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 option  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

Constructability Evaluation Investigation and

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) o Increased compressive strength (e.g. ≥ 50 psi) o Reduction of leaching to meet regulatory requirements o  Construction Techniques Conventional full depth ISS – proven technique o Discrete zone ISS – pilot tested technique o

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 o Implemented for geotechnical/stability applications o  Discrete ISS: Successfully Pilot Tested at CERCLA Site  Baseline Laboratory Treatability Testing on CCP Material Properties – physical and chemical o Reagent and proportion selection (e.g. Portland Cement, o Slag, Bentonite) Performance testing (hydraulic conductivity, compressive o strength, monolithic leaching) Impoundment water reuse evaluation o

CCP ISS Treatability Testing 10% Portland 7.5% GGBFS 6% GGBFS 8% Portland 18% GGBFS Grout Amendments and Cement 2.5% Portland 8% Portland 2% Portland Cement 6% Portland Cement Proportions 0.5% Bentonite Cement Cement Cement 0.5% Bentonite 2% Bentonite 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/ft 3 ) (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 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 (cm/sec) -- -- -- -- GGBFS = Ground Granulated Blast Furnace Slag

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 o Structural integrity – Calculated factors of safety requirements o Liner construction – Liner demonstration and/or composite liner o  This method is applicable for: Closure of impoundments that do not meet location requirements o or require groundwater corrective action Closure of impoundments that do not meet stability criteria o Corrective Action for impoundments that meet location and o 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 o Excavated ash will be disposed within 50 miles of the o impoundment One cubic yard of ash weighs 2,700 lbs o Excavation will require dewatering and water treatment o Impoundment will be backfilled and vegetated o  In situ Closure Assumptions: ISS volume is 366,000 cubic yards including 5’ thick discrete o bottom liner and 10’ wide fully penetrating perimeter walls to 25’ below grade Dewatered groundwater will be used in ISS batch plant o Impoundment will be capped with geo-textile and soil cover o Cost evaluated on recent experience and discussions with  contractors

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

Cost Evaluation Volume treated reduced by over 70% via in-situ  closure 1.29 million cubic yards for excavation and off-site disposal o 366,000 cubic yards for in-situ closure o  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 o Water – Inventory use o Energy – Input equipment specifications o Air – Input equipment specifications o Ecology – User defined o  Comparison of environmental footprint for in situ closure vs. excavation and off-site disposal