Can GeoelectricaU Methods Be
Used to Monitor NAPL Retried ation?

Dale Werkema, U.S. EPA, ORD, NERL, ESD, Las Vegas, NV, werkema.d@epa.gov

\A/hl	EPA's Strategic Plan includes the research and development of improved methods for evaluating the long-term

performance of non-aqueous phase liquid (NAPL) remediation.

How? Direct current (DC) geoelectrical methods can detect changes in the electrical properties of the subsurface due
to the remediation of light or dense non-aqueous phase liquids (LNAPL or DNAPL).

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GO

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o
u

<

DC geoelectrical method?

pe = a <|>-mS-npw

p e = resistivity of the earth

(]) = fractional pore volume (porosity)

S = fraction of the pores containing fluid

p ; = the resistivity of the fluid

n, a and ni are constants

Curren
source

Measured

H$H |-0nenti"

i|

/ \ / j Lines of

jX j equal potential

Current flow
lines

Measurements within a site will most likely
have the same cf>, S, n, a, and m.

Therefore, pe a pw

or the inverse, conductivity (a), Oe a Ow

LNAPL Biodegradation

50 100
Grain Size

Conductivity (mS/m)
0 15 30

j Silt/Clay
f -A-Sand
r -O-GraveI
^-¦w'-Unco nt.	i

Conductivity [

,	ntaminatedo

Conductivity I
I ~*0~ Microbes |

Conductivity (mS/m)
0 15 30

-80 -40 0
% change
oil degraders
cont. - uncont.

I

~	NoLNAPL

~	Residual LNAPL
£2	Free LNAPL

FH	Dissolved LNAPL

Anomalously high conductivity coincident with LNAPL
zone and high population of oil degrading microbes.

£

o
O

DNAPL Surfactant Remediation

Conductivity vs. Surfactant

Surfactant mixtures increase water conductivity (Ow). This suggests an
increase 111 the geoelectrical conductivity (oe) and shows potential
for the indirect geoelectrical measurement of surfactant remediation
applications at DNAPL sites.

So what? (outcomes)

Results suggest DC geoelectrical measurements have the potential to indirectly monitor remediation.
Geoelectrical methods may be used by OSWER and Regional Project Managers, for example,
to monitor and characterize the remediation of LNAPL and/or DNAPL impacted sites. Furthermore,
geoelectrical methods can be utilized as part of an integrated remediation plan because of their cost
effective, efficient, and geographically remote acquisition capabilities.

Partnerships

U.S. EPA, ORD, NERL, ESD
Western Michigan University
University of Missoun-Rolla

Notice: Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy. Mention of trade names or commercial products does not constitute endorsement or recommendation by EPA for use.

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