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EVALUATION OF WHITEX · 37 THE COMMIl l HE'S CONCLUSIONS IN PERSPECTIVE The committee cautions that its conclusions do not resolve whether EPA should require NGS to install the best available retrofit technology. First, the committee's conclusions are not binding on EPA or any other government agency. Second, even if accepted by EPA, the committee's conclusions would not dictate a particular result to EPA!s rule making. Section 169A of the Clean Air Act generally requires the installation of BART on any Major sta- tionary sources built after 1962 if that source remits any air pollutant which may reasonably tee anticipated to cause or contribute to anyimpairment of v~sibility~ in a listed Class I area, such as GCNP. The phrase "may reasonably be antici- pated" suggests that Congress did not intend to require EPA to show a precise relationship between a source's emissions and all or a specific fraction of the visibility impairment within a Class I area. Rather, EPA is to assess the risk in light of policy considerations regarding the respective risks of overprotec- tion and underprotection (U.S. Congress, 1977~. These considerations tran- scend scientific issues and are, therefore, outside this committee's purview. CONCLUSIONS The committee *oncludes that an experiment such as the WHITEX study provides a valuable data base that sheds light on the nature and magnitude of the haze problems at GCNP. The use of CD4 as a tracer was innovative and added- considerable power to the program. NPS and the members of the WHITEX team are to be commended for including the use of this unique and powerful tracer in WHITEX and for attempting to use CD4 in qualitative and quantitative assessments of the impact of NGS emissions on haze at GCNP. The NPS mounted a very complex atmospheric measurement and analysis program at many field sites in a region that is logistically difficult to service, and UPS went well beyond the original planned feasibility study. On the basis of the data presented in the NPS-WHITEX report, the committee concludes that, at some times during the study period, NGS contributed significantly to haze at Hopi Point in GCNP. The committee bases this qualitative assess- ment on evaluations of meteorological, photographic, chemical, and other physical evidence. The committee also concludes that aspects of the WHITEX data analysis preclude a quantitative determination of the exact fraction of the Grand Can- yon haze problem that is attributable to NGS. These aspects are primarily related to problems with implementation and interpretation of multiple linear regression models. The NPS-WHITEX report makes few attempts to quantify
38 · ~1ZE IN THE GRAND CANYON the sensitivity of the analyses to departures from model assumptions or to establish an objective and quantitative rationale for selecting among venous statistical models. In addition, there were weaknesses in the data base. Espe- cially damaging were the absence of measurements within the Grand Canyon itself and the inadequate consideration of background SO4= concentrations In the vicinity of the GCNP. The committee does not believe that its report resolves the regulatory issues before EPA regarding NGS. These issues involve policy considerations outside the committee's purview. In closing, the committee stresses that the deficiencies of the NPS- WHITEX report appear largely due to unexpected problems that often accompany the use of new scientific approaches. WHITEX may, therefore, be valuable to other researchers in designing and carrying out source- attribution studies. .,
