SCARBOROUGH — Citing slower revenue growth and continued fixed costs, Sanitary District Superintendent David Hughes said a proposed 20 percent rate increase could add $600,000 in revenue next year.

The public will have a chance to discuss the proposal at a 7:30 p.m. public hearing in the Scarborough High School cafeteria on Thursday, Oct. 25.

Sanitary District information details the first rate increase in nine years, which would boost residential rates from $82.50 per quarter (or $330 annually) to $99 per quarter (or $396 annually), an increase of 20 percent.

Commercial, institutional and industrial rates will also rise. Minimum user fees will be increased to match residential rates, while the charge per 100 cubic feet of water used will increase from $1.73 to $2.08, also a 20 percent rise.

If approved by the district’s Board of Trustees, the new rates would take effect Jan. 1, 2013. Customers would see the increases in their first quarterly bills at the end of March 2013.

Hughes said he expects the rate increases to boost district revenues from $2.6 million this year to $3.2 million next year. Fixed costs for the district include about $1 million on loan payments.

The district collects and treats waste water from about 4,500 total accounts using 70 miles of gravity-fed lines, and 25 miles of lines fed by 23 pumping stations. The treatment facility is on Black Point Road.

The district has expanded lines to the Haigis Parkway area in anticipation of development that has slowed in the last five years. Hughes said revenue growth was about 3 percent annually until five years ago and is about 1 percent annually now.

Waste-water flow has also remained constant at about 1.2 million gallons daily, or 450 million gallons annually.

Hughes said charging residential accounts a flat quarterly fee is likely less expensive than shifting to metered service for several reasons.

First, the district would have to buy monthly data from the Portland Water District for its own billing. Also, because some residential accounts use irrigation systems, Hughes said those would require sub-meters and staff time to read them.

“It gets convoluted and complex quickly,” Hughes said. “The bottom line is, it would increase the residential sewer bill because of data collection costs.”

David Harry can be reached at 781-3661 ext. 110 or dharry@theforecaster.net. Follow him on Twitter: @DavidHarry8.