current and emerging techniques for dnapl site …...current and emerging techniques for dnapl site...

Current and emerging techniques for

DNAPL site characterization

Gary Wealthall, Neal Durant (Geosyntec Consultants, Inc.)

Torben Højbjerg Jørgensen, Bernt Grosen (COWI A/S)

and Mette Broholm (DTU Environment)

[email protected]

Presentation Outline

Challenges to DNAPL site characterization

Site Characterization Methods

Qualitative versus Quantitative data

Current and emerging techniques

Examples from chlorinated solvents and coal tar sites

Guidance documents

Challenges to DNAPL site characterization

Early stage mass distribution

DNAPL Zone

Gro

undw

ate

r flow

Plume Zone

VOC<10% VOC >90%

Mass distribution dynamics

Source Plume

Low Permeability

Transmissive Low Permeability

Transmissive

Vapor

DNAPL

Aqueous

Sorbed

Reversible phase transfer

Irreversible phase transfer

Legend:

ESTCP, 2011

Site Characterization Methods Qualitative versus Quantitative

Qualitative versus Quantitative Data

The first category provides qualitative, dense spatial data and

generates decision-quality data that guides future investigations

Often with higher detection limits over a preset value

Generally of lower cost, produce vertical profiles of real-time data

Examples of such "decision quality" methods are laser-induced

fluorescence [LIF] profiling and membrane interface probing [MIP]

The second category of technologies that are quantitative and

typically compound-specific

They provide precise data that have low detection limit

Tend to be higher cost with longer turnaround times that preclude

on-site decision making

Examples include the use of fully cored boreholes (and associated

sub-sampling) and high-resolution multilevel well completions

Current and emerging techniques

Current tools and techniques

• No SINGLE technique available to characterise a DNAPL site

• Typically, resolution decreases with depth and hydrogeological

complexity and may constrain the selection, application and

performance assessment of remediation technologies

Direct measurement Indirect measurement

Visual observation Site history

Enhanced visual methods Soil (partitioning threshold)

Drive point tools Groundwater (Effective solubility)

Direct: Visual observation

From soil and rock core

or grab samples

• Rare at chlorinated solvent sites

• Common at coal tar sites

Samples recovered during from

pumping from wells

• Typically requires pooled DNAPL

Direct: Enhanced Visual

After Mercer and Cohen (1993)

60

55

50

45

40

35

30

25

20

15

10

5

0

5

10

15

20

25

Legend

Correct determination

of NAPL presence

or absence

Incorrect

determination

NAPL suspected

present when

it was present

NAPL suspected

present when

it was absent

NAPLwas

present

No NAPLpresent

Unaided

visual

UV

fluorescence

Soil-water

shake

test

Hydrophobic

dye shake

test

Centrifugation

of the dye

shake test

Nu

mb

er

of

sa

mp

les

60

55

50

45

40

35

30

25

20

15

10

5

0

5

10

15

20

25

Legend

Correct determination

of NAPL presence

or absence

Incorrect

determination

NAPL suspected

present when

it was present

NAPL suspected

present when

it was absent

NAPLwas

present

No NAPLpresent

Unaided

visual

UV

fluorescence

Soil-water

shake

test

Hydrophobic

dye shake

test

Centrifugation

of the dye

shake test

Nu

mb

er

of

sa

mp

les


Dye shake test using Sudan IV

Individual sample Depth profile

FACT NAPL FLUTe (Flexible liner underground everting membrane)

From: http://www.flut.com/sys_3.html


Direct drive tools summary

Method Advantages Disadvantages

Video imaging [GeoVis]

• Can be coupled with lithological logs • Data easy to interpret in suitable soil

matrix

• Limited by lithology • Transparent DNAPL not visible • Clays may smear the camera window

Membrane Interface Probe [MIP]

• Can be coupled with lithological logs • Range of detectors [FID, PID, ECD] • Excellent screening level data

• Limited by lithology • Semi-quantitative • High operator skill required

Laser Induced fluorescence [LIF]

• Can be coupled with lithological logs • Simple detection methodology • Excellent screening level data

• Limited by lithology • Semi-quantitative • False positives may be detected

Dye-LIF • Can be coupled with lithological logs • Applicable to non-fluorescing

compounds • Excellent screening level data

• Limited by lithology • Still under development

TarGOST • Can be coupled with lithological logs • Applicable to coal tar compound • Excellent screening level data

• Limited by lithology • Only applicable to coal tar compounds

Membrane Interface Probe

Permeablemembrane

DetectorHe gas

Sleeve

Cone

Heater

ASTM D7352 - 07 Standard Practice for Direct Push Technology for

Volatile Contaminant Logging with the Membrane Interface Probe (MIP)

0

1

2

3

4

5

6

7

0.0 0.5 1.0 1.5

DELCD (V)

0

1

2

3

4

5

6

7

0.0 1.0 2.0

FID (V)

0

1

2

3

4

5

6

7

0.0 2.0 4.0 6.0

PID (V)

0

1

2

3

4

5

6

7

0.0 200.0 400.0

Conductivity (mS m-1

)

Depth

(m

bgl)

0

4

3

1

2

5

6

7

PID

FID

DE

L

SP9

DNAPL

DNAPL

DNAPL

0-2V

2-4V

4-6V

PID response

No DNAPL

Potential DNAPL

DNAPL

Scatter Tar Fingerprint

% Reference Emitter Response =

Σarea under SAMPLE fluorescence peaks/Σarea under REFERENCE fluorescence peaks

Area under SAMPLE scatter peak/Area under REFERENCE scatter peak

Laser Induced FluorescenceTar-specific Green Optical Screening Tool, Tar-GOST ®

Converting LIF response to DNAPL saturation

NA

PL S

atu

ratio

n

PAH Concentration (ppm)

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0 20.000 40.000 60.000 80.000 100.000

%R

E

PAH Concentration (ppm)

LIF Tool and Green Laser

Indirect: Site history

• Previous investigations

• Aerial photographs

• Building plans

• Former lagoons, USTs, drains

• Production records

• Employee interviews

• Sale records

1954

2011

Soil core data

Indirect: Soil partitioning threshold

Where:

CD is soil concentration (mg/kg) corresponding to

threshold DNAPL saturation

Sr is threshold DNAPL saturation

f is the porosity

ρN is DNAPL density (g/cc)

ρb is dry soil bulk density (g/cc)

CT is amount of contaminant (mg/kg) in the samples,

including aqueous, vapour and sorbed

T

b

NrD C

SC

f 610

30

31

32

33

34

35

36

37

38

39

40

1 10 100 1000 10000 100000

Ele

vatio

n (

m a

od

)

TCE (mg/kg, wet weight)

ST76 (T1) 6 m

ST77 (T1+T4) 6 m

ST78 (T1) 6 m

ST79 (T1) 6 m

ST80 (T1) 6m

SF45 (T2) 10 m

SF46 (T2) 10 m

IW107 (T4) 13 m

SF52 (T3) 23 m

SF53 (T3) 23 m

DNAPL threshold

DNAPL sat = 1%

DNAPL sat = 2%

DNAPL sat = 5%

DNAPL sat = 10%

DNAPL sat = 20%

Provisional SABRE site data

Kueper and Davies, 2009

Indirect:

Theoretical pore water concentration

nK

CC

bd

btw

Cw is the pore water concentration (mg/L)

Ct is the soil concentration (mg/kg)

b is the bulk density (g/cm3)

Kd is the partition coefficient (cm3/g)

n is porosity (dimensionless)

Compare theoretical pore water concentration to the

solubility (S) or effective (Se) of the compound of interest

Feenstra et al., 1991

Inferred DNAPL presence

US EPA guidance indicates that

1% effective solubility infers

the presence of DNAPL

Where:

Sei is the effective solubility of component i in water

Xmi is the mole fraction of component i in a given mixture

Si is the solubility of component i in water

imi

e

i SXS

Consider concentration trends with depth

DNAPL

release 5 mg/l

35 mg/l

3 mg/l

1 mg/l N.D.

Gro

un

dw

ate

r fl

ow

Groundwater sampling downgradient

of a DNAPL source zone

75% mass flux

discharges through

5-10% plume

cross-sectional area

(Guilbeault, et. al., 2005)

MLS

DNAPL

Dissolved plume

Bedrock DNAPL

Emerging techniques

Rapid site characterization tools (CPT-based)

Decreasing limit of detection

MIP-GCMS

DyeLIF for chlorinated solvent source zones

Combined tools

FLUTe family

Geophysical tools

Increasing resolution

Compound specific

Real time data integration

Digital data capture

On-line GIS tools

TarGOST

LIF

Guidance Documents

UK Guidance (2003)

Developed conceptual models for a

range of DNAPLs in drift and bedrock

US EPA Guidance (revised 2010)

ITRC DNAPL Team Topics (2012-13)

Conceptual models of DNAPL fate and transport

The impact of geological and anthropogenic

heterogeneities on DNAPL migration

The effect of mobile and immobile pore spaces and

the back diffusion issue

Emerging methods to assess geology, DNAPL and

associated dissolved phase distribution, including

geophysics

The role of analytical and digital modeling in DNAPL

site characterization

What managers should consider when reviewing site

characterization plans

Cost benefit assessment for DNAPL site

characterization and sampling optimization

Questions?

[email protected]