Minnesota Department of Transportation

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Regulated Materials

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Cleaning of Grit Chambers

The guidance document is prepared by MnDOT personnel and is intended only for use on MnDOT projects, including partnership projects, and MnDOT Maintenance Operations.

MnDOT has prepared this guidance document to provide its internal procedures and requirements for work performed on MnDOT rights of way, including MnDOT-owned facilities.

This document should not be construed as a full description of all regulations pertaining to the subject matter. Contact the Regulated Materials Unit in the MnDOT Office of Environmental Stewardship for additional information or legal requirements.

Cleaning of Grit Chambers

Grit chambers are part of the storm water collection and distribution system located along certain segments of trunk highway. The purpose of a grit chamber is to allow coarse particulate matter (mainly sand) in surface water runoff received from the roadway to settle out of the water within the grit chamber. This reduces the amount of sand introduced to surface waters in the state, thereby improving overall water quality.

Periodically, sand accumulated in a grit chamber must be removed. Sand within grit chambers can be considered similar to street sweeping sand. Therefore, it is appropriate to handle grit chamber sand in the same manner as street sweepings, with the exception described in item 6 below.

Following is the recommended practice for cleaning grit chambers:

  • Clean the grit chambers frequently enough to ensure that the chambers work effectively. Having too much sand in the grit chamber can inhibit the settling process.
  • The grit chamber sand can be stored on either a paved or gravel surface at a MnDOT facility. Sand may be combined with street sweeping stockpiles as long as no staining or odors are exhibited from the material, indicating the possibility of chemical contamination. Contact the Office of Environmental Stewardship for further assistance if questionable staining or odors are noticed.
  • Trash and other debris should be removed from the sand by screening with a 3/4" screen. Material that does not pass through the screen should be collected and disposed of at an MPCA permitted sanitary (mixed municipal solid waste) landfill.
  • Material passing through the 3/4” screen may be used in road projects as sub-base or fill material. Cover the stockpile to prevent erosion.
  • Maintain the following minimum setback distances when using the material as clean fill:
    • At least 100 feet from surface water/wetlands,
    • At least 100 feet from drainage structures,
    • At least 3 feet above groundwater (the water table) and
    • At least 10 feet above fractured bedrock.
  • Exception for reuse of the grit chamber sand: If it is suspected that a large quantity of chemical may have entered a grit chamber, the chamber should be cleaned out and the material disposed of properly. The Office of Environmental Stewardship and Freight and Commercial Vehicle Operations can assist in determining what type of chemical spills received by a grit chamber require special handling and how the material should be transported and disposed of properly.

Example: A truck overturns on the highway and spills a large volume of chemical near the inlet to a grit chamber. Contact the Offices of Environmental Stewardship and Freight and Commercial Vehicle Operations for assistance in determining the appropriate procedure to clean the grit chamber and transport the material for disposal. It is possible that the entire cleanup operation in this scenario would be completed by a private contractor at the expense of the responsible party.

Optional practice for disposing of grit chamber sand

The grit chamber sand may be disposed of at an MPCA permitted sanitary (mixed municipal solid waste) landfill. The landfill may consider the material adequate for use as daily cover. The landfill may require laboratory analysis of the material prior to acceptance. Contact the Regulated Materials Unit for assistance in analyzing the materials.

Please contact the Regulated Materials Unit for further assistance.