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Dealing With "Dirty Dirt"

February 24, 2014

Dealing With "Dirty Dirt"

By Kate Kleiter, AET

We are often asked what to do with excess contaminated fill soils or “dirty dirt” from construction or redevelopment projects. Sometimes, without knowing it, excavation contractors move and reuse excess contaminated fill from one project to another, spreading it around.

Yes, it’s a “Dirty World!”

In the Twin Cities for example, just about all urban fill soils have some level of contamination from historical activities conducted on the site or due to import from some other unknown site. Beware -- this contaminated fill could be above Minnesota Pollution Control Agency (MPCA) concern levels. You can’t just take this “dirty dirt” anywhere. It should be managed or disposed of in accordance with applicable regulations.

The MPCA has published policy and guidance documents regarding Best Management Practices (BMPs) for off-site reuse of urban fill soils with contamination. Basically, there are two types of guidance for reuse.

There is guidance for “unregulated fill” where the identified contaminants in the fill are present at concentrations that are not a concern to the MPCA. And, there is also MPCA guidance for “regulated fill” which is applicable for fill that exceeds the unregulated fill criteria.

Contaminated fill that does not meet either of the requirements of these MPCA’s guidance documents have to be disposed of at an appropriate landfill.

Criteria for Unregulated Fill:

  • Free from solid waste, debris, asbestos-containing material, visual staining, and chemical odor.
  • Organic vapors less than 10 parts per million, as measured by a photoionization detector (PID).
  • Petroleum constituents less than 100 mg/kg diesel range organics (DRO) and/or gasoline range organics (GRO). These are analyzed in a laboratory.
  • Less than the MPCA’s Residential Soil Reference Values (SRVs) and Tier 1 Soil Leaching Values (SLVs) -- which can be found on the MPCA website.

Exclusions to MPCA’s Unregulated Fill BMP Guidance:

  • Soil that is contaminated above the unregulated fill standards will need to be managed as regulated fill at another brownfield site or will need to go to a landfill.
  • Debris-laden soils will need to go to a landfill or be separated first (see photo below).
  • Waste material such as bituminous, concrete, bricks, fly ash, etc. can be beneficially reused under another MPCA program.
  • Dredged materials follow a different set of MPCA guidance documents.
  • Fill soils contaminated with agricultural chemicals follow Minnesota Department of Agricultural policies.

When do you sample?
Soil should be sampled for contamination once it’s known that a potential concern exists. Maybe an old Phase I and II Environmental Site Assessment shows contamination exists but does not conclude that a cleanup was required. Just because the report says that the site is closed doesn’t mean that the contamination is gone. It may still be there and you cannot take it anywhere. If soil contamination is present (no matter what level), you have to manage or dispose of it properly.

Sampling requirements are based on information about the property (i.e. old gas station, dry cleaners or unknown fill source). What to sample for and the number of samples needed are based on MPCA or a landfill requirements. Professional judgment is needed to develop sampling plans to determine whether excess soil meets the criteria for unregulated fill.

If no sources of contamination are identified during environmental due diligence and subsequent field observations, then sampling of excess soil for laboratory analyses is not necessary. If required, fees for these services vary depending upon the location, suspected contamination, and volume of dirt that needs to be moved or possibly disposed at a landfill.

Movement and placement of unregulated fill (MPCA BMPs)
Unregulated fill is most suitable for use at industrial or commercial properties. However, the areas below are off limits:

1. Gardens where food for human or animal ingestion will be grown.

2. Schools, playgrounds, daycares, and residential properties.

3. A ten-foot separation distance between unregulated fill and the water table.

4. Where contaminants may be transported by run-off to lakes, rivers, wetlands, or streams.

Please Note: There may be stricter standards elsewhere. Some units of government may have local ordinances that restrict the off-site reuse of unregulated fill within their boundaries. Parties proposing to import unregulated fill should seek assistance.

All parties are encouraged to use the BMPs described herein in order to make good decisions about the off-site reuse of unregulated fill. It is the responsibility of the property owners and the contractor engaged in development and construction activities to make sure that their activities include appropriate environmental due diligence.

Excess soil and other materials generated by these activities need to be managed in an environmentally responsible manner. Planning and well written specifications will save you money in the long run.

Kate is a principal hydrogeologist and manager of AET’s St. Paul Environmental Department. If you have any questions for Kate, she can be reached at

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