This document discusses Missouri's effort to update its risk-based target levels (RBTLs), which were originally published in 2006 and are used in the state's risk-based corrective action process. The update is needed because EPA toxicity values and methodology have changed, to ensure the RBTLs remain protective, defensible, and consistent. The Missouri Department of Natural Resources is working with the Department of Health and Senior Services on the update. A subset analysis found RBTLs would decrease for around 50% of chemicals and increase an average of 163% for the others. A public review and comment period is planned for early 2014 before finalizing the updated RBTLs in June 2014.

1. Missouri Risk-Based Corrective
Action
Update of Risk-Based Target Levels
Chris Cady, PhD, ESIV
Hazardous Waste Program
November 5, 2013

2. Risk-Based Target Levels
• Published 2006
• Applicable at Tier 1 of MRBCA
• Based on conservative default values
– Toxicity, fate & transport, exposure,
physical/chemical properties
• Update effort does not include Tanks
RBCA

3. Risk-Based Target Levels
• RBTLs not updated since published
• Meanwhile, EPA changes in toxicity,
methodology, equations, exposure factors
• Update RBTLs to ensure protectiveness,
defensibility, and consistency

4. RBTL Update Process
• DNR working with DHSS
– DNR site characterization and risk management
– DHSS risk assessment and target level
calculation
• RBTLs to be consistent with EPA Regional
Screening Levels
– RBTLs for carcinogenic chemicals to be adjusted
to reflect Missouri’s 1x10E-05 risk level

5. Public Review and Comment
• After initial draft RBTLs and supporting
information become available
• Minimum 60-day public review and
comment period
• Meeting if warranted based on comments
received

6. Vapor Intrusion
• EPA uses generic attenuation factors for
GW, soil gas, and sub-slab VI target levels
– Update RBTLs using same approach
– EPA attenuation factors likely to change
• MRBCA includes RBTLs for VI from soil
– EPA does not use soil targets for VI
– MDNR evaluating options

7. New vs. Old
• No comprehensive comparison available yet
• Subset of 26 commonly encountered chemicals
– BTEX, TCE, PCE, cis-1,2-DCE, naphthalene,
VC, etc.
– For ~ 50% of chemicals, RBTL decreases
– Avg. degree of decrease ~ 57%
– Avg. degree of increase ~ 163%*

8. Tentative Schedule
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No external drivers, dates are goals
Initial draft updated RBTLs by end of 2013
Public review Feb – April 2014
Final RBTLs June 2014
RBTLs applicable July 2014

9. Contact Information
Chris Cady, PhD, ESIV, HWP
chris.cady@dnr.mo.gov
(573) 526-8916
Timothy Chibnall, ESIV, HWP
tim.chibnall@dnr.mo.gov
(573) 522-1833