On December 20, 1996, EPA proposed a State-administered "Intervention Level" Program under authority of the Clean Air Act to address short-term (5-minute) peak concentrations of SO2 in the ambient air. According to EPA, the program is designed to provide public health protection for asthmatics who may be exposed to elevated short-term concentrations of SO2 in very localized situations.
In May 1996, EPA announced its decision not to revise the existing health-based or primary national ambient air quality standards for SO2. EPA concluded that the current standards provide adequate nationwide protection from adverse health effects associated with sustained, low-level exposure to SO2. However, EPA remains concerned that some asthmatics in very localized situations may be repeatedly exposed to short-term peak SO2 levels of concern while engaged in mild physical activity.
According to the proposal, the Intervention Level Program would be managed by the States. Under the program, States, working in partnership with industrial sources and local communities, would tailor control programs, where necessary, to address any short-term peaks of SO2 in the most flexible and cost-effective manner possible.
Under the authority of section 303 of the Clean Air Act, EPA's proposed Intervention Level Program would establish two 5-minute ambient concentration levels: a concern level of 0.6 parts per million (ppm), and an endangerment level of 2.0 ppm. At or above the concern level, States would be encouraged to investigate the frequency, magnitude, and the sources of 5-minute peak concentrations; consider the risk to nearby populations; determine if corrective action is necessary; and implement the needed corrective action. If the endangerment level is exceeded, the affected State would be expected to take remedial action to prevent imminent and substantial endangerment to public health and welfare caused by high 5-minute ambient concentrations of SO2.
Under the proposed Intervention Level Program, States would be given the flexibility to relocate existing air pollution monitors to areas that may have high 5-minute ambient concentrations of SO2. If needed, States would work with industrial facilities and affected communities to decide upon the best course of corrective action, based on local circumstances, to provide public health protection for asthmatics.
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