The state Supreme Court has ordered Kauai County to conduct a new environmental assessment for a planned 18-inch waterline because the current EA does not consider all of the potential impacts of the project.

The unanimous ruling is a victory for the conservationists who challenged the project.

“A big win for the environment,” said Bridget Hammerquist of Friends of Maha‘ulepu and Kia‘i Wai ‘o Wai‘ale‘ale, which ended up appealing to the state’s highest court. In court the community group argued that the Kauai Department of Water didn’t comply with the law because the final EA did not analyze how the 9,000-foot pipeline in the Lihue area would facilitate larger water withdrawals and affect streams in Kauai’s southeastern watersheds.

The court, in a 54-page decision, said the project’s final EA failed to offer a “candid assessment” of the project’s purpose and function, and the Water Department erred in limiting the scope of its environmental analysis to the physical footprint of the proposed project.

The final EA, the court said, fell short of analyzing possible larger water withdrawals even though the document indicates the pipeline will carry more water from an upgraded water treatment plant to meet the needs of new developments.

The Hawaii Environmental Policy Act and its administrative rules require analysis of secondary impacts outside the physical footprint of a project, the court said in its opinion.

When Kia‘i Wai ‘o Wai­‘ale‘ale first challenged the project, it lost in Circuit Court. The case was appealed to the state’s Intermediate Court of Appeals, but before it was argued there, the Supreme Court agreed to hear the dispute.

The case was argued in April before the state Supreme Court. In its opinion, which came down Friday, the high court also sent the case back to 5th Circuit Judge Kathleen Watanabe to consider whether any work should be stopped while a new environmental assessment is conducted.