Pollutants & Sources

Phosphorus Ammonia & Nitrite Combined Sewer Overflows Mercury & Other Industrial Wastes Sediment Loading: Tully Valley Mudboils Salinity Nonpoint Source Pollution

During heavy storm periods, a mixture of raw sewage and street runoff overflows from the sewer system through relief structures called combined sewer overflows (CSOs), releasing harmful bacteria and viruses that eventually reach Onondaga Lake.

Combined Sewers

Combined sewers carry wastewater (domestic sewage, wastewater from commercial, industrial and institutional establishments, and groundwater infiltration) along with surface runoff from rain and snow. Under normal conditions, the mixed wastewater and runoff flows through the sewer system to the Metro plant. All wastes that reach the Metro plant are disinfected with sodium hypochlorite, which kills bacteria and viruses that might cause sickness and disease.

Combined Sewer Overflows

Combined sewer overflows are the main source of bacteria to Onondaga Lake.

During heavy storm periods, sewers may become overloaded because of the high volume of surface runoff. To avoid flooding, the excess water overflows from the sewer system through relief structures called combined sewer overflows (CSOs). The CSOs discharge directly into tributaries of Onondaga lake, thus bypassing sewage treatment at Metro. Bacteria and viruses present in the mixed wastewater and runoff are then discharged into the tributaries, and eventually to Onondaga Lake. There are 42 CSOs that discharge into Onondaga Creek, 19 CSOs discharge into Harbor Brook, and two CSOs discharge into Ley Creek.

Pathogenic Bacteria and Viruses

Microscopic bacteria and viruses are found in the intestinal tract and feces of human beings. Some of these microorganisms are pathogenic, which means they can cause sickness and disease. The contamination of lakes and rivers by fecal material increases the risk that people using those waters for swimming and other forms of recreation will become sick and spread disease. The last beach on Onondaga Lake was closed in 1940 because of public health concerns associated with sewage contamination.

Indicator Organisms

Public health officials use indicator organisms, common but harmless bacteria, to measure the potential presence of pathogens in water used for swimming or drinking. Total coliform and fecal coliform bacteria are the most common indicators because they are present in the digestive tracts of all humans, and their presence in water samples is easy to measure.

Bacterial Contamination in Onondaga Lake

Public health standards for levels of indicator bacteria are routinely violated throughout the southern half of Onondaga Lake following storm events. After a storm, the water in Onondaga Lake remains contaminated with bacteria from the CSOs for about 3 days. During average summer months there are 18 storms that can lead to about 54 days of violations. These violations prevent the lake from being used for swimming.