The aim of NRDAs is to restore damaged natural resources so that they can continue to be enjoyed by the public. This simple aim has complex scientific and economic consequences. Agencies must assess the extent of the injury and link it to a toxic release, devise a restoration plan, and determine the full value of what the public has lost. The three principal activities--assessing injury, planning for restoration, and determining damages--have evolved as scientific and economic understanding has increased and because of previous NRDA experience.
Among the two most important broad scientific issues in injury assessments are establishing a baseline from which to measure resource injuries and the debate over the significance of individual organisms versus populations and communities of organisms. The concept of baseline requires that any assessment identify a resource's normal condition--the condition that would have existed if the hazardous release had not occurred.
In damage assessments harm to wildlife is almost always judged in terms of individuals, This is done to protect individuals and because individuals serve as surrogates for higher order, but more difficult to examine, ecological effects. Critics argue that measuring injury in terms of individuals can overestimate injury to an environmental system or community. This is because a community of organisms may compensate for loss or injury to individual organisms so that the overall viability of the community is unaffected.
Damage assessments evaluate two environmental problems: restoration of the damaged natural resources (primary restoration) and compensatory damages. Economics plays a role in determining the value of primary restoration, but its role is crucial in determining compensatory damages. Compensatory damages are aimed at compensating the public for the loss of a resource from the time the damage occurred until restoration. Previously, these damages were valued in monetary terms, but the emphasis has shifted to compensatory restoration.
Habitat equivalency analysis is the new approach used to determine the appropriate amount of compensatory restoration needed to make up for the temporary loss of a resource. The objective of habitat equivalency is to find one aspect of a habitat--a metric--that accounts for several different types of lost services. The metric must be readily measured and amenable to incorporation into restoration planning. Once established, the metric is used to assess other habitats and to find comparable replacements. An example of a metric from a coastal setting is the average stem density and height of marsh grass.
In instances where it is impossible to find equivalent services, value-to-value methods are necessary. The value-to-value approach requires trustees to place a value on the service loss caused by the pollutant release and the resource gain that can be realized from the compensatory restoration. Once the trustees identify a restoration effort that produces a gain in value, equivalent to the lost value caused by the resource injury, they ask the responsible party to implement or pay for the restoration effort.
The Comprehensive Environmental Response, Compensation, and Liability Act of 1980, CERCLA or the Superfund law, established the NRDA program as a companion to its more well-known remediation actions. Unlike Superfund remediations, which are the sole responsibility of EPA, any federal, state, or tribal agency responsible for publicly owned resources can conduct an NRDA as a trustee.
This largest and most famous NDRA cost Exxon close to $1 billion in addition to a cleanup bill of nearly $2 billion.