In 2002, the Environmental Protection Agency (EPA) and the U.S. Army Corps of Engineers (the Corps) announced a reg ulation which redefined two key terms, "fill material" and "discharge of fill material," that identify the scope of certain activities subject to regulation under Section 404 of the Clean Water Act. The 2002 final rule completed a rulemaking begun in 2000 by the Clinton Administration. Its proposal had generated support from the mining industry and other regulated groups, and opposition from environmental groups. Their relative positions in support and opposition did not change when the final rule was issued, because it is substantially similar to the earlier proposal. The agencies received over 17,000 comments on the proposed rule. The revised rule was specifically intended to clarify the regulatory definition of fill material under Section 404 by replacing two separate and inconsistent definitions with a single, common definition. In terms of the types of regulated filling activities, it expanded the types of discharge activities that are subject to Section 404 permit requirements specifically to include construction or maintenance of the infrastructure associated with solid waste landfills and mining overburden. Further, the revised rule removed regulatory language which previously excluded "waste" discharges from Section 404 jurisdiction, a change that some argue allows the use of 404 permits to authorize certain discharges that could harm the aquatic environment. This part of the rule conforms with positions taken by the Clinton Administration and endorsed by the Bush Administration in litigation brought by environmental groups which challenged regulation of surface coal mining practices in Appalachia. The Administration's position supported industry's view concerning the proper Clean Water Act mechanism for regulating coal mining. However, that position was opposed by environmental groups, who believe that disposal of coal mining and other waste should be regulated more stringently under other provisions of the Clean Water Act, not Section 404. Thus, at issue was whether the rule change was largely procedural, as proponents argued, or whether it allowed weaker regulatory practices to apply to coal mining, as opponents argued. Under the Clean Water Act (CWA), it is unlawful to discharge any pollutant into waters of the United States without a permit issued in accordance with that act. The CWA contains two different permitting regimes: (1) Section 402 permits (called the National Pollutant Discharge Elimination System, or NPDES, permit program) address the discharge of most pollutants, and (2) Section 404 permits address the discharge of dredged or fill material into navigable waters of the United States at specified sites. The NPDES permit program is administered by EPA. The Corps and EPA have complementary roles under Section 404. Landowners seeking to discharge dredged or fill material must obtain a permit to do so from the Corps. EPA provides environmental guidance on Section 404 permitting and can veto a Corps permit, based on environmental impacts of the proposed discharge activity. The act's two separate permit programs differ in nature and approach. The NPDES program focuses primarily on the effects of discharges from industrial facilities and municipal sewage treatment plants on water quality and evaluates whether the discharge will adversely affect the chemical, physical, or biological integrity of the water. Under that program, pollutant discharges are controlled through the imposition of effluent limitations which restrict the quantities, rates, and concentrations of discharged constituents. Section 402 permits include limitations that reflect treatment with available pollution control technology, either to meet national minimum standards established by EPA, or more stringent treatment levels where needed to meet state-established water quality standards. The standard for issuance of a 402 permit is compliance with the effluent limitation and toxic pollutant control provisions of the act. EPA is authorized to issue NPDES permits; the agency has delegated this responsibility to 45 states, and EPA is the permitting authority in the remaining states. The Section 404 program focuses on discharges of two materials: dredged material and fill material. As described in the April 2000 proposal, "Fill material differs fundamentally from the types of pollutants covered by section 402 because the principal environmental concern is the loss of a portion of the water body itself." In contrast to the NPDES program's specific focus on water quality, the Section 404 program has a broader focus on effects of the discharge on the aquatic ecosystem as a whole, including wetlands. It requires evaluation of alternatives to the discharge and of measures to minimize and compensate for unavoidable adverse effects. Discharges that would have significant adverse effects on aquatic ecosystems are not allowed, and discharges also are not allowed if there are practicable alternatives with less adverse effects on the aquatic ecosystem. The standard for issuance of a 404 permit is consideration of the full public interest by balancing the favorable impacts against the detrimental impacts of a proposed activity to reflect the national concerns for both the protection and utilization of important resources. The Corps and EPA have complementary roles and regulations for the Section 404 program. The Corps' regulations (at 33 C.F.R. Parts 320-330) describe general regulatory policies, permit procedures and processing, and program definitions. EPA's regulations (at 40 C.F.R. Parts 230-232) provide the environmental guidelines for specifying disposal sites for dredged or fill material, procedures for a possible EPA veto of a permit, and definitions. Among the definitions of key terms contained both in the Corps' and EPA's regulations are two closely related definitions, "fill material" and "discharge of fill material." Neither term is defined in the Clean Water Act, leaving it to the administrative agencies to do so. Both the 404 and the NPDES programs regulate the "discharge of a pollutant," which the act defines as including, among others, dredged spoil, solid waste, chemical wastes, biological materials, rock, sand, and cellar dirt discharged into water. The determination of what is "fill material" is important, since fill material is subject to 404 permit requirements, while discharge of non-fill material is subject to NPDES permit requirements. EPA's and the Corps' definitions of "discharge of fill material" previously were identical and remain so in the revised definitions to mean "the addition of fill material into waters of the United States." They list, by way of example, activities typically related to construction for site development, roadways, erosion protection, etc., where the filling in of a waterbody occurs as a necessary element of the project. (40 C.F.R. §232.2 and 33 C.F.R. §323.2(f)) While before 2002 the two agencies defined "discharge of fill material" in identical terms, they had different regulatory definitions for the related term "fill material." The Corps' definition, at 33 C.F.R. §323.2(e), which was adopted in 1977, stated: The term "fill material" means any material used for the primary purpose of replacing an aquatic area with dry land or of changing the bottom elevation of an [sic] water body. The term does not include any pollutant discharged into the water primarily to dispose of waste, as that activity is regulated under section 402 of the Clean Water Act. While the Corps' definition centered on evaluating what is the primary purpose of a prospective discharge to determine whether it would be regulated by Section 404 or Section 402, EPA's definition, at 40 C.F.R. §232.2, focused on the effect of the material. EPA's definition had remained unchanged since it was adopted in 1988. It stated: Fill material means "any pollutant" which replaces portions of the "waters of the United States" with dry land or which changes the bottom elevation of a water body for any purpose. A central purpose of changing the agencies' rules was to conform the Corps' purpose-based definition of "fill material" with EPA's effects-based definition. This change was widely supported in public comments on the proposed rule. In the proposal and the final rule, the two agencies acknowledged that the different definitions and the "primary purposes" basis of the Corps' separate definition had caused confusion for some time, and had led to extensive litigation, as well. For example, the primary purpose test in the Corps' definition appeared to require the Corps to make a subjective determination about the primary purpose of a prospective discharge, and it also allowed a project proponent to seek to affect which regulatory regime would apply (Section 404 or Section 402) by simply asserting a purported purpose. Thus, in the May 2002 revision, the agencies said that they were adopting an identical definition of "fill material" that is more consistent with EPA's previous rule. It now states [T]he term fill material means material placed in waters of the United States where the material has the effect of: (i) Replacing any portion of a water of the United States with dry land; or (ii) Changing the bottom elevation of any portion of a water of the United States. In addition, however, the 2002 revised definition of fill material eliminated language contained in the Corps' previous regulation which had excluded "any pollutant discharged into the water primarily to dispose of waste" from Section 404 authorization. This change reflected the agencies' view that an exclusion for all waste is inappropriate, a view supported in industry comments but opposed by environmental groups. Simply because a material is disposed of for purposes of waste disposal does not, in our view, justify excluding it categorically from the definition of fill. Some waste (e.g., mine overburden) consists of material such as soil, rock and earth, that is similar to "traditional" fill material used for purposes of creating fast land for development. The agencies explained that, while trash or garbage discharges are "generally excluded" from Section 404 because of environmental and health concerns, such discharges may be permissible in some circumstances. "An example would be where recycled porcelain fixtures are cleaned and placed in waters of the U.S. to create environmentally beneficial artificial reefs. Such material would not be considered trash or garbage and thus would not be subject to the exclusion."