In Situ Coal Combustion Products Impoundment Closure Strategy Tim - - PowerPoint PPT Presentation

In Situ Coal Combustion Products Impoundment Closure Strategy

Tim Silar, PG - Silar Services Inc. John Magee, PE - Silar Services Inc. Glenn R. Luke, PE - Natural Resource Technology, Inc. Christopher A. Robb, PE - Natural Resource Technology, Inc. May 6, 2015

Presentation Objectives

Provide a permanent, engineered, technically sound, and lower cost impoundment closure

• ption
• Common impoundment challenges/concerns
• Impoundment closure method
• Cost Evaluation
• Regulatory applicability and stakeholder acceptance
• Environmental impact analysis

What’s Next? Site specific evaluation and implementation

Common CCP Impoundment Challenges/Concerns

• CCP below the water table
• Increased hydraulic head
• Saturated and differential hydraulic

conditions

• Feasibility of construction
• Extensive dewatering and treatment
• Historic infrastructure

CCP Impoundment Profile

Investigation and Constructability Evaluation

Closure Method In Situ Solidification/Stabilization (ISS)

• ISS: In-place mechanical mixing of contaminated media with

dry reagent or an injected engineered grout mixture

• Result: Monolithic structure with increased strength/stability

and decreased permeability

• Typical Reagents: Portland Cement, GGBFS, bentonite
• Typical Performance Goals
• Decreased Permeability (e.g. ≤ 1x10-6 to 1x10-7 (cm/sec)
• Increased compressive strength (e.g. ≥ 50 psi)
• Reduction of leaching to meet regulatory requirements
• Construction Techniques
• Conventional full depth ISS – proven technique
• Discrete zone ISS – pilot tested technique

ISS Drilling Concepts

Full Depth Construction Vertical Barrier and Geotechnical Stability Discrete Layer Construction Horizontal Hydraulic Barrier

Impoundment Site Preparation

Impoundment ISS Construction

Final Cover Construction

Proof of Methods

• Applications of ISS on CCP
• Previously need for active remediation was limited
• Implemented for geotechnical/stability applications
• Discrete ISS: Successfully Pilot Tested at CERCLA Site
• Baseline Laboratory Treatability Testing on CCP
• Material Properties – physical and chemical
• Reagent and proportion selection (e.g. Portland Cement,

Slag, Bentonite)

• Performance testing (hydraulic conductivity, compressive

strength, monolithic leaching)

• Impoundment water reuse evaluation

CCP ISS Treatability Testing

Grout Amendments and Proportions 10% Portland Cement 0.5% Bentonite 7.5% GGBFS 2.5% Portland Cement Curing Days Prior to Testing 14 14 14 28 14 28 14 28 14 28 Moisture Content (%) (pretreatment) 31 31 37 37 37 37 37 37 23.5 23.5 Density (lbs/ft3) (pretreatment) 102 102 97.63 97.63 97.63 97.63 97.63 97.63 97.63 97.63 Unconfined Compressive Strengh (psi) 221 184 80 101 38 76 70 86

• 1039

Hydraulic Conductivity (cm/sec) 4.1 x 10-7 1 x 10-6

• 8.1 x 10-6
• 9.1 x 10-6
• 6.4 x 10-6
• 2.3 x 10-8

GGBFS = Ground Granulated Blast Furnace Slag

8% Portland Cement 6% GGBFS 2% Portland Cement 8% Portland Cement 0.5% Bentonite 18% GGBFS 6% Portland Cement 2% Bentonite

Regulatory Applicability

• USEPA final Disposal of Coal Combustion Residuals

from Electric Utilities rule – April 17, 2015

• Numerous requirements are set forth for existing

impoundments including:

• Location – groundwater separation, wetlands, seismic zones
• Structural integrity – Calculated factors of safety requirements
• Liner construction – Liner demonstration and/or composite liner
• This method is applicable for:
• Closure of impoundments that do not meet location requirements
• r require groundwater corrective action
• Closure of impoundments that do not meet stability criteria
• Corrective Action for impoundments that meet location and

groundwater criteria but do not meet stability criteria

Cost Evaluation

• Compare in situ closure method to excavation and off-site disposal
• Assume the impoundment volume is approximately 1.3 million

cubic yards (40 acres by 20’ thick)

• Excavation Assumptions:
• Excavation volume is 1.29 million cubic yards
• Excavated ash will be disposed within 50 miles of the

impoundment

• One cubic yard of ash weighs 2,700 lbs
• Excavation will require dewatering and water treatment
• Impoundment will be backfilled and vegetated
• In situ Closure Assumptions:
• ISS volume is 366,000 cubic yards including 5’ thick discrete

bottom liner and 10’ wide fully penetrating perimeter walls to 25’ below grade

• Dewatered groundwater will be used in ISS batch plant
• Impoundment will be capped with geo-textile and soil cover
• Cost evaluated on recent experience and discussions with

contractors

Cost Evaluation

Item Estimated Quantity Units Unit Price $ Amount $ Unit Price $ Amount $ General Conditions Mobilization & Temporary Facilities Setup 1 Lump Sum $ 700,000 $ 700,000 $ 700,000 $ 700,000 Site Preparation 1 Lump Sum $ 1,500,000 $ 1,500,000 $ 1,500,000 $ 1,500,000 Clearing, Grubbing and Erosion Controls Installation, Maintenance & Monitoring 1 Lump Sum $ 300,000 $ 300,000 $ 300,000 $ 300,000 Demobilization & Record Documents 1 Lump Sum $ 250,000 $ 250,000 $ 250,000 $ 250,000 Excavation & Backfill Excavate Ash, Dewater, and Load 1,290,667 Cubic Yards $ 20 $ 25,813,340 $ - $ - Transport and Dispose of Ash 1,742,400 Tons $ 60 $ 104,544,027 $ - $ - Backfill with Off-site fill 645,334 Cubic Yards $ 25 $ 16,133,338 $ - $ - In-Situ Solidification Mobilize ISS Treatment Equipment and Materials 1 Lump Sum $ - $ - $ 500,000 $ 500,000 In situ Solidification/Stabilization (ISS) 366,000 Cubic Yards $ - $ - $ 80 $ 29,280,000 ISS Swell Management (15%) 54,900 Cubic Yards $ - $ - $ 4 $ 197,640 Geotextile Cap 40 Acres $ - $ - $ 50,000 $ 2,000,000 Dewatering - Excavation Frac Tank Mobilization, Setup and Demobilization 8 Each $ 3,000 $ 24,000 $ - $ - Site Water Management 104 Week $ 25,000 $ 2,600,000 $ - $ - Dewatering - ISS Frac Tank Mobilization, Setup and Demobilization 4 Each $ - $ - $ 3,000 $ 12,000 Site Water Management 52 Week $ - $ - $ 5,000 $ 260,000 Site Restoration Topsoil 32,267 Cubic Yard $ - $ - $ 26 $ 838,942 Seed and Mulch 40 Acres $ 2,000 $ 80,000 $ 2,000 $ 80,000 TOTAL

$151,945,000 $ 35,919,000

Excavation and Off-Site Disposal In situ Closure (ISS)

Cost Evaluation

• Volume treated reduced by over 70% via in-situ

closure

• 1.29 million cubic yards for excavation and off-site disposal
• 366,000 cubic yards for in-situ closure
• Total estimated cost for excavation and off-site

disposal is approximately $152 million at approximately $118/cubic yard

• Total estimated cost for in situ closure is

approximately $36 million at approximately $28/cubic yard.

• In situ closure cost less than 25% of the cost for

excavation and off-site disposal.

Stakeholder Acceptance

Stakeholder Acceptance

Sustainability Evaluation

• USEPA’s Methodology for Understanding and

Reducing a Project’s Environmental Footprint (EPA 542-R-12-002)

• Estimates a project’s environmental footprint
• Input Metrics
• Materials and Waste – Inventory quantities
• Water – Inventory use
• Energy – Input equipment specifications
• Air – Input equipment specifications
• Ecology – User defined
• Comparison of environmental footprint for in situ

closure vs. excavation and off-site disposal

Sustainability Evaluation

Excavation and Offsite Disposal Total In situ Closure Total Total M&W-1 Refined materials used on-site Tons 1,097,071 51,468 (1,045,603) M&W-2 % of refined materials from recycled or waste material % 0% 75% 75% M&W-3 Unrefined materials used on-site Tons

• M&W-4

% of unrefined materials from recycled or waste material %

• M&W-5

On-site hazardous waste disposed of off-site Tons

• M&W-6

On-site non-hazardous waste disposed of off-site Tons 1,742,400 (1,742,400) M&W-7 % of total potential waste recycled or reused %

• On-site public water use (by source)

MG

• E-1

Total energy used MMBtu 609,209 147,543 (461,666) E-2 Total energy voluntarily derived from renewable resources E-2A

• Biodiesel use and onsite generation or use

MMBtu 9,804 (9,804) E-2B

• Voluntary purchase of renewable electricity

MWh

• E-2C
• Voluntary purchase of RECs

MWh

• A-1

On-site NOx, SOx, and PM emissions Pounds 127,945 38,192 (89,753) A-2 On-site HAP emissions Pounds 9 1 (8) A-3 Total NOx, SOx, and PM emissions Pounds 1,481,328 166,328 (1,315,000) A-4 Total HAP emissions Pounds 2,656 1,542 (1,114) A-5 Total greenhouse gas emissions Tons CO2e 46,207 21,439 (24,768) "MMBtu" = millions of Btus "MG" = millions of gallons "CO2e" = carbon dioxide equivalents of global warming potential "MWh" = megawatt hours (i.e.,, thousands of kilowatt-hours or millions of Watt-hours) "Tons" = short tons (2,000 pounds) Water Footprint Core Element Metric Unit of Measure Materials & Waste Energy Air Land & Ecosystems Qualitative Description The above metrics are consistent with Methodology for Understanding and Reducing a Project’s Environmental Footprint (EPA 542-R-12- 002), February 2012

Beneficial Outcomes

• In-place closure/management of

impoundments

• Hydraulically isolates CCP from groundwater
• Reduction in leaching
• Increase in stability
• Eliminate need for removal of CCP from

impoundments

• Reduction in dewatering, treatment, and

discharge/disposal

• Reuse of water during ISS construction
• Eliminates the need for new landfill space for

CCP from existing impoundments

Beneficial Outcomes

• Satisfy regulatory requirements for closure or

stability/groundwater corrective action for:

• Impoundments that do not meet location or

require groundwater corrective action

• Impoundments that do not meet stability criteria
• Impoundments that meet location and

groundwater criteria but not stability

• Reduced cost to close impoundments
• Reduced environmental footprint

What’s Next

• Site specific adaptation
• Continued Bench Testing on CCP
• Pilot Testing
• Impoundment Closure

Implementation