NATIONAL PARKS & CONSERVATION ASSOCIATION; Malama Pono, Inc., Petitioners, v. U.S. DEPARTMENT OF TRANSPORTATION; Rodney Slater, Secretary, in his official capacity as Secretary of Transportation; Federal Aviation Administration, Jane in her official capacity as Administrator of the Federal Aviation Administration and William Withcombe, in his official capacity as Regional Administrator for the Western-Pacific Region of the Federal Aviation Administration, Respondents, State of Hawaii, Intervenor, 222 F.3d 677

KOZINSKI, Circuit Judge: National Parks and Conservation Association and Malama Pono (collectively National Parks) are environmental organizations that petition for review of the Federal Aviation Administration’s (FAA) approval of the expansion of Kahului Airport in Maui. National Parks contend that the FAA violated the National Environmental Policy Act (NEPA), 42 U.S.C. § 4321 et seq., by failing to analyze the impact of the expansion on the introduction of alien, or non-indigenous, species into Maui. National Parks further contend that the FAA violated the Airport and Airway Improvement Act, 49 U.S.C. § 47106(c)(1)(C), and

section 4(

f) of the Transportation Act, 49 U.S.C. § 303(c), both of which govern the impact of transportation projects on the environment. I Kahului is Hawaii’s second largest airport after Honolulu International. In addition to inter-island traffic, Kahului serves flights from the mainland United States and, less frequently, Canada. Kahului’s main runway can accommodate the arrival of any size airplane, but is too short for large carriers to take off with a full load of passengers, cargo and fuel. Such aircraft must either fly with a partial load or stop for refueling in Honolulu.

To accommodate rising demand, the Hawaii Department of Transportation (HDOT) and the FAA plan to repave and strengthen the runway, extend it from 7,000 to 9,600 feet and make related infrastructure improvements. The centerpiece of the project is the runway extension, which would allow fully loaded large carriers to depart Kahului nonstop. National Parks contend that the runway extension will lead to more flights arriving at Kahului, thus introducing dangerous alien species into Maui.

Alien species-a problem in Maui since the first Polynesian settlers arrived 1,500 years ago-are nonnative animals, insects and plants introduced into the island by air or sea. Some of these new arrivals-primarily disease-carrying organisms and insects such as fruit flies-ean become pests that damage crops, livestock and scenic areas. National Parks express special concern for nearby Haleakala National Park, the last intact habjtat for a number of native species.

Because the project is a major federal action that affects the environment, see 42 U.S.C. § 4332, the FAA and HDOT drafted an Environmental Impact Statement (EIS), held hearings and solicited public and agency input. In response to widespread concern over alien species, the FAA convened a Biological Assessment Technical Panel consisting of experts from federal and state agencies, Maui County and private organizations.

The resulting Biological Assessment reviewed the project, surveyed the alien species problem on Maui and proposed mitigation measures, though it acknowledged that “no one can predict which alien species might be introduced into Maui and/or Hawaii due to the Proposed Project.” Biological Assessment (BA) at 9-1.

In addition, the Fish and Wildlife Service (FWS) prepared a Biological Opinion pursuant to the Endangered Species Act, 16 U.S.C. § 1536(a)(2), that found the project was “not likely to jeopardize the continued existence of any endangered, threatened, or proposed endangered species on Maui.” Biological Opinion (BO) at 29. These documents were incorporated into the Final EIS, along with a report titled “The Threat of Alien Species to Natural Areas of Maui,” an extensive bibliography, numerous independent studies of the project and responses to public comments.

Based on this documentation, the Final EIS concluded that “the impact of the Proposed Project on [the] alien species introduction rate is, in and by itself, insignificant. However, the introduction of alien species is an existing statewide problem and therefore, the potential impact of the Proposed Project on the introduction rate of alien species, would be considered a significant cumulative impact.” FEIS § 3.11.3.3. II Our review of an EIS under NEPA is extremely limited.

We evaluate the EIS simply to determine whether it “contains a reasonably thorough discussion of the significant aspects of the probable environmental consequences” of a challenged action. Oregon Envtl. Council v. Kunzman, 817 F.2d 484, 492 (9th Cir.1987) (internal quotation marks omitted). We need not agree with the agency’s conclusions; we must approve the EIS if we are satisfied that the EIS process fostered informed decision-making and public participation. See Idaho Conservation League v. Mumma, 956 F.2d 1508, 1519 (9th Cir.1992).

If we determine that the agency took a “hard look” at a project’s environmental consequences, our review is at an end. Id. Given the volume of information in the EIS that addresses alien species, National Parks can hardly claim the FAA ignored the problem. Instead, they argue that, had the FAA taken a harder look, it would have concluded that the project’s alien species impact will be significant. Them claim hinges on two variables, the rise in international arrivals and the risk that such flights might carry dangerous alien species.

The EIS is replete with data regarding the project’s impact on international arrivals. The very first table of the Biological Assessment estimates that 50 foreign flights will land at Kahului this year, all from Vancouver. See BA Table 1-1. With the runway extension, this figure is expected to grow to 1,200 yearly flights-1,100 from Japan and 100 from Vancouver-over the course of a decade. But this increase-just three flights per day-pales in comparison to the total number of arrivals. Kahului currently serves 35,500 flights, a figure that is projected to rise to 40,350 in 2010 if the extension is built.

International arrivals, then, will account for only 3% of the total air traffic at Kahului. Even this modest increase, however, is not assured. As we have noted, airport demand projections are little more than guesses that depend on economic conditions, airline routing decisions and other variables. See City of Los Angeles v. Federal Aviation Admin., 138 F.3d 806, 807-08 & n. 2 (9th Cir.1998). The figures for Kahului are no exception. One independent study contained in the EIS found that tourism and airline executives expected “no or little lasting long-term growth-inducing impact” from the runway extension.

EIS, app. E at 4-66. Another study noted that Hilo Airport on the Big Island has had a 9,800 foot runway for nearly 30 years, but lack of demand led to the phase out of all direct overseas flights. See id. at 4-5. Currently, demand from Asia is so low that three Asian carriers have ended service to Honolulu due to economic and strategic considerations. See EIS § 8.2.1 at 8-6. When it comes to airport runways, it is not necessarily true that “ ‘if you build it, they will come.’ ” City of Los Angeles, 138 F.3d at 807.

Moreover, evidence in the EIS demonstrates that international arrivals could grow even if the runway is not extended. Kahului can already serve international flights, and cannot discriminate against a foreign carrier that wishes to establish a direct route. See EIS § 8.2.1 at 8-6. If service to Kahului becomes economically attractive, foreign flights could arrive in Maui regardless of the extension. See EIS § 8.2.4 at 8-8.

After all, planes don’t need to stop in Honolulu to land at Kahu-lui; if direct arrivals became profitable, a carrier could fly directly to Maui, but in-elude a layover in Honolulu upon departure. Additionally, factors such as lighter aircraft or other technological advances could allow fully loaded planes to depart nonstop, even on the shorter runway. The EIS also contains extensive discussion of the fact that the alien species impact of the project is highly uncertain. Foreign flights account for only 13% of the total number of animals, insects and plants introduced into Hawaii.

Of this relatively small influx, it is impossible to determine which species will be introduced at Kahu-lui, or whether they will be dangerous. National Parks cannot identify a single species that will become established as a result of the project, nor can they pinpoint a particular resource that will be adversely impacted. Moreover, new alien species may not be harmful; since the 1970’s, for example, 20 species of alien invertebrates per year have become established in Hawaii, only three of which have turned out to be economic pests. See BA at 1-1.

Though National Parks concede that there is “unquestionably some scientific uncertainty surrounding the potential alien species impact of the project,” Opening Brief at 31, they nonetheless fault the EIS for failing to analyze the problem with adequate specificity. They rely heavily on Hughes River Watershed Conservancy v. Glickman, 81 F.3d 437 (4th Cir.1996), where the court rejected an agency’s cursory discussion of the alien species impact of a dam construction project.

But in Hughes River, the evidence showed that the proposed dam would cause the introduction of a specific species-the zebra mussel-that would lead to identifiable environmental harm. Under the circumstances, the court held that the agency must analyze the impact of the particular species. See id. at 445. No such harmful species has been identified here, and possible environmental damage, if any, is purely speculative. It was therefore appropriate for the EIS to focus on broad mitigation measures to combat all types of alien species that might arrive at Kahului.

The detailed mitigation plan outlined in the EIS includes traveler education videos, training of airport personnel and hiring of Arrival Inspectors. See BO at 25-29. In addition, the project calls for a new air cargo building that would prevent escape of insects during inspection. After completion of the EIS, the FAA supplemented these measures with an Alien Species Action Plan that incorporates suggestions made by the National Parks Service and the public during the review process.

For example, the Action Plan establishes an Alien Species Prevention Team to conduct risk management assessments and monitor data on inbound flights. See Record of Decision at 55-56. The FAA conditioned its approval of the project on the implementation of the mitigation measures in the Alien Species Action Plan. See id. at 31. This analysis is nothing like the “perfunctory” two-paragraph mitigation discussion we found inadequate in Neighbors of Cuddy Mountain v. United States Forest Serv., 137 F.3d 1372, 1380 (9th Cir.1998).

In Cuddy Mountain, the Forest Service’s own experts found the mitigation plan so vague as to render it useless. See id.. at 1381. By contrast, the FWS concluded that the “state of the art” measures at issue here “should make Kahului Airport a better barrier to invasion by alien species than any other airport in Hawaii.” BO at 28-29. We have no difficulty concluding that the mitigation measures included in the EIS are sufficient to satisfy NEPA. In sum, National Parks seek too much from the EIS.

While they may disagree with the FAA’s substantive conclusions as to the alien species impact of the project, NEPA does not guarantee substantive results. See Northwest Envtl. Defense Ctr. v. Bonneville Power Admin., 117 F.3d 1520, 1536 (9th Cir.1997). So long as the agency has made an informed decision, we cannot intervene. See Laguna Greenbelt, Inc. v. United States Dep’t of Transp., 42 F.3d 517, 526 (9th Cir.1994). The discussion in the EIS is reasonably thorough, and we are satisfied that the FAA has made an informed decision.

Because the EIS contains the requisite hard look at the alien species problem, it satisfies NEPA. Our dissenting colleague goes astray by focusing solely on the flight projections contained in the Biological Assessment. See Dissenting Op. at 685. This data may seem concrete, but in fact is highly speculative. As we explained above, airport demand projections are notoriously unreliable. See City of Los Angeles, 138 F.3d at 807-08 & n. 2.

Moreover, the dissent ignores entirely the analysis, contained elsewhere in the EIS, indicating that the project may not affect arrivals at all, or that flight increases may occur regardless of the runway extension. See page 685 supra. We review the EIS as a whole, see Northern Plains Resource Council v. Lujan, 874 F.2d 661, 666 (9th Cir.1989), and where there is conflicting evidence in the record, the FAA’s determination is due deference-especially in areas of agency expertise such as aviation forecasting. See City of Los Angeles, 138 F.3d at 808.

Judge Fletcher also disregards the fact that the mitigation measures will be implemented whether or not an increase in flights occurs. Kahului may in fact become a better barrier to alien species invasion than if the project were not completed. See BO at 28-29. Ill For

section 4(

f) of the Transportation Act to apply, the project must “use” Haleakala National Park, a property protected by the Act. See 49 U.S.C. § 303(c). National Parks argue that the potential impact of alien species is a sufficient use of the Park to trigger

section 4(f). But “use” turns on whether the action “substantially impair[s] the value of the site in terms of its prior significance and enjoyment.” Adler v. Lewis, 675 F.2d 1085, 1092 (9th Cir.1982). National Parks cannot demonstrate that the runway extension will so increase the rate of alien species introduction as to substantially impair Haleakala’s economic or environmental value. The FAA’s determination that the runway extension would not use the Park was not arbitrary or capricious. See Citizens to Preserve Overton Park v. Volpe, 401 U.S. 402, 416-17, 91 S.Ct. 814, 28 L.Ed.2d 136 (1971).

Nor does approval of the project violate the Airport and Airway Improvement Act of 1982, 49 U.S.C. 47106(c)(1)(C), under which the FAA may not approve an airport development project that has “a significant adverse effect on natural resources” without first ensuring that “every reasonable step has been taken to minimize the adverse effect.” AAIA § 509(b)(5). The only “reasonable step” National Parks identify as missing-funding for the mitigation measures-does not have to be finalized for the FAA to approve the project. See Citizens Against Burlington v. Busey, 938 F.2d 190, 206 (D.C.Cir.1991) (section 509(

b) requires only “a reasonably complete discussion of possible mitigation measures”). The Petition for Review is DENIED. . Since this petition for review was filed, the Governor of Hawaii has canceled plans for the runway extension. See, e.g., Claudine San Nicolas, Governor Halts Kahului Runway-Extension Plan, Ending 10-Year Controversy, Maui News, Feb. 9, 2000. The FAA's approval of the project, however, remains in effect. Because the extension could still go forward based on the Environmental Impact Statement at issue in this case, National Parks' challenge continues to present a live controversy.

See County of Los Angeles v. Davis, 440 U.S. 625, 631, 99 S.Ct. 1379, 59 L.Ed.2d 642 (1979). . National Parks are primarily concerned with arrivals from Japan, as flights from a new port of origin carry a heightened risk of alien species introduction. . Domestic air traffic accounts for 27% of introduced species; first class mail, 23%; air and sea cargo, 18%; military vessels, 13%; and private boats and planes, 6%. See BA Table 1-5. . Contrary to National Parks’ assertion, a mitigation plan need not be legally enforceable, funded or even in final form to comply with NEPA's procedural requirements.

See Robertson v. Methow Valley Citizens Council, 490 U.S. 332. 352-53. 109 S.Ct. 1835. 104 L.Ed.2d 351 (1989) (requiring an EIS to include a complete mitigation plan would conflict with the principle that NEPA does not compel an agency to reach a particular substantive result); Laguna Greenbelt, Inc. v. United States Dep’t of Transp., 42 F.3d 517, 528 (9th Cir.1994) (NEPA does not require a fully developed plan that will mitigate all environmental harm before an agency may act).

In any event, National Parks fail to identify a single additional mitigation measure that they would have included had they been given the opportunity. . We are puzzled by the dissent's insistence that there is an inconsistency between our opinion and City of Los Angeles. See Dissenting Op. at 686-87. In both cases we sustain the FAA's decision to approve an airport expansion based, in part, on the fact that predictions about the future are, of necessity, speculative. See City of Los Angeles, 138 F.3d at 807 n. 2.

In reaching this conclusion, we defer in both cases to the agency’s own determination about the likely reliability of those prognostications. This is deference to agency expertise as we understand the concept. More difficult to understand is the dissent’s notion of deference, which extends only far enough to undermine the agency’s conclusions, but then fails to consider the EIS as a whole.