Lack of adequate sewer capacity is the key reason most of 344 preliminary applications for accessory dwelling unit permits have been denied by the city since the ADU program began in 2013, a problem that’s spurred Honolulu City Councilman Ernie Martin to urge Mayor Kirk Caldwell to speed up expansion of Oahu’s sewer system.

Martin called it “an embarrassment” that the administration is pushing people to apply for ADU permits while denying applications because of inadequate wastewater line capacity.

City officials acknowledge that a majority of rejected ADU “pre-check” applications were denied due to inadequate sewer capacity in their respective areas.

But Environmental Services Director Lori Kahikina said her department’s top priority is to comply with a federal consent decree that requires the city to put up an estimated $5 billion in sewer system improvements by 2020, not working on increasing capacity.

Many of the consent decree projects actually do increase the island’s sewage capacity, but they are nonetheless driven by the federal mandate, not housing demand, she said.

Martin’s Resolution 17-193 will be discussed at the Council’s Public Infrastructure and Sustainability Committee meeting Wednesday.

Martin said he introduced the resolution after hearing from a Kailua family that said it and neighbors had their ADU permit applications rejected by the Department of Planning and Permitting — after other Mapuana Street property owners were granted permits — due to a recent change in the method used to determine the area’s capacity.

ADUs are “second dwellings” on residential properties. Initiated by Caldwell in late 2013, the ADU program is aimed at increasing the affordable rentals inventory, be they for relatives, friends or strangers. Among the criteria for approval are a minimum lot size of 3,500 square feet, adequate water capacity and sufficient sewer capacity.

Martin said he was hopeful the ADU program would help the island’s housing crunch. “It’s very frustrating and, from my perspective, embarrassing that we didn’t have this issue cleared up before moving along with this program,” he said.

He said he wonders whether property owners in other areas are also being affected by both the lack of sewer capacity and the new methodology now being used to determine that.

The city Department of Planning and Permitting, in a statement, confirmed that an ADU pre-check application was denied to a Mapuana Street property owner “due to an inadequate 12-inch sewer line” on nearby Hele Street.

Kahikina, the environmental services director, said Caldwell is constantly pushing her to increase capacity, although he recognizes the limitations her department is under because of the consent decree. “There is a finite amount of money that the ratepayers can afford,” and additional projects would require higher sewer rates, she said.

However, “understanding this administration is very pro-development and very supportive of the ADUs because we are trying to help the homeless crisis … whenever we can combine it with a consent decree project to accommodate additional capacity, we are doing it,” she said.

A $10 million sewer line upgrade for the Hele Street pipe is in the planning stages but likely won’t be completed for another four to five years. The Hele Street project, like a majority of other Environmental Services projects, is tied to the consent decree, Kahikina said.

Capacity in Kakaako and other parts of urban Honolulu have been limited not by lines, but by what can be accommodated at the Sand Island Wastewater Treatment Plant. That problem is being met with the introduction of a recently completed second digester at the plant, Kahikina said.

As for the new method of measuring capacity, the estimates are now based on actual flow monitors within the sewer pipes. In most instances the estimates now allow for greater capacity. But that wasn’t the case for the Hele-Mapuana area, she said. “The people that got approved (under the old method), they lucked out.”

DPP’s statement said the 344 rejected pre-check applications came from across the island.

The DPP statement said the sewer line issue is not delaying the time it takes to process ADU applications, which by law must be completed within 60 days of accepting an application.