profiling transmissivity and contamination in fractures intersecting boreholes usepa-usgs fractured...
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Profiling Transmissivity and Contamination in Fractures
Intersecting Boreholes
USEPA-USGS Fractured Rock WorkshopEPA Region 2
14 January 2014
Claire Tiedeman and Tom Imbrigiotta, USGS
Profiling Transmissivity and Contamination in Boreholes 2
Motivation: Hydraulic Conductivity Varies byOrders of Magnitude in Fractured Rock
This variability results in complex groundwater flow and contaminant transport paths
Profiling Transmissivity and Contamination in Boreholes 3
Characterizes permeability variability with depth. Provides quantitative order-of-magnitude T estimates at a
scale of a few meters around borehole. Methods:
Profiling Transmissivity in Boreholes
Straddle Packer Testing
FluteLiner Installation
Borehole Flow Logging
Profiling Transmissivity and Contamination in Boreholes 4
Packer Testing Equipment
Profiling Transmissivity and Contamination in Boreholes 5
To determine depths of test intervals, use results from geophysical logging:
Acoustic & optical televiewer: Identify fracture locations Caliper: Avoid placing packers on fractured or rough borehole wall sections Flow logs: First cut at revealing permeable fractures
Overview of steps: Lower packers to first interval to be tested. Measure stabilized water levels before and after packer inflation, so that
ambient hydraulic head can be calculated. If interval is permeable enough, conduct a hydraulic test by pumping.
During the test, conduct geochemical sampling. If interval is not permeable enough to pump, conduct hydraulic test by
fluid injection. No geochemical sampling. Move packers to the next interval to be tested.
Transmissivity Profiling using Straddle Packers
Profiling Transmissivity and Contamination in Boreholes 6
After packer inflation, allow pressure to stabilize in test interval. Turn on pump. Datalogger records pumping rate, pressure in test interval, and
pressure in borehole above and below interval. Software shows real-time data.
Pressure in test interval: If becoming extremely low: Stop, perform injection test If not changing much: Interval may be too transmissive to conduct a
hydraulic test with the available pump Continue pumping until pressure roughly stabilizes – 10-20 min.
(Geochemical sampling will require longer pumping). Turn off pump.
Hydraulic Tests by Fluid Pumping – Permeable Intervals
Profiling Transmissivity and Contamination in Boreholes 7
After packer inflation, allow pressure to stabilize. Start injecting water from up-hole tank. Tank can be at
atmospheric pressure or higher. Record injection rate and pressures. Software shows real-time
data. Continue injection until pressure roughly stabilizes. Tests are
usually run for 10 to 20 minutes. If using a pressurized water tank, increase tank pressure and
conduct a second injection test. Conducting tests at two pressures allows evaluating if results are repeatable, and if so, increases confidence in T estimate.
Hydraulic Tests by Fluid Injection – Less Permeable Intervals
Profiling Transmissivity and Contamination in Boreholes 8
Theim equation for steady-state radial
flow to a pumping well
Profiling Transmissivity and Contamination in Boreholes 9
T values calculated by Theim equation are order-of-magnitude estimates because:
Test conditions typically do not perfectly conform to the conditions assumed by the Theim equation (steady-state purely radial flow with constant Q)
Uncertainty and variability in measurements of Q Uncertainty in radius of influence of test (this uncertainty has a much
smaller effect because the logarithm of R appears in the equation). Because of the large range of T at fractured rock sites, these
order-of-magnitude estimates are still valuable! These limitations apply to T estimates from both straddle
packer and FLUTe liner methods
Limitations of Transmissivity Estimates
Profiling Transmissivity and Contamination in Boreholes 10
Crystalline Rock
Profiling Transmissivity and Contamination in Boreholes 11
Sedimentary Rock
Profiling Transmissivity and Contamination in Boreholes 12
Evert liner into borehole. Borehole water below bottom
of liner is pushed into the rock. Flow rate into rock over a
borehole interval is calculated from liner descent velocities and ‘excess head’ that drives liner installation.
Transmissivity calculated from this flow rate.
Transmissivity Profiling using the FLUTe
Installation of Liner
From Carl Keller
Profiling Transmissivity and Contamination in Boreholes 13
The 3 methods compare well for the high-T intervals.
Greater differences between packer and FLUTe results for lower-T intervals.
Comparison of T Estimates in Schist
Packers FLUTe Flow Logging
Profiling Transmissivity and Contamination in Boreholes 14
FLUTe: Cost-effective means of obtaining T estimates if liner is
installed to prevent cross-contamination. Simpler equipment and easier to conduct Potentially has higher spatial resolution (but small-scale
variability may be caused by borehole effects). Packers:
Conditions conform much better to assumptions of Theim equation, so T estimates are likely more accurate.
Lower detection limit for T. In addition to T estimates, tests yield ambient heads of
packed off intervals, and opportunity for sampling geochemistry.
Comparison of Packers and FLUTe for T Profiling
Profiling Transmissivity and Contamination in Boreholes 15
Identification of high T fractures that may be advective contaminant transport pathways.
Identification of low T fractures and rock intervals where diffusion is likely a dominant transport process.
Use T results together with contaminant and geochemical profiling results, ambient hydraulic head estimates, and other borehole information to guide design of multilevel monitoring systems.
Summary: Value of Information from Transmissivity Profiling
Profiling Transmissivity and Contamination in Boreholes 16
Water-quality profiling conducted in same intervals being pumped for transmissivity testing
Samples collected using a submersible pump installed between two packers
Sampling method Water pumped to surface through splitter and flow-
through cell Field WQ parameters measured to stability Samples collected for VOCs and inorganics
Water-Quality Profiling
Profiling Transmissivity and Contamination in Boreholes 17
Water-Quality Sampling
Profiling Transmissivity and Contamination in Boreholes 18
1 10 100 1,000 10,000 100,0000
10
20
30
40
50
60
70
80
90
100
110
120
VOCs vs Depth NAWC 71BR Packer Test Samples 06/07
TCE
transDCE
11DCE
VC
cisDCE
Concentration (ug/L)
De
pth
(ft
BL
SE
)Packer Test Water-Quality Profiling
Profiling Transmissivity and Contamination in Boreholes 19
0 20 40 60 80 100 120 140 160 1800
20
40
60
80
100
120
Major Anions vs Depth NAWC 71BR Packer Test Samples 6/07
Alkalinity
Chloride
Sulfate
Concentration (mg/L)
De
pth
(ft
BL
SE
)Packer Test Water-Quality Profiling
Profiling Transmissivity and Contamination in Boreholes 20
0 5 10 15 20 25 30 35 40 45 500
20
40
60
80
100
120
Major Cations vs Depth NAWC 71BR Packer Test Samples 6/07
Ca
Mg
Na
K
Concentration (mg/L)
De
pth
(ft
BL
SE
)Packer Test Water-Quality Profiling
Profiling Transmissivity and Contamination in Boreholes 21
Packer Test Water-Quality Profiling
Sample ID
Sample Interval Depths
Sample Interval Length
Transmis-sivity
PumpingRate
CFC-12 (CCl2F2) Concentrations
Replicates
Mean Std Dev
(ft amsl)
(ft) (ft2/day) (gpm) (n) (pg/L) (pg/L)
H1 Open
684-459
225 2.6 0.53 3 168 5
H1-1 657-642
15 1.3 0.32 3 92 1
H1-2 586-571
15 0.7 0.98 3 77 5
Mirror Lake Well H1 – Depth Dependent CFC-12 Concs
Profiling Transmissivity and Contamination in Boreholes 22
Identification of depths with differing contaminant concentrations may help define which fractured rock intervals may be along transport pathways.
Identification of depths with differing water chemistries may help define which intervals have different terminal electron accepting processes ongoing.
Water-quality results together with transmissivity profiling results and other borehole information can be used to guide design of multilevel monitoring systems.
Value of Information fromWater-Quality Profiling