Pretreatment

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Example oil-grit separator USGS 2002 (Wikimedia commons)

PretreatmentInitial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms. devices may be constructed in close association association with one or more inlets. Different configurations of each exist to accommodate any design.

Overland sheet flow

The following pretreatements are recommended where sheet flow is being directed to a BMPBest management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls. (e.g. a bioretention cell) receiving flow from the edge of an impermeable surface such as an asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. parking lot or a paved plaza:

A gravel diaphragmA level spreading device placed at a runoff discharge location, perpendicular to flow, to maintain sheet flow and distribute runoff as evenly as possible across a pervious area or stormwater infiltration practice. A gravel diaphragm acts as a pretreatment device, settling out suspended sediments before they reach the practice. typically requires less setback between the catchmentThe land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale. and the BMPBest management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls.. Where space permits, these three designs can be used in combination to even greater effect!

Concentrated overland flowOpen space floodway channels, road reserves, pavement expanses and other flow paths that convey flows typically in excess of the capacity of the Minor Drainage System.

Where a curb cut, a disconnected downspout or a swale directs surface water to a point, increasing the flow rate, one or more of the following pretreatments should be considered:

  • Pretreatment features (well suited for bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. cells)
  • Sand filters (well suited for underground infiltration)

- Also see stone for erosion controlIncludes the protection of soil from dislocation by water, wind or other agents. at inlets.

Concentrated underground flow

This type of pretreatement is dominated by proprietary systems, some of which have undergone verification under the Environmental Technology Verification (ETV) program.

PretreatmentInitial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms. options
Type Description ETV products Other products (not verified)
OGSSystems designed to remove trash, debris and some amount of sediment, oil and grease from stormwater runoff based on the principles of sedimentation for the grit and phase separation for the oil. Baffles Baffles slow flow, encouraging larger, heavier particles to drop out of the water column. A skimmer may also trap floating debris, oils and grease.
Hydrodynamic OGSSystems designed to remove trash, debris and some amount of sediment, oil and grease from stormwater runoff based on the principles of sedimentation for the grit and phase separation for the oil. The shape causes rapidly flowing water to form a vortex which forces the larger, heavier particles are outwards and downwards into a lower chamber. Floating debris, oils and grease are trapped behind a baffle or in small tank area, towards the top of the main vortex chamber
Cartridge filters Uses advanced membrane technology adopted from water treatment plants.
CatchbasinBox like underground concrete structure with openings in curb and gutter designed to collect runoff from streets and pavement. inserts Great for improving water quality in retrofit situations


This article is particularly heavy on proprietary systems and information. Please inform us of any omissions or broken links using the box below: