Privacy | Legal

Table of Contents Back | Next | Home

Missoula Technology & Development Center

Treatment of Petroleum-Contaminated Soils

Treatment Options (continued)

Landfarming

In landfarming, as in composting, petroleum products are biodegraded by spreading the contaminated soil on the land surface in a relatively thin layer. However, in landfarming, air is not mechanically introduced into the soil with the same frequency as in composting. Diffusion into the soil matrix is the main mechanism for oxygen transfer. Soils with an air-filled porosity higher than 15 percent are best suited for this treatment. The contaminated soil can be placed directly on the ground surface or on an impermeable liner (depending on the native soil type). Temperature and soil moisture requirements are the same as in composting. Both biological activity and volatilization reduce the contamination.

Use in Cold, Wet, Remote Regions

While adaptations of the traditional form of composting allow for an extension of the time available for practical soil treatment, landfarming is restricted to the warmer summer months. For unlined landfarming operations, water infiltration during storms may cause petroleum contamination to penetrate underlying native soil. Biodegradation in the underlying soils may reduce this impact. Runoff is also a problem in areas with high precipitation. Berms will reduce petroleum-laden surface water runoff. Increases in soil moisture content and associated decreases in air-filled porosity are expected during precipitation events. Because landfarming relies on oxygen diffusion to maintain aerobic conditions, decreases in air-filled porosity will decrease the rate of oxygen transfer and temporarily slow the rate of biodegradation. The aerobic conditions should rebound as the water evaporates and drains from the soil.

If sufficient space is available and the soil to be treated meets the requirements for air-filled porosity, landfarming is perfectly suited for treating petroleum-contaminated soil in remote regions. Past experience has shown that turning the soil periodically will aid in oxygen transfer. Generally, after the contaminated soil has been spread, landfarming operations require little maintenance.

Landfarming of petroleum-contaminated soil has been successfully practiced in Alaska (information provided by Geosphere, Inc., appendix C). Several field demonstrations were completed in Bettles, Huslia, Chandalar Lake, and King Salmon. At each site, contaminated soil was spread in 1-foot layers across the unlined ground surface. Soil-moisture content, precipitation, infiltration, soil temperature, the concentration of gasoline and diesel range organics in the landspread soils and in the native underlying soils were measured at each site. Significant reductions were noted in concentrations of both ranges of organics in the landfarmed soil. Testing of the underlying native soils showed little increase in concentrations of diesel range organics. Biodegradation was credited for the low concentrations.

Engineers in Alaska have also noted a marked increase in the mass reduction rate during warm and dry periods. This increase can be attributed to greater volatilization during these periods.

Cost Estimate

Table 14 shows the items to be considered in developing a cost estimate for landfarming. Assumptions include:

• After landfarming, the treated soil can be used as fill material.
• The Forest Service owns the backhoe.
• The backhoe used for soil excavation can be used for spreading the contaminated soil and for removing treated material.
• The contaminated soil is spread in a 1-foot-thick layer.
• No hazardous waste is produced.

E-mail: wo_mtdc_webmaster@fs.fed.us

Back | Next Table of Contents

Missoula Technology & Development Center

---

This page last modified September 23, 2002
Visitor since September 23, 2002