er-20-12: a case study of corrective action investigation in a ...€¦ · er-20-12: a case study...
TRANSCRIPT
C.E. Russell, Science Advisor, Desert Research Institute (DRI)Nicole DeNovio, Golder Associates
Irene Farnham and Jeffrey Wurtz, NavarroEducational Session for the
Nevada Site Specific Advisory Board (NSSAB)April 19, 2017
ER-20-12: A Case Study of Corrective Action Investigation in a Challenging Environment
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Log No. 2017-034
ObjectiveTo highlight actions taken by the U.S. Department of Energy’s (DOE) Environmental Management (EM) Program in Nevada as an exemplary approach to corrective action investigations under challenging conditions
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Nevada National Security Site (NNSS)
• Historically used for nuclear testing (1951 – 1992)
• National Nuclear Security Administration is responsible for current national security missions along with overarching management of the NNSS
• DOE’s Office of EM is responsible for remediating historic locations on the NNSS and portions of the Nevada Test and Training Range
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UGTA• Underground Test Area
Activity (UGTA) is the Nevada EM program charged with characterizing the groundwater to address impacts of 828 underground nuclear tests– NNSS is separated into
groundwater characterization areas based on location and geology
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• Well ER-20-12 in the Pahute Mesa groundwater characterization area near the site of the underground nuclear test named Handley
Study Area on NNSSSite of underground nuclear test
Groundwater characterization well
Study Location
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Prior Conceptual Model
Western Pahute Mesa Water Table Map (DOE, 1996)Caldera Boundaries (DOE, 1992)
Site of underground nuclear test
Groundwater characterization well
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Phase I Characterization – 1999 to 2007• Drilling, testing, and sampling 8 wells• Geophysical surveys• Geologic mapping/modeling• Recharge studies• Geochemical mixing models• Radiochemical source term• Tracer tests• Colloid studies• Laboratory based studies of matrix
diffusion Drilling at ER-EC-2a (Jan. 2000)
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Phase 1 Modeling Results
Particle path lines (DOE, 2009) Transport – 50 years(DOE, 2009)
HANDLEY
PM-3
Sites of underground nuclear tests
Groundwater characterization well
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Log No. 2017-034
Phase II Characterization – 2009 to Present• Added a second phase to reduce
uncertainty• Drill, test, and sample 10 wells• Updates to geologic model • Refined water-level analysis• Revised potentiometric surface • Conducted 16 Interference tests• Radiochemical source term analysis• Fracture analysis• Simplified 2-D water-balance model
Rainbows and Critters at ER-EC-14 (Oct. 2012)
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Well PM-3 Tritium Results
0.1
1
10
100
1000
10000
1/1/1988 6/23/1993 12/14/1998 6/5/2004 11/26/2009 5/19/2015
Triti
um (
Bq/
l)
Date
PM-3 OpenBorehole MDLResults
PM-3-1 MDLResults
PM-3-1 GT MDL
PM-3-2 MDLResults
PM-3-2 GT MDL
Tritium Time Series from PM-3Construction diagramWell PM-3
MDL: Minimum detectable levelGT MDL: Greater than minimum detectable level
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Log No. 2017-034
DOE Communication of Sampling Results
• Verbal notification to Nevada Division of Environmental Protection (NDEP)
• Presentation to NSSAB• Publication of results in the
Annual Site Environmental Report
• Poster-style presentations of results at town-hall-style meetings
Groundwater issues being discussed at NSSAB Meeting
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DOE Response – Documentation & Evaluation
• DOE ordered a complete review of the geochemistry– Frame recent monitoring results based on
historical context– Identify potential sources of tritium A surprising number of alternatives
• DOE convened panel of subject matter experts: geologist, hydrogeologists, radiochemists, numerical modelers, and a representative of NDEP– Evaluate evidence to evaluate alternatives– Recommend course of action
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Alternatives Sources
Revised Water Table (USGS, 2010) & Fracture Orientation
N
S
EW
11
11
11 11
22
22
22 22
33
33
33 33
44
44
44 44
Fallout Plumes (BN, 1999) & Surface Water Runoff
Localized InfiltrationSite of underground nuclear test
Groundwater characterization well
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Log No. 2017-034
Consideration of Alternative Characterization Strategies
• Continued routine monitoring/expanded monitoring to include Chlorofluorocarbons and noble gases
• Shallow drilling in nearby ephemeral wash • Drilling a single/multiple characterization well(s) upgradient• Recommendation based on a pragmatic approach
– General opinion that Handley was the likeliest source Consistent with tritium, Carbon-14, Chlorine-36, and revised
potentiometric surface Advective transport via groundwater the only pathway subject
to regulatory oversight– Drill single well upgradient – approach favored by state regulator
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Log No. 2017-034
ER-20-12 Design• Guidance committee reconvened to
develop scientific criteria for the well (well objective, depth, target units, data, etc.)
• Well drilling, construction, and testing designed to accommodate multiple objectives under uncertain conditions. Decision tree developed to guide the process based on observations in the field.
Process that guides well completion under uncertain
radiological conditions. Decision
points are yellow.
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Impediments to Road and Pad Construction
Wind and Tritiated
Discharge
Opportunistic Data Collection
ER-20-12 Construction
Site of undergroundnuclear test
Groundwater characterization well
PALANQUIN CABRIOLET
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ER-20-12 Results
Hydrostratigraphic Cross-section
2,234 Bq/l13.1 Bq/l5.6 Bq/l
1,720 Bq/l
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Results of Characterization
Activities• Depth dependent tritium
profile within ER-20-12 can only be attributedto Handley
• Very likely that tritium in PM-3 is the leading edge of the plume
Drilling at ER-20-12
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Summary of Challenges to Characterization Activities
• Challenges
– Tritium detections were episodic and low-level
– Site characterized by complex geology, great depth to water, remote, high elevation, rugged terrain, inclement weather, residual surface contamination
– Competing hypothesis for source of tritium
• Tritium detected in PM-3 in 2010
• 3 km from edge of testing area and 7 km from potential source
Oblique View of Hydrostratigraphic
Cross-section
Note: Cavity radius calculated from the minimum of the announced yield in NNSA/NFO (2015b) using the equations in Pawlowski (1999).
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Exemplary Actions by DOE• Flexibility in Federal Facility Agreement and Consent Order
strategy • Prompt and open communication with stakeholders• Incorporated input from member of regulatory authority into
Technical Guidance Committee • Thorough evaluation of alternative conceptual models to
explain the presence of elevated tritium in PM-3• Thorough yet pragmatic evaluating of alternative
characterization strategies• Observational approach used during well drilling/construction• Safety first• Opportunistic data collection