The Environmental Protection Agency on Thursday announced the completion of required upgrades to the Waimanalo Gulch Sanitary Landfill, ending a dozen years of federal scrutiny and oversight aimed at bringing Oahu’s only municipal landfill into compliance with laws designed to protect public health and natural ecosystems.

The city, which owns the landfill, and Waste Management of Hawaii Inc., which operates the facility, made the upgrades under a 2019 consent decree they entered into with EPA, the U.S. Department of Justice and the state Department of Health.

The origins of the consent decree date back to 2009, when the city and the landfill operator launched a project to expand the Kapolei facility and construct a new stormwater diversion structure. During construction, Waste Management used temporary stormwater pipes to divert stormwater around the landfill.

However, before finishing the permanent stormwater diversion, the operator began dumping waste into the landfill expansion area. In December 2010 and January 2011, several large storms overwhelmed the temporary pipes and flooded the landfill’s expansion area, resulting in hundreds of millions of gallons of contaminated stormwater finding its way into the ocean.

Raw sewage, sewage sludge, blood vials and syringes were among the things that washed up on the beaches of the Ko Olina Resort and elsewhere along the Waianae Coast for several weeks. Several beaches had to be closed.

In response to the incident, the EPA issued an order requiring a cleanup of the discharged waste.

A year later, in 2012, the EPA issued another order requiring Waste Management and the city to complete construction of the facility’s storm-water diversion system, finish a study of the landfill’s detention basin to evaluate its capacity to store and treat stormwater, and develop an interim stormwater monitoring plan. Those requirements have been completed, the EPA said.

In July 2015, Waste Management pleaded guilty to criminal violations for negligent discharge of pollutants over seven days in violation of the Clean Water Act.

The company ended up paying $400,000 in criminal fines, and restitution of $200,000, which was split by two area nonprofits, the Ko Olina Community Association and the Malama Learning Center, for “implementation of water quality monitoring and erosion control projects.”

None of the operator’s top officials still work for Waste Management.

In 2019 the EPA and state Health Department entered into a consent decree with both the city and operator to address ongoing compliance issues at the landfill.

Among the upgrades completed by the city and operator since then: retrofitting the landfill’s existing stormwater drainage pipeline; installing a trash screen; revising and upgrading their stormwater pollution control plan; complying with specific operational and monitoring limits to control pollution from the stormwater basin; and obtaining an individual stormwater permit for the facility.

Waste Management couldn’t be reached for comment Thursday, and the city didn’t respond to a request for more information on the total cost of the upgrades.

Under the consent decree, the city and Waste Management agreed to pay a combined penalty of $425,000, which was split evenly between the federal government and the state of Hawaii. The state has used the funds for coral reef and habitat restoration, monitoring and conservation on the Leeward Coast of Oahu, the EPA said.

The U.S. District Court in Hawaii granted the EPA’s request to terminate the consent decree Aug. 31.

In a news release, EPA Pacific Southwest Regional Administrator Martha Guzman said, “Addressing pollution in stormwater is a vital part of the Clean Water Act. Enforcement action such as the now completed consent decree helps protect the cherished groundwater, surface water, and beaches of Oahu.”

Meanwhile, the city has asked for an extension on the naming of the new landfill site and continues to look for an alternative site to build a new municipal dump.

Opened in 1987, the Waimanalo Gulch Sanitary Landfill takes in approximately 250,000 tons of waste per year, with roughly 72% being ash and residue from the HPOWER plant, where waste that is not recycled is burned to generate electricity, according to the city.