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City struggles to address problem with rainwater entering sewer system

Wednesday, October 3, 2012

By Ralph Pokorny

Nevada Daily Mail

"We built it to handle 2.5 million gallons per day with a maximum capacity of 10 million," Nevada Public Works director Roger Beach said recently of the city's new wastewater treatment plant.

Within the first week of its operation, Beach said that Nevada received a 5-inch rainfall and within hours the new treatment plant topped out at more than 15 million gallons per day.

"Obviously we have a problem in town that needs to be corrected. The normal daily flow in Nevada is 1 million gallons per day," he said.

Any sewage effluent that exceeds the capacity of the treatment plant bypasses the plant and discharges untreated into the Little Drywood Creek.

The problem is caused by infiltration and inflow, commonly referred to by water system professionals as I&I, which allows rainwater to enter the sewer system and overwhelm the capacity of the lines and eventually the sewer treatment plant.

The obvious signs of this problem are when sewage backs up into basements or floats the steel lids of manholes several inches above the ground on a column of rapidly flowing water that then runs across streets and yards.

The problem didn't come about because of the new plant; the city has been working on this problem for several years and the most obvious problems, like the manhole on West Ashland at the Nevada Regional Technical Center that routinely flooded the area after heavy rains, have been repaired.

Beach said that he thinks repairing these obvious problems has reduced the city's I&I problem by 25- to 30-percent.

Shawn Middendorf, Alliance Water Resource's local manager, said that although a lot of people think there are still a few large problems, he feels there are a lot of small leaks in the system.

"Eighty five percent of the pipes in town are old clay tiles, three foot long, with gaskets between the tiles," Middendorf said.

"Now 50 years later, those gaskets are gone and you have millions of little holes," he said.

In addition to the many leaks in the system, Beach said there is one major problem they have identified, and that is one of the city's interceptor sewer lines near Walton Lake.

Middendorf said the line goes northwest from Walton Lake to the north interceptor line which runs to the city's wastewater treatment plant west of town.

To help identify the locations of the problems, Alliance guided a camera through the corrugated metal pipe. Middendorf said they have identified 17 bad spots in the 24-inch pipe.

"We can see the water coming in," he said.

Alliance has documented those problems and reported them to the Missouri Department of Natural Resources.

He said that the city has been approved for funding through Missouri's State Revolving Loan Fund in 2013 to repair the line.

Since much of this additional water and sewage mixture will bypass the city's wastewater treatment facility and flow directly into Little Drywood Creek, which has been designated by the Environmental Protection Agency as a stream that is suitable for whole body contact, in other words, swimming, it affects the regulations the treatment plant operates under.

Not to mention the safety issues of sewage backing up into basements or running across a yard.

Beach said that three years ago when the city received the operating permit for the new wastewater treatment plant, the city was given a mandatory order to institute an I&I program and to come up with a plan to improve the problem.

Some of these problems were addressed when the city replaced the north and south sewer interceptor lines, which were 50-year old corrugated metal pipes that had numerous holes.

This order mandates that any new sewer lines in Nevada must be at least 8 inch lines to allow for multiple connections without overloading the line.

It also requires the city notify DNR within 24 hours if there is a sewer overflow and if they are not notified the city can be fined, Beach said.

One of the benefits that Alliance brings to Nevada is that they can run a camera down the sewer lines and identify potential problems so they can be fixed earlier, Beach said.

Once Alliance identifies the problems they rate them on a scale of 0-10 for urgency. The city then has its engineer draw up plans to fix the problem and send them to DNR for approval for funding, he said.

"It's a whole different process than in the past. We're trying to address the big picture instead of the little picture," Beach said.

"I&I is a priority, with a staff that works on it five days a week," he said.

Middendorf said that whenever it rains he also has crews visually inspect sewer manholes to measure the flow rate to help identify problemsareas.

This will help locate areas where there are abandoned sewer lines, basement drains or gutters that drain into the sewer mains.

"A lot of sewer lines, we don't know where they are," Beach said.

In the past, sewer lines were not mapped. If you wanted to know where something was located, you would ask other workers where they were.

"They never made it to paper," he said.

Now the city is using GIS, or digital mapping technology, to document the location of new lines as required by the state, he said.

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