Division of Spill Prevention and Response

Breadcrumbs

Tactic AM-3: Preventing Damage from Clean-up Activities

The goal of this tactic is to help responders stop clean-up activities before too much tundra damage occurs. There is no precise definition of too much damage, however, due to site-specific differences that determine the treatment goals and selection of tactics. Thus, making the key decision during a clean-up response when the risk of physical damage from continued clean-up activity does, or does not, outweigh the benefits of recovering additional spill residuals will depend on many factors.

When field indicators (Tactic AM-2) are used to monitor clean-up effectiveness and tundra damage, responders have access to the most recent information for using the decision trees to guide the clean-up (Tactic P-1). Guidelines are presented here to help determine when clean-up activities should stop. The guidelines rely on simple observations, but some training of observers may be necessary to provide accurate information. For example, damage to soil is often readily visible but disturbance to vegetation often is more difficult to determine, especially in winter. The short growing season in the Arctic often means that a meaningful assessment of vegetation recovery may not be possible until 3–5 years after a spill.

The three most likely forms of damage to result from a spill clean-up are the compression of the organic mat, the tearing of belowground plant materials (e.g., roots and rhizomes), and the removal of vegetation and soil. Damage is less likely to occur when soils are frozen, but accurately assessing tundra damage often is not possible until summer. Soil compression is dependent on the depth to which the soil is frozen, the soil type, the amount of water in the soil, as well as the weight of equipment, the number of passes of people or equipment over a specific area. Soils that are wet, or that were frozen when wet, have pore spaces filled with water (or ice), and are less susceptible to compression and shearing forces than drier soils that have air voids. In general, wet and moist tundra will be less susceptible than dry tundra to compression and shearing forces.

In winter, the first indication that tundra disturbance is possible is the incorporation of dead plant leaves (e.g., plant litter) into the snow pack, which indicates the snow pack is no longer thick enough to provide a protective layer to the tundra surface.

According to the Alaska Department of Natural Resources (DNR), vegetation damage is defined as any visible mechanical alteration of plant anatomy such as broken or abraded branches of shrubs and scuffed or crushed tussocks, while soil damage is defined as any visible depression or displacement of soil resulting in a defined track. Tables 10 and 11 provide additional information that can be used as an overall guideline to assess six levels (from negligible to severe) of physical damage to the spill site (see also Tactic AM-2).

When assessing the level of damage, it is important to compare the spill site with adjacent undisturbed tundra of the same type. For example, undisturbed dry tundra may naturally have areas of exposed soil. This ranking system is intended to be rapid, thus the estimates of cover are subjective and different from the quantitative method used in Tactic AM-6. To rapidly assess the level of damage, an observer visually estimates the proportion of an area (e.g., a treatment cell) according to the damage variables. This rapid assessment method is most useful for describing large differences.

Considerations and Limitations

  • If soil samples are collected to assess the depth of penetration by contaminants, the water content and bulk density of the soil also should be estimated to determine the likelihood of soil compression.

Equipment, Materials, and Personnel

  • Grid system - for sampling (Tactic AM-1).
  • Sample containers, drying oven, and scale - for calculating water content and bulk density.

Table 10. Classification and description of damage levels for tundra

Damage Level

Description

Negligible

0

No impact to slight scuffing of higher microsites. Disturbance not evident from the air or on air photos.

Low

1

The decrease in vegetation cover is <25% and the amount of exposed soil is <5%. Compression of standing plant litter and slight scuffing of soil is evident in wet, moist or dry tundra; tussocks or hummocks scuffed.

Moderate

2

The decrease in vegetation cover is 25–50%, and/or exposed soil is 5–15%. Compression of mosses and standing plant litter is evident in wet and moist tundra; tussocks or hummocks are crushed; portions of spill site may appear wetter than surrounding area; some tearing of vegetative mat within moist tundra along rivers and in dry tundra.

High

3

The decrease in vegetation cover is >50–75%, and/or exposed soil is >15–25%. Standing water is apparent on spill site that probably was not present before the spill; moist tundra changing to wet tundra; crushed tussocks or hummocks nearly continuous; change in vegetative composition; in moist tundra along rivers and in dry tundra, vegetation mat and ground cover substantially disrupted.

Very high

4

The decrease in vegetation cover is >75–95% and/or exposed soil is >25–90%. Ground depressions common in moist tundra. In wet tundra, thermokarst and ponding may result in a substantial area that is covered by water, especially where extensive areas of vegetation and surface soils have been churned or displaced. Dry tundra appears as barrens with only occasional patches of vegetation remaining.

Severe

5

Vegetation removal is essentially complete (>95%) and exposed soil is nearly continuous (>90%). Some colonizing plants may be present, but vegetation cover is less than 5%.

Table 11. Variables used to rank the damage level for tundra

Damage Variable

Damage Level

0

1

2

3

4

5

Vegetation Reduction
(% cover)

0–4

5–24 or increase

25–50

51–75

76–95

>95

Vegetation Height
(% of reference)

90–110

75–89
or >110

50–74

25–49

5–24

<5

Exposed Soil
(% cover)

0

1–5

>5–15

>15–25

>25–90

>90

Microrelief (cm)
(Depression, Compaction, Thermokarst, Excavation)

0

1–4

5–14

15–24

25–100

>100


Updated: 12/20/2010