LIHU'E, Kaua'i — The main county sewage treatment plant in Lihu'e has an interesting problem: The plant has the capacity to process far more sewage than the system is capable of delivering to it, or than the disposal system is capable of getting rid of.

The county has hired M&L Pacific to plan the future of the Lihu'e Wastewater Treatment Plant and its associated facilities for the next two decades. Among other things, the plan calls for the plant's treatment capacity to be better matched to its inflow and outflow potentials.

The plant, built in the 1960s, is between the Kaua'i Lagoons golf course and Lihu'e Airport.

The first fix is already in the permitting stage. It will expand the treated effluent disposal capacity of the plant to about 2.2 million gallons a day. That approaches its 2.5-million-gallon-a-day treatment capacity, said Ed Tschupp, head of the county Division of Wastewater Management.

The Lihu'e area is scheduled to grow extensively during the next few years, with much of the growth occurring on Lihu'e Land Co. property to the north of the developed Lihu'e-Hanama'ulu area. That growth could exceed the treatment capacity of the sewer plant in about 10 years.

There must be extensive improvements to the sewer lines in the region well before that, though, Tschupp said.

"We're at the point where the pipes, at peak conditions, are full," Tschupp said. Before any new development can take place, new sewer lines will need to be built, he said.

But perhaps a bigger problem is getting rid of the treated effluent. The facility is a secondary treatment plant, which produces water that is clear but not safe to drink.

Today, in normal conditions its entire flow can be delivered to the Kaua'i Lagoons golf course, where it is used for irrigation. As an alternative, the county has two injection wells that can take part of the flow. The county has built six other wells. Permits to use them are being processed. When they're all online, they should be able to handle all the present effluent, even when the golf course can't take any irrigation water.

With wastewater being injected underground, there can be contamination of groundwater with nutrients and other compounds. Tschupp said all county drinking-water wells are well inland and uphill from the sewer plant, and since water underground generally flows from the mountains toward the sea, there is no contamination risk.

In some areas, ground-injected nutrient-rich wastewater has been linked to increased algae growth at the shoreline, but Tschupp said studies have indicated that's not an issue in Lihu'e.

The longer term solution for the Lihu'e plant is to upgrade the treatment from secondary to tertiary, or advanced waste treatment, which can be done through any of several treatment design schemes. The effluent can be disinfected using ultraviolet light or chlorine,

"That opens up a lot of reuse potential" for the water, Tschupp said. One potential client of tertiary treatment effluent is Lihu'e Airport, which has problems with birds that are attracted to grass along the runway. The airport could use the sewer plant's water output to grow vegetation less likely to attract birds, he said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.