July 25, 2002

A funny thing happened on the way to the dump

  • Avoid surprises by testing soils before digging downtown


    It’s one of those “surprises” nobody wants.

    You’re halfway through excavating for an underground parking garage, and dump trucks are taking the excess soil to a playground for use as fill. You’ve already torn down the old warehouse that used to be at your site. The seller assured you that the site was “clean” and that contaminants were below residential cleanup levels.

    Then on the 10th truckload, a mother at the playground reports smelling something funny. It turns out to be a solvent in your dirt. Suddenly, you’ve got trouble with a capital T. Your “clean fill” is no longer clean, your project has come to a standstill, and disposal costs have increased 10- to 20-fold. You also have to worry about whether the first nine loads of fill are contaminated too.

    What’s a developer to do? Test soil before you dig. Better yet, test it before you buy. Especially if you’re building in downtown Seattle.

    Why we’ve got a problem

     Roosevelt Commons site
    Photo courtesy of GeoEngineers
    Below-grade parking excavation at the Roosevelt Commons project in the University District required special management of impacted soils during excavation.

    Few, if any, pristine building sites exist in our urban areas. Nearly all available land has been used over and over. It’s almost inevitable that contaminants of some kind are present in the soil. Common contaminants include petroleum, solvents, metals and polycyclic aeromatic hydrocarbons resulting from prior gas station, dry cleaning, manufacturing, painting, auto maintenance or chemical storage activities at the site. Petroleum contaminants are by far the most common.

    Contaminants may not be present at concentrations that would have regulators knocking at your door. In fact, the site may have been deemed “clean” by a consultant of the previous owner, or given a “no further action” from Ecology. Still, you will have a much harder time handling and disposing of soil if it is even marginally tainted.

    A gray area

    Marginally contaminated soil is tricky because it is not necessarily hazardous to human health or the environment. It could be perfectly safe for building on. You could pave it over for a parking lot and no one would mind. You could use it in road construction or haul it to the new airport site with no problem.

    It’s when you dig up impacted soil that issues arise. Truck drivers won’t transport and site managers needing fill won’t accept dirt with a sheen, stain or odor. Why? Potential liability, risk, and many times, just a lack of understanding of what may be a threat. The result is that you’re often stuck with more costly alternatives.

    The dirty low-down

    The best course of action is to determine exactly what you’re working with. A good way to develop a comfort level with contamination is to call in an environmental specialist before the first shovelful is dug.

    An urban development site is a lot like a worn shop towel. You know it’s been used before. But until you know exactly how, you wouldn’t use it to buff your brand-new Corvette.

    Do a historical study of prior usage at the site to identify if sources of contaminants exist. Then characterize the site by drilling soil borings to pinpoint areas of concern. That way you may be able to segregate soil during excavation, depending on the type of contaminant present and the construction schedule.

    Many times the information obtained from these same borings can be used by geotechnical engineers for foundation and shoring design.

    Armed with knowledge early in the project, you’ll be able to calculate soil volumes and in turn, incremental environmental costs due to soil contaminants. You can also use your consultant’s reports to characterize soil for disposal. That way you can get authorization from a landfill or treatment facility before excavation starts and keep your schedule and budget on track.

    Fairly reliable field screening methods for petroleum contamination can be established through initial testing and site characterization. One strategy that often works well is to document field screening results with “no detections,” and then rely on field screening for segregation. If no source or field screening evidence of a contaminant appears, you may not need to continue with chemical analysis.

    Once you’re certain whether contaminants are present (or not), it’s wise to distribute information to all members of the development team up front. For instance, the environmental consultant should identify and explain regulatory requirements to the owner or developer. Similarly, the consultant must interface with the construction manager and earthwork contractor to provide information about health and safety, contaminant type, location and end-use options.

    This is another opportunity for saving time and money. Establishing a good working relationship among team members, and understanding the schedule, cost and environmental risk, is key.

    If contamination proves to be at concentrations less than cleanup levels, you don’t need to notify Ecology. Nor do you have to pursue a “no further action” from the agency. Still, remember that not all recipients will want your soil if it’s been found to be marginally contaminated. Others will take it, but will likely charge extra.

    The ethical imperative

    An urban development site is a lot like a worn shop towel. You know it’s been used before. But until you know exactly how, you wouldn’t use it to buff your brand-new Corvette. Nor would you toss it to your son to wipe his face.

    Treat soil at a downtown site the same way you would the towel. Ask around and find out its history. Use accepted scientific methods to identify any contaminants. If it’s clean, great. You can do whatever you like with it. If it has marginal concentrations of contaminants plus an odor or other physical evidence, make sure to have a strategy to dispose of it in an ethical manner so nobody downstream gets hurt. And since disposing of polluted soil is a lot more costly than throwing a rag in the garbage, call in the experts. That way you’ll know for certain that you’re doing the right thing.

    Dave Cook, P.G., is an associate in GeoEngineers’ Seattle office. GeoEngineers Inc. is an environmental and geotechnical consulting firm headquartered in Redmond. Its Web site is

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