Every rain or snow storm is a weather event, and they don't end when the last drop or flake hits the ground
Managing the runoff—particularly from major storms—is serious business for big cities like Philadelphia, where the water flows underground and becomes a resource as stormwater.
Dr. Erica McKenzie, assistant professor of civil and environmental engineering at Temple College of Engineering, is part of a team working on how to best manage stormwater in Philadelphia. Funded by the Pennsylvania Department of Transportation, their work looks to determine better practices through water quality analysis.
The collaborative research serves to help understand the stormwater impact near I-95, the major freeway running along the Delaware River, straight through the heart of Philadelphia. Currently, PennDOT is in the middle of a major design project to reconstruct the aging highway, which is situated along some of the city's fastest growing neighborhoods.
In the area of focus for the project, the Girard Avenue Interchange, congestion can thwart travel between the Ben Franklin and Betsy Ross Bridges that bring cars to and from New Jersey. North Delaware Avenue has also become an entertainment destination, with clubs, bars and Sugar House Casino all near the research site.
The researchers have started to examine the water flowing off the roads and into stormwater facilities, many of which serve more densely-populated neighborhoods around the city.
On major roads, this water can be contaminated with metals from tires, brake pads, and during the snowy months in the Northeast, rock salt. Philadelphia has a combined sewer system, so that contaminated water could end up in the rivers during what PennDOT referred to as "a combined sewer overflow" (CSO) event. The goal is to find out what is getting in the runoff from the roadway, how much of it and how to best manage it.
The partnership with PennDOT is unprecedented among American universities in access and collaboration.
"The way that we use stormwater has changed in the time since I-95 was originally constructed [the late 1960s] until now," Dr. McKenzie said. "The fact that we're trying to manage these combined sewer overflow events is a challenge that Philadelphia and other cities are trying to address for stormwater management. This is one example of them trying to route the stormwater to a place where it can infiltrate. It's been a challenge because it's such a dense urban place. Where do you find a spare acre to allow water to soak in the ground? The neat thing that's come out of it is, not only do we have stormwater management functions that are recurring, that's the design, but, anecdotally, it seems like it's everyone's favorite dog-walking area, too."
The dog-walking area Dr. McKenzie described is a small patch of land bordering I-95 on Richmond Street between Shackamaxon and Marlborough Streets in the fishtown section of Philadelphia. Pipes feed runoff into this tract from the highway near the Girard Avenue exit. This area had been excavated to create bioswales for the water flow to infiltrate the ground.
On a brutally hot July day, Dr. McKenzie, joined by her College of Engineering colleagues Drs. Robert Ryan and Benoit Van Aken, student researchers, a partner team from Villanova University and the Philadelphia Water Department, used this area for a flood test, simulating runoff from a rain event that normally occurs once a decade.
Water flowed from a nearby hydrant, as hoses brought it to the storm drain opening that feeds into the land. Lysimeters dotted the area like white silos along a country river. Researchers tested the water by collecting from the stream with water bottles attached to long poles. They took samples in small vials and syringes. After a couple hours, the group added Fluorescein, a fluorescent tracer, which caused the water to turn bright green and yellow.
Currently, the testing has yet to encounter a massive precipitation event that sees the water flowing into the combined sewer system.
"On the one hand, from a water quantity perspective, that's pretty fantastic. We're not having any of that water go into the storm sewer," Dr. McKenzie noted. "From a contaminant perspective or a pollutant perspective, it raises a lot of questions. It means that either all those contaminants, like those that won't degrade like metals, are either accumulating in the soil or they're infiltrating the groundwater. Either one of those could potentially be a bad thing."
Dr. McKenzie added that, if it accumulates in the soil, the concern could turn to how a high concentration of contaminants could adversely impact the plants.
"Maybe. We're going to be looking at that," she said. "Do you end up having some conditions where you actually promote that mobility into the soil and into the underlying groundwater? Is that bad? What does that mean longer term in the performance of the stormwater management area? Plant health, maintenance activities, and different designs to get those contaminants to be sequestered in a certain area that you could more easily scoop out. We're looking at those questions."
Graduate student researcher John Kelley joined the project at its start, which he credits as a key factor in staying at Temple to pursue his master's degree after graduating in 2016. He sees the project going well and meeting established goals.
"We've taken samples from the site and the results we've seen have been interesting," he said. "We did a runoff test to see how these BMP [best management practices] perform at their max capacity and put in a couple tracers to see how the water moves. We've been able to do these things and get a lot out of it, as far as learning how these BMPs actually perform."
The current project grant runs through May of next year.