CCR Impoundment Closure: Reshaping your Ash! 2017 MWCC Technical Conference

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Simon Moody
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1 CCR Impoundment Closure: Reshaping your Ash! 2017 MWCC Technical Conference

2 Setting the Stage Who? SCS Engineers Consulting/Design Engineer Pat Goeke, P.E. Radmacher Brothers Earthwork Contractor Ben Cummings, Chief Project Manager

3 Setting the Stage What? Coal Combustion Residual (CCR) Impoundments Final Closure, Design, and Implementation Why? Meet Final CCR Rule Requirements

4 Setting the Stage How? Engineered design and closure approach Compliant with Final CCR Rule Provide financially beneficial approach Design Bidding Construction

5 Project Drivers CCR RULE ( ) PRIOR TO PLACING COVER Free liquids must be eliminated Waste stabilized sufficient to support cover

6 Project Drivers CCR RULE ( ) FINAL COVER Minimize, or eliminate infiltration of liquids 1x10-5 cm/sec or permeability of base Prevent probability of future ponding of water Minimize the need for future maintenance Minimize erosion Cover capable of sustaining native plant growth

7 What is CCR Often Underwater

8 What is CCR Often Not Stable

9 What is CCR Sometimes It s Cemented

10 What is CCR Not something to walk on

11 What is CCR Easy to construct on at times

12 What is CCR Sensitive to vibration

13 What is CCR CCR is a Construction Challenge

14 Typical Landfill Closure Concept Typical Landfill Dome with a 5% crown slope 500 foot width

15 Typical Landfill Closure Concept Typical Landfill Dome with a 5% crown slope 1000 foot width

16 Typical Landfill Closure Concept Typical Landfill Dome with a 5% crown slope 2500 foot width

17 Typical Landfill Closure Concept Summary Width (ft) Top Slope Fill Height (ft) Fill Volume (yds) Fill Cost ($/yd) Fill Cost ($) 500 5% ,600 $10 $386, % ,600 $10 $3,086, % ,882,500 $10 $48,825, % 2.5 7,700 $10 $77, % 5 61,700 $10 $617, % ,500 $10 $6,945,000 BASE WIDTH (feet) ,000,000 4,000,000 6,000,000 FILL VOLUME (cubic yards) 5% 1% Cap Slope combined with pond width has a SIGNIFICANT impact on Closure Cost

18 Design requirements and criteria FINAL SURFACE CONSIDERATIONS Conflicts in Rule requirements related to SLOPE Prevent future impoundment of water (steeper) Preclude infiltration (steeper) Sustain growth (shallower) Prevent erosion (shallower) Stabilize waste to support final cover (shallower) Less weight of cap on waste Final surface visual Large mound More natural surface topography

19 Data Collection Aerial Drone Survey Bathometric Survey

20 Data Analysis

21 SCS Inverted Bowl Design Thick Blue Lines Ridges Pink lines low areas Center high point and multiple low areas drove design Cut and fill to achieve greater than 1% slope

22 SCS Inverted Bowl Design PROs Reduced volume of ash grading volume More natural final topography 1% to 2% final cover grade to: prevent impoundment minimize cap erosion maximize water for vegetation Minimize load causing ash settlement CONs Requires excavation into ash Excavation may require more dewatering Concentrate cap runoff into channels versus sheet flow

23 Implemented Design Typical Final Cover Cross Section Removed berms Flatten slopes More natural look and easier maintenance

24 Flexible Design/Bid Approach No required final grade contours must generally meet final specified grade slope to achieve drainage no visible high or low points must allow water to runoff to designate discharge points Allow contractor choice of cover CCR Rule earthen cover CCR Rule Alternate cover options (GCL or HDPE membrane) Dewatering required only if needed Allow Contractors to use experience and ingenuity Save closure dollars Comply with CCR Rule

25 Contractor Reaction - Design Best Description FLEXIBLITY Recognized highly variable nature of coal ash ponds Addressed by providing options For Dewatering For Cap Construction For Final Grades to adapt to site conditions Bid Documents specified the desired Outcome Allowed Contractor to Use our Experience and Ingenuity

26 Contractor Reaction - Construction Dewatering Fly ash from Illinois coal each ash dewaters differently Tested Well Point and Trench/Sump System 5000 SF well point test area, successful, but costly and lengthy time $56/SF, but time was uncertain Settled on trench and sump system Excavated trench depths in stages, loaded sides with fill, compressed ash and pushed out water. Placed sand in trench to maintain contact with sump pumps. Estimated cost at $40/SF Sump system worked well in summer, not as well in winter Stabilized ash sufficiently to grade and place alternative cap

27 Contractor Reaction - Construction Cap Alternative Bid Project using CCR Rule earthen cap, Switched to CCR Rule alternate cap (GCL) for EFFICIENCY GCL placed faster, covering graded ash and reducing erosion GCL eliminated need for compaction and moisture control of clay liner in variable Midwest weather Ash Settlement during dewatering Ash settlement occurring during dewatering Settlement caused a potential material deficit Would have caused cost issues if contractor held to rigid design grades and not given flexibility

28 Construction Stages July 2016 October 2016 June 2017

29 Construction - Early Ash sliding towards dewatering area Dewatering Sump Pit and Pump

30 Construction - Early Dewatering Trench

31 Construction - Dewatering Well Point Dewatering Test Area Dewatering Trench

32 Construction Dewatering Trenches GCL Capped Area Dewatering Trench

33 Construction Dewatering Trenches Beginning of Dewatering Trench October 2016 Dewatering Trench filled with sand to drain to pump after filling with ash Dec 2016