Pursuant to a congressional request, GAO reviewed the Environmental Protection Agency's (EPA) decision to limit sulfur dioxide emissions from the Navajo Generating Station, focusing on: (1) the effect on emissions reductions and the associated costs that resulted from the negotiated agreement used by EPA in making its decision compared to its initial proposal; (2) the visibility improvements the agency estimated would result from the emissions controls and the means by which these improvements were determined; and (3) how contingent valuation was used to estimate the monetary value of visibility improvements.

GAO noted that: (1) the negotiated agreement is expected to result in greater emissions reductions at less cost than EPA had initially proposed; (2) the agency initially proposed limiting sulfur dioxide emissions at the Navajo Generating Station by approximately 70 percent at an annual cost estimated between $91.9 million and $128.3 million; (3) the negotiated agreement is expected to increase emissions reductions to approximately 90 percent at an estimated annual cost of approximately $89.6 million; (4) the lower costs resulted from several factors, according to the plant operators; (5) according to a project engineer for the Salt River Project, with its compliance determined on an annual basis, the plant can operate its emission control equipment most days at a rate greater than that needed to cut emissions by approximately 90 percent to make up for those days on which emissions are not controlled because the equipment is not operating; (6) also, delaying the initial installation of the emission control equipment by almost 3 years, from January 1995 to November 1997, allows the project to be completed in a more cost-effective manner; (7) EPA estimated that reducing the sulfur dioxide emissions at the Navajo Generating Station by approximately 90 percent would improve winter seasonal average visibility at the Grand Canyon approximately 7 percent--from about 124 miles to about 133 miles; (8) most of this improvement was estimated to result from improvements during certain winter weather conditions; (9) EPA initially estimated an approximately 14 percent improvement in the winter seasonal average visibility primarily on the basis of a National Park Service study of visibility in the vicinity of the Grand Canyon; (10) EPA revised this estimate to approximately 7 percent after considering the results of other analyses; (11) however, EPA noted that its revised estimated may be understated because it did not include visibility improvements: (a) below the rim of the Grand Canyon; (b) in seasons other than winter at the Grand Canyon; and (c) year round at other nearby national parks; (12) both EPA and the Navajo Generating Station's owners used contingent valuation to estimate the monetary value of visibility improvements; and (13) although relying on the same methodology, the studies were different and yielded widely different results.