Subsurface
Characterization
Dr. Bob Johnson
Argonne National Laboratory
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
Subsurface Characterization
A variety of scenarios can result in subsurface contamination:
 Subsurface releases (e.g., below building foundations, buried
tanks, buried pipelines)
 Old waste disposal practices (e.g., disposal pits, disposal
trenches, etc.)
 Surface soil reworking (e.g., landscaping, construction
activities, etc.)
 Subsurface contaminant migration (e.g., leaching,
contaminated groundwater flow)
 The use of contaminated soils as backfill
The end result is buried contamination that does not
necessarily have a surface footprint.
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
Subsurface Transport Possibilities…
 Most naturally-occurring radionuclides are not particularly
mobile in groundwater with the exception of uranium
 Not necessarily true for fission or activation by-products
– Examples of groundwater mobile radionuclides include Sr-90
and Tc-99
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
Subsurface Characterization is a Challenge
 Surface scans only “see” approximately top 15 cm of soil and
so provide no information on the subsurface
 Subsurface is a 3D problem rather than a 2D problem
 Subsurface issues potentially include both groundwater and
subsurface soils
 Understanding subsurface hydrogeology can be as important
as understanding current contamination extent
 Subsurface characterization is expensive (i.e., can’t afford the
same sampling density that we might with surface soils)
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
Subsurface Characterization Tools
Subsurface characterization tools fall into broad
categories:
Non-intrusive geophysics
 Intrusive sampling (soil and/or groundwater)
 Down-hole scans or ex situ core scans
 Geotechnical/hydro-geological exploration techniques
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
Non-Intrusive Geophysics
 Purpose is to provide information about subsurface structure (e.g.,
presence of tanks, pipelines, geological interface such as
soil/bedrock surface, etc.) important to understanding where
contamination might be and how it might be behaving
 Not good for actually “seeing” contamination
 Several types:
– Conductivity/resistivity methods
– Magnetic methods
– Ground penetrating radar
– Cross-hole resistivity
 Viewing depth varies with soil type
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
Example EM-31 and GWS Maps….
GWS (2x2 NaI) map shows
surface contamination with
limited extent
EM-31 survey suggests
conductivity variations
likely associated with burial
of material with much
larger extent
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
Another Example…Finding Burial Pits…
EM-31
Data
EM-61
GPR Data
Magnetic
Data
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
Intrusive Sampling
 Challenge is to cost-effectively obtain subsurface
soil and/or groundwater samples for analysis
 Unconsolidated media
– Direct push (retrieve intact soil cores)
– Soil augers (e.g., hollow stem auger)
 Consolidated media
– Standard rotary drilling
– Sonic drilling (no use of drilling fluids)
– Directional drilling
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
Example Direct Push Tools…
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
Core Scanning
 Provide information on the vertical
distribution of contamination by
scanning soil cores that have
been retrieved.
 Techniques include:
– Core scanning machines
– Scanning soil cores with a GM or NaI
detector
– Direct measurement of cores with
XRF or LaBr3 detector
 Issues include controlling
background noise for gross
activity detectors and obtaining
suitable detection limits
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
Down Hole Scanning/Logging
1
April 2011 | Argonne National Laboratory, USA
2
3
4
5
6
Depth (ft)
 Typically done with a small NaI
detector (e.g., 1”x1”)
 Stationary gross activity readings
taken at set depths
 Sensitivities depend on radionuclides
of interest:
– Ra-226/Th-232 – single digit pCi/g
– Cs-137 – around 10 pCi/g
– U-238 – tens to 100 pCi/g
– Sr-90/Tc-99/tritium – forget about it
 Useful for establishing contaminant
extent
7
8
9
10
11
12
13
14
5000
10000
15000
20000
cpm
12
IDN and ENVIRONET Training Course
GeoProbe NaI Probe
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
Hydro-geological Characterization
 Many parameters significant to contaminant fate and
transport in groundwater
 Examples include hydraulic conductivity, porosity,
geochemistry, infiltration rates, stratigraphy
 Complete discussion of data collection relative to these
parameters is beyond scope of this presentation
 Note, however, that these parameters can and do vary
significantly spatially, and those variations control
groundwater flow and consequently contaminant
transport
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
BEWARE the SUBSURFACE!!!.....
Things are never as
simple or predictable
as they might first
appear…
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
…The Real World is a Lot More Complicated
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
As an Example……….
MIP (membrane interface probe
with ECD detector)
data for chlorinated
solvents
April 2011 | Argonne National Laboratory, USA
Graphic adapted from Columbia Technologies
IDN and ENVIRONET Training Course
In This Context, the Conceptual Site Model is
Invaluable and Absolutely Essential
 Historical aerial photographs
 Topographical information
 Site layout/as built drawings/buried infrastructure locations
 Anecdotal information about what took place
 Site walk-downs
 Gamma walkover surveys
 Surface soil sampling results
 Non-intrusive geophysics
 Intrusive sampling/characterization information
April 2011 | Argonne National Laboratory, USA
IDN and ENVIRONET Training Course
April 2011 | Argonne National Laboratory, USA