PORTLAND – City officials have notified another commercial property owner that its sewer bill was incorrect for years and could increase sharply.

The owner of Maine Wharf has paid a $107 monthly sewer fee that was set at least six years ago by the city’s public works staff, according to Portland Public Services Director Michael Bobinsky.

Bobinsky sent a letter to Great Maine Wharf LLC last week saying the customized fee violates the city’s own codes and will be corrected in August.

It’s not clear what the correct fee should have been for those years.

Great Maine Wharf would have paid as much as $2,500 to $3,000 a month based solely on water use — the conventional way customers are charged.

However, it could have had its sewer bill reduced significantly by installing meters to show that its tenants discharged most of that water into Portland Harbor and not into the city’s sewers.

“They have paid fees, we’re just restating them to the current rate that everybody else is charged,” Bobinsky said. “The flat rate fee is an anomaly.”

Great Maine Wharf, owned by Eric Cianchette, is evicting some longtime tenants because of safety issues on the aging pier.

The evictions could reduce the company’s future sewer bills.

The improper billing of Great Maine Wharf came to light this spring, after the discovery of a far more costly billing error by the city.

In that case, a water line installed to the Shipyard Brewing Co. in 1996 was never added to the company’s bill.

The underpayment totaled as much as $1.5 million over 16 years before it was discovered. The company and the city are still negotiating a settlement of the back fees.

The error led Portland to hire an independent investigator to review sewer bills citywide and find any other mistakes.

The report identified 12 commercial/industrial water customers that should have paid sewer fees but were never billed. Some of the billing errors went back more than a decade. None was as costly as the one at the brewery.

The reasons for the errors vary, Bobinsky said.

In some cases, water lines were added or sewer lines were connected and the city failed to notify the Portland Water District, which handles the billing, he said.

The uncollected monthly charges ranged from $24 to $332, according to data provided by the city.

The total annual loss on the 12 errors was $14,598, and the total cumulative loss of revenue was as much as $46,672.50, according to the city.

Portland’s overall annual revenue from sewer fees is $20 million.

All 12 property owners were notified in April and are now paying the correct fees, city officials say.

Great Maine Wharf was not on the list of 12 customers because it was a unique case, Bobinsky said.

He said the Portland Public Services staff apparently settled on the $107 fee around 2006 as a way to compensate for all of the water that went into the harbor and not the sewers, without requiring the owner to install a meter to measure the flow.

One tenant on the Maine Wharf in recent years was Fresh Atlantic, a seafood processor that has a federal permit to discharge as much as 12,100 gallons of wastewater each day, as long as the water is within limits for a variety of pollutants, said Stuart Rose, environmental specialist in the state Department of Environmental Protection’s Division of Water Quality Management.

Such discharges apparently represent nearly all of the water used on the wharf in recent years, Bobinsky said.

Some tenants on the Maine Wharf, such as Three Sons Lobster & Fish, also primarily use recirculated sea water.

Bobinsky said that calculating past sewer fees would be difficult in this case, and officials have not discussed whether to ask for past, unpaid fees.

“Right now we want to make sure they get assessed correctly,” Bobinsky said.

Setting a correct fee could involve installing meters to measure how much water goes into the city’s sewers, he said.

Great Maine Wharf bought the pier in 2006.

Bobinsky said it wasn’t clear if the flat sewer rate was negotiated with the current owner or the previous owner.

“When we purchased the wharf, as far as I know, that’s the rate that was being charged,” said Deborah Vargo, manager of the Maine Wharf.

Vargo said she had not yet received the letter from the city but knew it was coming. “We’re going to have to work with the city and go from there,” she said.

Vargo said a big increase in sewer fees would be difficult for the wharf and its tenants.

However, the wharf’s water and sewer use has dropped dramatically because of the ongoing evictions of tenants.

Fresh Atlantic, for example, moved to Holyoke Wharf.

Three Sons is still looking for a new home on the waterfront.

Cianchette, who put the wharf up for sale last year, has tried to win permission to build a hotel there.

Hotels are not allowed in Portland’s central waterfront zone, and he has not been able to get a zoning change.

Staff Writer John Richardson can be contacted at 791-6324 or at: jrichardson@pressherald.com