HONOLULU (HawaiiNewsNow) - Connecting the Ala Moana Wastewater Pump Station and Sand Island Wastewater Treatment Plant are the city’s two new 7,500-foot long and 63-inch diameter wastewater force mains.

They were installed deep beneath the surface.

“We needed to make sure we had capacity to handle all the excess flow coming in, and also redundancy,” city Environmental Services Department director Lori Kahikina said.

Civil engineering firm Fukunaga & Associates Inc. designed the massive project, which took years to complete and was full of challenges.

Work required boring shafts 100-feet deep then using a giant drill to micro-tunnel through soil and lava rock to place the pipes under Honolulu Harbor.

"After you get down in the shaft you had to go across the channel, which then encountered some hard and soft material," company president Jon Nishimura said.

The pipes had to be set deep enough beneath the harbor bottom so construction wouldn't disturb shipping lines and other harbor traffic.