Land and Water: Finding the Balance

When stormwater runoff reaches our waterways the ecological balance suffers. Trash creates a risk for wildlife that might mistake it for food. Chemicals, such as motor oil and pesticides, can be toxic to those same animals. Fertilizers can cause algae to grow out of control and hog the oxygen supply in the water. Too much animal waste can introduce unhealthy levels of bacteria into the water system. These are considered water quality issues.

In 1989, Congress passed an amendment to the Clean Water Act that required municipal operators of sewer systems to develop infrastructure that would reduce non-point source pollution and combined sewer overflows during rain events.  Philadelphia’s response has been the Green City Clean Waters Program.  Green stormwater infrastructure mimicking nature is being developed throughout the city to reduce stormwater runoff.

The City of Philadelphia’s sewer system is comprised of both combined and separate sewer systems. A combined sewer system (CSS) is simply a single sewer system that carries both sewage and stormwater in one pipe, to a water pollution control plant for treatment before being released to a waterway. During moderate to heavy rainfall events, the system will reach capacity, overflow, and discharge a mixture of sewage and stormwater directly to our streams and rivers from the 164 permitted Combined Sewer Overflow (CSO) outfalls within the City. This is a water quality and quantity issue. Sixty percent of the City of Philadelphia, or 64 square miles, is within the combined sewer system drainage area. Four watersheds, generally comprised of the older areas of the City of Philadelphia, receive CSO discharges.

The remainder of the City of Philadelphia’s sewer system is drained by what is called a separate sewer system. A separate sewer system collects stormwater in a storm sewer pipe and discharges it directly to a waterway, while the sanitary sewage collected from homes, businesses, and industry is collected in a sanitary sewer pipe and taken to the water pollution control plant for treatment before being released to the waterways.

The earth has a very efficient method of cycling water through the atmosphere and the land.

As precipitation falls from the sky, it takes one of many different routes: some infiltrates, replenishing ground water, some is taken up by plants keeping them healthy, and some runs into waterways refreshing surface water. The heat from the sun warms the water and turns it into a gas and it rises back into the atmosphere, a process called evaporation. Transpiration, similar to “sweating”, releases water from plants as a gas into the atmosphere. These steps make up what we call the natural water cycle.

Modern towns and cities are full of impervious surfaces, like roads, sidewalks and parking lots, which cannot absorb rain water. Because infiltration is inhibited, stormwater will flow downhill until reaching a waterway or a man-made storm drain. This water that does not infiltrate, but runs off the land is called stormwater runoff. As stormwater runoff flows over impervious surfaces, it gathers pollutants like litter, pesticides, fertilizers, animal waste, loose dirt, and motor oil as it drains.

The problems caused by stormwater runoff impact everything and everyone who depends on the river, and that includes humans. In Philadelphia, all citizens get their drinking water from the Schuylkill and Delaware Rivers. The Philadelphia Water Department is responsible for cleaning the raw water from these rivers before they send it to citizens, and the more polluted the water is, the harder the PWD works to clean it up.

In order to keep stormwater runoff from polluting our waterways, the Environmental Protection Agency (EPA) implemented practices that change the way water runs off the land by absorbing or holding water, rather than having it rush into our creeks and rivers at high speed and volumes. These practices that mimic the natural water cycle and therefore help mitigate, or reduce the impact of stormwater were formerly called Best Management Practices (BMPs) but now are referred to as Green Stormwater Infrastructure (GSI). Trees and plants are especially good at absorbing these large volumes of water and they are used in these projects. PWD has become a model for other cities in the use of these GSI.

Increasing the green throughout a city encourages water to be absorbed into the soil and into the plants themselves, thereby reducing runoff and the pollution that it takes with it to our rivers.  There are many types of Green Stormwater Infrastructure and each is engineered to have maximum impact. Heavily paved areas such as in Philadelphia also depend on Green Stormwater Infrastructure to reduce damaging floods and combined sewer overflows, and to keep pollution from local waterways.  Green Stormwater Infrastructure is one essential tool for modern cities to help manage stormwater runoff but there are others .

With these GSIs in mind, the PWD has created the “Green City, Clean Waters” program. This program encourages property owners to implement different projects on their land to help capture the first one inch (“first flush”) of stormwater that carries the most pollutants. The more of these GSI we have on our land, the healthier our waterways will be.

The freshwater mussel provides a natural water filtration system. One adult mussel can filter up to 20 gallons of water per day. They suck in water through their incurrent siphon and trap organic matter such as dirt, algae or other pollutants. They release the clean filtered water through their excurrent siphon back into the water.

Freshwater Mussels are the subject of a huge research project on aquatic restoration in the Delaware Watershed. Every resident of the watershed should know about this important work.

Our rivers are gateways to Philadelphia, bridging the past and the future. How we care for them is a reflection of us, our innovation and our commitment to the natural world. They provide the majority of fresh water available for our everyday needs. Protection of our rivers is essential to a shared future.