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© 2014 ARCADIS 12 June 2015 1
Alternate Concentration Limits: What You
Really Need to Know
Imagine the result
National Mining Association
Uranium Recovery Workshop
June 8-9, 2015
Presented by:
ARCADIS US, Inc.
Stephen J. Cohen, PG
Patsy Moran, Ph.D.
© 2014 ARCADIS 12 June 2015 2
Agenda
• Regulatory Framework
• Alternate Concentration Limit (ACL) Selection
• Methods for Assessing ACLs
• Geochemical Data Needs
• Assessing ACL Selection
• Confirmation Monitoring and Assessment
© 2014 ARCADIS 12 June 2015 3
Regulatory Framework
• Atomic Energy Act, Section 275, as required by
UMTRCA
• 40 CFR 192, Subtitle D
• 10 CFR 40, App. A, Criterion 5B(5) – Groundwater
Protection Standards
• 10 CFR 40, App. A, Criterion 5B(6) – NRC information
needs
• NUREG 1620, REV 1 – Contains guidance for ACL
applications
© 2014 ARCADIS 12 June 2015 4
ACL Selection
• Criterion 5B(6) ACL requirements
• Licensees must provide the basis for any proposed limits
including:
• Consideration of practicable corrective actions
• Limits are as low as reasonably achievable (ALARA)
• Commission establishes the site-specific ACL if it finds
that the proposed limit is ALARA, after considering
practicable corrective actions, and that the constituent
will not pose a substantial present or potential hazard to
human health or the environment as long as the
alternate concentration limit is not exceeded
© 2014 ARCADIS 12 June 2015 5
ACL Selection (cont’d.)
• No standard method for selecting ACLs
• Proposed ACLs should be supported by data
and modeling/calculations
• Hazard and exposure assessments
recommended
• Monitoring plan
• EPA concurrence is not required
© 2014 ARCADIS 12 June 2015 6
ACL Selection (cont’d.)
• Statistical packages (e.g, ProUCL) may be used
to calculate ACLs
• For traditional POC (e.g. tailings impoundment)
• Best not to use a mean or a UCL
• Possibly use an upper tolerance limit (UTL) – different
standard for individual wells
• UTLs are used to compare with individual data
points.
© 2014 ARCADIS 12 June 2015 7
ACLs for ISRs
• ACLs for ISRs should be area-based not point-based
(alternative approach)
• Area-based groundwater protection
standards are currently standard for
ISRs
• For compliance,
compare UCL of
compliance data to
UCL.
• More monitoring points
are better
© 2013 ARCADIS 12 June 2015 8
Methods for Assessing ACLs
• Hydrogeologic component (e.g., MODFLOW)
• Geochemical component
• PHREEQC/Geochemists Workbench
• MT3D
• Hazard assessment
• Exposure assessment
© 2013 ARCADIS 12 June 2015 9
Geochemical Data Needs
Demonstrate a clear understanding of the geochemical
processes that control the release, speciation, transport,
and attenuation of Constituents of Concern (COCs)
• Common COCs
• uranium, arsenic, selenium, radium-226
• Key attenuation mechanisms
• Sorption
• Reduction
• Co-precipitation
www.andertoons.com
© 2013 ARCADIS 12 June 2015 10
Geochemical Data Needs (cont’d.)
• Demonstrate attenuation mechanisms
• Water quality
• Solids characterization
• Specialized testing
Moyes, A. 2013. (Thesis) Clay Mineralogy and Chemical Variation in uranium Roll-Front
Deposits in the Gas Hills Uranium District, Wyoming. M.S. Thesis. Available from: University
of Utah, Department of Geology and Geophysics, Utah. p. 105.
© 2013 ARCADIS 12 June 2015 11
Geochemical Data Needs (cont’d.)
• Water Quality
• Routine water quality parameters
• Understand Redox Conditions
• Oxidization-Reduction Potential
(ORP) and dissolved oxygen (DO)
• Supplement with additional data
• Speciation
• As(III)/As(V), Se(IV)/Se(VI),
Fe(II)/Fe(III)
• Speciation measurements are not
trivial
© 2013 ARCADIS 12 June 2015 12
Geochemical Data Needs (cont’d.) Solids Characterization
• Identify mineral phases that play a
role in attenuation
• Major/minor (e.g., clays, pyrite
• Trace (e.g., barite, uraninite)
Major Mineral Phases (QEMSCAN, Extracted from Moyes, 2013)
10
µm
Barium sulfate
(barite)
Publicly available dataset is growing
Core samples
Petrography X-ray Absorption
Spectroscopy (XAS)
© 2013 ARCADIS 12 June 2015 13
Geochemical Data Needs (cont’d.)
Specialized Testing – Additional Lines
of Evidence
• Column testing
• Adsorption/desorption tests to
refine estimates of reversible
(e.g., sorption) and irreversible
(e.g., reductive precipitation)
uptake
• Selective Sequential Extraction (SSE)
• A series of leaching procedures that target different
phases in the solid to evaluate metals partitioning
• Increasingly used to support natural attenuation and
refine predictive fate and transport models
© 2013 ARCADIS 12 June 2015 14
Geochemical Data Needs (cont’d.)
• Example SSE Scheme - Selenium
• Apply each increasingly
stronger extractant to the
same sample
• Operationally defined
fractions
• Thoroughly vet
methods and be
upfront about the
limitations
• Overlap in extraction
steps
• Use in conjunction with
other data
SSE method derived from Kulp and Pratt. 2004. Geochimica et Cosmochimica
Acta. 68:3687-3701. Additional steps can sub-divide the residual fraction, and
separate the water soluble and exchangeable fractions.
Step Extractant Targeted Phase
1 0.1 M KH2PO4 Soluble, adsorbed, and exchangeable fraction
2 15% Acetic Acid Carbonate fraction
3 0.1 M Sodium Pyrophosphate
Organic fraction
4 1.0 M NH2OH-
HCl – 25% Acetic Acid
Co-precipitated with amorphous Fe and Al oxyhydroxides and
amorphous and crystalline Mn oxides
5 Strong Acid Digestion
(HNO3+H2O2+HF)
Residual fraction (sulfides/selenide, silicates)
© 2013 ARCADIS 12 June 2015 15
Data Needs - Timing
• Pre-application – During Criterion 7 baseline studies
• Preoperational – After license issuance, before
extraction
• During operations
• Unaffected portions of wellfields
• In production zone
• During restoration
© 2013 ARCADIS 12 June 2015 16
Confirmation Monitoring and Assessment
• See NUREG-1620
• Compliance monitoring program should monitor all
groundwater exposure pathways
• Compliance monitoring well locations should not be
restricted solely to the POC
• Some locations between the POC and POE could be
included
• MCLs or Commission-approved background should be
used as the POE limit
© 2013 ARCADIS 12 June 2015 17
Conclusions
• NRC staff assumes ACLs required for U, Ra, As, Se
• Licensees should take advantage of the flexibility in ACL
determination
• Licensees/Applicants should collect data needed to
support ACL development
• Licensees/Applicants should perform the necessary
modeling/calculations to support ACL development and
monitoring plans.
© 2014 ARCADIS 12 June 2015 18
Imagine the Result
Contacts:
Stephen J. Cohen, PG
1114 Benfield Blvd., Suite A
Millersville, MD 21108
410-923-7821
Patsy Moran, Ph.D.
630 Plaza Drive
Highlands Ranch, CO 80129
303-471-3446
