Since the beginning of August, nine sewage spills have entered recreational waters around Oahu — the most in a single month since 2010 — and more could be on the way as two hurricanes barrel toward Hawaii.

Recent sewage spills prompted officials to warn the public to avoid coming in contact with waters at Waialae Beach Park, Kaneohe Beach Park, Ala Moana Beach Park, Hickam Beach, Lake Wilson and Sandy Beach.

Five of the spills, including a massive one that closed Ala Moana Beach Park for two days, were related to heavy rain. In total about 1.7 million gallons of sewage — most of it treated yet not disinfected — was discharged into the environment.

Lori Kahikina, director of the city’s Department of Environmental Services, said her department is now preparing for possible storms in the weather forecast for next week by making sure no pump stations or wastewater treatment plants are left incapacitated or otherwise vulnerable due to construction projects.

Her department is also hustling to ready large vacuum trucks for emergency response to flooding and spills. Currently, four of 21 trucks are inoperable, Kahikina said.

This month’s spills came as the city is five years into a $5 billion consent decree to bring the city’s sewer collection and treatment systems into compliance with the federal Clean Water Act. Part of the decree requires Honolulu to upgrade its sewer collection system and improve its maintenance program at a cost of $3.5 billion. The improvements are supposed to reduce sewage overflows and be completed in 10 years.

A second part of the decree orders the city to upgrade the Sand Island and Honouliuli wastewater treatment plants to secondary treatment by 2035 at a cost of about $1.5 billion.

Kahikina said the city has completed the mandated upgrades to its sewer pipes about six years before the deadline.

Repairs to 63 miles of the "worst-of-the-worst pipe" were finished by 2014. The city has a total of 2,100 miles of sewage pipes and is continuing to examine pipes for damage and repair the worst ones, she said.

Kahikina said the consent decree does not require increasing the capacity of the system. However, tight capacity is a factor in several recent spills.

The Sand Island Wastewater Treatment Plant typically handles about 60 million to 70 million gallons of sewage a day, but during heavy rainfall that volume can triple to about 200 million gallons a day.

The sewage system is not designed for that volume because it is separate from the storm drainage system, which carries storm runoff water to the ocean.

Kahikina said the influx of water into the sewage system comes from runoff entering through cracks in pipes and illegal connections, such as those from gutters or parking lots.

The city is working to reduce unauthorized connections to the system by way of smoke-testing and using closed-circuit television cameras in the pipes.

"We’ve got to get stormwater out of the sewer system," Kahikina said.

The last time Oahu had more than nine spills into recreational waters within one month was in December 2010, according to the state Health Department’s website. That month there were 12 sewage spills in Kailua, Kaneohe, Palolo, Hawaii Kai, downtown and other areas. Nine of the spills were tied to heavy rainfall on Dec. 19.

When asked about the condition of Honolulu’s sewage system, Kahikina said the city needs to remain vigilant and continue investing in the system’s maintenance.

She pointed out, however, that Honolulu ranks well compared with other jurisdictions, with 1.6 spills per 100 miles in fiscal year 2013.

Several of this month’s spills were related to capacity, contractor error or other issues and not aging infrastructure, Kahikina said.

One of the largest spills this month, a nearly 400,000-gallon spill that closed Ala Moana Beach Park, was caused by contractor error that left a key pump offline for several hours during heavy rainfall Monday morning, sending sewage up manholes in the Atkinson Drive area. Most of the sewage stayed on land, but about 129,000 gallons of it flowed into the ocean.

On Friday, warning signs advising the public to stay out of the water were still posted at Ala Wai Small Boat Harbor, Kewalo Basin, the canoe launch area adjacent to Ala Wai harbor, the pond and canal along Ala Moana Boulevard, and the western end of Kakaako Park. The Health Department is urging the public to avoid contact with the water in those areas until the warning signs are removed.

Another spill caused by contractor error was an 8,400-gallon spill in Kaneohe on Aug. 18, Kahikina said. In that incident a contractor was conducting maintenance work on a force main and shut down the wrong pump, resulting in sewage spilling out and 7,800 gallons of sewage entering the bay.

Kahikina cited only one incident of infrastructure failure among the recent spills: a pipe that collapsed, causing a small spill of 25 gallons at Waialae Beach Park on Aug. 6.

She said the city is working to maintain the sewer system by cleaning 500 miles of pipe a year. The decree requires cleaning at least 300 miles of pipes, excluding from the count any stretches that undergo repeated cleaning.

Meanwhile, some of the sewer spills occurred in systems not operated by the city.

The largest spill this month occurred at an East Honolulu treatment plant operated by Hawaii American Water. On Tuesday the plant discharged 1 million gallons of treated but not yet disinfected wastewater into the ocean, forcing officials to close Sandy Beach and surrounding areas. The spill was blamed on an electrical short during heavy rain.

According to the state’s Clean Water Branch, five of this month’s spills occurred during a two-day period, starting Monday morning. All were related to the heavy rain.

One of those was the Ala Moana spill, and another was the Sandy Beach spill. The remaining three were at the Kaneohe Pretreatment Facility, Joint Base Pearl Harbor-Hickam and Kailua Wastewater Treatment Plant.

The other coastal water spills in August involved a faulty valve near the U.S. Coast Guard piers that caused a 300-gallon spill into Honolulu Harbor on Aug. 4, and a power flicker at the Wahiawa Wastewater Treatment Plant that caused a release of partially treated water on Aug. 14.

Keith Kawaoka, deputy director of environmental health at the state Department of Health, said sewage spills have dramatically decreased over the past decade. He said the decline came as multiple enforcement actions have gone into effect.

"Both in terms of total volume as well (as) number of incidents, all signs point to improved wastewater system management and oversight," he said in a statement Thursday.

He said except for the Ala Moana spill, "nearly all of the wastewater incidents have involved highly treated sewage being released, and not discharges of raw sewage as in times past."