Geophysical methods for landfill characterization · 2020. 10. 28. · RAWFILL Geophysical methods...

RAWFILL

Geophysical methods for landfill

characterizationDavid Caterina2, Ben Dashwood1, Itzel Isunza Manrique2, Arnaud Watlet1, Cornelia M. Inauen1

1 British Geological Survey, Nottingham, UK, 2 University of Liege, Urban and Environmental Engineering, Belgium

RAWFILL 2

“The subsurface site characterization of the geology, geological

structure, groundwater, contamination, and human artifacts beneath the

Earth's surface, based on the lateral and vertical mapping of physical

property variations that are remotely sensed using non-invasive

technologies” (EEGS 2018)

INTRODUCTION

A short introduction to geophysics

RAWFILL 3

INTRODUCTION

Why geophysics for landfill characterization?

RAWFILL 4

Accurate information

BUT

Good spatial characterization

can be costly and lead to higher

cross-contamination risks

INTRIDUCTION

Traditional approach:

drilling – sampling - analysis

RAWFILL 5

Medical analogy

Combine geophysics with traditional techniques

RAWFILL 6

RAWFILL approach

How?

RAWFILL 7

Stainless steel electrodesExample: using electrical resistivity

tomography (ERT) & induced polarization (IP)

Principle 1:combine complementary geophysical methods and plan

the geophysical survey based on a-priory site

information

RAWFILL approach

RAWFILL 8

RAWFILL approach

Principle 1:combine complementary geophysical methods

RAWFILL 9

RAWFILL approach

Low resistivity+

High chargeability

Metals?

Resistivity model

Chargeability model

Principle 1: combine complementary geophysical methods

→ Increased certainty

RAWFILL 10

RAWFILL approach

Targeted sampling in

the zones of interest

revealed by

geophysics

Principle 2: targeted sampling

• Lower costs

• Reduced risk of

damaging

structures

• Reduced risks of

contamination or

exposure to

hazardous materials

RAWFILL 11

Pros and cons

• Non to minimally invasive

• Relatively low cost

• Large coverage

• See through technology

• Indirect information

• Resolution decreases with depth

• Prone to modeling errors

(artefacts)

RAWFILL 12

Proposed workflow

Archives & inventory report

• Gather and summarize all available information→ Build conceptual model→ Assess knowledge gaps

Geophysical characterization

• Use complementary geophysical methods planned according to the conceptual model→ Interpretation of geophysical results and detection changing properties

Calibration & validation

• Targeted sampling→ Build sampling plan according to geophysical results→ Verify and calibrate geophysical measurements to refine conceptual model

Resource model construction

• Build a resource distribution model based on refined conceptual model

Ad

dit

ion

al

mea

sure

men

ts r

equ

ired

?

RAWFILL 13

Proposed workflow

Landfill site

Potential knowledge gaps

Type of waste?Volume / Extent of the waste?Cover material?Contamination?

Initial stage

RAWFILL 14

Proposed workflow

Gather and summarize all available information

• Historical reports (from site owner, local authorities,…)• Aerial photography archives• Previous investigations

• Site visit• Information exchange • Discussing knowns and unknowns of the site

➢ Building conceptual model➢ Assessing knowledge gaps

1 Archives and inventory report

RAWFILL 15

Proposed workflow

Initial stage After gathering informationand visiting the site

1 Archives and inventory report

RAWFILL 16

Proposed workflow

Gathering and interpreting a priori information

First conceptual model

1 Archives and inventory report

RAWFILL 17

Proposed workflow

➢ Filling the knowledge gaps➢ Using non-invasive integrated approach

2 Geophysical characterisation

RAWFILL 18

Proposed workflow

Mapping techniques

2 Geophysical characterisation

RAWFILL 19

Proposed workflow

Geophysical imaging (here ERT/IP)

Profiling techniques

2 Geophysical characterisation

RAWFILL 20

Methods tested within RAWFILL

Method Bulk (geo)physical property

Relevant information for landfill characterisation

Sensitive to

Electrical resistivity tomography (ERT) or DC electrical resistivity

Electrical resistivity Cover layer thickness, waste zonation, leachate content, geology, groundwater table

Leachate contentClay contentMetal contentPore fluid conductivity

Induced polarization (IP) Chargeability Cover layer thickness, vertical extent, waste zonation

Metals, organics, wood, plastics

Ground Penetrating Radar (GPR)

Dielectric permittivity Electrical resistivity

Cover layer thicknessUtilities

Pore fluid conductivityClay and metal contentVoids

Electromagnetic induction (EMI)

Electrical conductivity and magnetic susceptibility

Lateral extentUtilitiesWaste zonation

Leachate contentPore fluid conductivityMetal content

Magnetometry (MAG) Magnetic susceptibility

Lateral extent, utilities, waste zonation

Metallic itemsMetal content

Seismics (refraction – SRT, surface waves - MASW, ambient noise – HVSNR or HV)

Elastic properties, density (seismic velocities)

Vertical extent, Geology StiffnessCompactionImpedance contrasts

RAWFILL 21

Methods tested within RAWFILL

Method Bulk (geo)physical property

Relevant information Acquisition/(ex. of main limitations)

Electrical resistivity tomography (ERT) or DC electrical resistivity

Electrical resistivity Water content, salinity, pore fluid, temperature, porosity, lithology

Borehole, cross-hole, surface/(impermeable membrane)

Induced polarization (IP) Chargeability Disseminated metallic particles (pyrite), clay, surface area, lithology

Borehole, cross-hole, surface (noise and inductive coupling)

Ground Penetrating Radar (GPR)

Dielectrical constant and electrical conductivity

Structures, faults, water content, salinity, pore fluid, porosity, lithology

Borehole, cross-hole, surface/(conductive ground)

Electromagnetic induction (EM)

Electrical conductivity and magnetic susceptibility

Water content, salinity, pore fluid, porosity, lithology, Ferrous materials

Borehole, cross-hole, surface, airborne or ATV mounted/(Metallic external objects)

Magnetometry (MAG) Magnetic susceptibility Ferrous materials (buried drums, containers…), lithology

Surface/(Metallic external objects)

Seismics (refraction – SRT, surface waves - MASW, ambient noise – HVSNR or HV)

Elastic moduli, density(seismic velocities)

Structures, faults, depth to bedrock, lithology

Surface, borehole, cross-hole/(velocity inversion, ambient vibrations)

Integrated approach:

• Using a combination of differentgeophysical methods

• Designed based on the a-prioriinformation available for a specific

landfill

Updated conceptual site model

RAWFILL 22

Proposed workflow

??

Use calibrated geophysical results for filling “gaps”

3 Targeted sampling to calibrate geophysics

Plan based on geophysical

results

RAWFILL 23

Electrical conductivity (EMI)

Low conductivity anomaly/background

High conductivity anomaly

Pipe:avoid utilities !!!

Knowledge gaps(e.g. depth calibration)

Anomaly other method

How to create a sampling plan?

RAWFILL 24

Proposed workflow

??

Final conceptual site model

Conclude all information into resource distribution model

✓ ✓

→ Information about volumes & feasibilityResource distribution model

4 Final conceptual site model

RAWFILL 25

• Location: UK, near Bristol

• Excavated for new housing in 2019

Case study: Emersons Green

RAWFILL 26

• Location: UK, near Bristol

• Excavated for new housing in 2019

→ ground truth data to calibrate

geophysics

Case study: Emersons Green

RAWFILL 27

Landfill size: 23,000m2

Depth: 3 - 5m

Operation (1984 – 1991)

• Inert & industrial/commercial waste

• Dilute & disperse basis

Step 1) Information gathering: site

historyArchives &

inventory report

RAWFILL 28

Step 1) Information gathering:

available ground truth dataArchives &

inventory report

Ground truth data available across site:

• 35 Trial pits

• 4 Boreholes

RAWFILL 29

Step 1: Identification of knowledge

gapsArchives &

inventory report

1. Waste thickness under defined especially

towards centre of landfill.

→ difficult to estimate waste volume

2. Structure of landfill unclear.

Is the landfill separated into different cells with different types of waste?

RAWFILL 30

Step 2) Geophysical characterisation: PlanningArchives & inventory report

Site conditions

Geophysical characterization

delineate extent & areas with high

leachate or metal contentdelineate extent & metallic materials

Top soil stripped off (about 30cm) In some places waste visible High groundwater table

→ Site well accessible for all geophysical measurements

RAWFILL 31

Step 2) Geophysical characterisation: PlanningArchives & inventory report

Selecting methods

Geophysical characterization

Lateral extent & areas with high

leachate or metal contentLateral extent & metallic materials

Electromagnetics Magnetics

MA

PP

ING

METH

OD

SP

RO

FIL

ING

METH

OD

S

MASW

Layers of different stiffness

Thickness of landfillWaste types & saturation

Thickness of landfill

ERT/IP

RAWFILL 32

Step 2) Geophysical characterisation:

Measurement extentArchives &

inventory report

Geophysical characterization

Magnetics EM: depths: 1.5m, 2.5m, 3m, 6m ERT and MASW

RAWFILL 33

Step 2) Geophysical characterisation:

Results Magnetics

Archives & inventory report

Geophysical characterization

Total magnetic field (nT) Vertical magnetic Gradient (nT)

Higher metalcontent?

RAWFILL 34

Step 2) Geophysical characterisation:

Results EM

Archives & inventory report

Geophysical characterization Cell type

structure?

Additional cell with less metal

content or thicker cover layer?

RAWFILL 35

Step 2) Geophysical characterisation:

Results ERT and IP

Archives & inventory report

Geophysical characterization

ERT

IP

RAWFILL 36

Step 2) Geophysical characterisation:

Results MASW

Archives & inventory report

Geophysical characterization

RAWFILL 37

Step 3) Calibration and ValidationArchives & inventory report

Geophysical characterization

Calibration & validation

Additional ground truth data through excavations

base of waste layer

cover layer thickness

clay stank dividing the waste cells

• The landfill was separated into three cells. These cells were

excavated into the natural clayey ground and filled with waste.

• A thicker clay cap and a thinner waste layer was found in cell 3.

• A step in the landfill base between cells 2 and 3 might be

associated with the underlying sandstone.

• The waste composition was a mix of

plastic, metal, wood, paper, fabric, inert

etc. with no strong compositional

changes across the site.

RAWFILL 38

Step 3) Calibration and ValidationArchives & inventory report

Geophysical characterization

Calibration & validation

EM: good delineation of waste cell extent and cover layer thickness

RAWFILL 39

Step 3) Calibration and ValidationArchives & inventory report

Geophysical characterization

Calibration & validation

IPresolves clay cap

and waste cells

ERTresolves

sandstone

interface

MASWresolves sandstone

interface, mudstone

interface less clear

cover layer

mudstone sandstone

waste cell 2waste cell 1waste cell 3

sandstonemudstone

inert waste?

RAWFILL 40

Step 4) Building Resource Distribution ModelArchives & inventory report

Geophysical characterization

Calibration & validation

Resource model construction

Trial pits & boreholes

Geophysical data

Correlation analysis

extract geophysicaldata in vicinityof samples

choice of relevantgeophysicalparameters

discretize sampling logs into relevantcategories (e.g. clay cap, saturated waste…)

Model buildingthrough supervised machine learning

(classification)

Cell 01 (North) Cell 02 (centre) Cell 03 (South) Total

Volume of waste

material (m3)15’258 10’654 9’547 35’450

RAWFILL 41

• Using geophysics:

• is cost effective

• allows targeted sampling

• delivers relatively high resolution data (when mapping and profiling techniques are combined)

• Our proposed workflow:

• integrates a priori information, geophysics and targeted sampling to build a resource distribution model specific to each landfill

• Provides “ready-to-use” information for decision makers (DST 2)

Take-home message

RAWFILL

RAWFILL 43

The Interreg North-West Europe Project is coordinated by SPAQuE and

unites 8 partners from 4 EU regions.

Raw materials recovered from

landfills