Environmental groups and government regulators have increased pressure on industrial facilities to comply with the General Industrial Stormwater Permit. This pressure includes the need to meet the benchmark levels, which may require the need for enhanced treatment. Stormwater run-off is generated when rain water flows over an industrial site and does not percolate into the ground. As the runoff flows through the facility it accumulates oil & grease, sediment and other pollutants that could negatively affect the quality of the stormwater discharge.
The water is discharged to what is known as an outfall, which is a designated place where the stormwater is supposed to leave the property. A facility can have more than one outfall and the outfalls are where the samples will be taken during the storm event. The outfall can be above ground or it can be a subsurface pipe that connects a municipal stormwater conveyance system.
A Stormwater Treatment System consists of a combination of different treatment technologies to remove the constituents below the permit benchmarks. A typical industrial stormwater treatment system consists of:
- Clarifier- Below grade concrete structure designed to reduce oil & grease and large solids. The clarifier is installed below grade so the stormwater can flow into it via gravity to reduce the emulsification of oil and water.
- Flocculation Injection System– Chemical process that forces small particles to adhere to each other to form a larger particle that can be more easily filtered.
- Holding Tank- Designed to slow down the flow of water so settling may take place. The tank can be used to store water for dust control and/or other reuse applications.
- Sand Filter- Mechanical Filtration designed to remove solids down to 75-100 micron in size and can be configured with an automated backwash to minimize maintenance time.
- Bag Filter– Mechanical Filtration designed to remove solids down to very small sizes. Pure Effect, Inc. offers bag filters from 100 to 1 micron in size.
- Media Vessels- Are designed to remove dissolved contaminants including VOC’s and metals. Typically a combination of medias and resins will be used to remove all of the constituents listed on the permit.
Here is a typical industrial stormwater treatment system:
Stormwater Treatment System
For more information on permitting and Stormwater Treatment Systems
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