City will build $40M desalination plant

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City will build $40M desalination plant

West Oahu will soon draw from an unlimited resource to provide fresh water for a growing population.

The Honolulu Board of Water Supply is going forward with the largest seawater desalination plant ever built in Hawaii on land that was part of the former Barbers Point Naval Air Station.

The 65,000-square-foot plant is expected to cost upwards of $40 million with construction slated to begin next year and be completed in 2006.

The facility will produce 5 million gallons of freshwater per day for residents and businesses from Campbell Industrial Park to Ko Olina, supplying about one-third of the region's water needs.

The growing population in the Kapolei and Ewa districts, along with drought conditions, are straining groundwater supplies. Water demand for the area is projected to reach 35 million gallons per day by 2025.

The board hopes to expand the Kalaeloa desalination plant's capacity in daily increments of 5 million to 10 million gallons, contingent upon the demands on Oahu's groundwater supply.

Advances in desalination have spurred the board to move forward with the project. The state previously operated a pilot desalination plant near the site of the board's new plant, but pulled the plug on it because it proved too costly.

"The technology is so much better [and] the cost is coming down," said Barry Usagawa, water resources principal executive at the board. "It provides a drought-proof supply of water."

The board's operation and maintenance costs for making desalinated water will be about $3.20 per thousand gallons, compared with less than $1 from groundwater sources.

The board has hired Honolulu-based research and engineering firm Oceanit to design the plant. Oceanit used its reverse osmosis technology at a small pilot facility at the site last year to test filters and control systems.

"Reverse osmosis requires quite a bit of energy," said Oceanit Marketing Manager Ian Kitajima. "But when the board looked at the alternative of building a pipeline from Windward Oahu to Leeward Oahu, the better option was to build a desalination facility near where the water was going to be needed."

Reverse osmosis works by pushing seawater through a filter so fine that salt ions literally can't pass through.

"It requires energy to push it through the filter," Kitajima said. "What comes through is the processed water. But it's so pure, it's too pure to drink."

The process actually removes trace minerals, which are added back by blending desalinated water with groundwater before going into the main water system.

The technology is used in other parts of the world, including the Middle East.

At Kalaeloa, seawater will be pumped from two 1,600-feet-deep source wells. The board expects to pump 11 million gallons of seawater to make 5 million gallons of freshwater. The remaining 6 million gallons is saline concentrate or brine, which will be injected into 300-feet-deep ground wells.

"The big environmental impact is what to do with the brine concentrate," Usagawa said. "When you discharge it into the ocean, it could affect marine life. By putting it into the ground, we are allowing it to dilute with all the seawater on the bottom. It has less environmental impact."

The state is coming out of a six-year drought that ran from 1998 to 2003.

"Many of our groundwater sources are starting to get impacted," Usagawa said.

Seawater desalination is just part of the board's strategy for meeting Oahu's long-term water needs, which include water conservation and recycling treated wastewater for agricultural use.