping of core materials

was identified. Because of this, piping of Oroville Dam core material is not considered credible. Additional issues related to

normal operating conditions are included in Section 7 - Other Considerations.

5.3 Earthquake Related Potential Failure Modes No earthquake related potential failure modes were identified. Issues related to seismic loading at Oroville Dam are included in Section 7 - Other Considerations.

5.4 Other Condition Potential Failure Modes No potential failure modes for other conditions were identified in the workshop. Issues related the River Outlet and penstocks at Oroville Dam are included in Section 7 - Other Considerations.

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6.0 Potential Risk Reduction Actions Identified The following are risk reduction actions associated with the identif'c=d potential failure mode. They are also included in Table 3 in Section 4.

•

• Continue monitoring seepage quantity and turbidity for any material

A number of risk reduction actiorts were also identified that were related to failure mode candidates that were not carried forward. These actions are listed below.

• Continue monitoring weirs for sediment

• Consider periodic crest surveys every 5 years for Bidwell Canyon and Parish Camp Saddle Dams. The survey monuments, located at the downstream edge of the crest, are currently surveyed biannually.

• West dam at Bidwell Canyon Saddle Dam - check crest elevations for settlement near shear zone after earthquakes

•

• Check frequency curve update based on new hydrology

• Check recant flood study report indicating a peak inflow of 341,000 cfs for the 1997 flood

• Resolve discrepancy in spillway rating documents on upper flows (305,000 cfs vs. 296,00O cfs)

• Check the effects on the rating curve of the changed conditions upstream of the emergency spillway (paved area, curbs, fences, trees)

41,

•

•

• Check functionality of spillway gates after significant earthquakes.

•

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7.0 Other Considerations Related to Study During the PFMA workshop, several candidate potential failure modes were postulated. However, after further discussion, it was agreed that they were not likely enough to warrant further evalua~H~n. These candidate modes are categorized as "other considerations" and are documented in the report along with the primary reason or reasons that they were not carried forward as a potential failure mode. These candidate PFMs are described below along with other facts and conditions related to them.

•

• Normal flood control operating criteria is not to exceed 150,000 cfs or 10,000 cfs change in 2 hours. Then emergency release procedures apply and release schedule is defined by USACE. However, once the reservoir reaches Elev. 901 feet, the emergency spillway will kick in. Discussed use of forecast based operation. No viable potential failure mode was identifiable.

• There is enough freeboard to handle an earthquake induced landslide in the reservoir. Assessments of the potential landslide areas indicated that they are submerged at high reservoir elevations and hence not generate significant displacement waves if they were to fail then. Conversely, if the reservoir was low enough for the slides to generate bigger displacement waves, the additional existing freeboard would be more than enough to contain them. No viable potential failure mode was identifiable.

•

•

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• Piping of core through the dam was examined as a candidate potential failure mode. It was not carded forward as a potential failure mode for two primary reasons: (1) The Zone 3 serves as a filter for the core and (2) there is essential no seepage through the core to produce the possibility of piping.

• Piping of core from the dam into the foundation was examined as a candidate potential failure mode. It was not carded forward for two primary reasons: (1) Although there may be open joints within the foundation the nature of the core gradation is such that it would be difficult to sustain movement of the core material through the joints (they would plug and or a filter would form at the enb'y point), also the length / continuity of open joints would have to be exceptionally long (2) there is very little seepage through the core into the foundation to produce the possibility of piping material.

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8.0 Summary of Potential Actions Identified in the PFMA with Respect to Performance Monitoring The following action items with respect to performance monitoring were identified during the PFMA:

•

• Continue monitoring seepage quantity and turbidity of flow

• Continue monitoring weirs

• Consider periodic cTest surveys every 5 years for Bidwell Canyon and Parish Camp Saddle Dams to determine actual crest elevations. Note that crest monuments are surveyed biannually.

•

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9.0 Summary and Conclusions Only one potential failure mode related to Oroville Dam was identified.

After discussion of this mode as a candidate potential failure mode it was recognized that this potential failure mode was probably not credible. However, it was carded forward as a PFM because of the long history of discussion of this issue and the desire to fully document it, using the "likeh/" and "not likely" factors. During the discussion of these factors it

would likely preclude

development of a sustainable potential failure mode scenario. This inference was reinforced subsequently

The PFM, which was rated a Category II/IV at the session is now, based on this additional information, considered to be a Category IV because is not considered credible.

The following additional conclusions are based on the PFMA workshop for Omville Dam:

• The new PMF, based on HMR 58/59, can be passed through the spillway with adequate freeboard on Oroville Dam and the Saddle Darns.

•

•

• The emergency spiIIway has significant capacity even if the flood control gates are dosed.

• The rating of the emergency spillway may be affected by the upstream parking area and the security fencing.

• Total seepage from Oroville Dam is very small for such a large dam.

• Steady-state seepage may not have yet developed in the dam due to the very impervious core and the large reservoir fluctuation.

• Recent stability analyses of Oroville Dam show that the dam has adequate factors of safety for all loading cond~ons based on original design material strengths. With updated material strengths, it is estimated that factors of safety will increase by about 40% in reanalysis.

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Appendix A - List of Reference Reports

1. Final Geologic Report on Foundation Conditions and Grouting, Orovilie Peripheral Dams (June 1968)

2. Final Geologic Report on Foundation conditions and Grouting, Oroville Dam, Part II, Foundation Grouting (July 1968)

3. Final Geologic Report on Foundation conditions and Grouting, Oroville Dam, Part I, Foundation Geology (December 1968)

4. Project Surveillance, Orovtlle Dam and Lake Performance of the Flood Control Outlet During the Storms of January-February 1969 (March 1969)

5. Final Design Report, Bidwell Canyon and Parish Camp Saddle Dams (June 1972)

6. Inspection and Review of Oroville - Thermalito Project Facilities (Orovifle Dam, Thermalito Diversion Dam, Thermalito Forebay Dam, Thermalito Afterbay Dam, Feather River Hatchery Dam) (1973)

7. Bulletin 200, California State Water Project, Volume III, Storage Facilities (November 1974)

8. Bulletin 203, Performance of the Oroville Dam and Related Facilities During the August 1, 1975 Earthquake (April 1977)

9. Bulletin 203-78, The August 1, 1975 Oroville Earthquake Investigations (February 1979)

10. 1979 Inspection and Review of Safety of Orville - Thermalito Project Facilities (Second F-we-Year Review) (February 1980)

11. Oroville Reservoir Flood Routing, (April 20, 1981), Inc. Consulting Civil Engineering (Response to letter)

12. Oroville Dam - Investigation of the Causes and Consequences of Abrupt Changes in Piezometer Readings, Memorandum Report (May 1982)

13. Bulletin 203-88, The August 1, 1975 Oroville Earthquake Investigations, Supplement to Bulletin 203-78 (May 1989)

14. 1989 Inspection and Safety Review (Fourth Independent Safety Evaluation), Oroville Dam and Bidwell Canyon and Parish Camp Saddle Dams (November 1989)

15. Oroville Dam, State Dam No. 1-48, Performance Report No. 9, July 1987 - December 1990 (January 1, 1991)

16. Investigation of Recent Instrumentation performance at Oroville Dam, Memorandum Report (October 1992)

17. Fifth Safety Inspection Report of the Oroville Dam Facilities (1994), WcxxJward-Clyde

18. Independent Review of Safety of Oroville Dam and Associated Darns and Structures (May 1994)

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19. Independent Consulting Board Meeting to Review Design of Remedial Instrumentation Grouting Program for Oroville Dam (August 17 & 18, 1994), Information Package

20. Hydraulic Model Study of the Oroville Dam Centers for Water and Wildland Resources University of California Davis

21. Second Independent Consulting Board Meeting to Review Design of Remedial Instrumentation Grouting Program for Oroville Dam, Information Package (December 7, 1994)

22.

23. FERC special Consulting Board, Remedial Instrumentation Grouting for Oroville Dam, December 12, 1995, Third Meeting (December 1995)

24. Omville Dam Remedial Instrumentation Grouting Program, Appendix (October 1996)

25. Oroville Division Lake Oroville, Geologic Assessment of the Bloomer Hill Landslide (December 1996), Project Geology Section Report No 20-11-33

26. Structural Inspection of the Radial Gates at Omvilia Dam Spillway, Memorandum Report (May 1997)

27. Spillway Repair Oroville Dam (1997), Spedfications Bid and Contract, Contract No C51141, Specification No. 97-22

28. Independent Review of Safety of Oroville Dam (Oroville Dam, Thermalito Diversion, Forebay, Afterbay Dams, Feather River Fish Barrier Dam) (May 1999)

29. Sixth Part 12 Safety Inspection Report for the Oroville Dam (September 1999), Gomez & Sullivan Engineers, P.E., Engineering Inc.

30.

31. Omville Dam, Performance Report No. 10, January 1991- July 2000 (August 2000)

32. Oroville Dam Radial Gate 4 Trunnion Pin Inspection (November 1, 2001), Chief Corrosion Engineering Services

33. Memorandum of Inspection, Hyatt Powerplant , Orovifle Dam (March 17, 2003)

34. Hyatt Pump-Generating Plan Inspection Report (March 17, 2003), by reviewed by

35. Memorandum of Inspection, Hyatt Powerplant , Oroville Dam (April 28, 2003), by PE

36. Lake Oroville Updated Probable Maximum Flood Memorandum (June 1,2003)

37. Oroville Darn Performance Report No. 11, August 2000 - June 2004 (August 2004)

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38. 2003 Stability Analyses, Oroville, Parish Camp and Bidwell Canyon Dams

39. Investigation of Spillway Routing During Probable Maximum Flood at Oroville Dam, Memorandum Report (December 2003)

40. Standard Operating Order Number PC 700.20, DWR, Division of Operations and Maintenance

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Appendix B - List of Reference Drawings/Figures

Figure 2-1 - General Location Map, Orovilla Dam

Figure 2-2 - Oroville Facilities Relicensing,

Figure 2-3 - Orovilla Facilities Relicensing,





Figure 2-8 - Omville Facilities Relicansing

Figure 2-9 - FERC Project No. 2100, Area Map

Figure 2 - 1 0 - Oroville Dam, Site Plan

Figure 2-11 - Oroville Dam Area, Site Plan

Vicinity & Location Map. Exhibit G-1

FERC Boundary Map North, Exhibit G-2

FERC Boundary Map Central-West, Exhibit G-3

FERC Boundary Map Central-East. Exhibit G-4

FERC Boundary Map South-West, Exhibit G-5

FERC Boundary Map South-East, Exhibit G-6

FERC Boundary Map South, Exhibit G-7

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APPENDIX C - PHOTOGRAPHS TAKEN DURING FIELD REVIEW

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