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[Closure Plan]

Partial Facility Closure Plan for
B-20 Detonation Area
March 1994

Section 5
Development of a Baseline Risk Assessment

If the B-20 site cannot be closed under risk reduction standard 2, and the results of the remedial investigation indicate the need for a baseline RA, the steps discussed in this section will be followed.  CSSA will use the information obtained from the remedial investigation to develop a baseline RA in accordance with 31 TAC 335 Subchapter S and the following guidance:

 
  • Risk Assessment Guidance for Superfund, volume I, Human Health Evaluation Manual (part A), EPA/540/1-89/002, December 1989.
 

  • Risk Assessment Guidance for Superfund, volume I, Human Health Evaluation Manual, Supplemental Guidance, Standard Default Exposure Factors, OSWER Directive 9285.6-03, March 1991.
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  • Exposure Factors Handbook, EPA/600/8-89/043, July 1989.
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  • Dermal Exposure Assessment:  Principles and Application, interim report, EPA/600/8-91/011B, January 1992.

    • The Baseline RA will evaluate potential risks that might exist if no remediation or institutional controls are applied at the site.  The media to be evaluated for the risk assessment are surface soil, subsurface soil, and surface water.  For the baseline RA, CSSA will use an industrial scenario with little to no exposure rather than the standard exposure factors for residential use of the facility.  31 TAC 335.563 allows for the use of scenarios other than residential, when other land use is more appropriate based on historical, current, and probable future land use and when the probability that the site will support residential use in the future is small.  CSSA has been a military installation since 1917 and has controlled access to the facility.  There are no plans in the future to close the facility or to increase public access to the facility.  Human exposure scenarios will be evaluated for pathway completeness based upon site conditions.  Only those pathways determined to be complete will be quantified in the risk assessment.  The rationale for selection or exclusion of pathways will be provided as part of the risk assessment.

    The baseline RA will be performed using data collected during the remedial investigation.  Background data for total metals will be used for comparative purposes for the site.  The background samples will be collected from a minimum of ten locations across the entire CSSA facility.  Steady-state conditions will be assumed in evaluating future potential risks.  Modeling will not be included in the baseline RA.  Carcinogenic and noncarcinogenic risks will be evaluated; chronic or subchronic noncarcinogenic risks will be utilized as appropriate for the site and actual exposure.  An acceptable risk of 1E-04 will be used as the acceptable upper bound carcinogenic risk value.