remediation in fractured rock aquifers: challenges and...
TRANSCRIPT
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Allen M. ShapiroAllen M. Shapiro U.S. Geological SurveyU.S. Geological Survey Reston, Virginia, USAReston, Virginia, USA
Designing and MonitoringDesigning and Monitoring Remediation in Fractured Remediation in Fractured
Rock Aquifers:Rock Aquifers: Challenges and ProgressChallenges and Progress
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Collaborators
Paul BradleyFrank ChapelleGary CurtisDan GoodePaul HsiehTom Imbrigiotta
Julie KirshteinPierre LacombeKinga RévészJorie SchulzMary Voytek
Mary DeFlaunScott Drew
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Even with the complexities of fractured rock aquifers, remediation technologies are being implemented. . .
Drilling bedrock boreholes (mudstone)Naval Air Warfare Center, West Trenton, NJ
Steam injection apparatus (limestone)Loring Air Force Base, Aroostook County, ME
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Geologic complexity of fractured rock aquifers
Matrixporosity
Fractures
Fault zones
Depth belowtop of casing
(meters)
Acousticteleviewer
log
Transmissivity(m2/s)
10-10 10-8 10-6 10-4
Detection limit
30
50
70
•Hierarchy of void space•Complex fracture connectivity•Large range of hydraulic properties
Granite and schist, Mirror Lake, NH
Borehole FSE6
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Even relatively “simple” fractured rock environments are subject to significant complexity in the characterization
of contaminant transport
Matrix porosity
•Hierarchy of void space•Complex fracture connectivity•Large range of hydraulic properties
Lockatong Mudstone, West Trenton, NJ
0
100
200
300
0 200 400 800600 1000Distance (feet)
Dep
th (f
eet)
Fault
Fractures (parallel and perpendicular to bedding)
Dep
th b
elow
land
sur
face
(ft)
Detection limit
Transmissivity (m2/s)
10-10 10-6 10-410-8
0
30
60
90
120
150
180
Naval Air Warfare CenterBorehole 68BR
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In fractured rock, where is the DNAPL ?
Small “pool” heights of DNAPL force DNAPL into small aperture fractures
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Small “pool” heights of DNAPL force DNAPL into small aperture fractures
•9 micron (9 x 10-6 meters) fracture aperture needed to stop 1 meter “pool” height of TCE
•Diameter of human hair ~50 microns
H = 2 σ
cosθ
(Pn – Pw )gb
H = DNAPL headb = fracture apertureg = gravitational accelerationθ = contact angle (DNAPL – water)σ
= interfacial tension (DNAPL – water)
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Complex topology of fracture surfaces
Chemical diffusion into matrix porosity
In fractured rock, where is the DNAPL,and where is the dissolved phase DNAPL ?
High permeabilityflow path
Fracture surface
DNAPL forced into small aperture sections of fractures
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Most remediation technologies are inconsistent with thegeologic complexities of fractured rock aquifers
Influent flushing solution(e.g., steam, alcohol, surfactants, chemical oxidizers,microbial agents, etc.)
Contaminated fluids pumped to on-site or off-site treatment
Chemical and/or microbial reactions with DNAPL and its dissolved phase, or increase mobility and/or solubility of the DNAPL
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Most remediation technologies requirecontact with the DNAPL or its dissolved phase
Dissolved phase contaminants in rock matrix
Dep
th b
elow
land
sur
face
(ft)
Detection limit
Transmissivity (m2/s)
10-10 10-6 10-410-8
0
30
60
90
120
150
180
High-permeability flow paths bypass small aperture fractures
Naval Air Warfare CenterBorehole 68BR
Remediation technologies will be effective in the most permeable fractures
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Matrixdiffusion
Recharge/DOC
Fe(OH)3
FeCO3
Mudstone
TCEDCE
DNAPLdissolution
TCEDCE
Clay
TCE
Sorption
Bioaugmentation
VC
Fe+2
Ca+2
OrganicDegradation(TEAPS: O2 , Fe(III)
SO4 , CO2 )
organics CO2 , CH4 , H2
Other reactions (precipitation, speciation, adsorption, exchange)
TCE and DCE are electron acceptors which compete with all other electron acceptors
Even with all the complexities associated with fractured rock. . . reducing contaminant mass in permeable
fractures may be a part of addressing project objectives
Reactive transport models will be critical in evaluating the cost/benefit of applying remediation technology in fractured rock
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Designing and monitoring remediation at the Naval Air Warfare Center, West Trenton, NJ
Bioaugmentation(US Navy, Geosyntec, USGS 2005)
Thermal conductive heating (US Navy, TerraTherm, Queens Univ., USGS, 2009)
Bioaugmentation(US Navy, USGS, Geosyntec, 2008)
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In situ bioaugmentation
•Water pumped from 36BR-A into 2 bladders (bladders pre-flushed with argon to keep formation water anaerobic)
•One bladder dosed with EOS and Vitamin B12•Injection of ~50 gallons EOS solution•Injection of 20 L microbial consortium KB-1•Injection of ~100 gallons EOS solution•Injection of ~100 gallons formation water (anaerobic)
Injection bladders
EOS
KB-1
October 15, 2008
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Bioaugmentation pilot study (2005)using EOS and KB-1
Red lines indicate injection and withdrawal well pairs to introduce amendments
41BR
Amendments added
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Red lines indicate injection and withdrawal well pairs to introduce amendments
41BR
Amendments added
Bioaugmentation pilot study (2005)using EOS and KB-1
Borehole drilled in 2007 showed no significant signs of remediation
TCE 10 ppbDCE 96 ppb VC 54 ppb
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Interpreting the contaminant concentrations at points ofground water discharge
Responses to pumping indicate potential contaminant pathways, but do not indicate the residence time and chemical mixing
Aquifer test conducted at the NAWC by manipulating thedischarge of pump-and-treat wells
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Ground water drawn into 15BRcomes predominantly along the strike of bedding
Ground water flow and transport models have been developed that represent the results of in situ hydraulic and tracer experiments
15BR draws significantly less waterfrom the down dip direction of bedding
Diagram of bedding used in theground-water flow model of the mudstone at the NAWC
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•Remedial design is improved through direct evidence of ground water residencetimes and chemical mixing
•Designing the monitoring of remediation is improved through the understanding of the geologic framework, flow regime, and direct evidence of chemical transport
•Multilevel monitoring boreholes (70BR, 71BR, and 73BR) were installed prior tothe bioaugmentation experiment
Interpreting the contaminant concentrations at points ofground water discharge
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From complexities of fractured rock, we should anticipate. . .
•Complex distribution of DNAPL (free and dissolved phase),with contaminant mass in small aperture fractures and the primary porosity of the rock
•Remediation technology will be most effective in most permeable fractures
•Designing containment and remediation requires understanding of geologic framework, ground water flow regime, and chemical residence time and mixing
•Monitoring at manipulated boreholes, pumped boreholes,and intermediate locations
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•We have had great success in developing tools forcharacterizing ground water flow and chemical transportin fractured rock. . .our success makes it possible to design and implement containment and remediationstrategies. . .
•Expectations of remediation success must be tempered by the reality of the complexities of fractured rock. . .
A few final thoughts. . .