Stormwater Issues 101

Stormwater Issues 101


Stormwater runoff is part of a natural hydrologic process.  Human activities particularly urbanization  and agriculture, can alter natural drainage patterns and add pollutants to rivers, lakes, and streams as well as coastal bays, estuaries, and ultimately, the ocean.  Numerous studies have shown urban runoff to be a significant source of water pollution, causing declines in fisheries, restricting swimming, and limiting our ability to enjoy many of the other benefits that water resources provide (USEPA, 1992).  Urban runoff in this context includes all flows discharged from urban land uses into stormwater conveyance systems and receiving waters and includes both dry weather non-stormwater sources (e.g., runoff from landscape irrigation, water line and hydrant flushing) and wet weather stormwater runoff.  Urban runoff and stormwater runoff are used interchangeably.

For many years the effort to control the discharge of stormwater focused mainly on the quantity (e.g. drainage, flood control) and, only to a limited extent, on the quality of the stormwater (e.g. sediment and erosion control).  In recent years, however, awareness of the need to improve water quality has increased.  With this awareness, federal, state and local programs have been established to reduce pollutants contained in stormwater discharges to our waterways.  The emphasis of these programs is to promote the concept and the practice of preventing pollution at the source, before it can cause environmental problems (USEPA, 1992).  Where further controls are needed, treatment of polluted runoff may be required.


Municipal NPDES Stormwater Program

 Municipalities with a population of over 100,000 or that have been determined to be a significant contributor of pollutants are required to obtain an individual NPDES stormwater permit. These municipalities are classified as Phase I communities and are typically referred to as MS4s (municipal separate storm sewer systems). To meet CWA Section 402(p) requirements, Phase I MS4s are required to implement a stormwater management program, which contains the following elements:

  • Program Management: including program structure, institutional arrangements, legal authority, and fiscal resources;
  • Illicit Discharges: including prohibition of illicit connections and dumping, and enforcement;
  • Industrial / Commercial Discharges: including identification of sources, BMPs, outreach, inspections, staff training, and coordination with state General;
  • New Development and Re-development: including planning processes, local permits, staff training, post-construction structural BMPs;
  • Construction: including erosion and grading permits, construction BMPs, site inspections, enforcement, and coordination with state General;
  • Public Agency (Municipal) Operations: including inventory and BMPs for corporation yards, parks and recreation, storm drain system operation and maintenance, streets and roads, flood control, public facilities, and ponds, fountains and other public water;
  • Public Information and Participation: including general and focused outreach, school education programs, citizen participation, and effectiveness evaluation of the public information; 
  •  Program Evaluation: including performance standards, annual and sub-annual reports, internal reporting and record keeping, and Stormwater Management Plan; and
  • Monitoring: including system characterization, source identification, control measure effectiveness, pollutant loading, and data.


Pollutant Impacts on Water Quality


Sediment is a common component of stormwaters, and can be a pollutant. Sediment can be detrimental to aquatic life (primary producers, benthic invertebrates, and fish) by interfering with photosynthesis, respiration, growth, reproduction, and oxygen exchange in water bodies.  Sediment can transport other pollutants that are attached to it including nutrients, trace metals, and hydrocarbons. Sediment is the primary component of total suspended solids (TSS), a common water quality analytical parameter.



Nutrients including nitrogen and phosphorous are the major plant nutrients used for fertilizing landscapes, and are often found in stormwater.  These nutrients can result in excessive or accelerated growth of vegetation, such as algae, resulting in impaired use of water in lakes and other sources of water supply.  For example, nutrients have led to a loss of water clarity in Lake Tahoe.  In addition, un-ionized ammonia (one of the nitrogen forms) can be toxic to fish.


Bacteria and Viruses

Bacteria and viruses are common contaminants of stormwater.  For separate storm drain systems, sources of these contaminants include animal excrement and sanitary sewer overflow.  High levels of indicator bacteria in stormwater have led to the closure of beaches, lakes, and rivers to contact recreation such as swimming.


Oil and Grease

Oil and grease includes a wide array of hydrocarbon compounds, some of which are toxic to aquatic organisms at low concentrations.  Sources of oil and grease include leakage, spills, cleaning and sloughing associated with vehicle and equipment engines and suspensions, leaking and breaks in hydraulic systems, restaurants, and waste oil disposal.



Metals including lead, zinc, cadmium, copper, chromium, and nickel are commonly found in stormwater.  Many of the artificial surfaces of the urban environment (e.g., galvanized metal, paint, automobiles, or preserved wood) contain metals, which enter stormwater as the surfaces corrode, flake, dissolve, decay, or leach. Over half the trace metal load carried in stormwater is associated with sediments.  Metals are of concern because they are toxic to aquatic organisms, can bioaccumulate (accumulate to toxic levels in aquatic animals such as fish), and have the potential to contaminate drinking water supplies.



Organics may be found in stormwater in low concentrations.  Often synthetic organic compounds (adhesives, cleaners, sealants, solvents, etc.) are widely applied and may be improperly stored and disposed.  In addition, deliberate dumping of these chemicals into storm drains and inlets causes environmental harm to waterways.



Pesticides (including herbicides, fungicides, rodenticides, and insecticides) have been repeatedly detected in stormwater at toxic levels, even when pesticides have been applied in accordance with label instructions. AB pesticide use has increased, so too have concerns about adverse effects of pesticides on the environment and human health.


Accumulation of these compounds in simple aquatic organisms, such as plankton, provides an avenue for biomagnification through the food web, potentially resulting in elevated levels of toxins in organisms that feed on them, such as fish and birds.


Gross Pollutants

Gross Pollutants (trash, debris, and floatables) may include heavy metals, pesticides, and bacteria in stormwater.  Typically resulting from an urban environment, industrial sites and construction sites, trash and floatables may create an aesthetic “eye sore” in waterways.  Gross pollutants also include plant debris (such as leaves and lawn-clippings from landscape maintenance), animal excrement, street litter, and other organic matter. Such substances may harbor bacteria, viruses, vectors, and depress the dissolved oxygen levels in streams, lakes, and estuaries sometimes causing fish kills.


Vector Production

Vector production (e.g., mosquitoes, flies, and rodents) is frequently associated with sheltered habitats and standing water. Unless designed and maintained properly, standing water may occur in treatment control BMPs for 72 hours or more, thus providing a source for vector habitat and reproduction (Metzger, 2002).


Pollutants of Concern in the San Francisco Bay and Delta


Storm drains can carry a variety of pollutants to creeks, the Bay, and the Delta.  Some of these can harm wildlife and humans-a few which cause particular concern, are listed below.


Much of the mercury that runs into the Bay is a remnant of the historic use of mercury in gold mining operations. Bacterial and chemical processes in the Bay cause Mercury concentrations to increase or “bioaccumulate” in the bodies of animals high in the food web. As a result, fish consumption advisories suggest that humans, particularly children and pregnant women, limit consumption of fish from San Francisco Bay to avoid harm to developing nervous systems.


The Sacramento-San Joaquin Delta Estuary (Delta) is impaired because of elevated levels of methylmercury in fish. The Delta is on the Clean Water Act 303(d) list for mercury and the State Water Resources Control Board has designated the Delta as a toxic hot spot under the Bay Protection and Toxic Hot Spot Cleanup Program. Mercury problems are evident region-wide. The main concern with mercury is that, like selenium, it bioaccumulates in aquatic systems to levels that are harmful to fish and their predators. Health advisories have been issued which recommend limiting consumption of fish taken from the Bay/Delta, tributaries to the Delta, and many lakes and reservoirs in the Central Valley. Concentrations of mercury in other water bodies approach or exceed National Academy of Science (NAS), U.S. Environmental Protection Agency (US EPA), and/or U.S. Food and Drug Administration (FDA) guidelines for wildlife and human protection.  (There is also concern for birds in the Delta, but no studies have been completed.)

Polychlorinated Biphenyls or PCBs

PCBs were used in the past in a number of industrial and commercial applications, most importantly as coolants, lubricants, and insulators in electrical equipment. Although new uses are banned, PCBs continue to pose a serious risk due to their persistence in the environment. PCBs are fisted by US EPA as a potential carcinogen, and are suspected of having negative effects on the human immune, reproductive, nervous, endocrine, and digestive systems. As with Mercury, PCBs pose human health risks because they accumulate in fish tissue.


Pesticides have been found in streams and storm drains throughout the Bay Area and California, often in concentrations toxic to aquatic life. Although a very small percentage of the amount that is applied finds its way into urban runoff, this is still enough to raise concerns about impacts to aquatic health.


At low concentrations, copper is beneficial to aquatic life, but at higher concentrations can be extremely toxic to aquatic life; this toxicity can occur at levels that are not harmful to humans. This metal finds its way down storm drains through runoff from building materials and roads where copper is released from the brake pads of cars.



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