Natural Resource Damage Assessment: Methods and Cases

damages not quantifiable at reasonable cost for adverse environmental effects caused by the spill.
Compensation should be based on the characteristics of the oil spilled (such as its toxicity and
persistence) and the sensitivity of the affected area. The latter depends on the location of the
spill, the habitat sensitivity, seasonal distribution of this sensitivity, importance of the area for
recreational, aesthetic or archaeological use and proximity of the spill to wildlife habitats.
Washington’s compensation-schedule method 4 uses minimal spill-specific information,
and only pre-existing information about resource vulnerability to the type of oil spilled. The
method has four major components:
(1) A relative “harmfulness” ranking of each of the classes of oil involved as determined
by their known chemical, physical and mechanical properties and factors that affect
severity and persistence of the effects of the spill on the environment.
(2) A relative vulnerability ranking of the receiving environment which takes into
account location of the spill, habitat and sensitivity of the resource to the spill,
seasonal distribution of the resources, areas of recreational use and aesthetic
importance, the proximity of the spill to important habitats for birds, aquatic
mammals, fish or other species listed as threatened or endangered, and areas of
special ecological or recreational importance.
(3) A method for calculating the resource damages from the oil spill based on (1) and (2).
(4) A method for adjusting the damages calculated in (3) based on actions taken by the
PRP such as immediate removal of oil from the environment, enhancing or impeding
the detection of the spill and extent of damage.
Part 1: Ranking of “harmfulness”
There are several facets to the “harmfulness” ranking of the released material. All three
rankings are on a scale of one to five. Acute toxicity indices (OILAT), which depend on the
properties of the oil and its solubility in seawater, have been developed by the state agency for
seven different types of oil. An acute-toxicity ranking of one represents the least harmful
substance. Relative scores for mechanical injury (OILMI) have been developed based on the
specific gravity of the oil spilled. Persistence scores (OILPER) have been developed on a one to
five scale depending on the length of time the spilled oil is known to persist in a variety of
habitat types. For example, a score of five is assigned if the effects of the oil spill will persist for
five to ten years while a score of one is assigned if these effects will only last for days or weeks.
Part 2: Ranking of “vulnerability”
Scores indicating how vulnerable an environment is to an oil spill are determined
separately for each of sixteen marine and estuarine regions and one hundred and thirty-one sub
regions in the state. There are vulnerability scores for spills in: marine and estuarine waters; the
4 For complete details including values of scores, see Washington (1992).
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