Sources of Runoff Pollution

What's the Big Deal?

san dieguitoPhoto GirlChasesGlobe.comUrban runoff is the single biggest threat to water quality in San Diego.

As we created cities and more people settled in our region, we paved over the "spongy" parts of watersheds. This means surfaces that previously allowed water to infiltrate became hard. This stops water from soaking into the ground or being used by plants. These impervious surfaces, like parking lots, roads and buildings, cause water to flow over the surface of a watershed. This surface flow, also known as stormwater or urban runoff, causes problems in our creeks, rivers and lagoons including increased pollution, faster and flashier flows and increased erosion.

Essentially, our human activities have disrupted how watersheds function.

During our long dry season, pollutants build on hard surfaces. When it rains, stormwater pushes the accumulated pollutants into our storm drains. In San Diego, like most of California, our storm drains generally do not connect to wastewater treatment plants, so everything flows untreated into our waters.

It does not take much pavement in a watershed to cause ecological harm—water quality and habitat impacts can start when as little as 10 percent of the watershed gets paved. This makes protecting and restoring water quality very challenging.

In addition to pollution from our cars, yards, and streets, contaminants flow into our storm drain system from industrial and construction areas, irrigation, the atmosphere and sewage spills. When not managed appropriately, industrial and construction sites can be significant sources of pollution.

Infrequent rain in San Diego allows pollutants to build on land, which leads to a dangerous "first flush" of pollutants into our waterways during the first rain after a long dry spell. But even during dry weather, we send pollutants from the land into the water. Every time a lawn is over watered into the streets or a carwash flows into the storm drain, pollutants move into our waters.

Urban runoff creates negative impacts such as:

Where does it come from?

48angUrban runoff is a result of pollution from the following areas:


Infrequent rain in San Diego allows pollutants to build on the land, which leads to a dangerous "first flush" of pollutants into our waters during the first rain after a long dry spell. But even during dry weather, we send pollutants from the land into the water. Mostly we do this by over-irrigating our landscape, but sometimes groundwater seeps can also carry pollutants into our surface water during dry weather.

Practice and share these tips to reduce how you negatively contribute to runoff pollution.

Residential Sources 

Our homes and neighborhoods are a significant source of polluted urban runoff. Every time you spread your lawn fertilizer a bit too far outside of your lawn, every dog poop left behind, every time ant or roach pesticide gets blown from its intended target, a little bit of pollution gets added to the system. Multiply this by the three million residents we have in the county, and it all adds up.

san elijoGirlChasesGlobe.com

Commercial Sources

Businesses also have a role to play in helping prevent urban runoff. Our commercial areas often have large parking lots that increase the amount of surface flow into our storm drains. Businesses like fast food restaurants and bars seem to attract trash and cigarette butts. Dirty mop water water poured into the storm drain is a source of nastiness in our rivers.

Agricultural Sources

You may not think of San Diego County as an agricultural powerhouse, but we have a huge amount of agriculture. San Diego County is the 12th-largest farm economy and has more small farms (less than 10 acres) than any other county. Local agriculture brings $5.1 billion annually into our economy. Farms, however, often contribute to nutrient pollution to our waters. San Diego Coastkeeper's water monitoring lab has shown that nitrates (a common form of nitrogen fertilizer) is a ubiquitous pollutant in our streams. Poor irrigation runoff management could explain much of that nitrate in our waters.

Industrial Sources

In San Diego County, our industrial areas often concentrate into small sections of town. Auto repair shops, shipbuilding, recycling centers and other industrial areas have the potential to contribute metals and oils into our stormwater system. These pollutants are especially serious because of their ability to be toxic in very low concentrations. Because of the seriousness of these pollutants, all stormwater in an industrial facility should be captured and treated on site.


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