It rained so hard in Waikiki the night of March 23 that at one point our Beachwalk Wastewater Pumping Station was moving wastewater at the rate of 37 million gallons per day. It normally averages 15 million gallons per day.

Wastewater from Manoa, Mo'ili'ili and most of Waikiki flows through gravity lines to the Beachwalk pump station, which pushes all of it through a 42-inch reinforced concrete pipe toward Ala Moana and, ultimately, to the Sand Island Treatment Plant.

Sometime on the morning of March 24, that 42-inch force main ruptured under Kai'olu Street, sending wastewater bubbling up to the street and into nearby storm drains.

From the moment the rupture was discovered, we mobilized to repair the main and minimize the amount of wastewater released into the surrounding environment. City crews fanned out along the Ala Wai Canal and the Waikiki and Ala Moana shoreline to begin daily collection of water samples.

They posted warning signs along the canal and its mouth. Other city workers launched small boats to begin daily tracking of ocean currents and the flow of water from the Ala Wai with drogues. On their way out, they warned surfers at Ala Moana Bowls, at the mouth of the canal, about the spill.

To repair the main, we had to stop the flow of wastewater into it and empty it. That created two gut-wrenching choices: Block the wastewater at the pump station, where it would inevitably overflow into the street and basements of buildings nearby and eventually back up into homes and hotels all over Waikiki, at every low point in the gravity collection system.

Or we could bypass the pump station altogether, which was what we chose to do. Given the volume of wastewater that had to be diverted, the Ala Wai Canal was the only choice. We placed huge pumps at five points along the canal and another at the site of the main break, where crews worked around the clock to get to the pipe — its top almost 10 feet below street level — and repair it.

The pumps along the Ala Wai removed wastewater from the sewer trunks and sent it into the canal.

Some people have suggested we should have hauled the wastewater away with trucks. Each standard pumper truck with a 5,000-gallon capacity would take approximately 20 minutes to fill. Another 40 minutes would be needed to deliver, unload and return to the site.

The minimum flow through the Beachwalk pump station is 350,000 gallons per hour. We would have needed 70 tanker trucks per hour running to and from the impacted site. Normal flow of 540,000 gallons per hour would have required 108 tanker trucks per hour.

There aren't that many tanker trucks available on O'ahu, and even if there were and we could have mobilized all of them, it would have created a traffic nightmare beyond imagination. And because of the daily heavy rains, higher-than-normal flows were expected because of runoff infiltrating the wastewater system.

Others say we should not have bypassed into the Ala Wai Canal, that we should have let the wastewater collect and surcharge in the collection system. That would have created more havoc and a far greater public health concern. Wastewater would have quickly filled the collection system. It would have overflowed from drains, sinks and toilets, filling basements and then flowing freely on the streets in Waikiki and eventually onto the beach.

That would have greatly increased public exposure to wastewater and created a much greater public health hazard than bypassing into the Ala Wai Canal. Instead of avoiding some stretches of beach, some people might have been trapped in homes and hotels.

Building a temporary bypass force main would have taken much longer than repairing the existing pipe. Forty-two-inch-diameter pipe is not readily available, and even it had been, installing that large a pipe on the street would have been impractical.

Connecting it to the existing pipe would have required additional excavation and diversion of wastewater. This scenario would have required us to bypass far more than the 48 million gallons we actually did.

As it turns out, the storm water runoff fed into the canal throughout that week helped dilute the wastewater and propel it out to sea. Throughout our monitoring, the drogues would consistently head away from shore toward deeper water, never once indicating any circulation back towards Waikiki.

The Beachwalk force main has been on the city's priority project list since 1993. Planning for a replacement was started in 1998 but was hampered by fierce community opposition and an apparent lack of political will.

The Hannemann administration made this project a top priority when we took office last year. We pushed forward the design and appropriated $30 million for construction in the current fiscal year's budget. We could not and did not allow this project to keep wallowing in the planning phase any longer.

Before March 24, we feared what might happen if the force main broke. Now we all know, and the Hannemann administration is determined to fix the problem once and for all.