New Iberia has an expensive problem with leaky sewage pipes.

Up to 41 percent of the wastewater the city treats is water that has entered leaky pipes, and the cost for the city — the taxpayers — could be as much as $1.3 million last year.

The rainwater infiltration is part of the reason New Iberia is paying fines, and part of the reason for the city’s subsequent agreement — called a consent decree — with the EPA, the U.S. Department of Justice and the Louisiana DEQ to upgrade the city’s system substantially by 2015. It’s part of the reason the city budgets millions of dollars for wastewater, part of the reason it charges a sewer user fee and part of the reason wastewater is New Iberia Mayor Hilda Curry’s “No. 1 priority” when she lobbies  in Washington.

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Expensive to treat

A sample rainless day of sewage flow provided by Wastewater Director Vince Palumbo showed the city’s plant received 2.1 million gallons of wastewater. He said this would be representative of an average dry day.

Over the course of a year, the plant receives a daily average of 3.5 million gallons of wastewater.

On rainy days, said Palumbo, the plant receives an extra 12 to 15 million gallons. This, he said, is four to five times the sewer plant’s average daily flow. It’s six to eight times a dry day’s flow.

In a 365-day sample provided by Palumbo, the plant received and treated 1.3 billion gallons of wastewater.

A dry-day sample flow of 2.1 million gallons, multiplied by 365, is 766.5 million gallons.

The difference between the two figures is 533.5 million gallons.

Using these figures, sewage, on average, contributes approximately 59 percent and rainwater contributes 41 percent of the sewer plant’s annual flow.

What does this mean in monetary terms for taxpayers and the city’s budget?

The Daily Iberian was unable to get an average cost for treating a gallon of sewage from the city.

“After speaking with Vince Palumbo, it has been determined that this information is not available,” said Curry.

“We do not calculate the cost of treating sewage in this manner.”

Palumbo said that while it is a simple question, there is not a simple answer, citing direct and indirect costs related to pumping.

Palumbo also said he could not provide an estimate for how much rainwater infiltration costs the city, as costs do not increase in a linear fashion.

Costs found online for other plants ranged from 1⁄8 of a cent to more than $4 per gallon of sewage.

The Daily Iberian therefore came up with an admittedly inexact estimate of the overall cost of the problem as follows:

The overall service/operating expenses, not including depreciation, for the new plant was $3,206,832 in 2007, according to the audit report.

This means the average cost to treat 1 gallon of sewage is 1⁄4 of a cent, which sounds small.

But since the above calculations mean 59 percent of the plant’s flow is sewage and 41 percent is rainwater, last year leaky pipes and illegal connections cost the city $1,314,801 in the newspaper’s estimate.

“It’s expensive because you have to treat it all,” Palumbo said not of the above figure but of the general costs of rainwater infiltration.

Monday: Where are the sources of the leaks and what progress has the city made in correcting them so far?