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Treatment of Petroleum-Contaminated Soils

Treatment Options

Evacuation and Proper Disposal

The quickest and possibly simplest method of reducing the amount of petroleum-contaminated soil is by excavating the contaminated soil and shipping it to an appropriate landfill for disposal or to a facility where the contaminated soil can be incorporated into paving material. This option is also the surest method of reducing human and ecological health risks at the location of the release. Another advantage of removing contaminated soil is that there are no operation and maintenance costs. The major disadvantages are cost, the requirement for clean material to fill the excavation, and the long-term liability associated with disposal of the material.

In Alaska, soil particles with diameters wider than 2 inches do not require treatment or proper disposal (Alaska Department of Environmental Conservation 2000b). Larger particles can be screened, removed from excavated contaminated soils, and set aside for fill material. Sorption of petroleum hydrocarbon compounds is greater on fine-grained soils (clays) because of their larger surface areas. Fine-grained soils have higher concentrations of organic carbon than large soil particles.

A possible use of the excavation and disposal option that has not been fully explored by the environmental engineering community is to combine excavation and disposal with other in situ soil treatments. In some—if not most—cases, in situ treatment technologies such as soil vapor extraction (SVE) are efficient for removing much of the volatile soil contamination. However, the removal of contaminants by in situ methods becomes less efficient with time because of the limitations of diffusion and mass transfer. At that point, it may be cost effective to excavate the remaining contaminated soil and dispose of it. Because the in situ process reduces the bulk of the contamination, the volume of soil requiring excavation and disposal will probably be much less than before treatment. The main advantage to combining excavation and disposal with an in situ technique is that the job will probably be completed more quickly. Also, the cost of restoring the contaminated soil site will probably be less than if the entire volume of soil had been excavated and removed to a proper disposal facility.

Use in Cold, Wet, Remote Regions

The challenges of excavation in cold regions apply to all ex situ treatment options. The shear strengths of soils that experience seasonal freeze/thaw cycles are generally much higher when the soils are frozen than when they are thawed. Practical excavation of contaminated soil in cold regions is limited to the months when the soil is thawed. Soils with low moisture content are an exception to this rule.

For proper disposal, excavated soils need to be placed in a container or containers. Dry soils are easier to store than wet soils. Soils are commonly wet in areas with high annual precipitation. In Alaska, engineers have had success with various types of containers (information provided by Nortech Environmental & Engineering Consultants, appendix C). The more common types of containers used have been overpacks (55-gallon open-top drums), large shipping containers (20- to 40-foot containers), and reinforced flexible bags. Each container has advantages and disadvantages. The choice of container is a function of the engineer's preference, site conditions, and the mode of shipping.

Efficient excavation requires powered equipment. Getting this equipment, and the fuel to run it, is a problem at remote sites. Shipping excavated soil to disposal areas is also a problem at remote sites. Once the contaminated soil has been removed, material may be required to fill the excavated site. An extended stay at the site should be figured into the cost estimate. The length of the stay depends on such factors as the volume of contaminated soil, the ease of excavation, weather conditions, and other factors.

Cost Estimate

Table 8 lists the items that need to be accounted for in a cost estimate for excavating and disposing of petroleum-contaminated soil in cold, wet, remote regions. Assumptions include:

• Soil contamination does not extend past the digging depth of a typical backhoe (about 15 feet).
• Typical rated power of the backhoe is equal to 98 horsepower.
• On average, the backhoe is operating at 67 percent of rated power.
• The Forest Service owns the backhoe.
• The density of bank-measure material is 1,895 kilograms per cubic meter.
• The density of loose-measure soil is 1,528 kilograms per cubic meter.
• Fill material can be wheel rolled by the backhoe for compaction.

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This page last modified September 23, 2002
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