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Methods for subsurface investigation and groundwater monitoringand groundwater monitoring

in the framework of MNA

Carsten Leven, Center for Applied Geosciences, University of Tübingen

Suggested multi-stage approach for Monitored Natural Attenuation (MNA)Monitored Natural Attenuation (MNA)

I. Assessment of prerequisites for MNA

II. Site specific investigation that MNA occurs

III Prognosis of and decision on MNAIII. Prognosis of and decision on MNA

IV. Monitoring and performance control


I. Assessment of prerequisites for MNA

Purpose

ssess e t o p e equ s tes o

Qualitative assessment whether site conditionsQualitative assessment whether site conditions allow the consideration of natural attenuation

Required technical investigations

• source area

• Plume

q g


II. Site specific investigation that MNA occurs

Purpose

S te spec c est gat o t at occu s

Identification of the relevant natural attenuation processesIdentification of the relevant natural attenuation processes and quantification of their effectiveness

Technical investigations

• Quantification of mass fluxes along control planes

• Estimation of biological degradation rates

g

g g

• Estimation of signatures of stable isotopes


III. Prognosis of and decision on MNA

Purpose

og os s o a d dec s o o

Prognosis on the future development of the contaminant source andPrognosis on the future development of the contaminant source and plume and determination of the monitoring approach

(e.g. duration, intervals, location, etc.)

• Information on occurrence, concentration and availability of electron acceptors


acceptors

• Information on occurrence of different (combinations of) contaminants and metabolites


IV. Monitoring and performance control

Purpose

o to g a d pe o a ce co t o

Continuous monitoring and control of the effectiveness and sustainabilityContinuous monitoring and control of the effectiveness and sustainability of the natural attenuation processes and verification of the prognosis

(target/actual comparison)

• Site monitoring


Where do we have to measure?

source oriented l i t d it i ti tisite investigation plume oriented site investigation

(after: Environmental Restoration Technology Transfer - ERT2)

Investigating the source zone Investigating the source zone

Characterization of source zone is of fundamental relevance as the source controls the extent and characteristics of the plume

→ Source zone characterization aims on • its spatial extent (source delineation)• the contaminant inventory (type of contaminant, distribution and

mass)• the determination of the source emission• the mobility of the contaminants

Investigating the plumeInvestigating the plume

The plume evolution and its characteristics are controlled by the emission from the source, the transport processes in the subsurface, and the hydrogeologic conditions

→ plume characterization aims on it ti l t t• its spatial extent

• the contaminant inventory (type of contaminant, distribution and mass)

• the determination of the temporal and spatial plume behavior

Summary – Site characterization methods (in the framework of MNA)(in the framework of MNA)

General site Source Plume Assessment of Data for Site monitoringcharacterization characterization characterization NA processes prognosis Site monitoring

Conventional drilling X X X X X X

Conventional monitoring wells / groundwater X X X X X Xwells / groundwater sampling

X X X X X X

Direct Push Technology X X X X (x) (x)

Specialized methods forSpecialized methods for source characterization (x) X (x)

Mass flux estimation methods

(x) X (x) X (x)

Hydraulic tests X (x) (x)

Tracer tests X (x) (x)

Monitoring de ices X ( ) X ( ) X

th th th d ( h i l t h i ) t ti d h

Monitoring devices X (x) X (x) X

there are many other methods (e.g. geophysical techniques) not mentioned here, which are also suitable for site investigation in the framework of MNA!

How to measure?

3 l fil2. spatially distributed1. point based

3. along profiles- control planes- along spreading path- profile across plume boundaries

along spreading path

How to measure? vertically integrated?

Note: importance of vertically resolved information for assessment of NA processes

vertically resolved!

How about changes in time?

snap shots temporally resolved temporally resolved

How about changes in time?

P3 P30

temporally integrated

dosimeter result P310 00

100.00

dosimeter result P3

toximeter result

1.00

10.00

P - Valuemax

dosimeter result P30

0.10

0.01Dec 93 Dec 94 Dec 95 Dec 96 Dec 97 Dec 98 Dec 99

Time

Summary – Site characterization methods (in the framework of MNA)

General site Source Plume Assessment of Data for Site monitoring

(in the framework of MNA)

characterization characterization characterization NA processes prognosis Site monitoring



X X X X X X




(x) X (x) X (x)



Monitoring de ices X ( ) X ( ) XMonitoring devices X (x) X (x) X

Conventional drilling for soil samples

classical method for source delineation and classical method for source delineation and contaminant inventorycontaminant inventorycontaminant inventorycontaminant inventory

many well established methods are many well established methods are available that are mostly well understood

h ld ll f lith l i l i f ti should allow for lithological information

check whether method is suitable for high quality investigationsg q y g

special focus on quality assurance

Sonic Drilling

Sonic drilling head producing 150 Hz ib tivibrations

SEITE 17 (from: Barrow 1994)

Sonic Drilling

1. Longitudinal expansion / compression of pipe

2. Liquifaction / fluidization (Bingham's law – non-newton fluid)

3. intertial effects

ear s

tress

Binham-plastic fluid

she

Newton fluid

SEITE 18shear rate

advantages: extremly high penetration rates no cuttings (only pure sonic) no cuttings (only pure sonic) cross-contamination is

minimized high quality cores possible







X X X X X X




(x) X (x) X (x)




Conventional techniques

Monitoring wells and their suitability

• Representative groundwater sampling: Samples reflect the physical, chemical and bi l i l diti f th if i thbiological conditions of the aquifer in the considered section

• Representativeness with respect to• Representativeness with respect to content support volume ti time

• Types of sampling: mixed sample (flux weighted K depend) mixed sample (flux weighted K depend) depth / layer oriented point measurement integral

(Schoenleber, 2005) integral


Monitoring wells and their suitability

Some prerequisites for representative samples p

• Monitoring well is suitable / fits the purpose

• Sampling equipment must not alter the sampleSampling equipment must not alter the sample

• Sampled water originates from aquifer – not from well pipe (no stagnant water)( g )

• Monitoring well must not have altered the groundwater flow in aquifer (e.g. causing

ti l fl i ll)vertical flow in well)

(Schoenleber, 2005)


Monitoring wells and their suitabilityInfluence of Suitability forType of

monitoring wellSupport volume

Influence of natural GW flow

conditionsSampling effort Packer

necessary

Suitability for groundwater monitoring

Fully screened entire aquifer thickness to High High Necessary (e.g. o

well thickness to single layers

High High multilevel)

Partially screened /

Aquifer sections to High High Necessary

oscreened /

multilevel wellsections to

single layersHigh High Necessary

Nested wellsSingle layers to

aquifer High Medium Usually not necessary

+

sections necessary

Clustered wellsSingle layers to

aquifer Low Medium Usually not necessary

++

sections necessary

Multiport wells Single layers to points Low Medium to low Not necessary

++p

(after DVWK, 1997 and Schoenleber, 2005)







X X X X X X




(x) X (x) X (x)




Direct Push Technologies

innovative method with tools for source innovative method with tools for source delineation and contaminant inventorydelineation and contaminant inventorydelineation and contaminant inventorydelineation and contaminant inventory

Direct Push (DP) refers to a technologyDirect Push (DP) refers to a technology that consists of a (vehicle-mounted) drive source that is used for advancing small-diameter stainless steel probes into the psubsurface.

The probes are advanced into the ground gto take depth-discrete samples and measurements along a vertical axis

(US-EPA 1997)

Direct Push Technologies

innovative method with tools for source innovative method with tools for source delineation and contaminant inventorydelineation and contaminant inventorydelineation and contaminant inventorydelineation and contaminant inventory

Multiple samples or measurements canMultiple samples or measurements can be taken in a single push to generate vertical profiles of subsurface information e.g. on hydraulic and g ygeophysical parameters or conta-minations.

DP technology has become widely accepted as a cost-effective means of collecting subsurface samples and stratigraphic information.

(US-EPA 1997)

Direct Push technologies: Advantages

• Direct Push systems are faster and more flexible than traditional drilling methodsg

fast sampling und data acquisition, number of points is maximized with a given time and monetary budget very flexible and mobile equipment (less disturbance to the site)

• with Direct Push no soil cuttings are generated minimizes the volume of soil cuttings for disposal i i i th t ti l f t t i t minimizes the potential for exposure to contaminants cost reduction

• less disturbances along probing channel and g p gchanges of in-situ conditions (e.g. geochemistry) are minimized

f t d ffi i t i t ll ti f i it li• fast and efficient installations of in-situ sampling

• variety of different sensors and sampling equipment are available• variety of different sensors and sampling equipment are available

Direct Push technologies: limitations

geological site conditions dictate whether DP can be used and to which depth

• limited to unconsolidated sediments

• limited probing depths (max. 50 – 60 m)

• limited probing diameters (at present max. 4.5" = ca. 114 mm)

• cross-contamination through dragging processes possible

• only low flow groundwater sampling possible (due to limited y g p g p (diameters)

Methods for advancing probe rods

Truck with hydraulic presses crawler with hydraulic percussion hammer

static pushing pushing and percussion hammering

(from: USGS fact sheet 028-03)

anchored crawler with hydraulic presses

(from: www.geomil.com)

Typical working steps for the li ti f Di t P happlication of Direct Push

Profiling Sampling Installations

Profiling

aims on the in-situ measurements of subsurface conditionsaims on the in situ measurements of subsurface conditions and uses probes to determine

• geophysical parametersgeophysical parameters (e.g. Electrical Conductivity logging aquifer / aquitard)

• hydrogeological parametersy g g p(e.g. Injection Logging hydraulic conductivity distribution)

• geotechnical parameters( C P t t T ti lith l il h t i ti )(e.g. Cone Penetrometer Testing lithology, soil characteristics)

• (geo-)chemical parameters(e g Laser Induced Fluorescence Membrane Interface Probe(e.g. Laser Induced Fluorescence, Membrane Interface Probe potential occurrence and distribution of contaminants)

Lithology: Geophysical parametersElectrical Conductivity ProfilingElectrical Conductivity Profiling

(Christy et al. 1994)

(KGS Open-File Report 99-40)

Hydrogeological parametersInjection LoggingInjection Logging

40,1 1 10 100 1000

K relative

Krelativ = f(Q,p,S)Q = injection ratep = injection pressureS t t

6

S – system parameters

8

m]

10

dept

h [m

12r 1220 ml/minr 1540 ml/min

750 l/ i

(Dietrich et al. 2008)

14r 750 ml/min

16

Lithology, soil classification Cone Penetrometer TestingCone Penetrometer Testing

(from: NCHRP, 2007)

Lithology, soil classificationCone Penetrometer Testing

Friction ratio (%)Tip resistance

(MN/m²)

Soil type

Cone Penetrometer Testing

(from: Wentworth and Tinsely 2005)

Contamination situationMembrane Interface Probing (MIP)Membrane Interface Probing (MIP)

carrier gas carrier gas to detectors

GC with detectorsdata acquisition unit

VOC

membrane

heater block

soil conductivity pole

heater block

control unitmembraneMIP probe

Contamination situationMembrane Interface Probing (MIP)

• enables the detection of the potential occurrence and distribution potential occurrence and distribution f l til i d (VOC) i th b f

Membrane Interface Probing (MIP)

of volatile organic compounds (VOC) in the subsurface

• it is only a qualitative method, i.e. it is a SCREENINGSCREENING method y q ,(under certain conditions: semi-quantitative)

it measures all detectable substances (dissolved and sorbed gas and• it measures all detectable substances (dissolved and sorbed, gas and liquid phases)

Contamination situationMembrane Interface Probing (MIP)Membrane Interface Probing (MIP)

MIP contaminantsdetectorsPID aromatic

hydrocarbons, BTEXBTEX

FID AlkenesDELCD chlorinated

hydrocarbonsy

(Rogge, 2001)

Contamination situationLaser Induced Fluorescence (LIF)Laser Induced Fluorescence (LIF)

higher energy and vibration states

el

fluorescentli hen

ergy leve

light

excitation radiation

ncreasing e

(Dakota Technologies, 2008)

in

(Dakota Technologies, 2008)ground state

brand names: UVOST – Ultra Violet Screening ToolROST – Rapid Optical Screening Tool


(from: Aldstadt et al. 2002)


Time dependency of LIF wavelength-time matrices

wavelforms

optically delayed fluorescence pulses

ensi

ty

nsity

fluorescence pulses

int

inte

n

time

(after: Aldstadt et al. 2002)


sapphire window

Direct Push based sampling methods

Soil sampling

www.geoprobe.com

EPA 1997, ASTM 6282-98 (2005)


Soil gas sampling

to pump

EPA (2006)


d) BAT® in situ sampler

a) Exposed screen b) Sealed screen

Groundwater sampling

c) Hydropunch® sampler

(from: US-EPA 542-R-04-017, 2004))

(Rein et al. 2009)

Result of conventional groundwater sampling campaigns in 2007/08

(Rein et al 2009)

Result of a Direct-Push-based groundwater sampling campaign (2 weeks)(Rein et al. 2009)

direct-push technologies: i t ll ti f d t liinstallations for groundwater sampling

IMW & Geomonitoring, 2001







X X X X X X




(x) X (x) X (x)




Specialized methods for source characterization

tools for source delineation and contaminant tools for source delineation and contaminant inventoryinventoryinventoryinventory

soil gas sampling with onsite PID-soil gas sampling with onsite PIDscreening

mapping of source using radonpp g g

determination of the phase mobility

…

(Schubert et al. 2001)







X X X X X X




(x) X (x) X (x)




Mass Flux Estimation

Estimation of mass flux along several transects across a plume

Mass flux in relation to transport distance shows the effect of remediation activities or NA processes

Available methods include

(from: Environmental Restoration Technology Transfer)

• Groundwater monitoring fences

• Integral Pumping Tests

• Passive mass flux meter

Mass Flux Estimation – GW Monitoring Fence

Calculation of mass flux from measurement of concentration, hydraulic gradient and hydraulic conductivity (or groundwater velocity)

The major limitation of this method is the uncertainty in the mass flux The major limitation of this method is the uncertainty in the mass flux calculation due to uncertainty in - source zone: spatial distribution and release of the contaminant - spatial variability in the hydraulic conductivity of the aquiferspatial variability in the hydraulic conductivity of the aquifer- seasonal fluctuation of concentrations in a monitoring well

However averaging over spatial and temporal data can reduce error in the However, averaging over spatial and temporal data can reduce error in the mass flux estimation


1. Characterization of the plume across transect in terms of idth d thi k f th l• width and thickness of the plume

• the distribution of contaminant concentrations within the plume using single or (better) multilevel monitoring wells using single or (better) multilevel monitoring wells

MTBE Concentration profile across a transect (adapted from Einarson 2001).


2. Estimation of groundwater fluxd t ti t f h d li di t ( ) d• needs representative measurements of hydraulic gradient (i) and

the hydraulic conductivity (K)• to characterize the specific discharge (q = K · i ) across plume p g (q ) p

transect• K-distribution from hydraulic tests, Direct Push investigations, etc.

(from: Environmental Restoration Technology Transfer)


3. Cumulative Mass Flux Across Transect

n

i i iM C A q1i

(adapted from Einarson 2001)(adapted from Einarson 2001)

Mass Flux Estimation - Integral Pumping Test

Pumping test with measurement of Pumping test with measurement of concentration vs timeconcentration vs timeconcentration vs. timeconcentration vs. time

Only suitable for aquifers with Only suitable for aquifers with moderate to high K valuesmoderate to high K values

T i t fl d d tiT i t fl d d ti Transient flow and advective Transient flow and advective transport model and inversion transport model and inversion algorithm neededalgorithm needed

(from: Environmental Restoration Technology Transfer - ERT2) analytical solution availableanalytical solution available

IPT are used for:IPT are used for:-- determination of the determination of the presence of plumepresence of plume-- mass flux estimationmass flux estimation across control planeacross control planemass flux estimation mass flux estimation across control planeacross control plane-- average concentrationaverage concentration across control planeacross control plane-- prioritize prioritize contaminated groundwater zones for remediationcontaminated groundwater zones for remediation


(after: Environmental Restoration Technology Transfer 2009)

Integral Pumping Test

contaminant plumecontaminant plume

once

ntra

tion

once

ntra

tion

ncen

trat

ion Isochrone at time t

p GW

flow

ncen

trat

ion Isochrone at time t

p GW

flow

co

time

co

timetime

con

extraction well

con

extraction well

once

ntra

tion

once

ntra

tion

once

ntra

tion

once

ntra

tion

c

time

c

time

co

time

co

time (after Bockelmann et al. 2001)


Advantages• Generates contaminant mass flow estimatesGenerates contaminant mass flow estimates• Interrogates large volumes of water• Can be used in deep aquifers

Limitations• Costly due to wastewater disposal and pumping well installation (if not

already present)• Heterogeneous aquifers will require a large number of pumping wells• Requires lengthy time execution (depends on transmissivity of site)


(from Herold et al. 2008)

Mass Flux Estimation – Passive Flux Meter

• measures simultaneously contaminant and groundwater flux in saturated zonesin saturated zones

• to determine mass flux, PFM are deployed along a transect

• so far available for chlorinatedso far available for chlorinated solvents, hydrocarbons, pesticides, and dissolved inorganics such as phosphate nitrate and metalsphosphate, nitrate, and metals.

(from : Environmental Restoration Technology Transfer - ERT2)







X X X X X X



Integral Pumping Tests (x) X

Groundwater monitoringGroundwater monitoring fences (x) (x) X


Tracer tests X (x) (x)Tracer tests X (x) (x)


Hydraulic tests

• Traditional pumping tests

• Slug testing for K profiles• Slug testing for K profiles

• Hydraulic tomography borehole with receiverspossible locations for direct push of the sourcepossible tomogram planes

(from: Dietrich and Leven, 2006)

p g p

1

Butler (1998) Model

0.4

0.6

0.8Butler (1998) Model Normalized Data - H0=0.082 m

K = 55 m/dayButler (2002) correction applied

lized

hea

d

-0.2

0

0.2

norm

a

0 4 8 12 16 20 24 28-0.4

time in seconds

(from: Butler et al. 2000)

Tracer Testing

• integral investigation method that allows ffto estimate effective parameters

describing non-reactive and reactive transport processes between the tracer i j ti d li l tiinjection and sampling locations

• Different methods:

• Natural and forced gradient tracer• Natural and forced gradient tracer test

• Multi tracer test

• Partitioning and interfacial tracer test: chromatographic separation of the tracers due to retardation processes

(Ptak et al. 2004)

tracers due to retardation processes affinity of reactive tracers leads to a separation of the breakthrough curves allows to calculate e.g. the residual gNAPL saturation

Tracer Testing

Natural gradient test Forced gradient test

depth

integrated multilevel

depth integrated

multilevel

main transport direction + + ‐ ‐

postulated position of contaminant source + + + +

spatial distribution of transport parameters ‐ + ‐ +

aquifer structure, connectivity, detection of preferential flow paths and spreading zones

‐ dense monitoring

required ‐ +

Validation of model predictions + + + +

Description of solute transport ‐ non‐reactive + + + +

Description of solute transport ‐ reactive requires long

timesrequires long

times + + times times

(after: Ptak et al. 2004)







X X X X X X



Integral Pumping Tests (x) X

Groundwater monitoringGroundwater monitoring fences (x) (x) X


Tracer tests X (x) (x)Tracer tests X (x) (x)


Monitoring devicesDiffusion sampler

Mini pressure pumps

Multi-level packer system

Conclusions

• A large variety of site investigation methods is available, and many other methods have not been shownother methods have not been shown

• The investigation objectives (have to) dictate which method is used (what is the question to be answered)

• Consider combinations of methods as typically one single method is not sufficient to tackle the investigation objective

• all the shown methods can also be used for management of contaminated site, e.g. in the framework of “traditional” site clean upup

• Always consider quality control

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