×

Water ruling shouldn’t affect W. Maui supply

Department says flow is sufficient, working on new supply sources

The county water department said Friday that there should be sufficient flow in the Kanaha Stream — 90 percent of the time — to meet needs of Lahaina customers and to comply with the state water commission’s order last week to restore 550,000 gallons of water per day to the stream.

During long-term droughts, lower stream flow may not be sufficient to meet the county Department of Water Supply needs in West Maui and will require water conservation measures, department officials said. These events should be relatively infrequent based on historical data, they added.

The department currently plans to drill wells to replace a portion of the surface water drawn from Kanaha Stream. The department currently takes most of the water from the stream, which is dry beyond the diversion at the 1,050-foot elevation, the state Commission on Water Resource Management report said. The water feeds the Lahaina treatment plant, which produces 1.65 million gallons of water day.

On Nov. 20, the commission set stream flow standards for the Kanaha and Kahoma streams. For Kanaha Stream, a tributary of the Kahoma Stream, the commission set an in-stream flow standard of 1.55 mgd but phased in the return of water, recognizing the domestic needs of the water department.

The decision called for the return of 550,000 gallons a day with additions of a total of 250,000 gallons a day for new kalo loi (taro patches) being planted and to supply continuous flow in Kanaha Stream. The commission acknowledged the water department’s plans to find other sources of water in the next five years when the full stream flow standard could be applied.

“The Department of Water Supply supports stream restoration and is actively preparing to shift to groundwater to reduce reliance on surface water long term,” said an email from the department Friday.

The responses to questions from The Maui News were provided in the email by Eva Blumenstein, department water resources and planning program manager; Wendy Taomoto, department engineering program manager; and Deputy Corporation Counsel Caleb Rowe.

The new wells are planned for the Launiupoko aquifer; the department currently taps the aquifer with the Kanaha and Waipuka wells, the email said.

Engineering studies are proposed in fiscal year 2020 to determine well location, capacity and costs. In addition, the department has partnered with U.S. Geological Survey to determine the best modeling for well development in an ecologically responsible manner, the email said.

The two existing Launiupoko wells show rising chloride levels “directly in response to increased pumpage,” the email said. In the aquifer, the freshwater sits on a lens of heavier saltwater.

“The development of smaller wells rather than concentrating withdrawals from a single large pump will mitigate saltwater intrusion and maintain sustainable groundwater withdrawals,” the email said.

Well development is expected to take five years, the email said. The new wells are needed both to replace surface water from Kanaha Stream and to meet projected new water demand in Lahaina.

The Kanaha Stream diversion was built by sugar companies to irrigate cane fields. When Pioneer Mill shut down in 1999, the water department assumed management of the diversion.

The diversion also feeds Lahainaluna High School with 100,000 gallons a day, and one other individual user with 30,000 gallons a day. The new flow standards should be sufficient to meet those needs, the commission report said.

* Lee Imada can be reached at leeimada@mauinews.com