GWIN, D. J., delivered the opinion of the court, in which CLAY, J., joined. SUHRHEINRICH, J. (pp. 985-89), delivered a separate opinion concurring in part and dissenting in part.
GWIN, District Judge.
Here, a Kentucky nonprofit corporation (the Kentucky Resources Council) and a national organization that advocates clean-living conditions for residents of the nation’s coalfields (the Citizens Coal Council) petition this Court to invalidate a final rule that the Environmental Protection Agency promulgated on January 23, 2002 (“Final Rule”).1 We refer to the Kentucky Resources Council and the Citizens Coal Council collectively as “Petitioners” and the Environmental Protection Agency as “EPA.”
The Final Rule applies to once-abandoned coal mines that operators later reopen and remine. In addition, the Final Rule applies to coal mines in the arid regions of the Western interior states. Petitioners argue that the EPA’s Final Rule exceeds its statutory mandate and urge this Court to strike it down.
For the following reasons, we invalidate the regulations the EPA promulgated in the January 23, 2002 Final Rule, and remand.
BACKGROUND
The Clean Water Act (“CWA”)2 is an enigmatical piece of legislation. Filled with more sesquipedalian jargon than a year’s subscription to any trade journal and a byzantine system of cross references, its intricacies are virtually indecipherable.3 Perhaps this explains the parties’ inability to agree on seemingly any aspect of the statute or the EPA’s Final Rule. What follows is our attempt to navi[972]*972gate this legislative labyrinth and to translate its environmentalese into English:
The CWA seeks to restore and maintain the integrity of the nation’s water.4 To further the goals of restoring and maintaining clean water, the CWA includes both technology-driven limits and water-quality-based limits on pollution.5 The technology-based limits aim to prevent pollution by requiring polluters to install and implement various forms of technology designed to reduce the pollution discharged into the nation’s waters.6 On the other hand, the water quality regulations kick in once a given body of water’s pollution level exceeds the level that a state deems acceptable for the body of water’s intended use or function.7 They endeavor to cure an aquatic tragedy of the commons where the aggregate impact of polluters’ activities-despite compliance with the technology-based regulations-causes unacceptable pollution. When this happens, the water-quality-based regulations ratchet up the pollution control required of individual polluters.8
The technology-driven regulations are complex, and take the form of “effluent limitation guidelines.” An “effluent limitation” is “any restriction [including schedules of compliance] established ... on the quantities, rates, and concentrations of chemical, physical, biological, and other constituents which are discharged from point sources into ... water[ ].”9 The CWA requires the EPA to issue effluent limitation guidelines for various types of “point sources.” A “point source” is “any discernible, confined and discrete conveyance ... [such as a pipe, ditch, or channel] from which pollutants are or may be discharged.” 10 The EPA’s effluent limitation guidelines are technology-based regulations. They require polluters to adopt certain technologies aimed at reducing pollution.
Section 304 of the CWA charges the EPA with duties related to setting effluent limitation guidelines for existing sources of pollution.11 Under § 304(b)(3), the EPA must identify the specific control measures and practices available to the various categories and classes of point sources.12 The EPA must then identify, in terms of the amount of pollutants, the pollution reduction (or, in Clean Water Act jargon, “effluent reduction”) attainable through application of the three different levels of technology-best practicable control technology (“BPT”),13 best available technology economically achievable (“BAT”),14 and best conventional pollutant [973]*973control technology (“BCT”).15 It must also identify the factors it will consider when deciding which control measures and practices apply to each of the various classes and categories of point sources.16
Beyond these § 304 requirements, § 301 of the CWA requires that the effluent limitations attainable by the various levels of technology “shall be achieved” by various dates, all at least fifteen years in the past.17 More specifically, point sources discharging toxic and nonconventional pollutants must apply the best available technology economically achievable (“BAT”) to meet the BAT effluent limitations.18 Similarly, point sources discharging conventional pollutants must apply the best conventional pollutant control technology (“BCT”) to meet the BCT effluent limitations.19
These limitations, however, are not self-executing. Instead, they create binding obligations on dischargers only through National Pollutant Discharge Elimination System (“NPDES”) permits.20 The CWA forbids anyone from discharging any pollutant without an NPDES permit.21 The EPA Administrator may issue permits to individual polluters only if the permitted discharges comply with the requirements for effluent limitations set out in § 301 of the CWA.22 In issuing an NPDES permit, the EPA places the polluter into the appropriate point source category and subcategory. The EPA next assigns the appropriate level of technology to the polluter. Finally the EPA sets limits, for various pollutants, on how much the polluter may discharge. In setting the limits in individual permits, the EPA imports standards from the effluent limitations guidelines issued under CWA § 304(b). EPA then applies the numeric limitations to the dis-charger 23 via the NPDES permit.24 Thus, the technology-based effluent limitations become binding on polluters through NPDES permits.
To set the effluent limitation guidelines under CWA § 304(b), the EPA broke down the various point sources by industry. The EPA established the Coal Mining Point Source Category as one of its industry categories.25 In 1985, the EPA amended the effluent limitation guidelines and requirements concerning the Coal [974]*974Mining Point Source Category by creating four subcategories. They were:
1) Coal Preparation Plants and Coal Preparation Plant Associated Areas
2) Acid or Ferruginous Mine Drainage
3) Alkaline Mine Drainage
4) Post Mining Areas.26
In seeking an NPDES permit, each coal mining operation was placed into one of these four subcategories. From then on, whenever a coal mining operation applied for an NPDES permit, the EPA incorporated the effluent limitation guidelines corresponding to the appropriate subcategory for that operation.
Under the 1985 regulations, these four subcategories did not include a category for coal mining operations that sought to remine previously mined, but later-abandoned, lands (“remining operations” or “reminers”). Technological advances made it feasible and potentially profitable to mine such lands. However, the same regulations for miners of virgin lands applied also to coal reminers. Faced with a need to bring remining operations into compliance with the same standards used for first-time mining, potential reminers allowed abandoned mines to remain fallow, often with resulting untreated pollution from “pre-existing discharges” that could otherwise have been treated. By using the same standards for both the mining of virgin land and the remining of abandoned mines, the regulations imposed a large potential liability for anyone who took over the land encompassing the abandoned mines.
Responding to the disincentive for re-mining, Congress passed several amendments to the CWA in 1987, including one that West Virginia Representative Nick Rahall proposed. The “Rahall Amendment” became § 301(p) of CWA.27
With his amendment, Rep. Rahall sought to stimulate the remining of abandoned coal mines by exempting certain remining operations from the otherwise-applicable national effluent limitations.28 Rather than requiring remining operations to meet the national effluent limitation guidelines mandated by the 1985 amendments, the Rahall Amendment allowed the NPDES permit writer (the EPA Administrator or a corresponding state administrator) 29 to waive these requirements in favor of a modified permit. Under the Rahall Amendment, modified permits incorporate site-specific numerical limits for pre-exist-ing discharges of iron, manganese, and pH based upon the Administrator’s “best professional judgment.” However, the Rahall Amendment forbade the EPA (or state) Administrator to issue a permit if remining would cause discharges that exceeded the pre-existing levels of pollutants found in surrounding waterways.30 The Rahall Amendment also required that applicants for these “Rahall permits” provide evidence that the remining operations would potentially improve the quality of the water in the area, and that the permits comply with applicable state water quality standards.
The Rahall Amendment sought to make remining economically feasible. Congress believed that remining would improve the [975]*975water quality of abandoned mines, an improvement that would not have occurred under the more stringent guidelines that applied to all mined lands.
EPA’S FINAL RULE
The challenged EPA Final Rule creates two new subcategories under the Coal Mining Point Source Category and sets regulations for both. These new subcategories are (1) the Coal Remining Subcategory, and (2) the Western Alkaline Coal Mining Subcategory. We discuss them in turn.
Coal Remining Subcategory
The Final Rule creates a first new subcategory known as the Coal Remining Subcategory. The regulations for this subcategory apply to all “pre-existing discharges” at “coal remining operations.” “Pre-existing discharges” are “any discharge[s] resulting from mining activities that have been abandoned prior to the time of a remining permit application.”31 A coal remining operation is “a coal mining operation at a site on which coal mining was previously conducted and where the site has been abandoned or the performance bond has been forfeited.”32
The regulations require that every re-mining operator create a site-specific Pollution Abatement Plan and submit it to the EPA or the state agency with authority to issue NPDES permits.33 Remining operators must include in their Pollution Abatement Plans “best management practices,” and they must design the plans “to reduce the pollution load from pre-existing discharges[.]”34 Further, each Pollution Abatement Plan “must describe the design specifications, construction specifications, maintenance schedules, criteria for monitoring and inspection, and expected performance of [best management practices].”35 Under the Final Rule, these Pollution Abatement Plans qualify as the best practicable control technology currently available (BPT),36 the best achievable technology economically achievable (BAT),37 and the best conventional pollutant control technology (BCT) for remining operators.38
The Final Rule also sets effluent limitations for four pollutants-total iron, total manganese, net acidity, and total suspended solids (“TSS”). For each pollutant, the required effluent limitation is that the dis-charger “[m]ay not exceed baseline loadings[.]”39 Baseline loadings are background conditions — i.e., those that exist when remining commences. The Final Rule defines the procedures for measuring them.40 However, if the EPA or the state permitting authority concludes that collecting samples to measure baseline pollutant loadings is infeasible41 and that remining [976]*976“will result in significant improvement that would not otherwise occur,” then no measurable effluent limitations apply.42 The permitting authority apparently has unfettered discretion in making such determinations. These regulations apply to all three levels of technology.43
Western Alkaline Coal Mining Subcategory
The EPA’s Final Rule also creates, and establishes effluent limitations for, the Western Alkaline Coal Mining Subcategory: The Final Rule regulates certain types of drainage in certain areas of “western coal mining operations.”44 “Western coal mining operations” are “surface or underground coal mining operation[s] located in the interior western United States, west of the 100th meridian west longitude, in an arid or semiarid environment with an average annual precipitation of 26.0 inches or less.”45
EPA’s Final Rule sets no uniform standards for drainage at western coal mining operations. Instead, western alkaline coal mining operators must create “a site-specific Sediment Control Plan ... designed to prevent an increase in the average annual sediment yield form pre-mined undisturbed conditions.”46 Like the Pollution Abatement Plans described above, each Sediment Control Plan “must identify best management practices (BMPs) and also must describe design specifications, construction specifications, maintenance schedules, criteria for inspection, as well as expected performance and longevity of the best management practices.”47 Sediment Control Plans need not include numerical limitations on sediment. Instead, Operators must demonstrate “[u]sing watershed models” that the Sediment Control Plans “will result in average annual sediment yields that will not be greater than the sediment yield levels from pre-mined, undisturbed conditions.”48 Beyond that, the operators’ only obligation is to implement and maintain the best management practices described in the Sediment Control Plan.49 These requirements constitute BPT,50 BAT,51 and BCT.52
STANDARD OF REVIEW
Petitioners challenge an EPA rule promulgated through informal rulemaking. Therefore, we review the Final Rule under the Administrative Procedure Act (“APA”).53 Under the APA, we invalidate an informal rule if it is “arbitrary, capricious, an abuse of discretion, or otherwise [977]*977not in accordance with law;” “in excess of statutory jurisdiction, authority, or limitations, or short of statutory right;” or “without observance of procedure required by law.”54
An agency rule is arbitrary and capricious “if the agency has relied on factors which Congress has not intended it to consider, entirely failed to consider an important aspect of the problem, offered an explanation for its decision that runs counter to the evidence before the agency, or is so implausible that it could not be ascribed to a difference in view or the product of agency expertise.”55 Further, an agency abuses its discretion when it fails to consider a factor the statute directs it to consider in promulgating regulations.56 The Court must undertake a “searching and careful review” to determine whether an agency action was. arbitrary and capricious, but “the ultimate standard of review is a narrow one.”57
This standard directs courts to grant substantial deference to administrative agencies. The Court may not substitute its own judgment for that of the agency. Instead, the Court must decide whether a rational relationship exists between the statute’s purposes and the agency’s action and whether “there is substantial evidence in the record to support it.”58 Further, the agency’s decision “is entitled to a presumption of regularity.”59 With this standard in mind, we turn to Petitioners’ challenges to the Final Rule.
PARTIES’ ARGUMENTS
Petitioners attack the Final Rule on several fronts. Regarding the Coal Remining Subcategory, they argue that it is inconsistent with CWA § 301(p), the Rahall Amendment. Petitioners claim four inconsistencies. First, they argue that the definition of “coal remining operation” in the Final Rule differs from the Rahall Amendment’s definition of that term. Second, Petitioners say, the Final Rule adds total suspended solids (“TSS”) to the list of pollutants that are to receive relaxed standards. While the Rahall Amendment relaxes standards for only pH, manganese, and iron, the Final Rule includes TSS. Third, Petitioners argue that the Final Rule’s lack of numerical limits on effluents runs afoul of the Rahall Amendment’s requirement of numerical limits. Finally, Petitioners argue that the Final Rule differs from the Rahall Amendment by applying the otherwise-applicable standards (rather than modified standards) to preexisting discharges that reminers commingle with discharges from active mining operations. According to Petitioners, the EPA should regulate these discharges under the relaxed Rahall Amendment standards. For these reasons, Petitioners argue that the Final Rule is inconsistent with the text, and also the purpose, of the Rahall Amendment.
Concerning the Western Alkaline Coal Mining Subcategory, the Petitioners offer four arguments for their challenge. First, they argue that best management practices are not appropriate effluent limitation [978]*978guidelines because they do not impose numeric limitations on pollution. Second, they argue that the Administrator has not, shown that continued imposition of the currently applicable effluent limitations is infeasible. Third, they argue that the entire subcategory of Western Alkaline Coal Miners is irrational and overbroad. Finally, Petitioners argue that the EPA’s goal in creating the subcategory is inconsistent with the CWA and the Surface Mining Control & Reclamation Act (“SMCRA”).
The EPA defends the Final Rule, both subcategories, and its regulations applicable to them. In general, the EPA says that the Rahall Amendment does not constrain the EPA’s power to issue generally applicable regulations. Further, the EPA argues that requiring “best management practices” as the only effluent limitations for the Coal Remining Subcategory is a reasonable exercise of the EPA’s discretion under the CWA. Finally, the EPA argues that we must affirm its rulé applying the more strict, otherwise-applicable regulations (as opposed to weakened alternative regulations) to commingled waste streams because the EPA relied on an existing regulation in promulgating it.
The EPA defends the Western Alkaline Coal Mining Subcategory with several arguments. First, it repeats its argument that non-numeric effluent limitations are acceptable under the CWA. Next, with regard to western alkaline coal mines, the EPA argues that numeric limitations are infeasible. .The EPA bases this argument upon its scientific conclusion that sedimentation ponds cause serious, adverse non-water-quality impacts in the arid West, and upon the assumption that using sedimentation ponds is necessary for a miner to comply with the numerical limitations. Third, the EPA .argues that its scientific conclusions support the decision to create the subcategory, and this decision was not arbitrary, capricious, or unreasonable. Finally, the EPA argues that setting effluent limits at premined background levels is consistent with both the CWA and the SMCRA.
ANALYSIS
We enter this analysis with caution. Most challenges to administrative agency action involve an agency’s construction of a single word or phrase in its enabling statute. In contrast, we here examine an agency’s construction of the statute (more or less), as a whole. Instead of relying upon a single séction or subsection of CWA as its authority to promulgate the Final Rule, the EPA references no fewer than seven sections.60 In reviewing the EPA’s Final Rule, we must therefore look to each of these seven sections, all of then-subsections, and all of the cross-referenced sections within to determine the scope of the EPA’s power.
I. Coal Remining Subcategory
A.
We first decide whether CWA § 304 grants to the EPA the power to create a subcategory under the Coal Mining Point Source Category and to promulgate regulations that conflict with the Ra-hall Amendment for that subcategory. The Petitioners argue that the CWA does not, and that the Final Rule must be stricken down for this reason. The EPA, however, contends that it had power to create regulations for remining under the CWA even where such regulations conflict with the Rahall Amendment.
We review an agency’s construction of its enabling statute under the two-step [979]*979test articulated by the Supreme Court in Chevron, U.S.A. v. Natural Resources Defense Council.61 First, we ask whether Congress has spoken directly to the specific issue at hand.62 If it has, we must give effect to Congress’ clearly expressed intent. However, if the statute is ambiguous, we move to the second step, which calls for broad deference to the administrative agency. In the second step, we may invalidate an agency action only if it relies on an impermissible construction of the statute.63
Applying the Chevron standard, we conclude that the CWA does not explicitly address whether the EPA has the power to create a subcategory under the Coal Mining Point Source Category and to promulgate regulations for that subcategory that conflict with the Rahall Amendment. CWA § 304(b) provides the EPA with a general authority (indeed, a duty) to create regulations (“effluent limitation guidelines”) for various classes and categories of point sources. It does not address the Rahall Amendment’s relationship to these regulations. Further, the Rahall Amendment is silent on the issue of the Administrator’s power to create additional subcategories under the Coal Mining Point Source Category. We must therefore move on to the second prong of Chevron-whether the agency’s interpretation of the statute is reasonable.
Generally, when an agency issues a rule that contradicts the enabling statute, the rule is “in excess of statutory jurisdiction,” and therefore violates the APA. This case presents an exception to that rule because the Rahall Amendment does not define or even limit the EPA’s authority to issue generally applicable regulations. Instead, the Rahall Amendment merely provides a way for coal reminers to opt out of generally applicable effluent limitation regulations and to obtain permits that include modified effluent limitations. The Rahall Amendment is wholly silent regarding the EPA’s authority to promulgate implementing regulations that go beyond its provisions.64
CWA § 304(b) requires the EPA to issue effluent limitations for various pollutants and for various levels of technology. CWA § 402(a) further directs the EPA Administrator to incorporate these regulations into NPDES permits issued to individual polluters. The Rahall Amendment gives reminers an alternative to the generally applicable effluent limitation regulations. Under the Rahall Amendment, the Administrator (or other NPDES-permit-issuing authority) may issue a modified permit. The Rahall Amendment thus does not create a particular regulatory scheme that applies to all coal remining operations. On the contrary, it creates an avenue for reminers to opt out of the generally applicable regulations.
The Clean Water Act’s text and structure support this interpretation of the statute. First, CWA § 304(b) directs the EPA to issue generally applicable guidelines. Second, these guidelines gain the force of law through CWA § 301(b). Third, they create obligations on polluters through NPDES permits. The Rahall [980]*980Amendment says that the Administrator “may issue a permit ... which modifies the [generally applicable effluent limitations]” 65 for pre-existing discharge in various areas of a coal remining operation. In no way does the Rahall Amendment require coal remining operators to seek such modified permits. Instead, remining operators remain able to seek permits under the generally applicable effluent limitation guidelines that the EPA promulgated under CWA § 304(b). Such permissive language conflicts with Petitioners’ argument that the Rahall Amendment creates a generally applicable regulatory scheme, with which EPA’s § 304(b) regulations must remain consistent. To the contrary, the § 304(b) regulations precede (both temporally and logically) any application of the Rahall Amendment. In these ways, the Rahall Amendment does not create a generally applicable scheme of regulating remining operators, binding on all such operators. Instead, it creates a way for remining operations to avoid the generally applicable EPA regulations issued under § 304(b).
Here, the EPA promulgated a rule that created new generally applicable regulations for coal reminers. These regulations parallel the Rahall Amendment in some respects and run contrary to the Rahall Amendment in others. Because the text and structure of the Clean Water Act compel the conclusion that the Rahall Amendment is an opt-out, rather than a generally applicable regulatory scheme, these inconsistencies with the Rahall Amendment do not put the Final Rule in tension with the statute. Instead, the new Final Rule provides a new set of generally applicable regulations (applicable to all remining operators), from which remining operators are still free to opt out via the Rahall Amendment’s alternative procedures.66
For these reasons, the EPA’s reading of the Clean Water Act, allowing it to promulgate regulations for the Coal Remining Subcategory, is reasonable. Having concluded that the EPA has the authority to issue regulations of this type, we now turn to the validity of the individual regulations.
B.
Even though the EPA’s conclusion that it may issue regulations that differ from the Rahall Amendment is reasonable, the EPA’s Coal Remining Subcategory regulations cannot stand because they are “without observance of procedure required by law.”67
The CWA contemplates a five-step process of creating and implementing effluent limitations. First, the EPA must identify which control measures and practices are [981]*981available to the various categories and classes of point sources.68 Second, the EPA identifies the factors that it will take into account when deciding which of these control measures and practices apply to point sources within the various categories and classes.69 It must do so for the three levels of technology described in the statute-BPT,70 BAT,71 and BCT.72 Third, the EPA must determine, “in terms of amounts of ... pollutants, the degree of effluent reduction attainable through the application of’ the three technological levels.73 These three steps each occur under CWA § 304(b).
Fourth, these guidelines gain the force of law under CWA § 301(b), which states that compliance with the guidelines created under § 304 “shall be achieved” by certain dates.74 Finally, the EPA must incorporate the guideline limitations into NPDES permits given to individual polluters.75 At this step, compliance with the requirements becomes mandatory for individual dischargers, as CWA § 402(a) establishes that compliance with § 301 is a prerequisite to issuance of a permit76
Under the statute, the EPA should have first identified the technological tools available to coal reminers and then determined the amount of effluent reduction attainable. Instead, the EPA started the regulation process by defining the level of pollution the agency desired (maintaining “baseline loadings”) and then worked backward to define the technological tools as site-specific “plans” that would achieve the desired level of pollution. This is problematic not only because it is backwards-the EPA defines the pollution control technologies in terms of the desired outcome, rather than defining required outcomes in terms of that which the available technology can achieve-but more importantly because it shirks the EPA’s duty under CWA § 304(b) to determine the degree of effluent reduction attainable. Essentially, the EPA’s Final Rule defines the attainable reduction at zero, without ever exploring the prospect of accomplishing more.
In some circumstances, such as when the levels of pollution have fallen so low as to reach fully the technological controls’ capabilities, the degree of effluent limitation attainable might actually be zero. However, setting the attainable effluent limitation at zero is arbitrary and capricious when the EPA effectively defines the available levels of technology as those that will result in no increase of pollution, without any requirement that the limitations actually reduce pollution. Such circular reasoning contravenes “the national goal of eliminating the discharge of all pollutants” expressed in CWA § 301(b)(2)(A).77 It further contravenes the EPA’s duties under CWA §§ 304(b)(1)(A), (b)(2)(A), and (b)(4)(A) to “determine ... the degree of effluent reduction attainable ” for the various levels of technology, and to do so “in terms of amounts of constituents.”78 We hold that where the EPA fails to deter[982]*982mine how much reduction in pollution is possible, and to do so by reference to the amounts of pollutants, the EPA deviates from CWA’s statutory commands.
The EPA’s decision to use background conditions as effluent limits is also problematic because it results in a different effluent limitation for each site. Such a “keep it as it is” approach does not even approximate needed uniformity in the regulations. While the CWA does not mandate strict uniformity,79 courts have recognized that the CWA disallows plant-by-plant regulations. In Texas Oil & Gas Association v. EPA, the Fifth Circuit held that the CWA does not require the EPA to maintain absolute uniformity among effluent limitations within a single category or subcategory of point sources.80 However, the court also noted “the textual mandate of the CWA that [effluent limitation guidelines] be established for ‘categories and classes’ rather than individual point sources,”81 and “agreefd] that Congress intended to foreclose plant-by-plant evaluation of facilities within a subcategory.”82 The EPA’s decision to set effluent limitations through sole reliance upon site-specific factors thus runs afoul of this policy against site-specific regulations.
For the above reasons, we conclude that setting background conditions as effluent limitations violates the text of CWA and thus relies on an unreasonable reading of the statute.83 Therefore, we strike down the regulations setting effluent limitations for the Coal Remining Subcategory.84
C.
An additional problem with the EPA’s Final Rule lies in the EPA’s failure to consider all the factors the CWA requires it to consider. Subsections 304(b)(1)(B), (b)(2)(B), and (b)(4)(B) require the EPA to consider a list of factors when establishing which control measures [983]*983shall become BPT, BAT, and BCT.85 These factors are
the age of equipment and facilities involved, the process employed, the engineering aspects of the application of various types of control techniques, process changes, non-water quality environmental impact (including energy requirements), and other such factors as the Administrator deems appropriate.86
Although the EPA has broad discretion in determining the amount of weight to assign to each factor,87 it may not ignore a factor altogether.88
The record in this case provides no evidence that the EPA took each of these factors into account when prescribing the pollution control measures that became part of the various technological levels for the two new subcategories. The EPA’s Proposed Rule89 goes so far as to list the factors in its discussion of BPT for the Coal Remining Subcategory,90 yet it contains no evidence that the EPA actually considered them. For instance, the Proposed Rule contains no discussion or even information on the age of the equipment and facilities or of “the engineering aspects of the application of various types of control techniques.” The discussions of BCT, BAT, and NSPS do not even list the factors.91 The Final Rule fares no better.92
Therefore, from the record before us, we cannot conclude that the EPA followed Congress’ statutory directives in determining the appropriate pollution controls to assign to point sources in the new subeate-gories. For this reason, we must further strike down the EPA’s decision to set Pollution Abatement Plans featuring best management practices as BPT, BCT, and BAT for the Coal Remining Subcategory.
D.
The final issue we decide with regard to the Coal Remining Subcategory is whether the EPA may apply different standards to pre-existing discharges that have been commingled with wastes from active mining operations. Under the Final Rule, the EPA applies a lower standard for cleanup of pre-existing discharge at remining operations. However, for preexisting discharge that became intertwined with wastes from active mining operations, the higher standard applicable to waste from active mining operations applies.93 Petitioners challenge this regulation as too demanding. The EPA defends its decision to apply alternative standards to waste streams that have been commingled by arguing that it merely applied an existing regulation to the new context of coal rem-iners.
Petitioners argue that the Rahall Amendment prohibits the EPA from applying the stricter standards of the generally applicable § 304(b) regulations to pre[984]*984existing discharges that have commingled with other waste streams. As described previously, this argument is incorrect. Again, the Rahall Amendment functions only as an opt-out, not as a mandatory, generally applicable regulatory scheme. The Rahall Amendment therefore does not prohibit the EPA from applying its general commingling rule94 to commingling of preexisting discharges. Nor does any other provision of the CWA so prohibit. For these reasons, we grant the EPA the deference due to it in construing its own regulations, and conclude that the EPA may apply its commingling rule to preexisting discharges.
II. Western Alkaline Coal Mining Subcategory
Petitioners also mount several arguments against the second new subcategory created by the Final Rule — the Western Alkaline Coal Mining Subcategory. First, they repeat their argument that the EPA lacks authority to impose non-numeric effluent limitation guidelines. Next, they say that even if the EPA had such authority, the decision to do so here was arbitrary, capricious, and inconsistent with the goals of the CWA and the SMCRA.
The regulations for the Western Alkaline Coal Mining Subcategory contain no numeric effluent limitations for total suspended solids, and no effluent limitations at all for settleable solids and pH. Under the regulations, each operator “must submit a site-specific Sediment Control Plan ... designed to prevent an increase in the average annual sediment yield from pre-mined, undisturbed conditions.”95 Like the Pollution Abatement Plans applicable to the Coal Remining Subcategory, these Sediment Control Plans are to feature best management practices.96 Additionally, operators must demonstrate the plans’ effectiveness “[u]sing watershed models.”97 These Sediment Control Plans constitute the only effluent limitation required for all three levels of technology,98 and they contain no numeric limits on sediment whatsoever. Beyond the initial models there are no measurable checks on sediment levels at all.
The same reasoning detailed above in Parts I.B. and I.C. applies equally to the non-numeric limitations in the Western Alkaline Coal Mining Subcategory. By adopting non-numeric effluent limitations based upon background conditions, the EPA shirked its duties under CWA § 304(b) to determine in terms of the amounts of pollutants, the degree of effluent reduction attainable by the various levels of technology. Additionally, the EPA abused its discretion by failing to consider the factors spelled out in CWA §§ 304(b)(1)(B), (b)(2)(B), and (b)(4)(B) when deciding which control measures would become BPT, BAT, and BCT. For these reasons, we strike down the regulations implementing the Western Alkaline Coal Mining Subcategory.
[985]*985CONCLUSION
For the reasons described above, we invalidate the regulations contained in the EPA’s Final Rule. We therefore REMAND this matter to the EPA with instructions to either withdraw the Final Rule or to issue a new rule, and to ensure that the provisions of which are consistent with this opinion.