# Characterization of Subsurface DNAPL Movement with Ground Penetrating Radar and Inverse Multiphase Flow Simulations

*By* Raymond H. Johnson

Ph.D. Thesis, Colorado School of Mines, 2003

## Abstract

The presence of dense non-aqueous phase liquid (DNAPL) source zones in
the subsurface is a limiting factor in the remediation of sites affected
by the uncontrolled release of DNAPLs. For successful remediation, the
distribution of the DNAPL source zone must be characterized and the
DNAPL locations in relation to material permeability contrasts at large
and small scales will determine the effectiveness of alternative
remedial techniques. The goal of this research is to provide the
necessary information to determine the best remedial strategies. Four
related investigations evaluate the potential for using ground
penetrating radar and inverse multiphase flow simulations to
characterize subsurface DNAPL movement and identify the strengths and
limitations of the procedure. The following four paragraphs are the
abstracts from each of those investigations, which are presented in
Chapters 2 through 5 of this dissertation.

![](media/image1.pct)

For accuracy, an iterative Bruggeman-Hanai-Sen (BHS) mixing model with
an air/water/sand system must consider which two-material end member
(air/sand or water/sand) to use as the matrix. For a given porosity, a
new weighted BHS model provides the best match to measured data. Two BHS
curves, one with air/sand as the matrix and one with water/sand as the
matrix, are weighted based on the water saturation.

![](media/image2.png){width="3.5625in" height="2.220138888888889in"}

Perchloroethylene (PCE) saturations determined from GPR surveys are used
as observations for inversion of multiphase flow simulations of a PCE
injection experiment, allowing for the estimation of optimal intrinsic
permeability values. Synthetic simulations reveal that saturation data
alone are sufficient to estimate optimal intrinsic permeability values,
but the character and magnitude of error in the saturation data are
critical to accurate estimation. The resulting fit statistics and
analysis of residuals (observed minus simulated PCE saturations) are
used to improve the conceptual models of permeability zones and
capillary pressure-saturation relationships. Remaining bias in the
residuals is attributed to the violation of assumptions (lack of flat,
infinite, horizontal layers) in the one-dimensional GPR interpretation
due to multidimensional influences. However, this bias does not affect
the calculation of the optimal permeability values. The effort to
improve model fit and reduce residual bias decreases simulation error
even for an inversion based on biased observations. This effort is thus
warranted and provides information on bias in observation data when this
bias is otherwise difficult to assess.

![](media/image3.jpeg){width="2.6333333333333333in"
height="4.022916666666666in"}

A laboratory-scale DNAPL injection is monitored using ground penetrating
radar (GPR). Saturation of DNAPLs, determined using the GPR data,
provides calibration data for multiphase flow simulations. This paper
investigates the value of GPR-derived DNAPL saturations as observations
for inversion of multiphase flow simulations for the purpose of
characterizing subsurface heterogeneities. The capillary
pressure-saturation function and intrinsic permeability of the #45
Ottawa sand used in the experiment is measured, but the permeability
varies over an order of magnitude once it is sifted into a tank. Inverse
multiphase fluid flow simulations are used to estimate intrinsic
permeabilities and the resulting fit statistics and analysis of
residuals (observed minus simulated DNAPL saturations and observed minus
simulated injection rates) are used to improve the conceptual model of
permeability heterogeneities. An inverted simulation with homogeneous
sand produces a permeability value that is 15% less than the measured
vertical permeability. However, the fit statistics and residuals
indicate an incorrect conceptual model of permeability. Additional
simulations are explored using different conceptual models of
permeability zones. These simulations indicate the importance of
fine-scaled permeability variations and lead to an improved fit of
simulated versus observed DNAPL mass distribution and injection rates.
Inversion of the multiphase flow simulation is non-unique with respect
to the geometry and permeability values of those zones. These
fine-scaled permeability variations are imaged by the GPR data, but the
interpretation of the geometry of the zones is non-unique. Future
application of GPR and inverse multiphase flow simulations to determine
DNAPL flow must include a procedure to minimize this geometry
non-uniqueness in order to completely identify smaller-scale
permeability contrasts.

![](media/image4.png){width="2.252755905511811in"
height="1.4181102362204725in"}![](media/image5.png){width="2.336220472440945in"
height="1.8771653543307087in"}

### Full document 

(<http://minerals.cr.usgs.gov/publications/Johnson_thesis.pdf>, PDF
Format, 8.9 MB)

### Thesis Publications

Each thesis chapter will be published as individual research papers. The
current publications as of October, 2003 are:

Johnson, R.H., and Poeter, E.P., 2003, Interpreting DNAPL saturations in
a laboratory-scale injection with GPR data and direct core measurements:
U.S. Geological Survey Open-File Report 03-349, 40 p.
(<http://pubs.usgs.gov/of/2003/ofr-03-349>)

# 

### Related Publications

Johnson, R.H., and Poeter, E.P., 2002, Key factors for characterizing
DNAPLs within heterogeneous aquifers using ground penetrating radar
\[abs.\]: Geological Society of America, Abstracts with Programs -- 2002
Annual Meeting.
(<http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_40655.htm>)

Johnson, R.H., and Poeter, E.P., 2001, Inverting multiphase flow
simulations with DNAPL saturation observations estimated from
geophysical surveys *in* Proceedings of the MODFLOW 2001 and other
Modeling Odysseys, eds. Poeter, Zheng, and Hill, International Ground
Water Modeling Center, Colorado School of Mines, Golden, CO, 976 p.

Johnson, R.H., Sneddon, K., Olhoeft, G., Poeter, E., McCray, J., and
Powers, M., 1999, The simultaneous use of inverse modeling and ground
penetrating radar data to enable the successful use of DNAPL flow models
for design of remedial action \[abs.\]: Geological Society of America,
Abstracts with Programs -- 1999 Annual Meeting.
(<http://rock.geosociety.org/absindex/annual/1999/51013.htm>)

Poeter, E.P., and Johnson, R.H., 2002, Residual bias in a multiphase
flow model: calibration and predition, in Calibration and Reliability
*in* Groundwater Modeling: A Few Steps Closer to Reality (Proceedings of
ModelCARE'2002, Prague, Czech Republic), International Association of
Hydrological Sciences Redbook, Publ. No. 277, p. 259-266.
(<http://www.cig.ensmp.fr/~iahs/redbooks/a277/27736.htm>)

> Link to slide show presented at the ModelCARE'2002 conference is
> <http://www.mines.edu/~epoeter/research/gprdnapl/slides_ep_ModelCare2002/ModelCare2002_gpr_dnapl.htm>

Sneddon, K.W., Powers, M.H., Johnson, R.H., and Poeter, E.P., 2002,
Modeling GPR data to interpret porosity and DNAPL saturations for
calibration of a 3-D multiphase flow simulation: U.S. Geological Survey
Open File Report 02-451, 29 p.
(<http://pubs.usgs.gov/of/2002/ofr-02-451/>)