Overcoming Challenges on a Fast-Track Ash Pond Conversion … · 2013-05-17 · OVERCOMING CHALLENGES ON A FAST‐TRACK ASH POND CONVERSION AND CLOSURE PROJECT TO MEET REGULATORY

OVERCOMING CHALLENGES ON A FAST‐TRACK ASH POND CONVERSION AND CLOSURE

PROJECT TO MEET REGULATORY DEADLINES2013 WORLD OF COAL ASH CONFERENCE

Presenters:

Jimmy Mullins (TVA)

David Mason (CDM Smith)

April 25, 2013

World of Coal Ash (WOCA) Conference (April 22-15, 2013) in Leixngton, Kentucky (www.flyash.info)

Presentation OutlinePresentation Outline

• Introduction and Background

• Regulatory Initiatives

• Design Process

T h i l Ch ll D i D i• Technical Challenges During Design

• Issues During Construction

• Conclusions and Lessons Learned• Conclusions and Lessons Learned


Project BackgroundProject Background

• Watts Bar Fossil Plant near Spring City, TN

• Constructed in the 1940’s

• Ceased power production• Ceased power production in 1982

• Partial closure of slag and chemical pond areas in 2007

• Plant demolition in 2012• Plant demolition in 2012


Primary Goals for the Closure ProjectPrimary Goals for the Closure Project

1. Reduce future maintenance of the Borrow Area, Slag Processing Area, and Chemical Pond Area;

2. Close the Red Water Pumping Station/Caustic Pond, Ash/Stilling Pond; andAsh/Stilling Pond; and

3. Provide stabilization of up to 1,500 linear feet of riverbank.

4. Create a new, final storm water pond.


Regulatory InitiativesRegulatory Initiatives

• US EPA’s ongoing efforts to assess the management of coal combustion residuals– Poor rating due to lack of information and potential threat for

environmental damage

• Ash/Stilling Pond Area Outfall 002 falls under the WBF NPDES modified permit No. TN0005461

h bj l d• Other areas are subject to TDEC rule 1200‐1‐7‐.04 and 1200‐4‐2.01 (Solid Waste Processing and Disposal)

• TVA Dam Safety Program follows the federal dam safetyTVA Dam Safety Program follows the federal dam safety program of the Federal Emergency Management Agency (FEMA).


The Challenge…The Challenge…

• Initiate the closure project ’consistent with TVA’s budget

realities– Required breaking project up into q g p j p

separate pieces

• Address the stated condition of the dam in an appropriatethe dam in an appropriate manner and timeframe– Required a fast‐track design

schedule

• Allow input from all appropriate parties throughout the processparties throughout the process


ures

Dry Ash Area

e Featu

Security Access Road

& Site

Ash Pondions &

Perimeter Containment

Berm

Nuclear Security

Splitter Dike

onditi

Stilling Pond

Barriers

ing Co

Regulated NPDES Outfall

Existing Riser

StructuresExist


Selected Alternative from Project Planning Selected Alternative from Project Planning Document (PPD)Document (PPD)Document (PPD)Document (PPD)

• Dewater both ponds

• Replace the existing pond outlet device with an overflow weir spillway

• Safely pass the 100 year design storm• Safely pass the 100‐year design storm event without overtopping the containment dike

• Install a downstream concrete channel for conveyance of flows to riverriver

• Breach the perimeter containment dike to reduce storage volume in the pond


Initial Project ScheduleInitial Project Schedule

• Notice to Proceed – May 10th

• Submit Draft 50% Design – June 8th

• Submit Draft 90% Design – July 6th

• Submit Draft IFC Design – July 27th

• Target Dam Breaching – August 31st


Internal Discipline and TVA Department Internal Discipline and TVA Department CoordinationCoordinationCoordinationCoordination

• Multi‐Discipline Coordination (Internal)– Environmental/Stormwater

– Structural

– GeotechnicalGeotechnical

– CAD Design

• Multi‐DepartmentCoordination (TVA)– Coal Combustion Products

– Civil ProjectsCivil Projects

– Environmental

– Nuclear Security

– Dam Safety


Project CoordinationProject Coordination

• Weekly Conference Calls with Internal Staff

• Weekly Conference Calls with TVA Staff

• Face‐to‐Face Progress Meetings at Key Milestones– Kickoff/Walk Down 50% Design 90 % DesignKickoff/Walk Down, 50% Design, 90 % Design

• Internal, Technical Review Committee Meetings


Design ChallengesDesign Challenges

• Schedule

• Coordination with Watts Bar NuclearBar Nuclear

• Archaeological SiteArchaeological Site

• Summer/Winter Pool


Scheduling ChallengesScheduling Challenges

• Fixed End Date to Initiate Construction– Regulatory driven

• Delayed Start DateApprovals etc– Approvals, etc.

• Subsurface Investigation– Procurement

– Training

• Technical Review (internal andwith TVA)with TVA)

• Summer Vacation Season


Coordination with Watts Bar Nuclear SecurityCoordination with Watts Bar Nuclear Security


Accommodating Security Procedures Throughout Accommodating Security Procedures Throughout the Projectthe Projectthe Projectthe Project

• Pond acts as a natural vehicle barrier and is included in the security plan for the sitep

• Security patrols the perimeter every 30 i tminutes

• Impeding security was mostly non‐negotiabley g


Surprise…Archaeological SiteSurprise…Archaeological Site

• Performed Categorical ( )

Drainage Impacts

Exclusion Checklist (CEC) mid‐design (2 weeks prior to 90% design

Revised Spillway Alignmentp g

submittal

• Discovered previously k h l i l M difi dunknown archaeological

site

• Required modification

Modified Coffer Dam

qto spillway, coffer dam, and site drainage


Summer and Winter Pool ElevationsSummer and Winter Pool Elevations

• River/Lake is operated at various levels based on seasons

• Need to design a controlledNeed to design a controlled discharge to river and prevent erosion

• Limitations on fill within Waters of the State

Summer Pool: El 682Winter Pool: El 675


Spillway and Energy Dissipation Design & Spillway and Energy Dissipation Design & Construction ConsiderationsConstruction ConsiderationsConstruction ConsiderationsConstruction Considerations

• Will require a phased construction sequence depending on season


Final Design and Construction SequencingFinal Design and Construction Sequencing

• Dewater the ponds

h h li dik• Breach the splitter dike to connect the ponds

• Excavate ash in the coffer dam area; h ff dconstruct the coffer dam

• Excavate the breach in the existing containment dike

• Excavate and construct new spillway; backfill

• Redirect security traffic back over the containment dike

• Construct second breach in splitter dike

• Grout existing risers


Construction Phase ChallengesConstruction Phase Challenges

• Re‐Assessment of Nuclear Security Alternatives– Required installation of new road and barriers

• Dewatering– Normal Year to Date Precip: 17 16 inchesNormal Year to Date Precip: 17.16 inches

– Actual Year to Date Precip: 19.34 inches

– 6” water surface rise when not pumping

• Water Control and Water Quality– Challenges meeting TSS discharge limits during dewatering

• Significant Additional Ash Material• Significant Additional Ash Material– 4‐5 feet observed vs. 1‐2 feet predicted

• Coffer Dam Area Soft Spotsp– Two areas required significant overexcavation


Existing ConditionsExisting Conditions


Complete Nuclear Barrier with “King Complete Nuclear Barrier with “King TutsTuts””


DewateringDewatering


Water Control and Water QualityWater Control and Water Quality


Additional Ash Material in PondAdditional Ash Material in Pond


Soft Spots in the Coffer Dam AreaSoft Spots in the Coffer Dam Area


Conclusions and Lessons LearnedConclusions and Lessons Learned

• What Can Go Wrong Will Go Wrong

• Plan Ahead if a Fast Track Design is Anticipated

• Interdisciplinary Coordination is Vital

• Ensure That You Have Buy‐In On Important Decisions


WrapWrap‐‐up & Questionsup & QuestionsWrapWrap‐‐up & Questionsup & Questions


Documents

Overcoming Challenges on a Fast-Track Ash Pond Conversion … · 2013-05-17 · OVERCOMING CHALLENGES ON A FAST‐TRACK ASH POND CONVERSION AND CLOSURE PROJECT TO MEET REGULATORY