Profiling Transmissivity and Contamination in Fractures Intersecting Boreholes USEPA-USGS Fractured Rock Workshop EPA Region 2 14 January 2014 Claire Tiedeman and Tom Imbrigiotta, USGS

2Profiling Transmissivity and Contamination in Boreholes Motivation: Hydraulic Conductivity Varies by Orders of Magnitude in Fractured Rock This variability results in complex groundwater flow and contaminant transport paths

 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 3Profiling Transmissivity and Contamination in Boreholes Straddle Packer Testing Flute Liner Installation Borehole Flow Logging

4Profiling Transmissivity and Contamination in Boreholes Packer Testing Equipment

 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 5Profiling Transmissivity and Contamination in Boreholes

 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 – min. (Geochemical sampling will require longer pumping).  Turn off pump. Hydraulic Tests by Fluid Pumping – Permeable Intervals 6Profiling Transmissivity and Contamination in Boreholes

 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 7Profiling Transmissivity and Contamination in Boreholes

8 Theim equation for steady-state radial flow to a pumping well

 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 9Profiling Transmissivity and Contamination in Boreholes

10Profiling Transmissivity and Contamination in Boreholes Crystalline Rock

Sedimentary Rock 11Profiling Transmissivity and Contamination in Boreholes

 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 12Profiling Transmissivity and Contamination in Boreholes Installation of Liner From Carl Keller

 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 13Profiling Transmissivity and Contamination in Boreholes PackersFLUTeFlow Logging

 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 14Profiling Transmissivity and Contamination in Boreholes

 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 15Profiling Transmissivity and Contamination in Boreholes

 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 16Profiling Transmissivity and Contamination in Boreholes

Water-Quality Sampling 17Profiling Transmissivity and Contamination in Boreholes

Packer Test Water-Quality Profiling 18Profiling Transmissivity and Contamination in Boreholes

Packer Test Water-Quality Profiling 19Profiling Transmissivity and Contamination in Boreholes

Packer Test Water-Quality Profiling 20Profiling Transmissivity and Contamination in Boreholes

Packer Test Water-Quality Profiling 21Profiling Transmissivity and Contamination in Boreholes Sample ID Sample Interval Depths Sample Interval Length Transmis -sivity Pumping Rate CFC-12 (CCl 2 F 2 ) Concentrations ReplicatesMeanStd Dev (ft amsl)(ft)(ft 2 /day)(gpm)(n)(pg/L) H1 Open H H Mirror Lake Well H1 – Depth Dependent CFC-12 Concs

 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 from Water-Quality Profiling 22Profiling Transmissivity and Contamination in Boreholes