Thank you for your letter of May 19, 2000, transmitting the Science Advisory Board (SAB) Advisory on the Draft Agency Case Study Analysis of the Residual Risk of Secondary Lead Smelters (EPA-SAB-EC-ADV-00-005). During the review of the Residual Risk Report to Congress in August 1998, the Science Advisory Board requested that the Environmental Protection Agency (EPA) provide an example residual risk assessment for its evaluation. We submitted our draft assessment of the secondary lead smelter source category and would now like to respond to your letter transmitting the SAB advisory for this case study.

The purpose of seeking an SAB advisory was to get feedback on the methodologies EPA will use to assess residual risks and the application of those methods to a specific source category. We asked the SAB to comment on: 1) the appropriateness of the methods used, given the currently available methods; and 2) the appropriateness of the application of those methods. We sought SAB feedback early in our residual risk assessment process in order to be able to apply the advice received to other risk assessments under the residual risk program which, due to statutory requirements, needed to be started soon.

This draft case study does not include all risk assessment components needed to make a regulatory decision under the Residual Risk program (e.g., an assessment of population risks). Because of this, we agree with the SAB that peer review of the final complete assessment is needed. We intend to seek such a review in 2001.

We are pleased that the reviewers recognize that methods used in this case study assessment are consistent with the methods described in the Residual Risk Report to Congress, that the assumptions used are consistent with current methods and practice, and that the models used for the air pathway are the most appropriate for the task. Our response to additional comments and recommendations highlighted in your review are enclosed.

This SAB advisory will help us design the final iteration of the secondary lead smelter risk assessment. We are also applying your advice to the other risk assessments we are required to conduct under the residual risk program. Thank you for your assistance.

Sincerely,

Carol M. Browner

Response to Additional Comments and Recommendations

SAB comment: Population risk estimates are lacking from the case study.

EPA response: EPA will include an assessment of population risks in the final iteration of the assessment, following the method we outlined in the draft case study.

SAB comment: Ecological screen is adequate but refined ecological risk assessment is lacking, as are the methodologies.

EPA response: EPA did not present a more refined ecological risk assessment in the draft case study, as we have not yet completed development of a refined ecological risk assessment methodology for the residual risk program. We are working to develop a refined methodology and will use our most current methodology in the final iteration of the secondary lead smelter risk assessment.

SAB comment: Uncertainty and variability analysis should be fully integrated into all phases of the assessment, not just an auxiliary analysis after the deterministic assessment.

EPA response: EPA agrees with the Science Advisory Board that integrating uncertainty and variability analysis into the overall assessment rather than conducting it as an add-on analysis of the deterministic results is important. EPA is incorporating that advice into our assessments. We are conducting uncertainty and variability analyses at each phase of the assessment to determine how assumptions are supported by the data, and what the implications are for each assumption. While there is no consensus among experts on a methodology to conduct uncertainty and variability analysis, we will continue to seek out experts and use methods which are appropriate to the task.

SAB comment: The model used for multimedia fate, transport and multipathway exposure assessment, the Indirect Exposure Methodology (IEM) has several limitations, and has not been sufficiently evaluated. Results should be viewed with informed caution and results ground-truthed against available data. TRIM is seen as major improvement.

EPA response: EPA recognizes the importance of evaluating models and ground-truthing the results of the models we use in support of regulation. EPA intends to evaluate model inputs and ground-truth results to the extent data are available. (Data were not readily available on the four facilities we evaluated but may be available for others; for other source categories, such information maybe more (or less) available.). EPA will ensure that the limitations and uncertainties of IBM outlined by the SAB are clearly articulated to the risk managers. We agree that TRIM will generally be an improvement relative to IEM. We look forward to further comments on our approach to multimedia modeling in the peer review of the completed assessment.

SAB comment: There is insufficient explanation about the interface between risk assessment and risk management; without this context it is difficult to adequately review the assessment.

EPA response: EPA will explain more about the Residual Risk program mandate and its approach to risk management in the final iteration of the assessment. We will specifically describe how the risk assessment feeds into the risk management process.

SAB comment: There is incomplete toxicity data on some HAPs and the data in Integrated Risk Information System (IRIS) may be seriously out of date for others.

EPA response: EPA is not limited to using data within IRIS. EPA has identified a number of additional peer reviewed data sources, from which relevant information can be obtained. These data sources include peer reviewed databases developed by the Agency for Toxic Substances and Disease Registry and California EPA. The SAB concurred with our use of the data from these sources, which allow EPA to both assess HAPs for which assessments are not currently available on IRIS and to consider information from other sources that may be more current and relevant than that available on IRIS. HAPs with no assessments on IRIS or elsewhere receive priority in our yearly list of IRIS assessment starts. Additionally, we are carefully considering the SAB's recommendation to develop interim methods for assessing HAPs without available assessments.

Several members of an ad hoc Science Advisory Board (SAB) panel are criticizing a commentary issued by the SAB's own executive committee that questioned whether EPA was equipped to implement a major residual risk analysis program Mat requires EP.6, to assess 174 industrial source categories.

The residual risk analysis program, mandated by section 112(f) of the Clean Air Act, requires the agency to conduct assessments of 174 industrial source categories after their air toxics emissions sources have been controlled by maximum achievable control technologies (MACT) to determine if further controls are necessary. Under the CAA amendments of 1990, residual risk assessments must he completed eight years after the MACT standards for each hazardous air pollutant (HAP), are set.

Prompted by the ad hoc SAB panel's critical review of the agency's approach to the residual risks posed by secondary lead smelters, the executive committee July 25 urged EPA Administrator Carol Browner and Congress to "seriously reconsider the current Clean Air Act Amendments mandate and their implementation strategy that depends on scientific analyses that will be resource-demanding at a minimum, and, quite possibly, impossible to carry out in a credible manner.'' While the committee endorsed the concept of science-based decision making at the agency, it also recognized "that no one is well served by asking science to take on an impossible task."

But several members of the ad hoc SAB lead smelters panel now say the commentary goes too far. According to one panelist, "we were highly critical but took a constructive approach by emphasizing that the agency needs to have a probabilistic approach to the data early on." This source says it is "quite possible for the agency to carry out such analyses in a credible manner." Several members reportedly have approached the ad hoc panel's chair, Phillip Hopke, with their concerns about the executive committee's commentary. Another smelter panel source emphasizes that the investment of more time and resources in the program would be worthwhile in the residual risk program "given that you're dealing with a sophisticated industry with some past history of litigation." The issue captured the attention of Senate lawmakers who scheduled a hearing on the residual risk issue in late July, but cancelled it because of scheduling conflicts.

EPA officials, meanwhile, have maintained that the agency has the resources and technical skill to conduct the analysis and will work with industry stakeholders to collect the data required to conduct residual risk analyses and move forward with decisions (Risk Policy Report, May 15, p7; April 18, p33). One of the central reasons the executive committee opted to write a commmentary was that EPA has substantial information on lead anissions unlike many of the other HAPs that must still be reviewed. Residual risk analyses call for the characterization of multiple HAPs, ecological risk analysis, population risk estimates and careful assessment of uncertainty and variability (Risk Policy Report, June 19, p15).

According to one EPA official "in my view the commentary went beyond what rbe SAB is charged to do which is to peer review science. Should the board tell the agency when there is an adequate basis for a decision? That is the essence of making a policy call, and without seeing the details of the original analysis, in my view they went over the line."