Heavy rain spells trouble for aging wastewater plants. We've told you about multiple spills this year at Burlington's treatment plant, leading to closures at city beaches. Now, it turns out that Vermont's largest wastewater plant in Rutland is also routinely overwhelmed with more water than it can handle.

The sky in Rutland Wednesday was a mixture of sun and clouds. A far cry from Monday when almost two inches of rain fell in two hours, overwhelming the city's only sewage plant. More than 9 million gallons of storm runoff and almost a half million gallons of raw sewage went into the Otter Creek.

"This resulted in the system overflowing which it's designed to do prevent backups from getting into buildings and bubbling up on streets and things like that," said Jeff Wennberg, the head of Rutland Public Works. "Because it rained so much, the amount was unusually large."

Large, but not uncommon. This treatment plant is the largest in the state. On a normal day, it treats 22 million gallons of water. But Wennberg says the combination of downpours and aging pipes leads to 15 to 20 of these overflows a year.

In fact, on Wednesday afternoon, there was another small discharge at what's called a sewer overflow location about a mile away from the treatment plant.

"So it was basically 17 minutes, 18-minute overflow and the total volume was 70,000 gallons," Wennberg said.

About 3,500 gallons of that was untreated sewage.

One solution to the discharge problem on Otter Creek is for the city to build a large holding tank that would collect both sewage and stormwater, but that wouldn't be cheap.

"Tens of millions of dollars, we don't know, we are going to come up with some plans in the next two years," Wennberg said.

Monday's discharge into the Otter Creek is the biggest ever recorded. And Wennberg says it not a question of if, but when another large discharge happens again.