Environmental Cleanup at Navy Facilities Risk-Based Methods (1999) / Chapter Skim
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2 Review of Risk-Based Methodologies
2 Review of Risk-Based Methodologies
Pages 35-67
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From page 35... ...
, the EPA Science Advisory Board's Integrated Risk Project, the Lawrence Livermore National Laboratory/University of California studies on leaking underground fuel tanks, and numerous state variations on the practices and methods of ASTM and the EPA. A risk-based methodology is defined as a process that combines environmental data obtained for a hazardous waste site, risk assessment calculations, and a series of risk management decisions.
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From page 36... ...
Risk management decisions generally consider societal values, economic cost, and other factors that are outside the formal risk assessment process. Risk Assessment Risk assessment is generally applicable to a wide variety of scenarios, including environmental cleanup of hazardous waste sites.
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From page 37... ...
to 10= for one' s lifetime risk from exposure to carcinogens and a hazard quotient of 1.0 for noncarcinogens. As our state survey shows, acceptable risk levels across the state regulatory agencies tend to mirror EPA guidance.
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From page 38... ...
When such factors as feasibility and cost are not considered in an analytic paradigm similar to risk assessment, risk management frequently results in the misdirection of resources, incomplete protection of public health and the environment, and the loss of institutional credibility, public trust, and standing. One of the most important risk management decisions to be made at hazardous waste sites is the selection of a remedy.
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From page 39... ...
· volatilization from ground water to outdoor air · volatilization from ground water to indoor air or other confined space · volatilization from vadose zone (free product or soil) to outdoor air, indoor air, or other confined space · volatilization from surface water to outdoor air · erosion and surface water runoff · fugitive dust (wind erosion)
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From page 40... ...
These documents guide regulators, responsible parties, and stakeholders through the risk-based portion of the investigation, characterization, and remedy selection and implementation at a hazardous waste site. The first document, Risk Assessment Guidance for Superfund, Part A, focuses on developing a baseline risk assessment.
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From page 41... ...
/Remedial Action (RA) Technical plan preparation.
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From page 42... ...
Part A of RAGS is used for an initial estimation of risk at a hazardous waste site that can be compared to some acceptable target risk level. The risk estimate is generally calculated for both soil and ground water contamination.
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From page 43... ...
Only residential land use is considered, and six exposure pathways are specified, including direct ingestion of soil and ground water contaminated by soil, inhalation of volatiles and dust, dermal absorption, ingestion of produce that has been contaminated by soil, and migration of volatiles in basements. These criteria are used to formulate generic Soil Screening Levels (SSLs)
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From page 44... ...
· Organize and Analyze existing site data receptors Identify known sources of contamination Identify affected media Identify potential migration routes, exposure pathways, and · Construct a preliminary diagram of the CSM · Perform site reconnaissance Confirm or modify CSM Identify remaining data gaps Step Two: Compare Soil Component of CSM to Soil Screening Scenario · Confirm that future residential land use is a reasonable assumption for the site · Identify pathways present at the site that are addressed by the guidance · Identify additional pathways present at the site not addressed by the guidance · Compare pathway-specific generic SSLs with available concentration data · Estimate whether background levels exceed generic SSLs Step Three: Define Data Collection Needs for Soils to Determine Which Site Areas Exceed SSLs Develop hypothesis about distribution of soil contamination (i.e., which areas of the site have soil contamination that exceed appropriate SSLs?
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From page 45... ...
Data collected from sites with contaminated soil are compared to generic Soil Screening Levels (SSLs)
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From page 46... ...
The generic Soil Screening Levels developed by the EPA have many counterparts in regulatory programs at the state level. (Many states have devised generic screening levels for contaminated ground water as well)
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From page 47... ...
These activities are evaluated by means of five-year reviews. If continued monitoring of all remedies demonstrates that the site no longer poses significant risk to human health and the environment, the site may be closed out.3 At any time during the investigation or cleanup phases, interim remedial actions (IRA)
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From page 48... ...
Petroleum RBCA (E 1739-95) Petroleum RBCA provides a tiered approach for developing a remedial action plan for leaking USTs (similar to the tiered approach of the Soil Screening Guidance)
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From page 49... ...
· Reclassify site as appropriate following initial response action I interim remedial action, or additional data collection. Tier 1 Evaluation · Identify reasonable potential sources, transport pathways, and exposure pathways (use flowchart given in Figure 2)
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From page 50... ...
. Sources include tanks, pipelines, and free product.4 Possible exposure pathways include movement with the ground water, sorption onto solids, and volatilization and migration to the surface.
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From page 51... ...
Because of the potential for their misapplication, considerable attention has been given to the RBSL values given in the appendixes of the petroleum RBCA standard guide. Table 2-2 compares these RBSLs to the RBSLs found in the chemical RBCA standard guide, the EPA generic soil screening levels, RCRA cleanup criteria, and several state generic screening levels.
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From page 52... ...
52 Cq be = a' VO o VO C)
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From page 53... ...
The major driver here is cost: will the cost of a tier 2 analysis and its projected outcome be less than remedial action to achieve RBSLs? The tier 1 analysis does not consider uncertainty in the data used to make the decision.
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From page 54... ...
If concentrations of CoCs are greater than SSTLs for one or more exposure pathways, the user must decide whether to proceed to a tier 3 analysis or to institute remedial action. Again, the major driver is cost.
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From page 55... ...
The major additions are a consideration of ecological risk and cumulative risk and details contained in the appendixes where examples of the framework are given. The chemical RBCA framework is summarized in Figure 2-4, which is almost identical to Figure 2-3, except for (1)
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From page 56... ...
FIGURE 2-4 The three-tiered chemical RBCA flowchart. Note the inclusion of ecological risk at each stage, and the option of returning to a tier evaluation if site conditions change.
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From page 57... ...
The flowchart is used during the tier 1 evaluation in conjunction with Figure 1 from ASTM, 1998. This version of the tier 1 evaluation contains a consideration of relevant exposure pathways that can lead to early site closeout.
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From page 58... ...
If concentrations of CoCs are less than SSTLs and SSEC, limited further action may be required. If concentrations of CoCs are greater than SSTLs or SSEC for one or more complete or potentially complete exposure pathways, the user may proceed to a tier 3 analysis or institute remedial action.
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From page 59... ...
A major addition to chemical RBCA is Appendix X1, "Considerations for Development of a RBCA Program." Here general, although minimal, guidance is given regarding cumulative risk, the acceptable risk level, site characterization, ecological risk assessment, selection of remedial actions, monitoring network design, performance criteria, reopening of sites, site closure, and public involvement and risk communication. The appendix provides a matrix for use as an aid in making technical policy decisions and a checklist for implementing a RBCA program.
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From page 60... ...
There is considerable variation in the differences between each state's riskbased decision-making process and the ASTM RBCA standard guidance. Many states have begun using the ASTM standard guide for petroleum releases at storage tank sites and have made only minor changes to the methodology.
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From page 61... ...
Generic soil and ground water screening levels developed by states represent a type of tiered approach, because they allow low-risk sites to be eliminated from further consideration in the same way that a RBCA tier 1 evaluation does. Table 2-2, which compares RBCA tier 1 RBSLs with state generic screening levels, reveals the substantial variability in the value of these screening levels for direct ingestion of soil.
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From page 62... ...
Many states and the ASTM RBCA standard guide also consider free product to be a source. For many technical reasons, source removal of free product is particularly difficult (NRC, 1994~.
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From page 63... ...
Almost all states protect the quality of ground water with statutes that declare all ground water to be a potential drinking water supply. This assumption introduces many more potential exposure pathways into the risk assessment process.
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From page 64... ...
In some states, the acceptable levels of individual and cumulative risk are different, with the cumulative risk level often being 10 times less conservative than the individual risk level. Another major difference between petroleum RBCA and chemical RBCA is the inclusion in chemical RBCA of ecological risk assessment.
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From page 65... ...
The EPA, recognizing the increased use of risk-based approaches, is currently drafting guidance for the states on some of these emerging issues, such as ecological risk assessment, natural attenuation, and institutional controls (EPA, 1997a, b, c, 1998b)
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From page 66... ...
1998a. Risk Assessment Guidance for Superfund, Volume I, Human Health Evaluation Manual (Part D, Standardized Planning, Reporting, and Review of Superfund Risk Assessments)
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