IN-SITU IMPOUNDMENT Tim Silar, P.G. Principal Geoscientist - - PowerPoint PPT Presentation

IN-SITU IMPOUNDMENT CLOSURE AND GROUNDWATER CORRECTIVE ACTION TECHNOLOGY

World of Coal Ash 2019

• St. Louis, Missouri

Tim Silar, P.G.

Principal Geoscientist

John Magee, P.E.

Principal Engineer

FIRST UP CONSUL TANTS

PRESENTATION OBJECTIVE

To present a permanent, technically sound, minimally disruptive and cost effective impoundment closure and groundwater corrective action option including:

• Common impoundment

challenges/concerns

• Impoundment closure remedial

technology

• Proof of technology
• Cost evaluation
• Stakeholder acceptance and risk

reduction

• Applicability

2

Common CCP Impoundment Challenges/ Concerns

• CCPs below the water table
• Ponded water/increased hydraulic

head

• Structural stability
• Remedial Construction safety
• Extensive dewatering and treatment
• Historic infrastructure and disposal

practices

CCP Impoundment Profile

Technology – Hydraulic Containment via In Situ Solidification(ISS)

ISS: In‐place mechanical mixing of media with dry reagent or an injected engineered grout mixture

Result: Monolithic structure with increased strength/stability and decreased permeability Typical Reagents: Portland Cement, Slag, Bentonite Typical Performance Goals

• Decreased Permeability (e.g. ≤ 1x10‐6 to 1x10‐8 (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 – proven technique via CERCLA Site Pilot Test

ISS Drilling Methods

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

Investigation and Constructability Evaluation

=>Evaluate dewatering =>Complete Geotechnical Eval =>Perform GW Assessment to establish baseline conditions & interface => Evaluate Grading Plan

Major Activities ‐ Review records and develop CSM ‐ Conduct Constructability evaluation ‐ Perform ISS treatability study to determine performance criteria/construction parameters ‐ Conduct on‐site investigation

Impoundment Site Preparation

ASH IMPOUNMENT FILL CAN BE UNEVEN & UNSTABLE CONCERN: Grading & Stabilization may be required to construct liner. =>Regrade/stabilize ash to establish construction platform

ASH IMPOUNMENT SATURATED/ POSSIBLE STANDING WATER CONCERN: Impoundment may require dewatering over time and hydraulic head can exacerbate leaching =>Begin dewatering to facilitate construction and overall effectiveness

• f remedy.

Impoundment Site Construction

Begin ISS construction of linear system and perimeter columns. ISS full depth along perimeter berms to construct perimeter containment and provide stability.

Impoundment Site Construction

Begin ISS construction of linear system and perimeter columns. ISS full depth along perimeter berms to construct perimeter containment and provide stability.

Plan View:

Both Full and Discrete ISS provides complete coverage

40 ACRE POND: ~18,000 COLUMNS

~1,000 FULL ISS ~17,000 Discrete ISS

Final Cover Construction

Complete ISS construction of liner system and final cover system

Import fill or ISS swell to establish subgrade for final cover. Low permeability layer (e.g. geomembrane, compacted clay, Closure Turf TM ) Final Cover protective layer (e.g. soil, Closure Turf TM )

Proof of Technology

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

Full depth ISS mixing recently proven at CCP impoundment

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

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

Compare in situ closure to excavation & off-site disposal

Cost Evaluation: Assumptions

Volume Assumptions: Assume the impoundment volume is approximately 1.29 million cubic yards (40 acres by 20’ thick)

Excavation Assumptions:

• Excavation volume is 1.29

million cubic yards

• Excavated ash will be

disposed within 20 miles

• f the impoundment
• One cubic yard of ash

weighs 2,700 lbs

• Excavation will require

dewatering and water treatment

• Impoundment will be

partially 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 swell , geotextile, and soil cover

Cost evaluated on recent experience and discussions with contractors

General Conditions General Conditions Excavation & Off‐ Site Disposal vs lSS Technology Excavation & Off‐ Site Disposal vs lSS Technology Dewatering Dewatering Site Restoration Site Restoration

Cost Categories

Cost Evaluation: Details

Excavation and Off-Site Disposal In situ Closure (ISS) Item Estimated Quantity Units Unit Price $ Amount $ Unit Price $ Amount $ General Conditions

$ 2,750,000 $ 2,750,000

Mobilization & Temporary Facilities Setup 1 Lump Sum

$ 700,000 $ 700,000 $ 700,000 $ 700,000

Site Preparation, Site Survey, Remove Ponded Water 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

Cost Evaluation: Details

Excavation and Off-Site Disposal In situ Closure (ISS) Item Estimated Quantity Units Unit Price $ Amount $ Unit Price $ Amount $ Excavation / Disposal vs. ISS $ 69,373,351 $ 31,977,640 Excavate Ash, Dewater, and Load 1,290,667 Cubic Yards $ 20 $ 25,813,340 $ - $ - Transport and Dispose of Ash 1,742,400 Tons $ 25 $ 43,560,011 $ - $ - 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

Cost Evaluation: Details

Excavation and Off-Site Disposal In situ Closure (ISS) Item Estimated Quantity Units Unit Price $ Amount $ Unit Price $ Amount $ Dewatering - Excavation $ 2,624,000 $ 272,000 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 $ 10,598,942 $ 918,942 Backfill with Off-site fill 645,334 Cubic Yards $ 15 $ 9,680,000 Topsoil 32,267 Cubic Yard $ 26 $ 838,942 $ 26 $ 838,942 Seed and Mulch 40 Acres $ 2,000 $ 80,000 $ 2,000 $ 80,000 TOTAL COST $ 85,343,293 $ 35,918,582 COST PER ACRE $ 2,133,582 $ 897,965

Stakeholder Acceptance & Risk Reduction

Stakeholder Impoundment Closure objectives & In-situ Closure Technology are well aligned

Different Stakeholders – Shared Goals

In-situ Closure Technology Satisfies Key Objectives & Reduces Risk

• Secure CCP impoundments in‐place to prevent

catastrophic failure and leaching of CCP constituents into groundwater

• Combined closure and corrective action reduces

potential environmental impacts and risks associated with siting and permitting new landfills, ash excavation/handling, ash transportation, etc

• Closure technology is a cost‐effective remedy that

will meet regulatory closure requirements

• Timely implementation of closure

Stakeholders: Impoundment Owners, Regulators, Environmental Groups, General Public, Rate Payers

Applicability

This method is applicable for:

• Closure of impoundments that

require groundwater corrective action

• Closure of impoundments that

require improved stability

• Supplement to cap-in-place

where an active groundwater remedy is also needed

• Hydraulically isolates CCPs from groundwater

reducing groundwater impacts

• Increases impoundment stability
• Eliminates need for removal of CCPs from

impoundments and allows for future harvesting

• Reduces costs & risks
• Provides environmental benefits: landfill space,

emissions, etc.

• Relies on proven technology with readily

available resources

Continue to share the technology with stakeholders Seek collaborative opportunities to demonstrate the remedy and advance the technology ‐ Continue Bench Testing on CCP ‐ Impoundment Implementation ‐ Site Pilot Testing

What’s Next

www.silarservices.com 2019 WOCA Paper “In‐Situ Impoundment Closure and Groundwater Corrective Action Technology” In Situ Waste Remediation and Systems US Patent No. 9,909,277 B2

Thank you