Overview of the Proposed Draft B River Corridor Baseline Risk Assessment Report Public Workshop – January 10 & 11, 2008

Overview of the Proposed Draft B River Corridor Baseline Risk Assessment Report

Public Workshop – January 10 & 11, 2008

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River Corridor Closure Safety • Integrity • Teamwork • Disciplined Operations

River Corridor Baseline Risk Assessment – Draft A Comments and Revision

•Draft A issued for regulator and public review late June of 2007•Mid review briefing July 25, 2007•Comment period extended to September 12, 2007•Comment resolution period extension granted•October 30th comment resolution status meeting

–Tri-Parties and public•Path forward for key issues developed with the Tri-Parties

–COPC selection–calculation methodology–MTCA./CERCLA cross-walk

•January 10 and 11, comment resolution meeting

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Draft B RCBRA Overview Discussion

• Proposed structure and content of the Draft B RCBRA

• Discussion of the proposed changes in relation to specific comments

• Opportunity for discussion of specific Draft A comment responses

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Structure and content of the Draft B RCBRA

Changed title – “River Corridor Baseline Risk Assessment”

Report includes areas beyond the 100 and 300 Areas; Inter-Areas, expanded groundwater assessment, future risks

• Retains intent of being a baseline RA based on EPA guidance

• Relates to comments #: 30, 68, 76, 113, 115, 125, 140

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Reorganized Report• Two volumes

– Ecological Risk Assessment

– Human Health Risk Assessment

• Each volume will “stand alone” with separate Executive Summaries

• Each volume will contain text explaining how the reports are organized and where pertinent information can be found

• Relates to comments #: 69, 123

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Executive Summary• Separate Executive Summary in each volume

• Will follow recommended advice from HAB

• Will include important definitions, key to acronyms, and imbedded figures and text

• Relates to comments #: 1, 16, 25, 69, 75, 83

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Regulatory Framework• Risk assessment volumes will include regulatory framework

and future use sections

• Section will include

– Discussion of Remedial Action process at Hanford

– RA and RI/FS Process

– Development of final RODS

– Future use and the role of the CLUP

• Relates to comments #: 21, 28, 45, 80, 84, 111

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Refined Data Set• Corrected transmission errors in the CVP and RSVP data set

• Resampled sculpin for PCB congeners and organic/inorganic arsenic

• Adding Inter-Areas results to data set

• Adding groundwater data from an enlarged set of wells

• Additional reference site data – Inter-Areas and Central Plateau

• Relates to comments #: 20, 78, 85, 92, 124, 137, 143

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Refined Data Handling/Calculation Methodologies• COPC refinement process was developed

with Tri Parties input

• Representative Concentration (RC) calculation process was developed with Tri Parties input

• Relates to comments #: 6, 17, 57, 72, 116

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Contaminants of Potential Concern (COPC)

Overview• An appropriate list of COPCs is critical to preparing an

assessment that is representative of Hanford Site risks and useful for making remedial action decisions

• Comments on the Draft A report questioned the ability of the risk assessment to accurately differentiate between background materials, non-site related materials, and contaminants directly related to waste sites

• A process was developed to identify and focus the COPCs

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Regulations and guidance• RAGS Part A Chapter 5: Data evaluation

• Considerations include

– Data quality

– Background values

– Toxicity

– Detection frequency

Detected?SAP

IndicatorCont.?

Not a COPC

Further evaluatione.g., appropriate method?,

tox value?, process knowledge?Outcomes are “not a COPC”

or “uncertain COPC”no

yesyes

>Backgroundor reference?

Not a COPC

yes

yes

no

Toxic? no

mettargetDL?

no

Uncertain COPC

no

yes

Narrative analysise.g., detect freq.?, multimedia?,

process knowledge?Outcomes are “COPC”

or “not a COPC”

COPC Refinement Logic

Notes:COPC list is developed for each Operating Areabased on soil, sediment, water, and tissue data.

Short half-life or essential

nutrient?

Not a COPCyes

no

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Path forward

• Methodology will be included in Draft B of the report

• List of COPCs will be developed for initial regulatory review in early March 2008

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Representative Concentrations

Overview• Representative concentrations are used in the human health

and ecological risk assessments

• The risk assessments include an evaluation of the central tendency exposure (CTE) and the reasonable maximum exposure (RME)

• The CTE and RME provide risk managers with estimates of typical and high-end exposures

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Overview (cont.)• In Draft A representative concentrations were calculated using

means as CTE estimates and upper 95% confidence limits (UCLs) on the mean as RME estimates

• Approach was applied across all data sets and analytes– In several cases data had not been collected with the intention of

supporting UCL calculations

• UCLs were based on a default assumption of lognormal and were calculated using Land’s method– Some UCL values in were much higher than the maximum value

• Process proposed for Draft B follows EPA guidance as provided in the ProUCL Version 4 User Guide and Technical Guide

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• Issues to consider for determining the most appropriate methods for estimating representative concentrations for CTE and RME scenarios.

– How many sample results are available for the exposure unit?

– Are the data censored (are there non-detect sample results)?

– What estimation methods are mathematically stable for the data being evaluated and therefore provide reasonable estimates of the mean and upper bound on the mean?

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Regulations and guidance

• ProUCL Version 4

• WAC 173-340-740(7) Compliance Monitoring for Soil

• Considerations include

– Number of samples

– Statistical distribution

– Detection frequency

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Considerations for handling non-detects include:

• Ensure detection limits are adequate prior to eliminating non-detected contaminants (COPC evaluation)

• Use ranking methods or other replacement methods that eliminate problems associated with replacing all non-detects with a single value (half detection limit)

• Determine if transparency of results is improved by emphasizing detected values in the calculations

• ProUCL Version 4 recommends two methods

– Kaplan-Meier estimation

– Regression on Order Statistics

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• Considerations for determining Representative Concentrations include:

– Number of samples and number of detections

– Sample type for CVP/RSVP data

– Data distribution

– Spread in the data

– Ratio of the maximum to the median

– Selection of a widely acceptable statistical estimating tool (ProUCL)

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• Approaches for small numbers of detects:

– n = 1; then result is the CTE, no RME,

– n = 2; then maximum detect is the CTE, no RME, and

– n = 3 or 4; then the average is the CTE, maximum detect is used as RME. RME values based on the maximum detect will be flagged in the RC tables and this protocol will be clearly explained in the text.

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Approaches for five or more detects:

• Take median of three estimators for RME

– Parametric UCL

• Adjusted gamma or bootstrap

– Non-parametric UCL

• Chebyshev or bootstrap

– Student’s t

• Further evaluation for deviant estimators (>10% difference)

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Path forward

• Methodology will be included in Draft B of the report

• Consensus from the Regulators is to use methods based on ProUCL for the Draft B report

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Reference Site Evaluation• Clear discussion and evaluation of reference sites and

reference site data

• Additional reference site results added to the data set

– Inter-Areas reference area results

– Central Plateau Ecological RA reference area results

– Applicable results from the Surface Environmental Surveillance Program (SESP)

• Relates to comments #: 6, 92, 137, 143

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Presentation of Risk• Focus on Hanford-related contaminants

• Clear discussion of incremental (above background) risk

• Enhanced assessment of groundwater, including qualitative assessment of future risks

• Assess and clearly present total risk and risk pertinent to remediation decision-making

• Relates to comments #: 8, 9, 10, 11, 12, 13, 14, 15, 19

Presentation of Risk (cont’d)• Package risk conclusions for 6

operating areas along the River Corridor

– 100-B/C Area

– 100-K Area

– 100-N Area

– 100-D and 100-H Areas

– 100-F Area and 100-IU-2/100-IU-6

– 300 Area

• Corresponds to future for RODs


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Application of Model Toxics Control Act (MTCA)• Provide stand-alone information comparing remediated sites

to MTCA levels

– Comparison of residual soil contamination concentrations to MTCA levels

– Shallow and deep soil sample results will be compared to groundwater protection cleanup values using the MTCA 3-phase leaching model

• Relates to comment #: 77

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In response to comments, the Draft B RCBRA will:

• Expanded the risk assessment by adding inter-areas, expanded groundwater assessment, and future risks

• Include additional data from several sources

• Provide a clearer presentation of risk and conclusions

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Discussion of Specific Draft A

Comment Responses

Documents

Overview of the Proposed Draft B River Corridor Baseline Risk Assessment Report Public Workshop – January 10 & 11, 2008