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image of Preserver pretreatment device
Heavy Leaf and Debris Loading in Pretreatment Manhole Sump [Ramsey Conservation District, 2017].
Caution: The Minnesota Pollution Agency (MPCA) received a request to provide information on management and disposal of sediments collected by pretreatment practices. We conducted a cursory review of the literature and developed this page. In developing this page, the MPCA is not providing recommendations for managing sediment and other materials captured by stormwater pretreatment practices. This page provides guidance and general information that can be used for managing these materials.

This discussion focuses on pretreatment practices. Pretreatment reduces maintenance and prolongs the lifespan of structural stormwater BMPs by removing trash, debris, organic materials, coarse sediments, and associated pollutants prior to entering structural stormwater BMPs. Implementing pretreatment devices also improves aesthetics by capturing debris in focused or hidden areas.

Because pretreatment practices remove material from stormwater runoff, they must be periodically cleaned to maintain their function. This page provides information on management of material collected in pretreatment practices, including disposal options.

For information on pretreatment, link here.

Types of practices

Below is a brief summary of the types of materials typically found in these practices.

  • Catch basins. A catch basin is an inlet to a stormdrain system that typically includes a grate where stormwater enters the catch basin, and a basin to capture sediment, debris, and associated pollutants. They may also capture floatables and settle some solids. Catch basins act as pretreatment for other treatment practices by capturing large sediments.
  • Grit chambers and oil/grit separators: Grit chambers are tanks designed to slow down water flow so that solids will settle out of the water. Oil/grit separators are underground storage tanks with three chambers designed to remove heavy particulates, floating debris and hydrocarbons from stormwater.

Description of material captured

The type of material collected in a pretreatment practice depends on the source of stormwater runoff. Primary constituents include sand, salt, leaves, and other litter and debris washed off streets, parking lots and sidewalks.

See the discussion below for results of sampling for materials collected by these practices.

Monitoring results

There is limited information for sampling of sediments and other materials captured by pretreatment practices. The Excel spreadsheet below summarizes results from sampling studies. NOTE: This spreadsheet may be updated periodically and includes a date at the top of the spreadsheet.

File:Pretreatment sampling data.xlsx

In general, concentrations of metals and organic pollutants are below levels of concern. The following bullets summarize results for these studies.

  • Florida Department of Environmental Protection
    • Examined street sweepings and catch basins
    • Upper 95% confidence limit concentrations for metals were below Florida criteria except for arsenic in catch basins; and iron, aluminum, and Beta-BHC in street sweepings and catch basins.
    • Upper 95% confidence limit concentrations of metals other than arsenic, iron, and aluminum were typically close to or more than an order of magnitude lower than Florida criteria
  • Townsend, 2003 - street sweepings
    • Average concentrations of metals other than arsenic were below residential criteria for Florida
    • Maximum concentrations of metals exceeded residential criteria for arsenic, barium, chromium, copper, and lead
    • Average concentrations of all metals were below industrial criteria for Florida
    • Maximum concentrations of arsenic, chromium, and lead exceeded industrial criteria for Florida
  • Townsend, 2003 - catch basins
    • Average concentrations of metals other than arsenic were below residential criteria for Florida
    • Maximum concentrations of metals exceeded residential criteria for arsenic, copper, and lead
    • Average concentrations of all metals were below industrial criteria for Florida
    • Maximum concentrations of arsenic and lead exceeded industrial criteria for Florida
  • Townsend, 2003 - leaching studies for street sweepings and catch basins
    • Average concentrations of nickel exceeded leaching criteria for Florida
    • Maximum concentrations of lead exceeded leaching criteria for Florida
  • Yu and Stopinski, 2001
    • Concentrations of metals other than chromium were below criteria for Isolator and Stormceptor pretreatment devices. NOTE: the criteria for hexavalent chromium was used in this analysis

Comparisons of results from these studies with Minnesota criteria, maximum concentrations of all metals except arsenic and lead are below industrial soil reference values.

Disposal of collected material

Analysis of stormwater runoff and sediments collected by pretreatment practices indicate that "typical" concentrations of pollutants do not warrant testing and the material can be disposed at a permitted landfill.

The following steps are typically found in guidance for handling these materials.

  • Remove the majority of water in the sump of the basin without disturbing the solid material below. The clear water may be discharged to one of the following.
    • Sanitary system (with prior approval from local sewer authority)
    • Curb and gutter
    • Back into the storm sewer system as long as it is contained within the system during dry weather condition to ensure no discharge into surface water
    • Applied to the ground adjacent to the catch basin (evenly distributed at a maximum rate of 250 gallons/acre/year)
  • The remaining material may be handled in one of the following manners.
    • The dewatered materials can be deposited at a permitted landfill.
    • The dewatered materials can be reused. The following steps are recommended when the material is reused.
      • The remaining liquid and solid may be screened to remove organic materials such as leaves, pine needles, branches, and grass cuttings. The organic materials can be composted.
      • Coarse sand may be screened and stockpiled for future use.
      • Screened soil may be reused for one of the following.
        • Feedstock material for topsoil operations
        • Fill in parks and recreational settings, provided it is covered with grass, sod, or other capping material
        • Construction fill for industrial or commercial sites, roadways, or parking lots
        • As the sub-grade beneath a paved municipal road or parking lot
        • As aggregate in concrete or asphalt
        • Landfill cover

Screening

Visual screening of water in a sump is recommended for the following.

  • Odor
  • Color
  • Turbidity
  • Floatables
  • Deposits and staining
  • Vegetation
  • Structural damage

For more information on screening, link here

Testing

Testing is recommended for the following.

  • Any facility or operation where the operator has knowledge that a potential hazardous waste has been placed in a sump or pit
  • Any pretreatment practice receiving discharges from chemical storage areas
  • Pretreatment practices receiving discharges from certain industrial or contaminated sites

Links

The following links generally align with the section heading, although there may be some overlap at a specific site. For a summary of our literature review, [File:Pretreatment waste disposal literature review.docx link here].

Catch basins

Grit chambers, hydrodynamic separators

Monitoring studies


Related pages

To see the above pages as a single page, link here

Pretreatment sizing for basins and filters strips

Guidance for managing sediment and wastes collected by pretreatment practices

Tables

Other information and links

This page was last modified on 3 October 2019, at 09:39.

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