OVERCOMING CHALLENGES ON A FAST TRACK ASH POND CONVERSION AND CLOSURE PROJECT TO MEET REGULATORY DEADLINES 2013 WORLD OF COAL ASH CONFERENCE

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Muriel Baldwin
7 years ago
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1 OVERCOMING CHALLENGES ON A FAST TRACK ASH POND CONVERSION AND CLOSURE PROJECT TO MEET REGULATORY DEADLINES 2013 WORLD OF COAL ASH CONFERENCE Presenters: Jimmy Mullins (TVA) David Mason (CDM Smith) April 25, 2013

2 Presentation Outline Introduction and Background Regulatory Initiatives Design Process Technical lchallenges During Design Issues During Construction Conclusions and Lessons Learned

3 Project Background Watts Bar Fossil Plant near Spring City, TN Constructed in the 1940 s Ceased power production in 1982 Partial closure of slag and chemical pond areas in 2007 Plant demolition in 2012

4 Primary 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; and 3. Provide stabilization of up to 1,500 linear feet of riverbank. 4. Create a new, final storm water pond.

5 Regulatory 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. TN Other areas are subject to TDEC rule and (Solid Waste Processing and Disposal) TVA Dam Safety Programfollows the federal dam safety program of the Federal Emergency Management Agency (FEMA).

6 The Challenge Initiate the closure project consistent with TVA s budget realities Required breaking project up into separate pieces Address the stated condition of the dam in an appropriate manner and timeframe Required a fast track design schedule Allow input from all appropriate parties throughout the process

7 ions & Site Featu ures Ash Pond Dry Ash Area Security Access Road Perimeter Containment Berm ing Co onditi Splitter Dike Stilling Pond Nuclear Security Barriers Exist Existing Riser Structures Regulated NPDES Outfall

8 Selected Alternative from Project Planning Document (PPD) Dewater both ponds World of Coal Ash (WOCA) Conference (April 22-15, 2013) in Leixngton, Kentucky ( Replace the existing pond outlet device with an overflow weir spillway Safely pass the 100 year design storm event without overtopping the containment dike Install a downstream concrete channel for conveyance of flows to river Breach the perimeter containment dike to reduce storage volume in the pond

9 Initial Project Schedule Notice to Proceed May 10 th Submit Draft 50% Design June 8 th Submit Draft 90% Design July 6 th Submit Draft IFC Design July 27 th Target Dam Breaching August 31 st

10 Internal Discipline and TVA Department Coordination Multi Discipline Coordination (Internal) Environmental/Stormwater Structural Geotechnical CAD Design Multi Department Coordination (TVA) Coal Combustion Products Civil Projects Environmental Nuclear Security Dam Safety World of Coal Ash (WOCA) Conference (April 22-15, 2013) in Leixngton, Kentucky (

11 Project 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 % Design Internal, Technical Review Committee Meetings

12 Design Challenges Schedule Coordination with Watts Bar Nuclear Archaeological Site Summer/Winter Pool

13 Scheduling Challenges Fixed End Date to Initiate Construction Regulatory driven Delayed Start Date Approvals, etc. Subsurface Investigation Procurement Training Technical Review (internal and with TVA) Summer Vacation Season

14 Coordination with Watts Bar Nuclear Security

15 Accommodating Security Procedures Throughout the Project Pond acts as a natural vehicle barrier and is included in the security plan for the site Security patrols the perimeter every 30 minutes Impeding security was mostly non negotiable World of Coal Ash (WOCA) Conference (April 22-15, 2013) in Leixngton, Kentucky (

16 Surprise Archaeological Site Drainage Impacts Performed Categorical Exclusion Checklist (CEC) mid design (2 weeks prior to 90% design submittal Revised Spillway Alignment Discovered previously unknown archaeological l Modified d Coffer site Dam Required modification to spillway, coffer dam, and site drainage

17 Summer and Winter Pool Elevations River/Lake is operated at various levels based on seasons Need to design a controlled discharge to river and prevent erosion Limitations on fill within Waters of the State Summer Pool: El 682 Winter Pool: El 675

18 Spillway and Energy Dissipation Design & Construction Considerations Will require a phased construction sequence depending on season

19 Final Design and Construction Sequencing Dewater the ponds Breach the splitter dike to connect the ponds Excavate ash in the coffer dam area; construct 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

20 Construction Phase Challenges Re Assessment of Nuclear Security Alternatives Required installation of new road and barriers Dewatering NormalYear to Date Precip: inches Actual Year to Date Precip: inches 6 water surface rise when not pumping Water Control and Water Quality Challenges meeting TSS discharge limits during dewatering Significant Additional Ash Material 4 5 feet observed vs. 1 2 feet predicted Coffer Dam Area Soft Spots Two areas required significant overexcavation

21 Existing Conditions World of Coal Ash (WOCA) Conference (April 22-15, 2013) in Leixngton, Kentucky (

22 Complete Nuclear Barrier with King Tuts

23 Dewatering World of Coal Ash (WOCA) Conference (April 22-15, 2013) in Leixngton, Kentucky (

24 Water Control and Water Quality

25 Additional Ash Material in Pond

26 Soft Spots in the Coffer Dam Area

27 Conclusions 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

28 Wrap up & Questions

Best Management Practices for Coal Ash Storage Facilities

2009 World of Coal Ash (WOCA) Conference - May 4-7, 2009 in Lexington, KY, USA http://www.flyash.info/ Best Management Practices for Coal Ash Storage Facilities Presented by: Christopher D. Hardin, PE