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Characterizing
Ground-Water Chemistry and Hydraulic Properties of Fractured-Rock Aquifers
Using the Multifunction Bedrock-Aquifer Transportable Testing Tool (BAT3)
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Shapiro, A. M., 2001, Characterizing Ground-Water Chemistry and Hydraulic
Properties of Fractured Rock Aquifers Using the Multifunction Bedrock-Aquifer
Transportable Testing Tool (BAT3): U.S.
Geological Survey Fact Sheet FS-075-01, 4 p.
Table of Contents
Characterizign
Fluid Movement and Chemical Transport in Fractured-Rock Aquifers
In many aquifers in the Nation,cracks, joints,and faults (collectively
referred to as "fractures ") act as the principal conduits of ground-water
flow. In these fractured-rock aquifers,water-resources managers and hydrologists
responsible for issues ranging from water supply to the restoration of
contaminated ground water need to assess the availability of ground water
and the potential for contaminant migration.
 |
Figure 1.
Oriented digital image (S=South,W=West, N=North,E=East)of a borehole
wall and core synthesized from a digital borehole camera. Geophysical
logging tools,such as the digital borehole camera (see,for example,
Williams and Lane,1998),provide critical information about borehole
conditions to design the location of hydraulic tests and the collection
of water samples conducted by the Multifunction BAT 3. |
Water-resources managers and hydrologists drill boreholes in fractured-
rock aquifers to collect hydraulic and chemical data needed to characterize
fluid movement and chemical transport. Data collected from boreholes in
fractured-rock aquifers,however,may yield ambiguous interpretations because
a borehole acts as a high permeability pathway that connects fractures,which
previously were unconnected. Open boreholes act to integrate hydraulic
and chemical data from all fractures intersecting the borehole. Collecting
hydraulic and chemical data in open boreholes does not quantify variability
in ground-water chemistry or hydraulic properties,which is crucial in
conceptualizing fluid movement and chemical transport in fractured-rock
aquifers.
Borehole packers reduce or eliminate the effect that open boreholes have
on the collection of hydraulic and chemical data. Borehole packers are
pneumatic or mechanical devices that isolate sections of a borehole by
sealing against the borehole wall. Hydraulic tests or collecting ground-
water samples for chemical analyses then can be conducted on the isolated
section of the borehole.
 |
Figure 2.
A borehole packer with inflatable bladder is being prepared for installation
in a bedrock borehole. The packer is supported by a pipe and lowered
down the borehole using a truck-mounted winch. |
Many types of hydraulic tests and chemical sampling configurations can
be designed using borehole packers. Thus, equipment used for hydraulic
testing and collecting ground-water samples for chemical analyses usually
has been constructed for a specific need at a specific site. The physical
dimensions of the downhole equipment and the need for various peripheral
components at land surface for data collection and data processing have
made borehole testing equipment cumbersome and not readily portable from
site to site.
The Multifunction
BAT 3
The U.S. Geological Survey (USGS)has a patent pending on a Multifunction
Bed- rock-Aquifer Transportable Testing Tool (BAT 3 ).The equipment
is designed to per- form the following operations by isolating a fluid-filled
interval of a borehole using two inflatable packers:
- collect water samples for chemical analysis,
- identify hydraulic head,
- conduct a single-hole hydraulic test by withdrawing water,
- conduct a single-hole hydraulic test by injecting water,and
- conduct a single-hole tracer test by injecting and later withdrawing
a tracer solution.
The equipment also can be configured to conduct these operations with
only one of the borehole packers inflated,dividing the borehole into two
intervals (above and below the inflated packer). The Multifunction BAT 3 is designed with two inflatable packers and three pressure transducers
that monitor fluid pressure in the test interval (between the packers),as
well as above and below the test interval; pressure transducers above
and below the test interval are used to ensure that the borehole packers
seal against the borehole wall during applications. The Multifunction
BAT 3 is designed with digital data- acquisition capabilities to collect
time- varying pumping or fluid-injection rates and fluid-pressure responses.
Data acquisition is integrated with a laptop computer to store and display
data in real time. Interpretation of fluid-pressure responses to pumping
or fluid injection are also integrated with the software on the laptop
computer to estimate hydraulic properties of the test interval in real
time.
 |
Figure
3.
This diagram illustrates the Multifunction BAT 3 in a bedrock borehole
with borehole packers inflated to seal against the borehole wall.
The transducer shrouds house the fluid-pressure transducers,the pump
shroud houses the submersible pump,and the fluid-injection shroud
houses a fluid-injection valve. Not shown in the diagram are the transducer
wires,electrical wires and tubing that extend up the borehole to land
surface and control the operation of the downhole equipment. The length
of the test interval is adjusted by adding additional sections of
pipe between the fluid-injection shroud and the bottom packer. The
equipment is lowered or raised in the borehole using steel pipe or
a cable attached above the transducer shrouds. |
The downhole equipment of the Multifunction BAT 3 is designed for easy
and rapid assembly with a test interval that can be adjusted to accommodate
different borehole conditions. The downhole and data-acquisition equipment
is designed to fit in a series of crates that can be shipped by overnight
carriers. The downhole equipment can be lowered down a borehole using
steel pipe,or a cable and winch. Prototypes of the Multifunction BAT 3
have been developed for applications in 4-and 6-inch (10.1 -and 15.2-centimeter)diameter
boreholes and have been used to characterize fractured rock for water-supply
and ground-water contamination projects, including the characterization
of hydraulic properties and collection of water samples at sites of ground-water
contamination by dense non-aqueous phase liquids (DNAPLs).
 |
Figure 5.
A prototype of the multifunction BAT 3 supported from truck-mounted
winch as it is being prepared for installation in a borehole. Shown
in the photograph are (A)inflatable packers,(B)transducer shrouds,(C)pump
shroud,and (D)fluid-injection shroud. Tubing and wires (E)used to
control the downhole equipment extend from the transducer shrouds.
In this configuration of the Multifunction BAT 3 ,pipe has been added
in the test interval to extend the test interval to approximately
8 feet; the minimum length of the test interval in this configuration
is approximately 5 feet. |
 |
Figure 6.
The prototype of the data-acquisition and downhole components of the
Multifunction BAT 3 is designed to fit in five shipping crates:(A)top
packer,transducers and submersible pump,(B) bottom packer,(C)flow
meters,(D)data-acquisition equipment,(E)controls for downhole components. |
Characterizing
Hydraulic Properties of Fractures
Sections of a borehole containing highly transmissive fractures are most
easily tested by withdrawing water,whereas fractures with low transmissivity
are tested by injecting small volumes of fluid. The Multifunction BAT
3 is configured with both a submersible pump and a fluid-injection
apparatus in the test interval to accommodate hydraulic tests that either
withdraw or inject water. With this capability,the Multifunction BAT 3
can estimate transmissivity ranging over approximately 8 orders of magnitude.
Hydraulic tests conducted on isolated sections of the borehole can be
interpreted to provide a profile of transmissivity as a function of depth
in the borehole. The transmissivity profile can be used in conjunction
with other site information to develop an understanding of the controls
on fluid movement and chemical transport in fractures (Shapiro and others,1999),for
example,transmissivity can be correlated with the orientation of fractures,rock
type, depth and other physical and geologic factors. In addition,the transmissivity
can be used to quantify the volume of fluid moving through fractures in
the aquifer (Hsieh and Shapiro,1996).
(click to enlarge) |
Figure
7.
The open and oriented view of fractures on the borehole wall is interpreted
from acoustic televiewer log conducted in the borehole (see,for example,Williams
and Lane,1998).The transmissivity of sections of the borehole containing
fractures is estimated by either injecting or withdrawing fluid,and
the length of the test interval is shown as the thickness of the tested
section. The transmissivity of the test interval is determined by
assuming steady-state radial flow (Shapiro and Hsieh,1998);other interpretations
of the measured fluid-pressure responses can also be applied. The
transmissivity of the tested intervals varies over more than 4 orders
of magnitude above the detection limit of the equipment. The detection
limit for the transmissivity using the prototype of the Multifunction
BAT 3 is approximately 10 -4 square feet per day (~10 -10 square meters
per second),which is dictated by the sensitivity of the flow meter
used to monitor fluid injection rates;the lower limit of the flow
meter used in the current configuration of the Multifunction BAT 3
is approximately 9 x 10 -4 gallons per minute (~3.4 x 10 -3 liters
per minute).The maximum transmissivity that can be estimated is dependent
on the capacity of the submersible pump. |
Collecting
Water Samples for Chemical Analyses
In open boreholes intersected by multiple fractures,the contribution of
water from fractures to the pump discharge is weighted according to the
transmissivity of the fractures,regardless of the location of the pump
intake. This results in an integrated water sample that is biased to the
chemical signature of those fractures with the highest transmissivity.
Integrated concentrations may be appropriate in assessing the quality
of domestic and public supply wells,but they are not useful in delineating
the spatial distribution of contaminated ground water,or understanding
the natural variability in ground-water chemistry.
The Multifunction BAT 3 isolates a short interval of the borehole and
reduces the volume of water necessary to purge from the borehole prior
to obtaining a water sample that is representative of the fluid in the
fractures,rather than the borehole fluid. Pressure transducers monitoring
fluid-pressure responses above and below the test interval ensure that
fluid is being withdrawn from the test interval. The submersible pump
in the prototype of the Multifunction BAT 3 can achieve flow rates as
low as 0.026 gallon per minute (0.1 liter per minute)to accommodate low-flow
sampling protocols (Puls and Barcelona, 1996).
|
Dichlorodifluoromethane
(CFC-12)concentrations in ground water collected from Borehole H1,Mirror
Lake wastershed,Grafton County,New Hampshire
|
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Test
Type
|
Test
Interval
(feet above mean sea level)
|
CFC-12
Concentration
(picograms per kilogram water)
|
|
Open
borehole
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684.4-459.0
|
163.2
|
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Multifunction
BAT3
|
656.8-641.7
|
91.2
|
|
Multifunction
BAT3
|
585.6-570.9
|
73.3
|
| *Denotes
saturated section of the open borehole. The open borehole is 732.0
-459.0 feet above mean sea level;the water level in the borehole is
below the bottom of the borehole casing. |
Table 1.
Chlorofluorocarbons (CFCs),such as CFC-12,are synthetic gases that
are released in the atmosphere from manufacturing. The historical
record of CFCs in the atmosphere and their concentration in ground-water
recharge is used to determine ground-water residence times (Busenberg
and Plummer,1992).Water samples were collected from borehole H1 (see
figure 7 for the description of fracturing and transmissivity in the
borehole)and analyzed for CFC-12. Samples were collected in borehole
H1 by pumping from the open borehole and by hydraulically isolating
intervals of the borehole using borehole packers. Chemical field parameters,
such as pH,temperature,specific conductance,and dissolved oxygen,were
allowed to stabilize in the pump discharge prior to collecting water
samples. The CFC-12 concentration of water in the open borehole prior
to pumping was most likely near the atmospheric equilibrium CFC-12
concentration at the time of sampling (approximately 323 picograms
per kilogram).The water sample collected from the open borehole is
most likely a mixture of water in the borehole and water drawn from
various fractures. The CFC-12 concentrations taken by isolating discrete
intervals in the borehole are appreciably less than the CFC-12 concentration
of water withdrawn from the open borehole. The water samples collected
by isolating discrete intervals of the borehole are more indicative
of the water in the aquifer than the integrated water sample collected
from the open borehole. |
References
Busenberg, E., and Plummer, L.N.,1992, Use of chlorofluorocarbons (CCl
3 F and CCl 2 F 2) as hydrologic tracer and age-dating tools- The alluvium
and terrace system of central Oklahoma: Water Resources Research, v.28,
no.9, p.2257-2283.
Hsieh, P.A., and Shapiro, A.M., 1996, Hydraulic characteristics of fractured
bedrock underlying the FSE well field at the Mirror Lake site, Grafton
County, New Hampshire, in Morganwalp, D.W., and Aronson, D.A., eds., U.S.Geological
Survey Toxic Substances Hydrology Program -Proceedings of the Technical
Meeting, Colorado Springs, Colorado, September 20-24,1993: U.S.Geological
Survey Water-Resources Investigations Report 94-4015, p.127-130.
Puls, R.W. and Barcelona, M.J., 1996, Low-flow (minimal drawdown) ground-water
sampling procedures: U.S.Environmental Protection Agency, Ground Water
Issue Report, EPA/540/S-95/504, Ada, Oklahoma,12 p.
Shapiro, A.M.and Hsieh, P.A., 1998, How good are estimates of transmissivity
from slug tests in fractured rock? Ground Water, v.36, no.1, p.37-48.
Shapiro, A.M., Hsieh, P.A., and Haeni, F.P., 1999, Integrating multidisciplinary
investigations in the characterization of fractured rock, in Morganwalp,D.W.,and
Buxton, H.T., eds., U.S.Geological Survey Toxic Substances Hydrology Program--
Proceedings of the Technical Meeting, Charleston,South Carolina, March
8-12, 1999--Volume 3 of 3--Subsurface Contamination from Point Sources:U.S.Geological
Survey Water-Resources Investigations Report 99-4018C, p.669-680.
Williams, J.H., and Lane, J.W.,1998, Advances in borehole geophysics
for ground-water investigations: U.S.Geological Survey Fact Sheet 002-98,
4 p.
For More
Information
For more information about licensing of this and other patents and for
cooperative research opportunities with the U.S.Gelogical Survey, please
contact:
Technology Enterprise Office
U.S.Geological Survey
12201 Sunrise Valley Drive, MS 211
Reston,VA 20192
Tel:(703)648-4403
Fax:(703)648-4408
e-mail:
For information about the technical details of this invention, please
contact the inventor:
Allen M.Shapiro
U.S.Geological Survey
12201 Sunrise Valley Drive,MS 431
Reston,VA 20192
Tel:(703)648-5884
Fax:(703)648-5274
e-mail:
More information about characterizing fluid movement and chemical transport
in fractured rock aquifers can be found at the following web sites:
U.S.Geological Survey, National Research Program, Transport Phenomena
in Fractured Rock: http://water.usgs.gov/nrp/proj.bib/shapiro.html
Ground-Water Flow and Transport in Fractured Rock, Mirror Lake, New
Hampshire:
http://toxics.usgs.gov/sites/mirror_page.html
The Fate of DNAPL in Fractured Rocks,Naval Air Warfare Center Research
Site, Trenton, New Jersey: http://toxics.usgs.gov/sites/nawc_page.html
U.S.Geological Survey, Office of Ground Water, Branch of Geophysical
Applications and Support: http://water.usgs.gov/ogw/bgas.
Additional information on the fate and transport of toxic substances
in the environment can be obtained at the U.S.Geological Survey Toxic
Substances Hydrology Program web site: http://toxics.usgs.gov.
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