According to the Environmental Impact Statement, construction at the Mosholu site is scheduled to last more than five years, during which time 28 acres of parkland--including the golf course and driving range--will be closed to the public, and will become an active construction site. Construction will require demolition of the clubhouse, roads and parking areas, which will later be restored. The driving range, however, will be rebuilt on the roof of the plant, above a layer of dirt. The Environmental Impact Statement further discloses that hundreds of trees and associated vegetation rare to New York City--whose "loss would represent a potential significant adverse impact"-- are threatened by the construction, and a million cubic yards of soil and rock will be removed from the park. During peak construction, more than a thousand workers will be at the site, and hundreds of vehicles will deliver construction materials and remove soil.

The plant will, moreover, change the gradient of the park. Though the plant is to be built underground in the sense that it will be below "finished grade," its roof will be between five and 30 feet above existing ground elevation. Additionally, vents and air intake louvers placed in berms surrounding the facility will extend above finished grade.

In January 1999, shortly after site selection, the State Attorney General advised the City that, in his view, legislative approval was necessary before parkland could be used for this project. Citizen groups opposed the project, arguing it was not authorized by the State Legislature; 33 State legislators similarly urged that the City did not have authority to build the plant in Van Cortlandt Park without legislative permission.

On July 21, 1999, the City Council approved the application for plant construction at the Mosholu site. By letter dated July 30, 1999, the Attorney General reiterated that use of the proposed site without first obtaining Legislative approval would violate State law, advising:

"construction of the Plant at the selected site in Van Cortlandt Park, a process which will include the closing of the golf course for six years, requires state legislation for the reasons we have discussed with counsel for the City beginning in January, 1999. We expect that the City will comply with [milestones 14 and 15] and request legislation and a home rule message from the City Council on or before July 31, 1999."

The City has not sought legislative approval for the project.

Pursuant to the consent decree dispute resolution provision, the State sought relief in the District Court, claiming the City violated its commitment by failing to seek legislative approval for construction and operation of the water treatment plant. Concerned citizens and community groups, similarly, commenced two lawsuits in State Supreme Court--Friends of Van Cortlandt Park, et al. v City of New York and Norwood Community Action, et al. v Department of Environmental Protection, et al.--seeking, among other things, to enjoin development and construction of the water treatment plant in Van Cortlandt Park on the ground that the City impermissibly sought to convert a considerable area of parkland from public use without an act of the State Legislature. Without objection, the two citizen suits were removed to the Eastern District, which had continuing jurisdiction under the consent decree. All of the parties sought summary judgment.

The District Court granted the City's motions, concluding that legislative approval was unnecessary. As the court explained, there being "no transfer of an interest in land to another entity * * * [and] no diminution of parkland available for public use after the plant is built, underground use of the parkland [was] not an alienation in the sense of diversion of parkland for non-park purposes" (96 F Supp 2d 195, 204).

Plaintiffs' appeals were consolidated. On June 30, 2000, plaintiffs State of New York and Friends of Van Cortlandt Park moved to certify to this Court the question whether State legislative approval is required for the proposed use of the Mosholu site. Mindful on the one hand of the desirability that this State law issue be resolved by the State Court of Appeals, and on the other hand of the burden certification of a time- sensitive issue would impose on us, on November 15, 2000 the Second Circuit granted plaintiffs' motion, so long as this Court concluded it could expeditiously resolve the issue (232 F3d 324). On November 21, 2000 we accepted certification (95 2 916), and now answer in the affirmative the following question: "Does any aspect of the proposed [water treatment plant] require state legislative approval?"[2]

We begin analysis with two points of agreement by the parties: that this water treatment plant is a non-park use, and that Williams v Gallatin (229 NY 248) is controlling precedent.

In Williams, a taxpayer sought to enjoin the New York City Commissioner of Parks from leasing the Central Park Arsenal Building to the Safety Institute of America, arguing the transaction was "foreign to park purposes." The lease was for a 10-year term, cancellable if the City needed the property for park use. In prohibiting the lease, this Court explained that a park is a recreational pleasure area set aside to promote public health and welfare, and as such:

"no objects, however worthy, * * * which have no connection with park purposes, should be permitted to encroach upon [parkland] without legislative authority plainly conferred.

[ ... ]

"The legislative will is that Central Park should be kept open as a public park ought to be and not be turned over by the commissioner of parks to other uses. It must be kept free from intrusion of every kind which would interfere in any degree with its complete use for this end" (id., at 253-254).

In the 80 years since Williams, our courts have time and again reaffirmed the principle that parkland is impressed with a public trust,[3] requiring legislative approval before it can be alienated or used for an extended period for non-park purposes (see, Miller v City of New York, , 15 NY2d 34, 37 [20-year lease]; Incorporated Village of Lloyd Harbor v Town of Huntington, , 4 NY2d 182, 190; Ackerman v Steisel, 104 AD2d 940, 941 [2d Dept] [storage of sanitation vehicles and equipment], affd , 66 NY2d 833; Stephenson v County of Monroe, 43 AD2d 897 [4th Dept]; Aldrich v City of New York, 208 Misc 930, 939 [Sup Ct Queens County], affd 2 AD2d 760 [2d Dept]; Matter of Central Parkway, 140 Misc 727, 729 [Sup Ct Schenectady County]; contrast, 795 Fifth Ave. Corp. v City of New York, , 15 NY2d 221, 225 [Park Commissioner properly determined that a café and restaurant could be constructed in Central Park where the project furthered park purposes]).

Where the parties disagree is as to application of these longstanding precedents to the present facts. The City argues that, even under Williams, legislative approval is not required, first, because there will be no alienation of parkland and second, because the plant will be substantially underground, with park surfaces fully restored, and therefore the proposed use is not inconsistent with park purposes. Both arguments lack merit.

Williams makes clear that legislative approval is required when there is a substantial intrusion on parkland for non-park purposes, regardless of whether there has been an outright conveyance of title and regardless of whether the parkland is ultimately to be restored. Indeed, in Williams itself there was no divestiture of ownership--there was a 10-year lease cancellable by the City--and upon expiration of the lease the property could return to park use. Nonetheless, without legislative approval the lease was prohibited.

Bates v Holbrook (171 NY 460, 465-468)--which predated Williams--is also instructive. There, the City Department of Parks permitted construction of storage buildings on parkland in connection with a subway project. Because the Legislature allowed the Department to grant "temporary privileges" for use of park property to facilitate construction, defendants urged that the structures were authorized. This Court disagreed, concluding no "direct legislative authority" warranted invasion of the park. Structures could not be considered "temporary" when "authorized to remain until the completion of the work" on a project that would take at least three years.

Here, the public will be deprived of valued park uses for at least five years, as plant construction proceeds. While there may be "de minimis" exceptions from the public trust doctrine, the magnitude of the proposed project does not call upon us to draw such lines in this case.