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Transcript of ASTM User Training in Risk-Based Corrective Action for Chemical Releases (Provisional ASTM Standard...
ASTM User Training
in
Risk-Based Corrective Action for Chemical Releases
(Provisional ASTM Standard Guide)
Day 1
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2
Course Objectives
Provide an understanding of the risk-based decision process.
Discuss the importance of Technical Policy Decisions
Emphasize the importance of the development and application of the site conceptual model
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Course Objectives
Provide an understanding of the development of corrective action performance goals and the role of risk assessment and fate and transport in the risk-based decision process
Discuss the issues and processes necessary to make Tier decisions
Discuss the evaluation and selection of remedial action options
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Course Expectations
Elementary understanding of the basic science necessary to make risk-based decisions
Understanding of the concepts and process necessary to implement a framework for making risk-based decisions
Understanding of the applicability of the RBCA framework to a variety of sites
Understanding of the issues related to the integration of the RBCA framework into an existing regulatory program
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Course Expectations
This course is NOT intended to provide specific applications to existing regulatory programs
This course is NOT intended to provide all the tools necessary to perform risk-based decisions
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– 8:00 - 8:30 Introduction– 8:30 - 9:30 Summarizing the Framework– 9:30 - 9:45 Break– 9:45 - 10:45 Summarizing the Framework– 10:45 - 11:00 Break– 11:00 -12:00 Technical Policy Decisions– 12:00 - 1:00 Lunch– 1:00 - 2:15 Technical Policy Decisions– 2:15 - 2:30 Break– 2:30 - 4:00 Developing the Site Conceptual Model– 4:00 - 4:15 Break– 4:15 - 5:00 Developing the Site Conceptual Model
Agenda: Day 1
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Agenda - Day 2
– 8:00 - 9:30 RBSL/SSTL Development– 9:30 - 9:45 Break– 9:45 - 10:45 RBSL/ SSTL Development– 10:45 - 11:00 Break– 11:00 -12:00 RESC/SSEC Development/Data Collection– 12:00 - 1:00 Lunch– 1:00 - 2:30 Tier Decisions/Remedial Options– 2:30 - 2:45 Break– 2:45 - 4:00 Source Reduction/ Activity and Land Use Controls– 4:00 - 4:15 Break– 4:15 - 5:00 Factors for Consideration in Remedial Action Selection
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ASTM “standards” are developed through a rigorous consensus-building process, that may also include external peer review (as in the case of RBCA).
Members vote to approve standards, and all negative ballots must be resolved.
ASTM is an organization that has historically focused on promulgating standards for engineering tests and specifications for engineering materials.
Who is ASTM?
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ASTM RBCA
Authored by a multi-functional and multi-disciplinary group of ASTM E-50 Subcommittee members, representing:
ASTM “RBCA”
State Regulators USEPA Staff Insurance Industry Banking Industry Chemical Industry Oil Industry Academia Consulting
Reimbursement Fund Managers
Regulatory Managers Hydrogeologists Toxicologists Environmental Engineers Environmental Scientists Modelers
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RBCA is a framework developed by ASTM in which exposure and risk assessment practices are integrated with traditional components of the corrective action process.
RBCA Goals:
protection of human health and environment
consistent and technically-defensible decisions
selection of appropriate and resource-efficient remedies
optimal allocation of limited resources
practical and resource-efficient approach
achievement of corrective action and redevelopment together
Risk-Based Corrective Action (RBCA) Process
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Why 3 Tiers (Levels) in RBCA?
Tier 1Tier 1
Tier 3Tier 3
TargetRisk
Every tier achieves the same level of public health protection
Tier 2Tier 2Less Site-Specific U
ncertainty
Greater Site-Specific Effort
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Technical Policy Decisions
RBCA Framework Regulatory Program
How is a RBCA Program Developed?
ASTM Risk-Based Corrective Action for Chemical Release Sites
– outlines a framework for integrating exposure and risk assessment practices with traditional components of the corrective action process.
– describes steps and philosophy to build the framework and to incorporate technical policy decisions into corrective action programs.
– identifies stakeholders and stakeholder involvement in the program development
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RBCA Framework Regulatory Program
Technical Policy Decisions
How is a RBCA Program Implemented?
ASTM Risk-Based Corrective Action for Chemical Release Sites
– provides mechanism for stakeholder involvement– makes technical policy decisions– integrates framework into regulatory program– provides training for stakeholders
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PolicyRBCA Customization: Technical Policy Decisions
Target risk limits Land use issues Ground water use issues Chemical(s) of concern Data requirements Site classification
procedures Exposure assumptions and
pathways Point(s) of demonstration
Fate and transport– natural attenuation– modeling procedures
Remedy selection criteria Interim remedial action Institutional controls Engineering controls mass reduction vs. risk
reduction Stakeholder involvement
Summarizing the Framework
Definitions
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Definitions
The Corrective Action Process – the sequence of actions that include site assessment and
investigation, interim remedial action, remedial action, operation and maintenance of equipment, monitoring of progress, and termination of the remedial action.
– Chemical Release– any spill or leak or detection of concentrations of
chemical(s) of concern in environmental media
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Risk Toxicity & Exposure
Exposure Concentration & Intake
Definitions
Risk Assessment– an analysis of the potential for adverse effects on
receptors and relevant ecological receptors and habitats caused by a chemical(s) of concern from a site
– the basis for the development of corrective action goals and determination of the need for interim remedial action, remedial action or a combination of these actions
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Definitions
Technical Policy Decisions – the choices specific to the user that are necessary to
implement the Risk-Based Corrective Action framework• involve professional judgment to evaluate available data• may be more then one scientifically supportable answer• the choices represent different approaches• appropriate technical policy decisions may have already been
made by the regulatory agency
– Examples of technical policy decisions:• data quality objectives, target risk levels, land use, ground water
use, natural resource protection, relevant ecological receptors and habitats and exposure
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Definitions
Chemical(s) of Concern (CoCs)– specific constituents and their breakdown products that
are identified for evaluation • identification can be based on their historical and current use at
a site, detected concentrations in environmental media and their mobility, toxicity, and persistence in the environment
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Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
Step 8
Step 9
Step 10
ASTM Risk-Based Corrective Action (RBCA) Flowchart
YesNo
Initial Response Classification & Risk Reduction
Tier 1 Evaluation
Initial Site Assessment
Decision Point?
Interim Remedial
Action
Yes
Yes
No
Tier 2 Evaluation
No
NoNo
No
Yes
Yes
Yes
Tier 3 Evaluation
Yes
No
NoYes
Remedial Action Program
MonitoringNo
Further Action
NoYes
Yes
Yes
No
No
Decision Point?Decision Point?
Decision Point? Decision Point? Decision Point?
Decision Point? Decision Point?
Decision Point? Decision Point?
Decision Point?
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Step 1
Initial Site Assessment
Identify all available information concerning– nature of the release– physical condition and setting of the site– environmental condition of the site
Focus on developing the site conceptual model – identifying incomplete exposure pathways
Determine if further action is necessary
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Step 1
Initial Site Assessment
Non-intrusive and intrusive data collection activity to support
– initial response action evaluation– risk reduction activities– refinement of site conceptual model– comparison of concentrations of chemical(s) of concern
in environmental media to risk-based screening levels (RBSL)
– comparison of site conditions to relevant ecological screening criteria (RESC)
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Step 2
Ris
k
Initial Response Action
Initial Response Action& Risk Reduction
Risk Reductio
n Activity
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Site Off-Site
Residual Phase
Source Area
Free Phase
Dissolved Phase
Free Phase
Vapor Phase
Vapor Phase
Source Area(s) - the location of non-aqueous phase liquid (NAPL) chemical, the locations of highest soil or ground water concentrations of the chemical(s) of concern or the location releasing the chemical(s) of concern
Step 1Initial Site Assessment Source(s) and Source Area(s)
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Step 1
Atmospheric fate & transport
deposition
Site
Soil to Ground Water
Soil to air
Ground Water to Air
Ground Water Transport
Runoff
Dust to airOff-Site
Initial Site AssessmentTransport Mechanisms
Chemical(s) of concern dissolved in ground water
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Initial Site AssessmentReceptors
Site Off-Site
Receptors
Step 1
Industrial land use Future land use ? Residential land use
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Initial Site AssessmentRelevant Ecological Receptors and Habitats
Ecological resources that are to be protected are– communities with threatened and endangered species – recreationally or commercially important communities– that are regionally or nationally rare– communities with high aesthetic quality– communities that afforded special protection by law or
regulation– habitats that support these communities.
Identification may come from applicable federal and state regulations
Step 1
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Point(s) of Exposure - The point(s) at which an individual or population may come in contact with a chemical(s) of concern originating from a site.
Step 1
Site
Point(s) of Exposure
Off-Site
Initial Site AssessmentPoint(s) of Exposure
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Tier 1 EvaluationExposure Pathway
Receptor
Source Area
Transport Mechanism
Step 3
Exposure Pathway - describes a mechanism by which an individual or population is exposed to a chemical(s) of concern and includes a source or source area, a transport/exposure medium (e.g., air or water), a point of exposure, and an exposure route.
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Site Conceptual Model - The integrated representation of the physical and environmental context, the complete and potentially complete exposure pathways and the likely distribution of chemical(s) of concern at a site
Leaching andGround Water
Transport
Leaching andGround Water
Transport
Wind Erosion and Atmospheric
Dispersion
Wind Erosion and Atmospheric
Dispersion
Residential Commercial/Industrial Construction worker Sensitive habitat
PRIMARY SOURCES
SECONDARYSOURCES
EXPOSUREROUTES
RECEPTORSTRANSPORT
MECHANISMS
AffectedSubsurface
Soils (>3 ft
depth)
AffectedSubsurface
Soils (>3 ft
depth)
Stormwater/SurfaceWater
Transport
Stormwater/SurfaceWater
Transport
SURFACE WATER Recreational Use/Sensitive Habitat
SURFACE WATER Recreational Use/Sensitive Habitat
Volatilizationand
AtmosphericDispersion
Volatilizationand
AtmosphericDispersion
Ground WaterPotable Water UseProcess Water Use
AIR Inhalation of Vapor
or Particulates
AIR Inhalation of Vapor
or Particulates
SOILDermal Contact
or Ingestion
SOILDermal Contact
or Ingestion
Product Storage Piping / Distribution Operations Waste Management Unit Other
Product Storage Piping / Distribution Operations Waste Management Unit Other
Volatilizationand Enclosed
Space Accumulation
Volatilizationand Enclosed
Space Accumulation
Mobile Free
Liquid Migration
Mobile Free
Liquid Migration
DissolvedGround WaterPlume
DissolvedGround WaterPlume
AffectedSurface Soils,Sediments or Surface Water
AffectedSurface Soils,Sediments or Surface Water
Free-PhaseLiquidPlume
Free-PhaseLiquidPlume
AffectedSurface
Soils (<3 ft
depth)
AffectedSurface
Soils (<3 ft
depth)
Residential Commercial/Industrial Construction worker
Residential Commercial/Industrial
Residential Recreational Sensitive habitat
Step 3
Site Conceptual Model
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RBSLs
c
o soil o d i air
g
kg soil
TR BW ATdays
years
SFkg
mgIR RAF SA M RAF SF IR VF EF ED
365
10 6sinh
Step 3
Risk-Based Screening Levels (RBSL)
Represent concentrations that satisfy the criteria for Not Further Action at Tier 1
– RBSL typically quantitative Use conservative values for risk and exposure
assumptions May use regulatory values
– MCL, aesthetic values (taste or odor)
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Ecological issues within the RBCA process
RBCA framework can be used to evaluate ecological risk
Ecological risk can follow a tiered process PS-104 provides guidance on how to get started Specific guidance is under development Responses tend to be evaluated for
populations/ecosystems, rather than individuals Guidelines for Ecological Risk Assessment
EPA/630/R-95/002F, 4/98, Final
Step 3
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Relevant Ecological Screening Criteria (RESC)
Non-site-specific Used in the Initial Site Assessment and Tier 1
evacuation Part of the technical policy decisions Can be qualitative or quantitative in nature
– qualitative - waterfowl feeding and nesting– quantitative - water quality criteria
Can be based on concentrations of chemical(s) of concern or biological measures
Step 3
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SiteOff-Site
Tier 1 EvaluationRisk-Based Screening Levels
CRBSL
CRBSL
CRBSL
CRBSL
CRBSL
CRBSL
CRBSLPoint(s) of exposure is assumed to be located proximal to the source area(s)
Compare highest concentrations of chemical(s) of concern to RBSL for complete and potentially complete exposure pathways
Compare site conditions to RESC
Step 3
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Tier 1 Decisions Factors
The basis for the RBSL or RESC are not representative of the site-specific conditions
– hydrogeology, exposure parameters, point(s) of exposure, reasonable land use options
The RBSL or RESC do not exist for a complete and potentially complete exposure pathway
An unacceptable risk to a relevant ecological receptor or habitat is identified during the Tier 1 qualitative ecological screening evaluation
Step 4
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Tier 1 Decisions Factors
Site-specific target levels (SSTL) or site-specific ecological criteria (SSEC) developed under further tier evaluation will be significantly different than the RBSL or RESC or will significantly modify the remedial action activities
The cost of remedial action based on RBSL will likely be greater than further tier evaluation and subsequent remedial action.
Step 4
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Tier 1 Outcomes
No further action– if the concentrations of the chemical(s) of concern are
below the RBSL – if the comparison of the site conditions to RESC indicate
that there is no unacceptable risk to relevant ecological receptors and habitats
Compliance monitoring– not confident that data support the conclusion that
concentrations will not be above RBSL in the future– to collect data sufficient to confidently conclude that
concentrations will not be above RBSL in the future.
Step 4
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Tier 1 Outcomes
Interim remedial action– address most significant concerns in an expedited fashion
Remedial action– reduce concentrations of chemical(s) of concern at the
point(s) of exposure– eliminate a complete or potentially exposure pathway– address an unacceptable risk
Step 4
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Tier 1 Outcomes
Further Tier evaluation– complete and potentially complete exposure pathways
with concentrations of chemical(s) of concern above RBSL or do not meet RESC
– maintains the same level of protectiveness, but uses site specific data to help make better informed decisions.
Step 4
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Tier 2 SSTL Step 5
Develop SSTL using RBSL methods, but replace default assumptions with site-specific parameters
– compare to concentrations of chemical(s) of concern in the source area(s)
Develop statistical representation of source area concentrations of chemical(s) of concern when appropriate data exist
– compare to RBSL or SSTL developed by using site-specific parameters
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Tier 2 SSTL and SSEC
Develop SSTL by applying RBSL at point(s) of exposure and back-calculating SSTL for chemical(s) of concern at source area(s)
– evaluate fate and transport of chemical(s) of concern in environmental media
– based on estimated, measured, or monitored attenuation Develop SSEC for relevant ecological receptors and
habitats based on additional qualitative or quantitative analyses
Step 5
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Example Tier 2 Evaluation
Substituting site-specific parameters in RBSL method
Step 5
CGW
CW
1
1 V GW
I W
W = source width parallel to ground water flow [m]
GW = thickness of ground water mixing zone [m]
I = infiltration rate [m/y]V = ground water flow velocity
[m/y]CW = dissolved concentration in
vadose zone source area [mg/l]CGW = dissolved concentration in
ground water source area [mg/l]
W
I
V GW
CW
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Example Tier 2 Evaluation
Statistical representation of source area concentrations
Step 5
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SiteOff-Site
Cpoe
Csoil
Cgw
Example Tier 2 Evaluation
Site-Specific Target Level Applied at Source Area
RBSL Applied at Point of Exposure
Source Area
Step 5
Back-calculating SSTL at source area(s) by applying RBSL at point of exposure
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Example Tier 2 Evaluation
Back-calculating SSTL at source area(s) by applying RBSL at point of exposure
Step 5
Cgw(x) = C f (degradation, seepage velocity, thickness of source zone, dispersion)
Cgw = chemical of concern along centerline of the plumeCsteady state source concentration
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Example Tier 2 Evaluation
Tier 2 site-specific ecological criteria (SSEC)– used in Tier 2 evaluations– usually quantitative in nature– part of technical policy decisions– Tier 2 refines Tier 1 RESC with more site-specific
parameters• refine a model by using site-specific soil characteristics• use a toxicity value that is more appropriate for a relevant
ecological receptor or habitat at the site
Step 5
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SiteOff-Site
Cpoe
Csoil
Cgw
Tier 2 - Point(s) of Demonstration
Source Area
Step 5
Point(s) of Demonstration - A location(s) selected between the source area(s) and the potential point(s) of exposure where concentrations of chemical(s) of concern must be at or below the determined target levels in media (e.g., ground water, soil or air).
Cpod
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Step 6
Tier 2 Decisions Factors
The basis for the SSTL or SSEC are not representative of the site-specific conditions
– hydrogeology, exposure parameters, point(s) of exposure, reasonable land use options
The SSTL or SSEC do not exist for a complete and potentially complete exposure pathway
An unacceptable risk to a relevant ecological receptor or habitat is identified during the Tier 2 comparison to SSEC
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Step 6
Tier 2 Decisions Factors
Site-specific target levels SSTL or SSEC developed under further tier evaluation will be significantly different than the SSTL or SSEC or will significantly modify the remedial action activities
The cost of remedial action based on SSTL will likely be greater than further tier evaluation and subsequent remedial action.
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Step 6
Tier 2 Outcomes
No further action– if the concentrations of the chemical(s) of concern are
below the SSTL – if the comparison of the site conditions to SSEC
indicate that there is no unacceptable risk to relevant ecological receptors and habitats
Interim remedial action– address most significant concerns in an expedited
fashion
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Step 6
Tier 2 Outcomes
Remedial action– reduce concentrations of chemical(s) of concern at the
point(s) of exposure– eliminate a complete or potentially exposure pathway– address an unacceptable risk
Further Tier evaluation– complete and potentially complete exposure pathways
with concentrations of chemical(s) of concern above SSTL or do not meet SSEC
– maintains the same level of protectiveness, but uses site specific data to help make better informed decisions.
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Step 7
Tier 3 SSTL and SSEC
Tier 3 involves the highest level of sophistication and resources
– the development and use of site-specific numerical models
– use of probabilistic data representations– address variability and uncertainty– development of site-specific exposure factors, exposure
scenarios, toxicity data, bioavailability, and biomagnification
Requires significantly more detailed site-specific data collection
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Step 7
Example Tier 3 Evaluation
Uncertainty and Probabilistic Analysis – Uncertainty represents ignorance or lack of perfect
knowledge about poorly characterized phenomena or models
• addressed in Tier 1 by conservative assumptions• addressed in Tier 2 by site-specific measurements• addressed in Tier 3 by better measurements or probabilistic
analysis
– Probabalistic analysis is the use of distributions of input values
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Step 7
Example Tier 3 Evaluation
Bioavailability, biodegradation and biomagnification
– bioavailability is a measure of the fraction of the chemical(s) of concern in environmental media that is accessible to an organism for absorption
– biodegradation is natural plant, animal or microbial metabolism that results in the reduction of mass of chemical(s) of concern
– biomagnification a measure of the fraction of chemical(s) of concern that transfer and accumulate in a organism as a result of food web consumption
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Step 7
Example Tier 3 Evaluation
Tier 3 site-specific ecological criteria– used in Tier 3 evaluations– usually quantitative in nature– part of technical policy decisions– Tier 3 completely site-specific and refines Tier 2 SSEC
• use a toxicity value that is more appropriate for a relevant ecological receptor
– can involve lab toxicity studies applicable to ecological exposure• e.g., round worm exposure tests in soil
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Step 8
Tier 3 Outcomes
No further action– if the concentrations of the chemical(s) of concern are
below the SSTL – if the comparison of the site conditions to SSEC
indicate that there is no unacceptable risk to relevant ecological receptors and habitats
Interim remedial action– address most significant concerns in an expedited
fashion
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Step 8
Tier 3 Outcomes
Remedial action– reduce concentrations of chemical(s) of concern at the
point(s) of exposure– eliminate a complete or potentially exposure pathway– address an unacceptable risk
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Step 9
Remedial Action Option Evaluation
Effectiveness of the remedial action in protecting human health and the environment,
Long-term reliability and probable success in meeting the remedial action goals now and in the future,
Short-term risks posed by the implementation of the remedial action,
Amenability of the remedial action to integration with property redevelopment plans,
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Step 9
Remedial Action Option Evaluation
Acceptability of the remedial action to the stakeholders,
Implementability and technical practicability of the remedial action, and
The cost-effectiveness of the options to meet the remedial action goals.
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Remedial Action Plan
Based on the appropriate RBSL, SSTL, RESC, SSEC or remedial action goals , source area(s) and point(s) of exposure, choose measures to achieve the corrective action goals or eliminate exposure pathways
Remedial options may include combinations of active and passive measures
Considerations: source removal or reduction eliminate exposure natural attenuation engineering controls institutional controls
Weight of considerations are based on a technical policy decision
Step 9
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Step 10
Monitoring Program
Following, or during remedial action, a monitoring plan is needed to insure that the appropriate RBSL, SSTL, RESC, SSEC or remedial action goals established in the Tier analysis continue to be met
Verify assumptions and predictions used in Tier 2 and Tier 3.
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“No Further Action” and Conditions of Closure
Ease of obtaining an NFA is related to confidence in supporting data and requirements of the governing regulatory framework
Example NFA letter contents– reservation of rights / re-opener clauses– monitoring requirements
• demonstrate the effectiveness of implemented remedial action• confirm that current conditions persist or will improve with time
– maintenance requirements• ensure integrity and continued performance
– financial responsibility provisions
Step 10
Technical Policy Decisions
RBCA: How to Implement a Program
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Technical Policy Decisions
Assumptions and values used in the risk-based decision process to ensure that decisions are protective of human health and the environment
– “set the floor” – made “up front”– performance-based
• acceptable levels of conservatism and uncertainty
– involve professional judgment– more than one scientifically supportable answer possible– include social, economic and other considerations
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Technical Policy Decisions
Technical and Policy Decisions
Political and
SocialEconomic
Scientific
Regulatory DrivenDecisions made as part of a regulatory program that
apply to all sites or a set of circumstances
Site DrivenDecisions made at an
individual site based on site-specific circumstances
Business DrivenDecisions made at an individual site based
on business-specific circumstances
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Topics
Identify some of the more controversial topics– stakeholder involvement – ground water resource and use– point(s) of demonstration– uncertainty and conservatism– data quantity and quality objectives– adequacy of site assessment– target risk and hazard quotient– activity and land use– ecological risk
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Stakeholder Involvement
Who are they? When do they get
involved? How should they be
involved? – regulatory program
development– site-specific decisions– informational
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Stakeholder Involvement Who are They?
Regulatory agency Owners Community Real estate interests Financing interests State and local government Environmental groups
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Stakeholder InvolvementProgram Element
Many state and federal programs develop regulations, policies and guidelines with specific consensus building requirements and formal or informal requirements for representation by balanced stakeholder groups.
It is extremely important for the program development process to consider the use of such representation to reach consensus on some of the widely debated issues which could impact the application and implementation of the RBCA process.
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Stakeholder Involvement Site-Specific Element
The level of site-specific involvement will depend on the type and severity of the situation
– land and activity use decisions– impact to surrounding areas– community concerns
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Stakeholder Involvement Informational
Constructive dialog that acknowledges the needs and expectations of the stakeholders
Education and outreach Identify stakeholder concerns on potential
corrective action
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Class Exercise # ?? Site-Specific Stakeholder Involvement
A truck spills 20 gallons of diesel fuel on the interstate highway
– who to tell? – who to ask?
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Class Exercise # ??Site-Specific Stakeholder Involvement
How about this stuff?– bottles of discarded ant poison, circa 1930s– suburban residential neighborhood.
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Corrective Action Goals
What are the appropriate goals for corrective action?
– background– analytical detection limits– generic standards– technical impracticability– financial impracticability– site-specific risk-based– environmentally acceptable endpoints
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Chemical(s) of Concern
What is the criteria for selection of chemical(s) of concern and indicator chemicals?
– all chemicals based on analytical detection– specific chemicals based on knowledge of material
released
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Decision Criteria
What criteria should be considered when making decisions?
– timing– long and short term reliability– implementability– costs– acceptability to stakeholders– others?
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Fate and Transport
What criteria should be used to select models to predict fate and transport of a chemical?
– model performance-based– strict list of acceptable models
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Exposure Pathways
What is the process for identifying exposure pathways and receptors for consideration and the criteria for exclusion or elimination of an exposure pathway?
– documentation and tracking requirements– hierarchy of land use and resource use criteria
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Technical Policy DecisionGround Water Resources and Use
What criteria should be used to determine the need and extent for restoration of ground water and beneficial resources?
– drinking water everywhere and always– current and potential future use determination– classification of ground water
• yield rates• quality (e.g. presence of salt water or nitrates)• hydrogeologic considerations - barriers and confining layers• ecosystem impacts, surface water connection• natural resource value
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Technical Policy DecisionGround Water Resources and Use
What criteria should be used to determine the need and extent for restoration of ground water and beneficial resources?
Classification of ground water is a technical policy decision
Classification decisions may consider: – yield rates– quality (e.g. presence of salt water or nitrates)– hydrogeologic considerations - barriers and confining
layers
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Future Use of Groundwater
Drinking water everywhere and always Other extreme: never any water use anywhere. Consensus on this issue is important to implement
RBCA
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Consensus
What is the most effective compromise on groundwater issues which best balances social, scientific and financial concerns?
Examples: time (natural attenuation) or location (off-site plume) exceptions to DW.
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Class Exercise # ??
Rural area on growing suburban fringe and no municipal drinking water supply
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Class Exercise # ??
RCRA facility with municipal drinking water supply and river greater then 3 miles from the facility
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Summary of Ground Water Resources and Use Issues
How did you come to a decision in your group? What did you decide and why? Did you consider drinking water as well as
agricultural uses? Did you provide for exceptions to your
classification scheme?
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Point of Demonstration for Chemicals in the Ground Water
Where should the point(s) of demonstration be located?
– at the property line?– at points defined by regulation– at site-specific determined point(s) of exposure?– different application for current potential exposures and
future potential exposures– at the point of access for water uses?
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Point of Demonstration for Chemicals in the Ground Water
How should travel time be accounted for? What are the contingency ways to prevent contact
with a receptor? What soil and bedrock characteristics will
contribute to natural attenuation?
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High Uncertainty&
Conservatism
Low Uncertainty&
Conservatism
Tier 3 Tier I
Uncertainty
How should uncertainty be addressed?– better measurements– conservative assumptions– probabilistic analyses
This issue exists in many endeavors. Learn how to manage uncertainty early on in the
RBCA Process
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Managing Uncertainty
How will Data be Used? – physical, chemical and hydrogeolocical data
What quantity and quality of data is required?– indicators and screening– confirmatory and detailed site-specific– practical quantitation limits.– minimum number of samples– the safety net– the statistical approach.
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Managing Uncertainty
Better measurements needed to address both: – variability (true heterogenuity in a well-characterized
phenomenon, cannot be reduced by further measurements) and
– uncertainty (ignorance about a poorly characterized phenomenon that can be reduced through further measurements).
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Managing Uncertainty
Uncertainty can be addressed by better measurements or by making conservative assumptions.
The effect of conservative assumptions is to:– overestimate mass– overestimate concentrations at the point(s) of exposure– overestimate resulting doses– overestimate health effects
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Managing Uncertainty
Conservatism assumptions may result in an overestimate of:
– mass of chemical(s) of concern– concentrations at the point(s) of exposure– doses to receptors– health effects on receptors
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Cancer and Non-Cancer Risk
What is the appropriate target risk and how should cumulative and additive effects be treated?
– used to calculate screening levels and site-specific levels– cancer
• individual chemical• cumulative of all carcinogenic chemicals
– non-cancer• individual chemical• additive of all non-carcinogenic chemicals
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Cancer RiskTarget Risk Levels
USEPA excess lifetime cancer risk range– EPA’s guidance (OSWER Directive 9355.0-30)
• Where cumulative carcinogenic site risk to an individual based on reasonable maximum exposure for both current and future land use is less than 10-4 , action is generally not warranted.
• Action may be taken at less than 10-4 based on site-specific concerns, but all records of decisions for remedial actions taken at sites posing risks within 10-4 to 10-6 must explain why remedial action is warranted.
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Background Risk: Existing risk of cancer incidence.
Excess Risk: Additional risk of cancer incidence due to exposure to site constituents.
BackgroundCancer Risk
ExcessRisk Limit Total Risk
0.25 1.0E-6 0.250001
0.25 1.0E-5 0.25001
0.25 0.25011.0E-4
Cancer RiskExcess vs. Total Cancer Risk
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Cumulative Cancer RisksExample
Massachusetts has a significant risk definition of 1 X 10-5 for total site cancer risk.
– Method 1 Tables and Method 2 formulas are based on a 1X10-6 for individual chemicals where there are no more than 10 chemicals.
– Method 3 total site risk may not exceed 1 X 10-5
Texas Risk Reduction Program– has a significant risk definition of 1 X 10-5 for individual
chemicals– requires a cumulative adjustment to 1 X 10-5 where there
are more then 10 chemicals
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Non-CancerHazard Quotient
Quantifying non-cancer effects– evaluated by comparing the estimated dose with a
reference dose– ratio is called the Hazard Quotient– a Hazard Quotient of less than one is typically
considered to be of no concern.
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= Risk for a single chemical in Tier 1
= Risk of all chemicals in Tier 3
Additive Non- Cancer RisksExample
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Adequacy of Site Assessment
How much site assessment is necessary?– Command and Control approach: the full vertical
horizontal extent of contamination.– The prescriptive approach: three groundwater wells, 10
foot grids and thousands of soil samples.– The compromise: Data quality objectives and how the
data will be used.– Safety net issues.
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Data Quantity and Quality
What quantity and quality of data is appropriate to make corrective action decisions?
– how will data be used? • indicators and screening• confirmatory and detailed site-specific• statistical representations• fate and transport modeling
– what type of data is needed• physical, chemical and hydrogeological data
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Activity and Land Use
How can land and activity uses other than residential land use be established for a property?
– how to define residential, commercial, industrial or other activities
– use of institutional controls How effective are land and activity use controls in
ensuring that future users will not be adversely affected if chemical(s) of concern remain at a site?
– long term effectiveness and reliability of control– effects of current and future exposures to releases
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Identification and selection of relevant ecological receptors and habitats
General versus specific receptors– example:
• general - a surface water resource passing through a region• specific - a bald eagle in the wetlands adjacent to a site
– could also include habitats– need to consider receptors/habitats and complete
exposure pathways– what decision criteria will be used for the selection?
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Identification and selection of relevant ecological receptors and habitats
Societal versus scientific value– public perception does not always equate to ecological
health• a recreational water body is devoid of fish and water fowl
because the sediments supporting higher levels of aquatic life are non-existent
• society looks at the recreational fish and aesthetics of the water fowl
– scientists looks at the worms
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Identification and selection of relevant ecological receptors and habitats
Individual versus a population/community– individual considered only when rare, threatened or
endangered species are involved– population/community is usually what is considered
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Identification and selection of relevant ecological receptors and habitats
Ecological risk assessment– utilize entry/exclusion criteria as relevant ecological
screening criteria (RESC)• size of site or of population impacted• experience base and characteristics of the site
The process is parallel but much more complicated than for human health
Extensive problem formulation and regulatory discussions required
Re-evaluation is needed with new information
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Wrap up
We have learned why the key technical policy decisions are important.
The decisions must be dynamic, not carved in stone and be flexible enough to change as the program changes.
Social and political considerations must be balanced with
The science of risk assessment and Business and financial interests
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Key Points
Three levels of decisions – the whole program, site-specific and business-specific.– consensus among stakeholders important at all levels.– decisions must deal with uncertainty
Important issues are:– the level of stakeholder involvement– groundwater use and point of demonstration; – target and cumulative or additive risk– adequacy of site assessment– land use– ecological risk assessment
Developing the Site Conceptual Model
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Risk Management under RBCA
Planning and scoping• technical policy decisions• site conceptual model
Iterative evaluation• data collection• fate & transport analyses
Risk-based decisions• further evaluation• remedial action• interim remedial action
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Receptors:
• Residents
• Commercial or Industrial
workers
• Construction workers
• Recreational Users
• Relevant Ecological
Receptors and Habitats
PRIMARY SOURCES
SECONDARY SOURCES
EXPOSUREROUTES RECEPTORS
TRANSPORTMECHANISMS
AffectedSub-surface
Soils (> 3 ft depth)
Sources:
• Product Storage
• Piping/Distribution
• Operations
• Waste Mgmt Units
• Other
Above Ground Storage Tank Piping
Leaching andGround WaterTransport
GROUND WATER
Potable Water Use
Commercial or Industrial Workers
Source Area:
• Surface Soils
• Subsurface Soils
• Dissolved
Ground Water
Plume
• Non-Aqueous
Phase Liquid
(NAPL)
• Sediments
Transport Mechanisms:
• Wind Erosion &
Atmospheric
Dispersion
• Volatilization and
Enclosed Space
Accumulation
• Leaching to Ground
Water Transport
• Mobile NAPL
Migration
• Storm water/Surface
Water Transport
Exposure Routes:
• Dermal Contact
• Ingestion
• Inhalation of
Particulate
• Inhalation of
Vapors
• Potable Water Use:
• Ingestion
• Cooking
• Showering
• Cleaning
• Swimming
Exposure Pathway
Source Transport Receptor
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Site conceptual model (SCM)
An inventory of sources, transport mechanisms, and receptors
Exposure pathway analysis – focus on complete exposure pathways– current and reasonable potential future land
and water use– hydrogeologic characteristics
Factor in characteristics of the material– both toxicity and physical/chemical
Account for potential mitigating factors– including regional characteristics
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Initial Site Assessment
Initial SCM Risk-based Decision• Remedial Action• Collect Additional data• Tier upgrade
Refined SCM
Site Conceptual Model Development
Working hypothesis of site management needs– Updated as new data become available
Valuable communication tool
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Source/Source Area – a source and mechanism for chemical release
into the environment– physical/chemical, toxicological properties
Source
Source
Sources, Transport Mechanisms and Receptors
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Means by which a chemical moves from source to receptor
– transport medium (e.g., air, soil, ground water)
– mechanism (e.g.,ground water flow, air dispersion)
Tra
nsp
ort
Transport
Sources, Transport Mechanisms and Receptors
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Sources, Transport Mechanisms and Receptors
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Receptor
Sources, Transport Mechanisms and Receptors
Based on reasonable potential current & future land and water use
– residents - visitors– relevant ecological receptors & habitats– reasonable potential future receptors
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Sources, Transport Mechanisms and Receptors
Point of Exposure - A point of potential contact of the receptor with the medium
Route of Exposure - means for taking the chemical into the body
Receptor
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Sources, Transport Mechanisms and Receptors
Relevant ecological receptors and habitats
– identify specifies and habitats– develop exposure scenarios– how do we identify?
Receptor
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Example of a conceptual model
Surficial Soil
Potential Receptors
Future Land UseCurrent Land Use
On-Site
Volatilization/Vapor Migration
Volatilization/Vapor Migration
Volatilization/Vapor Migration
Non-AqueousPhase Liquid
DissolvedPhase
Subsurface Soil
Res
iden
ts
Vis
itors
/Oth
er
Com
mer
cial
/Ind
ustr
ial
Wor
kers
Com
mer
cial
/Ind
ustr
ial
Wor
kers
Res
iden
ts
Con
stru
ctio
n W
orke
rs
Res
iden
ts
Vis
itors
/Oth
er
Con
stru
ctio
n W
orke
rs
Com
mer
cial
/Ind
ustr
ial
Wor
kers
Vis
itors
/Oth
er
Con
stru
ctio
n W
orke
rs
Off-SiteOn-SiteOff-Site
TransportMechanisms
ExposureRoute
SecondarySources
Con
stru
ctio
n W
orke
rs
Res
iden
ts
Com
mer
cial
/Ind
ustr
ial
Wor
kers
Vis
itors
/Oth
er
Volatilization/Vapor Migration
Inhalation (Enclosed Space)
Inhalation (Ambient/Outdoor)
Inhalation (Enclosed Space)
Dermal Contact
Inhalation (Enclosed Space)
Inhalation (Ambient/Outdoor)
Dermal Contact
Inhalation (Ambient/Outdoor)
Inhalation (Enclosed Space)
Ingestion
Ingestion (Potable Water)
Ingestion (Non-Potable Water)
Dermal Contact
Inhalation (Ambient/Outdoor)
Inhalation (Ambient/Outdoor)
Wind Erosion/Dispersion
Potentially Completed Pathway - SSTL Calculated
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Chemical Storage Piping / Distribution Operations Waste Management
Unit Soil or Waste Piles Lagoons or Ponds Other
ResidentialResidentialCommercial/IndustrialCommercial/IndustrialConstruction workerConstruction workerRelevant Ecological Relevant Ecological ReceptorReceptor
ResidentialResidentialCommercial/IndustrialCommercial/IndustrialConstruction workerConstruction worker
ResidentialResidentialCommercial/IndustrialCommercial/Industrial
RecreationalRecreationalRelevant Ecological Relevant Ecological ReceptorReceptor
PRIMARY SOURCES
SECONDARYSOURCES
EXPOSUREROUTES
RECEPTORSTRANSPORTMECHANISMS
AffectedSubsurface
Soils (>3 ft depth)
Stormwater/SurfaceWater
Transport
SURFACE WATERRecreational Use/Relevant Habitat
Volatilizationand
AtmosphericDispersion
GROUND WATERPotable Water Use
AIRInhalation of Vapor
or Particulates
SOILDermal Contact
or Ingestion
AffectedSurface
Soils (< 3 ft depth)
Wind Erosion and Atmospheric Dispersion
Volatilizationand Enclosed
Space Accumulation
Mobile NAPL
Migration
DissolvedGround Water
Plume
Leaching andGround Water
Transport
AffectedSurface Soils,Sediments or Surface Water
Non-Aqueous Phase Liquid
(NAPL)
ResidentialResidential
Relevant Ecological Relevant Ecological ReceptorReceptor
Example of a conceptual model (ASTM PS-104-98)
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Scenario Medium Exposure Exposure Receptor Receptor ExposureOn-Site/
Type ofRationale for Selection or
Exclusion
Timeframe Medium Point Population Age RouteOff-Site
Analysis of Exposure Pathway
Current Ground WaterGround Water
Aquifer 1-- Tap Water
Resident Adult DermalOff- Site
QuantResidents currently live next to the
site, and their wells draw from Aquifer 1.
IngestionOff- Site
QuantResidents currently live next to the
site, and their wells draw from Aquifer 1.
Child DermalOff- Site
QuantResidents currently live next to the
site, and their wells draw from Aquifer 1.
IngestionOff- Site
QuantResidents currently live next to the
site, and their wells draw from Aquifer 1.
Trespasser/ Adult DermalOn-Site
NoneNo groundwater seeps or wells on
site.
Visitor IngestionOn-Site
NoneNo groundwater seeps or wells on
site.
Child DermalOn-Site
NoneNo groundwater seeps or wells on
site.
IngestionOn-Site
NoneNo groundwater seeps or wells on
site.
AirAquifer 1--
Water VaporsResident Adult Inhalation
Off-Site
QuantResidents currently live next to the
site, and their wells draw from Aquifer 1.
at showerhead
Child InhalationOff-Site
NoneChildren are assumed not to
shower.
Example of a conceptual model (RAGS Part D)
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Another example of a conceptual
model
From Guidelines for Ecological Risk
Assessment, EPA/630/R-95/002F,
4/98, Final
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Exposure Pathway Analysis
For each complete exposure pathway, a quantitative evaluation of risk can be performed
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Exposure Pathway Analysis
A quantitative evaluation of risk can be performed for each complete or potentially complete exposure pathway
ExposureExposureConcentrationConcentration
xxExposureExposureFactorsFactors
== Health RiskHealth Riskxx ToxicityToxicity
Target Level Calculation
Risk Estimation
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Assessing risk along a pathway
Source
Conceptual Model
Tra
nsp
ort
SourceConcentrations
Risk Estimation
ExposureConcentrations
Dose
HealthRisk
Target Level Calculation
AllowableRisk
AllowableSource
Concentrations
Receptor
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More site-specific
Each step uses a Model
Less site-specific
Components of risk assessment
Fate & Transport
Exposure
Toxicity
Dose
ExposureConcentrations
HealthRisk
SourceConcentrations
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Risk Characterization
Dose-Response
Assessment
Exposure Assessment
Transport Assessment
Source Characterization
Fate &Transport Exposure Toxicity
HealthRisk
SourceConcentrations
ExposureConcentrations
Dose
Risk Assessment Process
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RESEARCH RISK ASSESSMENT
RISK MANAGEMENT
Understanding the mechanistic linkages between:
SourcesExposureDoseResponse
(1) Hazard Identification
(2) Exposure Dose Response Assessment(3) Exposure Assessment
(4) Risk Characterization
(5) Identification of Research Needs
Risk Management Options
Public Health, Economic, Social, Political Consequences of Options
Risk Management Decisions and Actions
Adapted from “Science and Judgement in Risk Assessment”, NRC, 1994
Classic risk assessment paradigm
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Ecological Risk Assessment
Follows a tiered evaluation similar to human health risk assessment
Parallel BUT NOT identical to human health risk assessment
Site conceptual model assists in – putting together scenarios– determining potential risk and exposure
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Ecological Risk Assessment
Important questions in ecological risk assessment are:
– what is important to protect?– how do we identify relevant ecological receptors and
habitats? Requires extensive
– problem formulation– discussion of technical policy decisions with the
regulatory agencies
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Planning and scoping• technical policy decisions• site conceptual model
Iterative evaluation• data collection• fate & transport analyses
Risk-based decisions• further evaluation• remedial action• interim remedial action
Risk Management under RBCA
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Transport
Exposure AssessmentData Collection
Primary objective– evaluate pathways in order to make risk-
based decisions Fundamentally need to address
– what? where? how much? when?– uncertainty in estimate
Data quantity and quality needs vary with tiers and decision-points
– screening level versus modeling effort versus validation
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Transport
Source
Exposure Assessment Sources
Chemicals of concern– e.g., physical, chemical, toxicological
Representative concentration Physical setting
– e.g., soil characteristics, hydrogeology, climate
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Transport
Exposure AssessmentFate & Transport
Partitioning between media Cross-media transfers
– soil-to-groundwater leaching– migration in groundwater– soil-to-air migration
Simple to more complex Empirical versus modeling data Variability and uncertainty
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Exposure
Exposure AssessmentOther Considerations
Land and water use– reasonably current and potential– typically defines receptors
Pathway selection– fate & transport important
Exposure assumptions– who, how much and how often
Chemical availability (bioavailability) Variability and uncertainty
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ToxicityToxicity assessment
Non-carcinogenic effects– leads to the development of malignant cells
• reference Dose (RfD) (mg/kg-day) (oral, dermal)• reference Concentration (RfC) (mg/m3) (inhalation)
Carcinogenic effects– impacts the development, size or functioning of the
whole body or specific organs (including skin and the nervous system) but does not lead to the development of malignant cells
– cancer slope factor (or cancer potency factor) (mg/kg-day)-1
• unit risk (mg/m3)-1 (inhalation, oral)
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Dose-Response Curve (non-carcinogenic effects)
RfD NOAEL LOAEL
Dose (mg/kg/day)
% R
espo
nse
LOAEL - Lowest Observed Adverse Effect Level
NOAEL - No Observable Adverse Effect Level
RfD - Reference dose
X
Toxicity AssessmentNon-Carcinogenic Effects Toxicity
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Toxicity
Toxicity AssessmentNon-Carcinogenic Effects
Reference Dose = NOAEL/(UF1 * UF2 * .... * MF)– Uncertainty Factor(s) (UF) (uncertainty factor is set
equal to 10)• account for variation in general population to protect sensitive
subpopulation.• extrapolate from animals to humans to account for interspecies
variability.• estimate a chronic NOAEL derived from a subchronic study.• estimate NOAEL from LOAEL.
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Toxicity
Toxicity AssessmentNon-Carcinogenic Effects
Reference Dose = NOAEL/(UF1 * UF2 * .... * MF)– Modifying Factor (MF) (ranges from > 1 to 10 with a
default of 1)• reflects a qualitative professional assessment of additional
uncertainties in the study and in the entire database for the chemical(s) of concern and not explicitly addressed in the uncertainty factors.
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Hypothetical Dose-Response Curve
(carcinogenic effects)
0 500 1000| Human exposure | | Animal experiments range | range
Dose (mg/kg-day)
0
0.05
0.1***
*
*
*
95% UCL
Occ
urre
nce
of C
ance
rToxicity AssessmentCarcinogenic Effects Toxicity
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Toxicity
Toxicity AssessmentCarcinogenic Effects
EPA Weight-of-Evidence Classification System for Carcinogenity
Group Description Examples
A Human carcinogen, with sufficient evidence from epidemiological studies Benzene
B1 or B2 Probable human carcinogen
B1 - with limited evidence from epidemiological studies
B2 - with sufficient evidence from animal studies and inadequate evidence or no data from epidemiological studies
Benzo(a)pyrene
C Possible human carcinogen, with limited evidence from animal studies in absence of human data
PCE
D Not classifiable as to human carcinogenicity, owing to inadequate human and animal evidence
EthylbenzeneTolueneXylenes
E Evidence of noncarcinogenicity for humans, with no evidence ofcarcinogenicity in at least two adequate animal tests in differentspecies or in both adequate animal and epidemiological studies
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ToxicityToxicity Assessment
Sources of toxicity information (in order of preference)– state specific toxicity values– Integrated Risk Information System (IRIS)
• only RfDs and slope factors that have been reviewed by EPA.• no external peer review of safe dose estimates (RfDs, SFs).
– EPA Criteria Documents– Health Effects Assessment Summary Tables (HEAST)
• summarizes all toxicity data.• no internal or external peer review of quality of data.
– Agency for Toxic Substances & Disease Registry (ATSDR)
– peer-reviewed literature
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Toxicity Assessment
New directions– benchmark dose– mechanistic
Toxicity
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RiskRisk Characterization
Quantifying non-cancer effects Quantifying cancer effects Other considerations
– cumulative risk/additive effects– addressing uncertainty and variability– synergistic effects
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RiskRisk Characterization
Quantifying cancer risks– estimated as the incremental probability of an individual
developing cancer over a lifetime as a result of exposure to the potential carcinogen
IELCR = Cancer Slope Factor x Lifetime Average Daily Dose
IELCR = Individual Excess Lifetime Cancer Risk
Development of target risk is a policy decision
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RiskRisk Characterization
Quantifying non-carcinogenic effects– evaluated by comparing the estimated dose with the safe
dose (reference dose or reference concentration).– ratio is called the Hazard Quotient (HQ)
HQ = Intake / safe dose• Intake = Applied Dose or Absorbed Dose
– For single chemical evaluation, an HQ<1 means the chemical does not show an effect
– Technical policy on additive effects of multiple chemicals
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ExposureExposureConcentrationConcentration
xx ExposureExposureFactors (Intake)Factors (Intake)
== Health RiskHealth Riskxx ToxicityToxicity(Slope Factor)(Slope Factor)
Target Level Calculation
Example Quantifying Carcinogenic Risks
Residential drinking water
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Intake (mg/kg-day) = CW x IR x EF x ED
BW x AT
CW = Concentration in Water of chemical of concern (mg/l)IR = Ingestion Rate (l/day)EF = Exposure Frequency (days/yr)ED = Exposure Duration (yr)BW = Body Weight (kg)AT = Averaging Time (period over which exposure is averaged) (days)
For noncarcinogens: AT = ED * 365 days per year and intake is called Chronic Daily Intake (CDI).For carcinogens: AT = Lifetime (70 years) * 365 days per year and intake is called Lifetime Average Daily Dose (LADD).
Example Quantifying Carcinogenic Risks
Intake Equation for Ingestion of Drinking Water
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Example Quantifying Carcinogenic Risks
Parameter Definition Units RME MLE
BWa Body Weight, Adult kg 70 70
BWc Body Weight, Child kg 15 15
ATc Averaging time (Cancer) days 25550a 25550a
ATnc Averaging Time (non-Cancer)
days ED x365d/y
ED x365d/yIRwr Drinking water ingestion -
res.l/day 2 1.4
EFr Exposure frequency -resident
day/yr 350 274
EDr Exposure duration -residential
years 30 (6) 8 (6)
Note: value shown in parenthesis represents child valuea - 365 days per year x 70 year lifetime
Exposure Factors for ingestion of drinking water
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IELCR (Risk) = Slope Factor (SF) x Intake
Cw = Risk x BW x AT SF x ED x EF x IR
Risk = SF x CW x IR x EF x EDBW x AT
Example Quantifying Carcinogenic Risks
Calculating concentration in ground water (Cw) - ground water ingestion
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Class Exercise # ??Quantifying Carcinogenic Risks
An adult drinks water containing 0.05 mg/l benzene for 30 years.
– estimate the Individual Excess Lifetime Cancer Risk– estimate the concentration of benzene that will result in
an acceptable risk of 1 X 10-5
The slope factor for benzene is 2.90E-02 (mg/kg-d)-1
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Factor Typical Point
Value Distribution Mean Range
Days at Homeper Year (days/yr) 350 351 323 - 365
Years at Home(yrs)
30 8 1 - 50
Ingestion Rate (L/day)
2 1.4 0.1- 4
Body Weight (kg)
70 71 32 - 115
Deterministic Calculation
Probabilistic risk analysis (PRA) addresses both variability and uncertainty. Example: Residential drinking water pathway
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Concentration (ppm)0.00 0.04 0.08 0.12 0.16
Forecast: Residential Drinking Water Pathway
Mean = 0.03 ppm
Point Estimate = 0.002 ppm95th Percentile = 0.002 ppm
Median = 0.01 ppm
Risk Level =10 -6
Pro
babi
lity
Deterministic Calculation Probabilistic Risk Analysis Results
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Risk Management
Risk-Based Decisions
Policy Decisions – how much risk is acceptable?– data quantity and quality– use of engineering/institutional controls– ecological receptors and habitats to be considered
Other Factors– economics, community issues, aesthetics
Transport