Timeline of visibility and regional haze-related actions affecting the Navajo Generating Station

SRP submitted a proposed BART modeling protocol to EPA in September 2007, and submitted an initial BART report to EPA in November 2007. Based on an evaluation of the five statutory factors, SRP concluded that BART for NGS can be achieved by installing Low-NOx Burners and Separated Overfire Air (LNB/SOFA) on all three units at NGS. The primary basis for this conclusion is that the cost of the more stringent NOx control option, selective catalytic reduction (SCR), is more than 10 times the cost of LNB/SOFA, and is only predicted to result in a small visibility improvement relative to LNB/SOFA. Accordingly, SRP concluded that SCR cannot be justified as BART.

EPA revised its regional haze rule and issued guidelines for making BART determinations. The rule calls for imposition of BART if a source "may reasonably be anticipated to cause or contribute to any impairment of visibility in any mandatory Class I Federal area." In determining what constitutes BART for a particular source, the states (and EPA) must consider five factors, including the cost of compliance and the degree of visibility improvement which may reasonably be anticipated to result from the use of the technology. The guidelines include presumptive limits for nitrogen oxide (NOx) emissions from large coal-fired power plants, and say that these presumptive limits "are extremely likely to be appropriate" for such plants. "Based on our analysis of emissions from power plants," EPA said, "we believe that applying these highly cost-effective controls at the large power plants covered by the guidelines would result in significant improvements in visibility and help to ensure reasonable progress toward the national visibility goal." EPA's presumptive limits are based on the use of combustion controls, such as low-NOx burners, at such plants.

The United States Court of Appeals for the District of Columbia Circuit found EPA's regional haze rule contrary to the Clean Air Act in important respects, including because it forced the states to require BART controls at sources without any empirical evidence of the particular source's contribution to visibility impairment in a class I area.

EPA issued its final regional haze rule. The rule required that all states submit an implementation plan that provides for reasonable progress toward achieving "natural background conditions" in national parks and wilderness areas by 2064. The rule required that the states identify those sources that are subject to BART requirements and then determine what constitutes BART for such sources.

EPA issued a notice of proposed rulemaking for regional haze, and received more than 1,300 comments on its proposed rule.

The GCVTC issued its report to EPA. The report included a series of recommendations for reducing visibility impairment attributable to man-made sources.

EPA proposed to revise the federal implementation plan for Arizona to address winter visibility impairment at the Grand Canyon that it claimed was associated with sulfur dioxide (SO2) emissions from Navajo Generating Station (NGS). In October of that year, EPA issued a final rule that required a 90 percent reduction in SO2 emissions from NGS. The Central Arizona Water Conservation District (CAWCD), which operates the Central Arizona Project (CAP), challenged that rule, but the rule was upheld by the United States Court of Appeals for the Ninth Circuit. In order to comply with the rule, Salt River Project (SRP), the operator of NGS, installed SO2 scrubbers at NGS at a cost of more than $400 million.

Congress again amended the Clean Air Act, adding section 169B, which required, among other things, that EPA undertake research to identify "sources" and "source regions" of visibility impairment in Class I areas and establish a visibility transport commission for Grand Canyon National Park. EPA established the Grand Canyon Visibility Transport Commission (GCVTC) in 1991.

EPA disapproved the state implementation plans of 29 states, including Arizona, for failing to comply with the visibility regulations. Over the next few years, EPA investigated visibility impairment at several class I areas, including Grand Canyon National Park.

Environmental groups sued EPA to compel it to adopt federal implementation plans for those states that had failed to submit revised state plans. The parties reached a settlement agreement in 1984 that required EPA to review all state implementation plans for deficiencies and allow states to cure those deficiencies. If the states failed to cure the deficiencies, the consent decree required EPA to issue its own visibility implementation plans for such states.

EPA adopted visibility regulations under section 169A of the Act. The regulations adopted a "phased approach to visibility protection." Phase I was directed at visibility impairment "that can be traced to a single stationary facility or a small group of stationary facilities." EPA required all states to submit revised visibility implementation plans within nine months. Most states failed to do so. EPA deferred addressing other types of visibility impairment, such as "regional haze" caused by a multitude of sources.

EPA identified 156 mandatory class I Federal areas, including Grand Canyon National Park.

Congress substantially amended the Clean Air Act. The amendments included section 169A, which declared "as a national goal the prevention of any future, and the remedying of any existing, impairment of visibility in mandatory class I Federal areas," such as national parks. Congress required EPA to adopt regulations to assure "reasonable progress toward meeting this national goal." Measures for achieving reasonable progress were to include best available retrofit technology or "BART" for certain existing stationary sources and a long-term strategy.