The Storm Drain System
The City's storm drain system conveys stormwater runoff from developed areas to local waterways to prevent flooding. This system includes publicly-owned storm drain inlets (which are the grated inlets commonly located in gutter flowlines adjacent to streets or in parking lots), and a network of underground piping and manholes, open channels, and roadside ditches. The City's storm drain system also includes publicly-owned streets, sidewalks and gutters. Stormwater flows from these surfaces into the storm drain system. Privately-owned drainage systems usually discharge to the City's storm drain system as well.
The storm drain system is different from the sanitary sewer system.
Sinks, toilets, and interior floor drains must be connected to the sanitary sewer system. The wastewater discharged to the sanitary sewer receives treatment to remove pollutants prior to release to creeks and rivers. Pollutants contained in stormwater runoff flow directly into local waterways, without treatment where they can be harmful to humans and the environment. Oil and grease, food waste, paint, concrete-related wastewater, chemicals and even dirt must be prevented from entering the storm drain system in order to preserve our local waterways.
When rainfall comes into contact with pollutants, the pollutants can be washed into the storm drain system and in turn, into our local waterways. Examples of situations where stormwater runoff could be polluted through exposure to pollutants include:
- Improper or incomplete clean-up of a release or spill of hazardous or non-hazardous materials or wastes in an outdoor, uncovered, area;
- Poor housekeeping in outdoor storage areas;
- Inadequate secondary containment and/or coverage of hazardous or non-hazardous materials or wastes;
- Leaky dumpsters, or dumpster lids left open;
- Liquids or powdery materials tracked outdoors by forklifts or other vehicles from indoor processing areas; and
- Leaky vehicles, equipment, compressors, etc.
Pollutants can also be washed into the storm drain system and local waterways by non-stormwater discharges such as irrigation runoff or in wastewater from hosing down or pressure washing polluted surfaces into the storm drain system.
Best Management Practices (BMPs)
BMPs are measures that reduce or eliminate pollutant discharges to the storm drain system. BMPs commonly fall into three categories:
- Provide stormwater BMP training to employees
- Conduct regular facility self-inspections to monitor for prohibited non-stormwater discharges or conditions
- Utilize your existing facility, or design your new facility, to minimize the threat to stormwater quality from your activities. If necessary, you may need to conduct activities that are not compatible with your facility (for example, commercial vehicle washing if you don't have a wash rack, or other means to contain, collect, and properly dispose of vehicle washing wastewater) at an offsite commercial facility.
- Consider the weather when you plan outdoor activities. You should not conduct pollutant-generating activities outdoors when it is raining or when rain is forecasted, as stormwater contact with the pollutants would be more likely to occur.
Source Control BMPs:
- Implement good housekeeping practices such as:
- Keeping outdoor areas swept and clean
- Cleaning spills promptly using dry methods (as opposed to hosing spills into a storm drain, which is prohibited)
- Install erosion control measures
- Stabilize exit points from unpaved areas with 2" or larger rock
- Repair any leaking vehicles or equipment
- Install secondary containment for stored fluids, preferably under a covered area to prevent stormwater from filling the containment device
- Construct roofs over outdoor material storage areas
Treatment Control BMPs (install and maintain):
- On-site storm drain inlet protection devices, such as appropriately-selected storm drain filter inserts
- Vegetative swales, sand filters, and bioretention devices
- Stormwater treatment vaults
- Detention basins
All treatment control BMPs require regular inspection and maintenance to ensure proper operation.
BMPs should be considered and implemented in the above order: administrative, source control, and then treatment control. Implementing BMPs in this order is the most cost effective and does the best job of protecting stormwater quality. Administratively eliminating pollution sources will almost always be the best solution. Using source control BMPs to eliminate pollutant sources prior to polluting stormwater runoff should be your next option. Your last option is to treat stormwater runoff in an effort to remove pollutants. Treatment is likely the most expensive and often least effective way to go. Treatment control should be a part of your overall stormwater pollution prevention strategy as a last and final effort to remove pollutants that could not feasibly be addressed through administrative and source control BMPs. Treatment control BMPs should not be used as stand alone BMPs.
Good Housekeeping can help prevent stormwater pollution
- Dumpster lids should be kept closed when not in use to keep rain out and uncontained liquids should never be placed in a dumpster — they will leak out.
- All wastes should be contained and managed in a responsible manner that prevents exposure to rainfall or discharge to the storm drainage system.
- Shop and restaurant floors should never be hosed out so that the wash water can run outdoors or into a storm drain. Dry cleanup methods should be used as often as possible.
- Spills, leaks and other messes that occur should be immediately cleaned, preferably using dry methods such as absorbent materials which must be properly disposed of.
- Dirty, oily, or rusty junk items should not be left outdoors. Consider properly disposing of these items or placing them in covered locations to prevent stormwater contact. At a minimum, these items should be covered with weighted or fastened tarps and stored off the ground (e.g., on pallets). Fluids from engine crank cases, differentials, and radiators should be drained and properly disposed of prior to storage.
- Sweep indoor and outdoors areas as often as necessary to prevent sediment or other pollutants that may be generated, from being tracked outdoors or offsite.
Pressure washing is an excellent way of removing pollutants from outdoor surfaces. However, pressure washing wastewater should never be discharged to a storm drain. Storm drains should be covered, or the path to the drain should be blocked during pressure washing. With the property owner's permission, the collected wastewater can then be pumped into a sanitary sewer clean out, or, in some instances, discharged to a landscaped area, provided that the discharge does not overflow the landscaped area, contain hazardous constituents, or create nuisance conditions. Sump pumps and wet/dry shop vacuums can be used to pump the wastewater.