CSO discharges contain municipal and industrial wastes, floating debris, and disease causing pathogens, among othercontaminants. These pollutants are harmful to the environment, human health, and detract from our ability to use the waters where the discharges occur to the full extent possible. The discharges from the more than 9,000 CSO outfalls has a significant impact on downstream waters and communities that use those waters.

The table below presents the concentration of several pollutants in a variety of water discharges including untreated and treated waste water, urban runoff, and CSO discharges. The discharge from CSOs is a combination of untreated waste water and urban runoff. It is for that reason that the pollutant loads are similar between these three categories of discharge.

Chemical Pollutants

These pollutants are chemical compounds that are either discharged by industry, homeowners, or washed from the street into the combined sewer systems. It is important to remember that every chemical that we put in our sinks or empty onto our streets will be discharged directly into our waters during wet weather events. These pollutants have a serious impact upon the aquatic life in our streams and can render the water undrinkable in the absence of expensive treatment. They may be either inorganic or organic compounds.

The inorganic pollutants tend to be metals, including but not limited to, zinc, copper, nickel, mercury, and lead. The organic substances found in CSO discharges include oil, grease, benzene, chloroform, phenol, toluene, and many other organic compounds. To view concentrations of organic and inorganic substances in CSO discharges


Pathogens include bacteria, viruses, and parasites. Untreated sewage contains virtually every well known disease causing pathogen that we take so many steps to avoid in our everyday lives. Some of the pathogens that can be found in CSO discharges include E. coli, Salmonella, Fecal coliform, Enterococci, Shigella, typhoid, cholera, dysentery, hepatitis, diphtheria cryptosporidium, and giardia. These pathogens pose a risk for those who ingest contaminated water directly or indirectly. Particularly, vulnerable are those with weakened immune systems, such as young children and the elderly.

Direct routes of exposure can occur through inadequately purified drinking water, swimming, boating, etc. Indirect exposure includes the consumption of food that has been contaminated by pathogen tainted water. CSO discharges limit our use of waters for recreation, drinking, and for food supplies. An example of these limitations are the closure of shellfish beds and fishing areas. Many of these shellfish beds are constantly in a state of closure due to the activity of CSOs. In fact, between 10 and 20 percent of harvest-limited shellfish acreage, amounting to nearly 600,000 acres, is attributed to CSOs according to a 1991 National Oceanic and Atmospheric Administration report


The most aesthetically obvious environmental effect of CSOs are the floatables that are discharged from outfalls. The EPA Demonstration study of Newark, New Jersey compiled information about the composition by volume of floatables from CSOs. They found that plastic and paper bags, styrofoam, and plastic bottles all account for substantial portions of floatable volume while glass bottles, wood, straws, cans, and medical waste account for smaller but still significant amounts. These floatables are often is often the source of the trash that we find in and along our waterways. For example, a CSO near Philadelphia was seen to have discharged condoms, tampons, and fecal matter.