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Effects | Regs | Pollutants

What is Stormwater Runoff and why worry about it?

Words in italics are linked to a definition in the glossary

When it rains or when snow melts over an impervious area (for example paved streets or parking lots), water is not absorbed into the ground and it "runs off" to a lower elevation. This runoff picks up pollutants such as dirt and oil and carries them to the nearest water body. If this runoff or stormwater is not treated, it will pollute the river or lake where it ends up.

Development Effects on Runoff
Construction of man-made features such as homes, other buildings, or parking lots, creates a lot of impervious areas. This affects the quantity of water draining off the landscape: more water runs faster to nearby waterways, creating floods after precipitation events, and droughts in between. It also affects water quality: animal wastes, sediments, heavy metals, etc. are carried along and degrade wildlife habitat and water quality in ponds and streams.
Massachusetts Stormwater Management Standards must be used by developers to satisfy statutory and regulatory requirements of the DEP, including the Wetlands Protection Act, the Rivers Protections Act, and the State Clean Waters Act. One standard requires that new development install stormwater management systems that remove 80% of the average annual load of Total Suspended Solids and that no new stormwater conveyances may discharge untreated stormwater directly to or cause erosion in wetlands or waters of the Commonwealth.

EPA, under the NPDES stormwater program, requires construction activities that disturb one acre or more to develop and implement stormwater pollution prevention plans.

Controlling Stormwater Runoff
Proper runoff control reduces pollutants and the rate of discharge to waterways. There are basically three ways to deal with runoff: site planning; installing non-structural controls such as detention basins and grass swales; and installing structural Best Management Practices (BMPs) such as catch basin inserts.
Site Planning

The most effective approach to address stormwater problems is to plan for stormwater management before development occurs: indeed, the cheapest and best technique is to prevent or minimize stormwater on the site. The basic steps are:

  • Minimize impervious surfaces (maintain natural buffers and depressions; put as few roads on porous soils as possible; use creative planning such as building clusters and reduced lanes and sidewalks, etc.)
  • Fit the development to the terrain
  • Preserve and utilize natural drainage systems (avoid curbs and stormdrains)
  • Reproduce pre-development hydrologic conditions (create opportunities for infiltration and water storage to avoid greater runoff and floods).
Non-Structural controls

These include strategies such as:

  • Local bylaws and regulations
  • Materials management at industrial sites
  • Fertilizer management in residential areas
  • Reduced road salting in winter
  • Erosion and sediment controls at construction sites, and
  • Comprehensive snow management.
Structural BMPs

These are constructed facilities to help protect receiving water quality and control stormwater quantity, such as:

This clearinghouse contains exclusively structural BMPs, namely infiltration, filtration, and pretreatment BMPs.

Typical Stormwater Pollutants
Stormwater Pollutant
Related Impacts
Nutrients: Nitrogen, Phosphorous
Urban runoff; animal waste; fertilizers; failing septic systems
Algal growth; reduced clarity; lower dissolved oxygen; release of other pollutants
Solids: Sediment (clean and contaminated)
Construction sites; other disturbed and/or non-vegetated lands; eroding banks; road sanding; urban runoff
Increased turbidity; reduced clarity; lower dissolved oxygen; deposition of sediments; smother aquatic habitat including spawning sites; sediment and benthic toxicity
Pathogens: Bacteria, Viruses
Animal waste; urban runoff; failing septic systems
Human health risks via drinking water supplies; contaminated shellfish growing areas and swimming beaches
Metals: Lead, Copper, Cadmium, Zinc, Mercury, Chromium, Aluminum, others
Industrial processes; normal wear of
automobile brakelines and tires; automobile emissions; automobile
fluid leaks; metal roofs
Toxicity of water column and sediment; bioaccumulation in aquatic species and through food chain
Hydrocarbons: Oil and Grease, PAHs (Naphthalenes, Pyrenes)
Industrial processes; automobile wear; automobile emissions; automobile fluid leaks; waste oil
Toxicity of water column and sediment; bioaccumulation in aquatic species and through food chain
Organics: Pesticides, PCBs, Synthetic chemicals
Pesticides (herbicides, insecticides,
fungicides, rodenticides, etc.);
industrial processes
Toxicity of water column and sediment; bioaccumulation in aquatic species and through food chain
Salt: Sodium, Chlorides
Road salting and uncovered salt
Toxicity of water column and sediment
* Content borrowed from MA DEP & MA CZM Stormwater Management - Stormwater Technical Handbook (1997)
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