Lawmakers approved a bill Wednesday preventing landfills from being placed over sensitive drinking water sources, dealing a blow to Honolulu’s efforts to relocate its main dump.

The measure prevents landfills from going on the most productive agricultural land in counties with a population of more than 500,000 and includes already existing buffer zones to protect homes, schools and hospitals.

House Bill 969 was amended to drop the previously existing term “significant aquifer” but bars landfills from being built inland of the “underground injection control line” in a county with a population of more than 500,000 people. That has essentially the same intended effect but is more defined and specifically targets Oʻahu.

The measure was the only one that passed out of several bills introduced in response to backlash to Mayor Rick Blangiardi’s announcement late last year that the city planned to open a new landfill on a pineapple field outside Wahiawā as it faces deadlines to close Waimānalo Gulch in Nānākuli.

Modern engineering would ensure this drinking water source below the proposed site remains uncontaminated, Blangiardi and his waste management head Roger Babcock assured residents. But after Navy jet fuel contaminated some of the island’s drinking water during the Red Hill water crisis, few people were comforted by the mayor’s claim.

The mayor’s proposed location would have replaced Waimānalo Gulch Sanitary Landfill, the island’s only current municipal landfill. Its lifespan has been extended multiple times since opening in 1989, frustrating nearby Nānākuli residents.

In the Senate, only Waiʻanae Coast Sen. Samantha DeCorte voted no. In the House, seven lawmakers — most from the Westside — voted no and three voted yes with reservations.

The bill now goes to Gov. Josh Green’s desk for signature. If Green signs the bill, the city would likely apply to again extend Waimānalo Gulch’s lifespan past its permit’s 2028 expiration date, rather than shift operations to somewhere else on the island.

“I’m not voting no against water protection,” Nānākuli Rep. Darius Kila said on the House floor. “I’m just voting no because we’re removing one option without securing another.”

Meanwhile, Majority Leader Sean Quinlan — whose district would have been the site of the mayor’s proposed landfill — framed the vote as a win.

“To protect our agricultural lands,” he said on the House floor, “and to protect our precious fresh drinking water, I’m in strong support.”