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Breadcrumb Start you are here >Home/ StormWater Management Program/Six Pollutants of Concern

Six Pollutants of Concern


Storm water runoff from impervious surfaces carries large amounts of various pollutants to the surface waters of the United States.  These pollutants include nutrients, silt/sediment, pathogens, oil/grease, metals, debris and litter. Of particular concern to the water bodies surrounding Long Island, and to be addressed by the NCSWMP, are pathogens, phosphorus, PCB’s, silt and sediment, and nitrogen.


Human exposure to pathogens can cause illness, most often gastroenteritis, but also potentially more serious diseases such as salmonellosis and hepatitis A. This can result from ingesting contaminated shellfish, or contact with contaminated water. Long Island’s waters generally support bathing and shellfishing, but public health warnings and occasional beach closures result from increased pathogen and bacteria levels in the water. Nassau County has, along with our surrounding counties, a beach water quality monitoring program.

In many parts of the Northeast, nitrogen, phosphorus, and pathogens enter stormwater through the commingling of sewage and storm water runoff, namely through Combined or Sanitary Sewer Overflows (CSO’s or SSO’s). CSO’s and SSO’s occur when stormwater adds a burden to the sewer system that it is unable to bear, and untreated sewage escapes into surface waters.  While this is a factor for the health of the greater Long Island Sound and Atlantic Ocean region, Nassau County has separate, well-maintained sewer systems for stormwater and for sewage, and does not regularly contribute raw sewage to our surface waters. Incidences of private septic systems overflowing are isolated and rare.

The major contributor of new pathogens into Nassau’s stormwater is excrement left by wild and domestic animals that is carried by storm water into our storm sewers, lakes and streams. Dogs and permanent populations of geese are the main contributors to the problem. 

When walking your dog, consider these statistics:

    • Each gram of dog feces contains 23 million fecal coliform colonies.  
    • It has been estimated that for some watersheds, two to three days of droppings from a population of about 100 dogs would contribute enough bacteria and nutrients to temporarily close a bay to swimming and shellfishing (US EPA, 1993).

Storm Water RunoffIn addition, vast numbers of Canada geese have settled on Long Island, and many have ceased to make annual migrations. These permanent populations increase in number every year. The rise in geese population, paired with their yearlong presence, has resulted in dramatically increased depositions of waste. In order to address these problems, the County has embarked on a public education campaign on the effects of geese and of not cleaning up pet wastes. All pet owners are encouraged to take responsibility for the condition of our bays and streams by always picking up after your dogs when walking them and maintaining a clean yard. Members of the public are also asked not to feed geese on County property.


PCBs, or polychlorinated biphenyls, were banned from domestic manufacture in 1977. PCBs were used widely for hydraulic fluids, capacitors and transformers, heat transfer fluids, lubricating and cutting oils, and as additives in pesticides, paints, adhesives, sealants, plastics, and reactive flame retardants. However, they are classified as a persistent organic pollutant, and over thirty years later PCBs continue to be found in sediment in Long Island Sound, although not suspended in its waters.

PCBs are endocrine disruptors, and in high concentrations have been linked to certain kinds of cancers. As a result, several fish consumption advisories exist for fish taken from Long Island Sound which may be contaminated with PCBs. However, it is important to note that these advisories not necessarily the result of PCB contamination in the waters themselves, but regard specific migratory species such as Striped Bass which have accumulated PCB’s during their migrations throughout the world, or from fish that have spent time at the General Electric Superfund site in the Hudson River.   

More information about fish consumption advisories is located at www.health.state.ny.us/environmental/outdoors/fish/fish.htm.


Nitrogen, Phosphorus, and Oxygen Demand


Phosphorus and nitrogen are considered nutrients, and when deposited in excessive amounts into water bodies can cause a condition known as eutrophication. Eutrophication, or an excess of nutrients, causes vast ecological imbalances, including algae blooms.  When large algal blooms die, the naturally occurring bacteria that decompose them multiply rapidly, using up the dissolved oxygen in the water. In extreme cases, this can lead to hypoxic zones (where there is not enough oxygen to sustain most marine life) and dead zones (where the lack of oxygen has lead to the growth of toxic anaerobic bacteria). Algae blooms may also be of concern as some species of algae produce neurotoxins. At the high cell concentrations reached during some blooms, these toxins may have severe impacts on wildlife.  

Seasonal low dissolved oxygen in Long Island Sound has been the focus of considerable concern and study. Hypoxia in the bottom waters of the western Long Island Sound have caused fish and crustacean kills and induced finfish to avoid the area. The Long Island Sound Study (LISS) has determined the dissolved oxygen problem is primarily due to algal die-off.

Due to the integrity of Nassau’s sanitary sewer system, the primary sources of nitrogen and phosphorus in Nassau County’s storm water are wild and domestic animal wastes and excessive or improper use of commercial fertilizers. Because of the decline of large-scale agriculture, commercial fertilizers in the county are applied primarily by private consumers.


Silt and Sediment

Large amounts of silt and sediment, when dislodged and swept by storm water into watersheds or water bodies, can disrupt ecosystems in a number of ways. Storm water runoff that contains sediment can deposit harmful amounts of silt in sensitive areas such as wetlands and wildlife preserves, and exacerbate erosion of stream banks and beaches. Dense clouds of particulate matter suspended in water bodies such as Long Island Sound block sunlight, inhibiting photosynthesis by phytoplankton and bottom-dwelling marine plants, and can suffocate finfish; when this same sediment settles on the sea floor, it can stifle the benthic organisms that support the greater marine ecosystem.  Sediment that is washed from urbanized areas can carry significant amounts of toxic petrochemicals, nutrients, fertilizers, pesticides and bacteria.  Specific sources of sediment that are addressed through the NCSWMP are construction sites, which can contribute tons of sediment, and winter road de-icing procedures.