Since the 1980s, Maui’s Lahaina Wastewater Reclamation Facility has been using injection wells for daily disposal of millions of gallons of treated sewage, pumping it into groundwater about a half-mile from the shoreline.

The ugly upshot is ample evidence that the flow is reaching waters off Kahekili Beach Park — contributing to coral demise and algae blooms.

Six years ago, Earthjustice sued Maui County on behalf of community groups, maintaining that the county was violating the Clean Water Act (CWA), which bans the dumping of pollutants directly into surface waters, including oceans. The dispute hinged on whether the federal law should also apply to indirect dumping — by way of injection wells.

After losing in court twice, the county appealed to the U.S. Supreme Court. Finally, last week, in an encouraging win for the health of reef and marine life, the high court rejected the county’s argument that it doesn’t need to comply with the CWA.

However, what compliance will look like at the West Maui site is still murky.

In its 6-3 decision, the justices held that the CWA requires a permit “if the addition of the pollutants through groundwater is the functional equivalent of a direct discharge” from a “point source into navigable waters.”

But rather than directing the county to secure a National Pollutant Discharge Elimination System Permit, the high court sent the case back to the 9th Circuit, which is expected to return it to district court. Moving forward, the lower court will likely decide whether Maui’s wastewater discharge meets the new bar of “functional equivalent.”

In his statement, Maui Mayor Mike Victorino described the ruling as a step toward clarity he had sought on the matter.

What’s already clear is that the county has been polluting ocean waters for decades. University of Hawaii researchers and federal agency studies have shown that treated wastewater traveling in the groundwater has undermined the health of near-shore waters off Kahekili Beach.

Victorino should begin to set right this wrong by positioning the county to sign off on a shelved conditional settlement it had reached five years ago. Among other things, it calls for the county to fund at least $2.5 million in West Maui projects to divert treated sewage from the injection wells and to pay a $100,000 penalty to the federal government.

Last fall, before the Supreme Court heard the case, Maui’s County Council voted to settle and pursue fixes, but Victorino persisted in his push for clarity — apparently hoping a favorable ruling by the high court could allow Maui to continue using the injection well system until the county could find a feasible method to replace it.

This shortsighted move resulted in spending a cumulative $4.3 million for outside counsel, and unabated discharge flow.

To prep for the likelihood of needing the CWA-required permit, the county should now work in tandem with local regulators to chart a path toward meeting standards for wastewater quality and quantity. Failing to hold the required permit can subject polluters to daily fines of more than $50,000.

In addition to strongly suggesting that the permit will be needed, the Supreme Court’s ruling serves as a welcome rebuff of efforts to loosen water pollution requirements. The Trump administration had filed a brief supporting Maui County, contending that the law should not apply to discharges that travel through groundwater before reaching protected waters.

A strong Clean Water Act is needed to genuinely protect the nation’s surface waters, ranging from wetlands and lakes to rivers and oceans. In Hawaii, it’s our responsibility to safeguard the health of near-shore waters from land-based sources of pollution. To that end, Maui should forge forward with a push prioritizing mitigation.