Frequently Asked Questions (FAQ)

Doesn't urban runoff get treated in the same way as sewage?

Runoff, which can occur in both wet and dry weather, usually receives no treatment before discharge. During a rain storm, after enough initial rainfall occurs, water will flow across the land downhill into the nearest gutter, drain, stream, or river. Runoff can also occur when it's not raining, for example, when springs naturally flow, when swimming pools are drained, when landscaping is over-irrigated, when businesses wash down equipment in parking lots or alleys, or when there are accidental or deliberate fluid spills. However, most of the daily flow in Southern California rivers during dry weather is highly treated sewage. It can also be joined by other smaller permitted discharges like air conditioning condensate. The volume of rainfall runoff is many times greater than that of dry weather runoff.

The daily dry weather flow entering the ocean can amount to several million gallons per day along areas such as the Santa Monica Bay coast. Very little of this flow is treated because the drainage system has no connection to existing treatment plants (the flood control system was never intended to provide treatment of the runoff). Several southern California municipalities are trying to treat dry weather flow. A number of cities, including the Cities of Los Angeles and San Diego and the County of Los Angeles, have built structures to divert dry weather flows to local sewage treatment plants, and the City of Santa Monica has built a treatment plant solely dedicated to the treatment of runoff.

It is likely that the amount of treated dry weather flow will increase in the future. Some older cities also have combined sewer systems that carry both sewage and storm water to sewage treatment plants. The problem with these systems occurs when sewage spills into a waterway during a heavy rain storm when the sewage treatment plant reaches capacity.

Stormwater treatment is a much more difficult task. When it rains on Southern California cities, the water rapidly drains from paved areas into the flood control system and flows to the ocean. Sending stormwater to existing sewage treatment plants would easily exceed the plant's treatment capacity, resulting in spills of raw sewage into the ocean and on city streets. In fact, just the relatively small amount of stormwater that now unintentionally enters the sewage system can place a dangerous burden on sewage treatment plants.

  L.A. Regional Water Quality Control Board

  Santa Monica Urban Runoff Recycling Facility