Kansas Geological Survey, Open File Report 99-40
Part of the Direct Push Methods for Hydrostratigraphic Characterization Project
Hydrostratigraphic Characterization of Unconsolidated
Alluvial Deposits with Direct-Push Sensor Technology
J.J. Butler, Jr., J.M. Healey, and L. Zheng
Kansas Geological Survey
The University of Kansas
Lawrence, KS 66047
|
|
W. McCall
Geoprobe Systems
601 North Broadway
Salina, KS 67401
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M. K. Schulmeister
Kansas Dept. of Health and Environment
Bureau of Environmental Remediation,
Bldg 740, Forbes Field,
Topeka KS, 66620
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KGS Open-File Report 99-40
Prepared for presentation at
The Geological Society of America
1999 Annual Meeting in Denver, Colorado
October 27, 1999
Abstract
The incorporation of down-hole sensors into direct-push equipment
provides a novel method for the rapid and detailed hydrostratigraphic
characterization of unconsolidated deposits. The potential of this
technology was assessed through two field investigations in
unconsolidated alluvial deposits (60-70 ft thick) using downhole
electrical conductivity and cone penetrometer sensors. At both sites,
these sensors served as excellent tools for the lateral and vertical
delineation of hydrostratigraphic units. Electrical conductivity surveys
at a lateral spacing of less than 2 to more than 200 feet graphically
demonstrated the spatial variability inherent in alluvial deposits.
Core samples, hydraulic tests, water-level data, and well-bore
geophysics corroborated the information provided by the direct-push
sensors. The results of these investigations indicate that this
technology can provide detailed information about the hydrostratigraphic
framework of unconsolidated deposits in a rapid and cost efficient
manner without generation of cuttings or the need for a pre-existing
borehole or well.
Introduction
In the last decade, direct-push (DP) technology has become a viable
alternative to conventional drilling methods for sampling soils,
sediments and ground water in unconsolidated formations. This
technology has been particularly widely used for a range of activities
in support of environmental site investigations. The DP technology
utilized in this study employs high-frequency (~ 30 Hz) percussion
hammers and hydraulic slide systems, mounted on conventional pick-up
trucks, vans or specialized track machines, to rapidly advance pipes
into the subsurface. Advantages of DP technology over conventional
drilling methods include (Thornton et al., 1997):
- smaller less-expensive systems with greater mobility
- simpler operation with less physical labor required
- no generation of drill cuttings
- less disturbance of the subsurface
In this presentation, we will demonstrate the level of
hydrostratigraphic detail that can be obtained by coupling DP technology
with a new generation of down-hole sensors.
DP Electrical Conductivity Logging
Direct-push electrical conductivity logging (DP e-logging) is a
modification of conventional borehole resistivity logging. A
significant difference between the e-logging methods of borehole
geophysics and DP e-logging is that no pre-existing borehole or well is
required for the latter. The DP e-logging probe is simply attached to
the leading end of the tool string and advanced into the subsurface
using the percussion hammer and hydraulic slides on the DP vehicle. The
DP e-logging probe used in this work is a Wenner array design that is 15
inches long with a maximum diameter of 1.5 inches. A current is applied
to the outer two electrodes and the voltage is measured across the inner
two electrodes (Christy et al., 1994). The measurement is transmitted
via a pre-strung coaxial cable to signal processing hardware at the
surface where a real-time log (reading every 0.05 ft) is displayed on a
laptop computer. A string pot mounted on the mast of the DP unit tracks
the depth and speed of advancement of the Wenner array probe. In this
study, a two-person team routinely completed 70 foot DP e-logs in about
one hour.
Figure 1--Schematic showing truck with direct-push tool attached and
example log.
Figure 2--DP e-logging probe. Scale bar is 3 inches total.
Figure 3--Example electrical-conductivity log and site stratigraphy.
Site Descriptions
Figure 4--Location map of two study areas.
The Geohydrologic Experimental and Monitoring Site (GEMS)
GEMS is an experimental research area of the Kansas Geological Survey
located in the floodplain of the Kansas River just north of Lawrence,
Kansas. Established in the late 1980s, GEMS overlies approximately 70
feet of alluvial deposits of the Kansas River. These unconsolidated
Holocene sediments overlie and are adjacent to materials of
Pennsylvanian and Pleistocene age. The alluvial facies assemblage at
GEMS is a complex system of stream-channel sand and overbank deposits
that essentially consists of 35 feet of clay and silt (with minor
amounts of silty sand) overlying 35 feet of coarse sand and gravel. The
site map shows the locations of the two sampling transects (A-A' and
B-B') that will be referred to in this poster.
Figure 5--Map of GEMS site showing location of cross sections.
Figure 6--E-Logs at GEMS--A to A' Cross Section. A
larger version
of this figure is available.
Figure 7--E-Logs at GEMS--B to B' Cross Section. A
larger version
of this figure is available.
Figure 8--GEMS site--Electrical-conductivity profile from A to A'. A
larger version
of this figure is available.
Figure 9--GEMS site--Electrical-conductivity profile from B to B'. A
larger version
of this figure is available.
Site Description
Salina Site
This site is located in the city of Salina in central Kansas on alluvial
deposits of the Smoky Hill River just a few miles upstream of its
confluence with the Saline River. The Quaternary Age alluvial deposits
at this site consist of granitic sands and gravels overlain by silts and
clayey silts. These deposits rest unconformably on the Permian shale
that forms a locally extensive aquitard. The site map shows the
sampling locations and traverses (A-A', B-B') referred to in this
poster.
Figure 10--Map of Salina site showing location of cross sections.
Figure 11--E-Logs from Salina site--A to A' Cross Section. A
larger version
of this figure is available.
Figure 12--E-Logs from Salina site--B to B' Cross Section. A
larger version
of this figure is available.
Figure 13--Salina site--Electrical-conductivity profile from A to A'. A
larger version
of this figure is available.
Figure 14--Salina site--Electrical-conductivity profile from B to B'. A
larger version
of this figure is available.
Assessment and Comparison
The DP e-log provides a record of electrical conductivity versus depth
at a level of detail that is not commonly obtained in hydrogeologic
investigations. In order to assess the value of this log for
hydrostratigraphic studies, additional data were collected at both sites
using other methods. A standard focussed induction borehole geophysical
log was run in a monitoring well at GEMS less than four feet from the
location of a DP e-log. The focussed induction tool provided a highly
smoothed version of the DP e-log. At both sites, cores were collected
adjacent to locations of DP e-logs. Core analysis found that many of
the variations observed on the DP e-logs were produced by lithologic
variations. Hydraulic conductivity estimates from slug tests at GEMS in
the sand-gravel and silt-sand intervals, and from permeameter analyses
of samples from the Salina site were in agreement with the relative
differences in electrical conductivity shown on the DP e-logs. In
addition, water-level data at GEMS indicated a hydraulic head difference
of greater than three feet across the zone of high electrical
conductivity separating the sand-gravel and silt-sand intervals, thereby
confirming the existence of the tight clay layer expected from the e-log
data. Finally, CPT logs adjacent to locations of DP e-logs displayed
sand-gravel and clay-silt distributions similar to those inferred from
the e-logs.
Figure 15--Focussed induction and direct-push EC comparison. Separation
distance 3.7 ft. A larger versionof this
figure is available.
Figure 16--E-Log and Lithologic Profile at GEMS.
A larger versionof this
figure is available.
Figure 17--E-Log and Lithologic Profile at Salina Site.
A larger versionof this
figure is available.
Figure 18--Salina Site Comparison--Sieve Results from Lower Zone.
A larger versionof this
figure is available.
Figure 19--Salina Site Comparison--Sieve Results from Upper Zone.
A larger versionof this
figure is available.
Figure 20--CPT and EC logs: GEMS comparison 1.
A larger versionof this
figure is available.
Figure 21--CPT and EC logs: GEMS comparison 2.
A larger versionof this
figure is available.
Conclusion
In this presentation, we demonstrated the effectiveness and efficiency
of direct-push sensors for providing detailed information about the
hydrostratigraphic framework in unconsolidated alluvial deposits to
depths greater than 70 feet. The DP e-logging data was in agreement
with information obtained from wellbore geophysics, core samples,
hydraulic tests, and water-level data. The results of this work
indicate that DP e-logging has considerable potential as a tool for the
hydrostratigraphic characterization of unconsolidated deposits. The
variations seen in the e-logging responses at the two sites described
here appear to be primarily a function of lithology. For sites where
the specific conductance of the groundwater varies significantly,
auxiliary data are required to distinguish e-log responses produced by
lithologic variations from those produced by variations in water
chemistry (Mack, 1993).
This poster is a progress report on one component of an ongoing
cooperative research project directed at the development and evaluation
of direct-push techniques for the detailed hydraulic, geochemical, and
stratigraphic characterization of unconsolidated deposits. Further
reports will be presented at the Special Session on Direct Push Sensor
Technology to be held at the Spring 2000 Meeting of the American
Geophysical Union in Washington, DC (May 30-June 3, 2000).
References
Christy, Collin D., T.M. Christy, V. Wittig, 1994. A Percussion Probing
Tool for the Direct Sensing of Soil Conductivity. In: Proceedings of the
Eighth National Outdoor Action Conference and Exposition. NGWA.
Geoprobe Systems, 1998. Geoprobe SC400 Soil Conductivity Probe, Product
Bulletin No. PBSC40398. Kejr Inc., Salina, Kansas.
Mack, Thomas J., 1993. Detection of Contaminant Plumes by
Borehole Geophysical Logging. Ground Water Monitoring and
Remediation. v. 13, no. 1.
Thornton, Daniel, S. Ita, K. Larsen, 1997. Broader Use of Innovative
Ground Water Access Technologies. In: Superfund XVIII Conference
Proceedings, Vol. 2.
Kansas Geological Survey
Updated Nov. 24, 1999
Scientific comments to Jim Butler
Web comments to webadmin@kgs.ku.edu
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