Q&A Storm Water Discharge System

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Q & A Storm Water Discharge System


Date of Record: 2012-10-23

"Coronado is committed to water quality" - City Manager Blair King

The City of Coronado is committed to water quality. We want the public to know what we do to keep our bay and ocean clean and to comply with regional, state and federal water quality mandates. To increase awareness of storm water management and surface water quality, the City of Coronado has put together this Q&A.

Sanitary sewer systems and storm drain systems are distinct and must be kept separate. Everything that goes into the sanitary sewer system - from toilets, sinks, laundry water - is sent to the Point Loma Wastewater Treatment Plant to be treated and discharged into the local receiving waters. The storm drain system helps prevent flooding by transporting water away from developed areas. The City's storm drains typically carry untreated rain water from the City's streets and release it into the bay or ocean..

Sewage is expensive to treat. Rain water is much cleaner than sewage. To help prevent sewage treatment plants that treat millions of gallons of raw sewage daily from being overwhelmed during rain events and spilling contaminated sewage into the environment, most storm water in cities around San Diego County, including Coronado, either freely flows or is piped directly to the local receiving waters. 

In addition to overwhelming the Point Loma treatment plant, the City's infrastructure could not handle storm water runoff. The City of Coronado's sewer system was designed and built to transport sewage and does not have the capacity to handle more without risking system failure. Furthermore, the cost of treating the City's sewage is a huge consideration. Last year, Coronado residents paid $2.1 million in treatment costs. Any increases to the system must be shared by users, Coronado residents. 

Storm water from rain events is itself very clean. However, once it hits the ground, it begins to collect the contaminants and pollutants it encounters on its journey to the bay or ocean. Coronado has a very robust program to capture these pollutants before they reach the receiving waters. The City uses "best management practices," guidelines created to reduce pollutants from reaching receiving waters, including frequent street sweeping, diverting dry-weather flows to the sewer system, use of perimeter runoff controls at construction sites, and other approved techniques.


Coronado has 13 dry-weather diverters on many of the storm drain outlets as an extra protection to its receiving waters. The diverters capture all summertime or dry-season runoff - from home car washing, over-irrigating lawns, illegally discharged water - and sends it to the sanitary sewer system to be treated so that no runoff besides rain enters the bay or ocean. Additionally, during storm events, the "first flush" of rainwater rushing through the storm drain system, usually the most heavily polluted, also goes to the sanitary system. These systems are continually inspected and cleaned to ensure proper working order. 

The sanitary sewer system in Country Club Estates is similar to the rest of the City. However, storm water there is managed differently because of the existing topography. Country Club Estates was constructed on property that sits at a relatively low elevation and has a high ground water table. As seen in an early map of the City (below), the area under Country Club Estates was once a waterway. In the early 1940s, the Spanish Bight, initially separating North Coronado Island from South Coronado Island, was filled to allow for military runways, housing and training facilities on North Island. Because of the low elevation and flat topography, storm water will not naturally gravitate toward the ocean; therefore, it must be pumped to the ocean. Some minor flooding may occur.

This map from 1886 shows the streets and plots mapped out for building before the Hotel del Coronado was constructed. On the left, the Spanish Bight waterway is noted and was located where the Country Club Estates now sits. It was filled in sometime in the early 1940s to create more room for the military.

A storm drain system of new pipes and pump stations was installed in the early 1990s and has greatly reduced flooding in the area. Because the system uses mechanical means to pump the water to the ocean, minor flooding may still occur if there is any type of mechanical problem. Should anyone notice storm water levels approaching the top of the curb, they should notify the City's Public Services Department. Dozens of homes and roads were built decades ago over the former waterway. Its water table will remain where it has always been. For a time, the City routinely pumped water out of the area to help prevent flooding of nearby streets and property. However, since the City could not guarantee that everything it pumped was 100 percent clean, the San Diego Regional Water Quality Control Board stopped the practice. Now, the City may only pump during rain events. Without the constant pumping, the ground water has returned to its natural level.

In September of each year, the City submits a National Pollutant Discharge Elimination System, or NPDES, Storm Water Annual Report to the San Diego Regional Water Quality Control Board for review. This report is a thorough analysis of the City's storm water management program's effectiveness in improving water quality. Specific areas of program implementation address development and construction activity; municipal operations; commercial business inspections; and residential outreach. All cities within San Diego County are required to submit an NPDES report annually. Additionally, the County's Environmental Health Department performs weekly water quality sampling in the City. Should samples exceed safe water quality levels, the City is notified and an appropriate level of public notification and protection is made.

There are multiple layers of safeguards in place to prevent system failures. All sewer stations in the City have alarm systems to notify the City of failure on a 24/7 basis. The system is inspected, reviewed and repaired on a regular basis. The City's main waste water pump, the Transbay Pump Station, has a permanent generator and portable generators are used at the remaining pump stations. The City has a Master Plan, which evaluates the sewer and storm systems' structure, integrity and capacity. City workers monitor the weather to prepare for major rain events.

A smart city is an informed city. If you witness an unusual event that may impact the storm drains, give us a call. Calls we have received range from cars leaking oil to bad odors and from excessive irrigation runoff to backed-up plumbing. Typical response time for after-hour calls is within 45 minutes. Residents are encouraged to report these unusual events during regular business hours by calling Public Services at (619) 522-7380. After hours - from 4:30 p.m. to 7 a.m. Monday through Thursday and 3:30 p.m. Friday until 7 a.m. Monday -- residents should call the Coronado Police Department at (619) 522-7350. Reportable items also can be submitted through the Action Centerof the City's website. Residents are encouraged to use home cleaning practices that minimize or eliminate potential pollutants from entering gutters when they perform tasks such as washing cars, applying fertilizer, tending to their landscaping, washing driveways and patios, and cleaning pools. This San Diego County brochure has some easy steps residents can take..

Q&A Storm Water Discharge System October 23, 2012
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