Tactic CR-13: Excavation for Offsite Disposal
Excavation of tundra soil may be necessary when treatment goals include the rapid and complete removal of spill residuals. Excavation should be considered if contaminant levels are high enough to be toxic to plants, if the entire organic mat is saturated with contaminants, or when other treatment options have been deemed inadequate for achieving the treatment goals.
Dozers, backhoes (Fig. 64), trimmers (Figs. 65–66), and jackhammers (Fig. 67) can be used to excavate the organic mat and underlying mineral soils. Contaminated soil is typically removed from the site for treatment or disposal.
The depth of infiltration by contaminants determines the depth of soil that should be removed. It may be feasible to remove only the organic mat, before the spilled material infiltrates down to mineral soil. Minimize the volume of soil excavated by using a spotter to direct the operator to contaminated areas. For example, at many sites, contaminants tend to flow into a network of polygon troughs, leaving higher areas relatively unaffected. However, soil testing (Tactic AM-4) is often needed to identify areas to excavate, because even highly visible substances (e.g., crude oil) are difficult to see under certain conditions, especially during winter with artificial lighting. Consider removing only “hot spots” and leaving as much tundra as possible intact to prevent excessive damage to the tundra (see Tactic AM-3).
In most cases the excavated area must be backfilled (Tactic TR-12) to minimize the risk of thermokarst (Fig. 68). Therefore, a source of approved replacement material must be identified before excavation begins. Excavation may create a tundra environment suitable for some plants but not others. Backfilling may not be necessary if creation of aquatic habitat is an acceptable rehabilitation option.
Considerations and Limitations
- Remove soil only to the depth to which contaminants have infiltrated.
- Identify a source of approved fill material before beginning excavation.
- Ensure backfill has suitable properties (e.g., particle size, relative amounts of gravel, sand, and silt).
- Allow for settling after backfilling in order to maintain proper surface grade relative to the surrounding tundra.
- Monitoring surface elevation over time may be necessary to document site stability.
- Consider disposal options and required approvals before using this tactic.
- On-site sampling of contaminated soil can expedite the excavation process.
Equipment, Materials, and Personnel
- Backhoe or trimmer (1 operator) – to excavate contaminated soil or ice.
- Front-end loader (1 operator per loader) – to transport excavated material.
- Dump truck (1 operator) – to transport contaminated material to disposal site.
- Polyethylene sheeting – lining for stockpiles.
- Spotter – to guide excavation of visibly contaminated soil.