Human error by wastewater workers contributed to the massive discharge of stormwater and raw sewage into waters off Ala Moana Beach in August 2015, city Environmental Services Director Lori Kahikina said Friday.

The city announced that under an Administrative Order on Consent agreement reached with the state Department of Health, it will pay a $100,000 fine and make a series of improvements as a result of the Aug. 24, 2015, sewage and stormwater spill at Ala Moana, other South Shore areas and two smaller spills in Windward Oahu.

At a press conference Friday, Kahikina said the cost of the improvements will be determined by the kind of equipment that might need to be installed. The $100,000 penalty is to be paid to the state within 90 days.

The department estimated 462,050 gallons spilled into waters off the Ala Moana-Kakaako region, 125,000 gallons from the Kailua Regional Wastewater Treatment Plant went into a nearby pond, and 4,950 gallons from the Kaneohe Pretreatment Facility spilled into a stream.

Remnants from Tropical Storm Kilo caused more than 3 inches of rain in Honolulu during a 24-hour period, setting a record for that date.

State waters from Waikiki Beach to Kakaako were closed after the spill. City officials at the time blamed the inability of a pump station to process the sewage and stormwater, and Kahikina reiterated that explanation Friday. Only one of two pumps at the Keawe Street Wastewater Pumping Station was operating during the deluge because the other was undergoing refurbishment, city officials said.

Much of the backflow spilled out of manholes at Atkinson Drive and Ala Moana Boulevard and then entered storm drains leading into the ocean, city officials said. One witness reported a small geyser shooting out of Ala Moana Boulevard near Fisherman’s Wharf resulting in “a sea of gray water” spilled that smelled like a toilet and left behind undissolved hygiene items.

City officials insisted that Waikiki beaches were closed “out of an abundance of caution” the day of the spill as the result of a brown-water advisory issued by the Health Department. Ala Moana was closed off for several days due to contaminants found in water samples.

The city has already begun to implement some of the improvements, including changing the standard operating procedures to ensure there is better communication between divisions when alarms go off, Kahikina said. The Treatment and Disposal Division operates the sewer system’s Supervisory Control and Data Acquisition program, while the pump stations are operated by the Collection System Maintenance Division.

“When the SCADA people see the alarms, they need to notify Collections Systems Maintenance that ‘Eh, there could be a problem at this pump station, start mobilizing,’” Kahikina said. “The spill that happened in August of 2015, there were so many alarms going off at SCADA that somehow they missed the Ala Moana Pump Station. They never notified Collections System Maintenance, and they deactivated the alarm.”

The SCADA staff has now been instructed to ensure Collections System Maintenance is notified about each alarm, and Collections System Maintenance needs to physically check each pump station and call back SCADA before the alarm can be deactivated, Kahikina said.

No employees were fired but some were disciplined for inaction, Deputy Environmental Services Director Ross Tanimoto said. Both he and Kahikina declined to say how many employees were disciplined or what actions were taken. “It wasn’t intentional,” Kahikina said.

Other improvements the city needs to make include revising its sewage spill volume estimate procedures, upgrading its SCADA system and developing a high-density urban area stormwater inflow detection, identification and quantification study.

The city is already spending more than $1 billion in wastewater treatment improvements as a result of a 2010 global consent decree issued against it for other spills. The city’s 2018 budget calls for $655.9 million to be spent on such improvements, $165.5 million more than this year.