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

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

2. 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

3. 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

4. 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

5. Structure and content of the Draft B RCBRA 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

6. Structure and content of the Draft B RCBRA 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

7. Structure and content of the Draft B RCBRA 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

8. Structure and content of the Draft B RCBRA 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

9. Structure and content of the Draft B RCBRA 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

10. 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

11. Contaminants of Potential Concern (COPC) Regulations and guidance • RAGS Part A Chapter 5: Data evaluation • Considerations include • Data quality • Background values • Toxicity • Detection frequency

12. River Corridor Closure Safety • Integrity • Teamwork • Disciplined Operations COPC Refinement Logic Short half-life or essential nutrient? yes Not a COPC Further evaluation e.g., appropriate method?, tox value?, process knowledge? Outcomes are “not a COPC” or “uncertain COPC” no no SAP Indicator Cont.? no Detected? yes yes met target DL? >Background or reference? yes Not a COPC no no Not a COPC yes Uncertain COPC Toxic? no yes Notes: COPC list is developed for each Operating Area based on soil, sediment, water, and tissue data. Narrative analysis e.g., detect freq.?, multimedia?, process knowledge? Outcomes are “COPC” or “not a COPC” E0801019_12

13. Contaminants of Potential Concern (COPC) 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

14. 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

15. Representative Concentrations 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

16. Representative Concentrations • 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?

17. Representative Concentrations Regulations and guidance • ProUCL Version 4 • WAC 173-340-740(7) Compliance Monitoring for Soil • Considerations include • Number of samples • Statistical distribution • Detection frequency

18. Representative Concentrations 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

19. Representative Concentrations • 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)

20. Representative Concentrations • 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.

21. Representative Concentrations 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)

22. Representative Concentrations 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

23. Structure and content of the Draft B RCBRA 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

24. Structure and content of the Draft B RCBRA 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

25. River Corridor Closure Safety • Integrity • Teamwork • Disciplined Operations Structure and content of the Draft B RCBRA 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 E0801019_25

26. Structure and content of the Draft B RCBRA 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

27. 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

28. Discussion of Specific Draft A Comment Responses