Division of Spill Prevention and Response


Tactic AM-2: Field Indicators

Field indicators are standardized, simple measurements or qualitative observations that can be made periodically at a site to monitor and document contamination, treatment effectiveness, and ecological damage associated with the cleanup operation. Field indicators also provide a context for interpreting chemical analyses of soil samples (Tactic AM-4 and Tactic AM-5) and data on vegetation response (Tactic AM-6). Field indicators are important components of a baseline site assessment or monitoring program.

Four categories of field indicators may be measured or observed:

  • Spill Residue: Treatment progress may be monitored by visually assessing the degree of contamination on soil and vegetation (Table 7).
  • Soil Conditions: The rooting zone, where contamination is most harmful to plants, usually extends 1 to 8 inches (2 to 20 centimeters) below the ground surface. Evaluating the infiltration of contaminants into this zone provides a helpful indicator of how vegetation is likely to respond (Table 8).
  • Ecological or Physical Damage: Cleanup operations can result in physical damage with long-term ecological consequences, including thawing of permafrost (thermokarst). Monitoring physical damage can help determine the point at which intensive treatment should stop. The thickness of the active layer (thaw depth) should be measured periodically, so that thermokarst can be monitored over time (Table 9).
  • Ecological recovery: Recovery at a site is indicated by growth of native plants and re-establishment of drainages, and a stable thermal regime typical of permafrost terrain.

Table 7. Field sample coding sheet for visual assessments of oilspills on tundra*


Measurement or Observation

Residue thickness on ground or vegetation

• No visible residue

• If sheen is present, thickness is 0.0001 millimeters (mm)

• If stain is present, thickness is 0.1 mm

• If coating can be scraped with an object, thickness is 1 mm

• If thickness is >1 mm, measure with ruler

Residue consistency

• No visible residue

• Liquid (flowing) residue

• Emulsified crude oil (mousse)

• Waxy, gelatinous

• Hardened, crystalline, plastic, tar

• Crumbly, friable

• Sheen

Residue expulsion (residual hydrocarbons can be squeezed out of surface organics or soil with foot pressure)

• No expulsion

• Sheen on water

• Liquid droplets or thicker film

• Pooling on surface

• Undetermined: test not done if surface oil present

Residue color

• Silver-gray sheen

• Rainbow sheen

• Light orange-brown

• Dark brown

• Blue-black

* Field indicators for other types of residues must be developed on a case-by-case basis. Adapted from Cater and Jorgenson 1999

Table 8. Some field indicators of soil conditions*


Measurement or

Organic layer

• Measure thickness of organic layer (includes mosses and peat)

• Note any discoloration

• Note odor

Mineral soil layer

• Measure depth that mineral layer begins

• Note any discoloration

• Note odor

Mineral soil texturea

• Gravel (gravel, sandy gravel, silty gravel)

• Sand (sand, loamy sand, gravelly sand)

• Loam (silt, silt loam, sandy loam)

• Clay (silty clay, silty clay loam)

Thaw depth

• Use metal probe to measure depth of active layer of soil

Water depth

• Measure depth of water above (+; surface water) or below (-) ground surface

Containment infiltration

• Saturation: soil pores filled with spilled substance

• Coatings: noticeable coating on mineral or organic particles, void spaces in soil are evident, or substance does not flow out of soil matrix

• Sheen: sheen is visible when soil squeezed but not evident on particles

* Adapted from Cater and Jorgenson 1999

a Classification based on Natural Resources Conservation Service, U.S. Department of Agriculture (Schoeneberger et al. 2002)

Table 9. Some field indicators for physical or ecological damage *


Measurement or Observation

Tundra type

• Aquatic tundra

• Wet tundra

• Moist tundra

• Dry tundra

• Bare soil

Vegetation cover (Tactic AM-6)

• Cover estimates
(0 to 5%, 6 to 25%, 26 to 50%, 51 to 75%, 76 to 95%,
96 to 100%) for shrubs, graminoids (i.e., grasses and grass-like plants), mosses, and bare soil

Vegetation damage (Tactic AM-3)

• No apparent damage

• Partially crushed (some stems and leaves crushed, but structure mostly intact)

• Mostly crushed (stems and leaves recognizable, but mostly laying flat on ground)

• Stressed (wilted, dropping leaves, or leaves discolored)

• Dead

• Roots exposed

• 1 to 5 inches of organic layer or soil removed

• >5 inches of organic layer or soil removed

Birds and mammals (use data form)

• Species and number observed at the entire site

• Condition (healthy, diseased, dead)

• Note whether spill residue is visible
on animal

• Animal dead, probably due to
other causes

* Adapted from Cater and Jorgenson 1999

Measure and observe field indicators at pre-established sampling points, preferably at discreet points on a sampling grid. The number and locations of sampling points should be established by agreement between the responsible party and regulatory agencies. Field sampling points should represent the entire site, with no bias to either heavily or lightly impacted areas. The number of sampling points that are needed will depend on the degree of contamination and the size of the affected area. A small site with heavy contamination may require a relatively intensive sampling approach (e.g., 10 field sampling points per 0.1 acres). For larger sites, spread field sampling points out more widely to characterize the entire site (e.g., 1 sample per 0.2 acres). In many cases, it will be appropriate to divide the site into zones of severity (e.g. lightly, moderately and heavily affected); several samples should be collected in each zone. Field indicators should also be measured in similar tundra types in the surrounding area unaffected by the spill (background or reference areas) for comparison.

Field sampling points preferably should be established at nodes on the surveyed sampling grid (Tactic AM-1). Ideally, the same measurements and observations should be made at all field sampling points.

If necessary, use survey nails or other permanent markers to physically mark the sampling points and record their locations on a scaled site map (Tactic AM-1) so they can be accurately relocated in the future. If an individual sampling location is not located at a node on the grid, record a waypoint, or the distance and direction of the sample location from a grid node. Most observations of field indicators are specifically related to the tundra surface. When subsurface soil observations are necessary, dig a small test pit and examine the sidewall of the pit, or cutting out a soil sample for easier observation.

Sample datasheets for recording field indicator data are located at the end of this section.

Considerations and Limitations

  • Avoid placing stakes in locations that may interfere with treatment operations.
  • Water-soluble spill residues may not be visible on the tundra surface.
  • Most observations or measurements of field indicators require a thawed active layer and the absence of snow cover.
  • Use plywood walkways to minimize trampling of site.

Equipment, Materials, and Personnel

NOTE: Generally a team of two workers measures and records observations of field indicators.

  • Ruler or measuring tape – to measure residue on tundra surface and the depth of infiltration.
  • Metal probe – to measure depth of thaw, water depth.
  • Shovel – to dig small test pit to observe soil horizons.
  • Large survey nails, wooden laths, or steel “rebar” stakes – to mark areas where field indicators were measured or observed so they can be relocated during subsequent monitoring events.
  • GPS – to record sample point locations.
  • Standard data forms - to record observations.

Updated: 12/20/2010