Ž .
Journal of Applied Geophysics 44 2000 67–83 www.elsevier.nlrlocaterjappgeo
Mathematical models and controlled experimental studies
Three-dimensional inversion of induced polarization data from simulated waste
1
A. Weller
a,
, W. Frangos
b
, M. Seichter
c
a
Institut fur Geophysik, Technische UniÕersitat Clausthal, Arnold-Sommerfeld-Str. 1,
¨ ¨
D 38678 Clausthal-Zellerfeld, Germany
b
Earth Science DiÕision, Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, CA 94720, USA
c
Institut fur Geophysik und Meteorologie, Technische UniÕersitat Braunschweig, Mendelssohnstr. 3,
¨ ¨
D 38106 Braunschweig, Germany Received 25 March 1998; accepted 13 November 1998
Abstract
Ž .
Ž .
The Idaho National Laboratory INEL Cold Test Pit CTP has been carefully constructed to simulate buried hazardous Ž .
waste sites. An induced polarization IP survey of the CTP shows a very strong polarization and a modest resistivity Ž
. response associated with the simulated waste. A three-dimensional 3-D inversion algorithm based on the simultaneous
Ž .
iterative reconstruction technique SIRT and finite difference forward modelling has been applied to generate a subsurface model of complex resistivity. The lateral extents of the waste zone are well resolved. Limited depth extent is recognized, but
the bottom of the waste appears too deep. With a modelling experiment, the intrinsic polarizability of the waste material is determined. Since IP is a technique for detection of diffuse occurrences of metallic material, this method holds promise as a
method to distinguish buried waste from conductive soil material. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Electrical resistivity; Geoelectrical prospection; Induced polarization; Inversion algorithm
1. Introduction
A variety of radioactive and hazardous waste material has been disposed of over the years at
the Idaho National Engineering Laboratory Ž
. INEL . Precise location is unknown for some
Corresponding author. Tel.: q49-5323-722233; Fax: q49-5323-722320; E-mail: andreas.wellertu-clausthal.de
1
This paper was also published in Journal of Applied Ž
. Geophysics, Vol. 41 1999 31–47. PII no. of original
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article: PII: S0926-9851 98 00036-6.
of the waste dumps. In order to test various methods of non-invasive subsurface waste loca-
tion techniques, a simulated waste pit has been constructed using safe materials, and designed
to resemble old waste pits as closely as possible Že.g., size, depth, order and disorder of contents,
. allowance for deterioration of containers . This
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Cold Test Pit CTP has been investigated by a number of workers using several different meth-
ods. The present work was carried out as part of the Electromagnetic Integrated Demonstration
Ž
. EMID , which also includes an assortment of
Ž electromagnetic techniques
VETEM, 1996; .
Pellerin and Alumbaugh, 1997 .
0926-9851r00r - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž
. PII: S 0 9 2 6 - 9 8 5 1 0 0 0 0 0 0 7 - 0
The CTP was constructed as a 13 = 70 m trench, segmented by transverse berms into cells.
The southernmost cell investigated in the EMID Ž
. project
Fig. 1 contains stacked drums and
boxes and a variety of randomly positioned barrels, pipes, a large metal tank, etc. This
location is referred to as the Large Object Pit Ž
. LOP . The buried drums located in the centre
of the trench include both cardboard and metal Ž
drums containing scrap metal both ferrous and .
non-ferrous and non-metallic materials. The
cardboard drums and wooden boxes have metal- lic rims. The cell is described as being a 3-m
waste seam with about 1.5 m of soil cap, thus the depth of the bottom of the waste is about 4.5
m. The cap is composed of clay-rich soil im- ported from other areas of the INEL complex.
Host material is local soil overlying resistive Snake River basalt.
The EMID project focused mostly on rapid electromagnetic techniques, which rely upon
variations of conductivity. In contrast, the slower
Ž . Ž .
Ž . Ž .
Ž . Fig. 1. Survey layout at the INEL CTP. 1 Boxes, 2 drum stack, 3 crushed drums, 4 steel tank, 5 concrete filled steel
Ž . Ž .
pipe, 6 drums, 7 steel casing over concrete vaults.
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and therefore more expensive induced polar- Ž .
ization IP
method exploits electrochemical phenomena at interfaces between regions of
metallic and electrolytic conduction within a heterogeneous medium.
While the first reported recognition of what Ž
. we now call IP was by Schlumberger 1920 ,
much of its early development sprang from mine warfare research during World War II
Ž .
Grow, 1982; Collett, 1990 . The principal ap- plication of IP has been prospecting for dissemi-
nated base and precious metal ore deposits, a technology transfer of the wartime research
Ž .
Bleil, 1953; Collett, 1990 . In an early investi- gation of cultural contamination of domestic
Ž .
water supplies, Angoran et al. 1974 used IP to trace town dumps in the state of Massachusetts,
Ž .
USA. Frangos and Andrezal 1994 reported IP measurements over a landfill and toxic waste
pond in Slovakia. The increase in resolution of small polarization effects in sediments enabled
the successful application of IP measurements in environmental investigations such as the de-
tection of contaminants or the determination of
Ž hydraulic properties
Vanhala et al., 1992; .
Weller and Borner, 1996 .
¨
2. Induced polarization and complex conduc- tivity
