PWSA to begin stormwater project in South Side Slopes, Flats
Last updated 9/12/2019 at 9:03am
Many of Pittsburgh's sewers were built in the turn of the 20th century and are still in pretty solid shape.
The problem in this watershed is that the sewers are combined sanitary and stormwater sewers creating an overflow problem during wet weather. If stormwater increases the volume to more that the sewer system can handle in this area. Here, the excess flows directly into the Monongahela River resulting in poor water quality.
Two conditions have added to the overflow problem: Increased development causing more runoff in the area and an increase in the amount of rain the area is now seeing.
Representatives from the Pittsburgh Water and Sewer Authority (PWSA) and Ethos Collaborative, recently invited area residents and stakeholders to learn more about and discuss options for the South Side Park Stormwater Improvement Project.
Ruari Egan, design project manager for PWSA, explained during dry weather the combined sewer system carries both waste water and stormwater to the ALCOSAN treatment center where it is treated and discharged into the Ohio River.
During times of wet weather, "and it doesn't take very much," the waste water and stormwater combine to overwhelm the system and in this area the overflow is discharged directly into the Allegheny River in the 21st Street area.
Ms. Egan said more recently there have been more instances of overflows into the river along with backups into homes and businesses in the area.
Normally, the Pittsburgh region has about 38 inches of rainfall a year, last year there were 57 inches and this year there has been already 38 inches of rainfall. The increased amount of rain has also increased the number of overflows.
She said historically there have been multiple agencies responsible for stormwater in the area including the county and city. PWSA is working to be the responsible agency for stormwater management to streamline the process.
Several years ago, PWSA began the process of examining all the sewer sheds in the city, narrowing it down to the top 30 according to volume. Taking those 30, they overlaid data concerning backups and overflows and developed a priority list of six.
Ms. Egan said the South Side Park sewer shed, identified as M16, was one of the top six with 100 million gallons of stormwater going into the system.
PWSA is planning to slow down the stormwater by mimicking nature through green infrastructure, allowing the water to be absorbed into the ground or sent to the Monongahela River and avoiding the combined sewer system.
Barton Kirk from Ethos Collaborative explained M16 is a diverse sewer shed that begins on Arlington Avenue and extends down through South Side Slopes and South Side Park, through 21st Street and eventually leading to the Flats and the Monongahela River. In the upper parts of the watershed it has a lot of forest and lawns leading down the Slopes to the South Side Flats which is very urbanized and dense.
"When we're thinking about stormwater issues and solutions, we had to think across the entire sewer shed," he said.
Historically, the watershed was a stream bed that followed the topography of the land and now is a target area for stormwater management.
Ethos was tasked by PWSA with looking at how to capture stormwater runoff in 23 acres in the M16 watershed and come up with three alternative plans. The goal was to handle the first inch and a half of rainfall in a storm in the most cost-efficient manner as possible.
"Which is really an infrequent event, it only happens typically a few times a year, but that's beginning to change," Mr. Kirk said.
He noted in the first phase of implementation, the current playground in South Side Park near the football field will be converted into a parking lot and the parking lot below the field will be made into a playground. A current paved area further down the hill is envisioned to be reclaimed in a natural way to be a series of cascading pools to collect stormwater along with a rain garden at the lower end of the park.
Mr. Kirk acknowledged the work Western Pennsylvania Conservancy is doing on 21st Street to develop a new streetscape between Josephine and E. Carson streets. The project will capture stormwater from about four acres of land and includes a new stormwater sewer.
He also noted in the early 2000s a separate stormwater sewer system was constructed on the downriver side of the M16 sewer shed. The separate sewer system provides an opportunity for them to tie into it to send rain water directly into the Monongahela River.
Ethos looked at three option areas: The 23 acres in South Side Park; The four acres making up the 21st Street corridor; and, looking exclusively in the South Side Flats. They settled on recommending a hybrid plan to PWSA that includes the park and Flats.
In the park there are opportunities to capture and store water in a variety of places such as under the playground and parking lots. In addition, they would like to enhance the existing stream running along and through the park to channel stormwater away.
In the Flats, they would look to direct the stormwater from homes, businesses and parking lots to the existing storm sewer on Wharton Street.
Mr. Kirk said the project would capture stormwater from a total of 67 acres at a cost of $5.4 million.