In urban watersheds like Nine Mile Run, much of the land is covered with impermeable surfaces such as blacktop, concrete, roofs, and sidewalks which do not allow water to filter into the soil. Approximately 27% of the Nine Mile Run watershed is covered by impermeable surfaces. Water flows quickly over these impermeable surfaces into storm drains. During wet weather, Nine Mile Run is quickly overloaded with water, causing stream bank erosion and degrading animal habitat. The water also carries everything it picks up (dirt, litter, road salt, pesticides, oil, etc...) into storm drains and then, ultimately, the stream. This is called non-point source pollution.
The stream often gives off the stench of sewage after a rain. This is because of inadequate storm and sanitary sewer systems in the watershed. There are two basic systems in place: a combined sewer system and a sanitary sewer system.
Most of the City of Pittsburgh uses a combined sewer system, meaning that both sewage and stormwater flow through the same pipes. This system was installed in the late 1800's to the early 1900's and is actually designed to overflow during heavy rains. This means that each time we have a rain that the pipes cannot contain, sewage spews from these overflow sites directly in Nine Mile Run. This can happen from as little as a tenth of an inch of rain. If you are around one of these sites during a heavy rain, you might see a "fecal fountain", or combined sewer overflow, pouring directly into the stream. Due to its inability to handle large amounts of water and its frequent sewage overflows, no permits for this type of sewer system have been issued since the mid-1930's, but most of the city still utilizes this antiquated system.
The smaller boroughs of Wilkinsburg, Swissvale, and Edgewood have a two pipe system called a sanitary sewer system. This system has two smaller pipes-one to carry sewage and one to carry stormwater. However, many watershed citizens have (often unbeknownst to them) their downspouts connected to the sewer drains instead of the stormwater drains. The smaller sewer pipes cannot handle the extra volume of water and overflow, and also dump sewage into Nine Mile Run. Many of the sewer pipes are also in disrepair. These old lines are often made of terracotta and there are even some brick manholes that are not watertight. The pipes are also often located in wetlands or near streams (many are right on the banks of Nine Mile Run) which means that any cracked pipe or leaky manhole puts sewage directly into waterways.
Beginning in 1999, watershed municipalities received consent orders from the PA Department of Environmental Protection (DEP) requiring them to identify the sources of sewage overflows and develop plans to fix their sewage infrastructure . (All municipalities in Allegheny County are now under these same consent orders). Municipalities are also faced with new DEP National Pollutant Discharge Elimination System (NPDES) permits to manage stormwater and non-point source pollution.
Some of these problems have been addressed by the $7.7 million dollar stream restoration sponsored by the City of Pittsburgh and the Army Corps of Engineers. The restoration entailed carving new stream channels, creating pool and riffle sequences, and replanting the area with native plants. These measures will help improve the health of the stream, but to truly restore the watershed every citizen must actively do their part. Our programs are an effort to find cost effective, citizen-based solutions that complement the municipal work being done.