Conservation officials hope stormwater retrofits can serve as an example for local towns

Murrysville officials would like their storm water detention ponds to do a little more detaining, and Westmoreland Conservation District members want to help make it happen.

Murrysville council will vote Wednesday night on a measure authorizing conservation district workers to retrofit five storm water detention basins in the municipality, part of state-mandated updates and improvements to its municipal separate storm sewer system, or MS4.

“In 2016, they did some retrofittings to make some of the existing ponds — which were holding very little water — hold additional water,” said municipal engineer Scott Hilty.

Rob Cronauer, watershed program manager for the conservation district, said detention ponds are one of the longest-standing examples of best-management practices when it comes to managing storm water, and they are certainly the most popular method in Westmoreland County.

Cronauer helped retrofit four ponds in neighboring Penn Township in 2015.

Conservation district storm water technician Kathy Hamilton said individual ponds are evaluated “to see how they are functioning versus how they were originally designed and how we could improve them.”

Many of Murrysville’s basins, she said, were built 30 years ago, when simply managing the amount of water was the goal. Today, there is also concern about water quality.

“A lot of the basins were developed to handle a 100-year storm,” Hamilton said. “What we found is that it’s the small storms that end up doing more damage, because they carry pollutants, and they keep erosive flows in the streams, which causes a lot of the sediment pollution we see.”

Part of the MS4 renewal requires the development of a pollutant reduction plan. The retrofitted basins will also play a role in that effort.

“Instead of right now, where practically none of that (storm water) is being held, this will change it and the idea is twofold,” Hilty said. “It keeps the sediment from getting out to commonwealth waters more quickly, and hopefully it will have more of an impact on flooding.”

Modifying the basins will be a key part of that effort, Hamilton said.

“We take the large (drainage) hole intended to deal with a 100-year storm, and make it smaller, more along the lines of a 25-year storm,” she said.

The idea is for the detention pond to do exactly as its name implies: detain more water for a longer period of time, allowing it to gradually seep back through the ground and into the water table.

Cronauer said there are plans to address six Murrysville ponds, in the Twelve Oaks, Franklin Estates, Manor Vue, Spring View and Lavalle Court housing plans.

“A lot of people in these neighborhoods where there’s a basin say they’ve never seen water in it,” Hamilton said.

That’s not how they’re supposed to work.

“There should be water in them, and it should trickle out slowly,” she said. “That’s what we want so we don’t get flooding or erosive flows that carry sediment.”

The Murrysville retrofits will be funded through a Growing Greener grant from the state’s Department of Environmental Protection.

“We do them because we have the expertise, and a little bit different access to funding streams,” Cronauer said. “This is to show places like Murrysville how these basins can be retrofitted, because we can’t do them all.”

Former Murrysville engineer and current conservation district board member Joe Dietrick agreed.

“We’re not going to get every basin in Murrysville retrofitted through the conservation district programs, we know that,” he said in a video outlining the retrofitting process. “There’s a lot that Murrysville is going to have to do on their own. But now, they’ll know how to do it.

“And even if they don’t do it themselves … they can contract it out and have a better understanding because of the conservation district,” Dietrick said.

Patrick Varine is a Tribune-Review staff writer. You can contact Patrick at 724-850-2862, pvarine@tribweb.com or via Twitter @MurrysvilleStar.