be plausibly estimated for some but not all forms of impact. Employment rates, health statistics, cultural consequences, number of people affected, duration of effects, and reversibility of effects are all aspects of magnitude, some of which are not plausibly metrical although very real.

Magnitude has spatial aspects. There is, first, a continuum between concentration and diffuseness but the two are not mutually exclusive. The Exxon Valdez disaster had a concentrated effect on more than 1,000 miles of coastal Alaska and the on livelihoods and ways of life of people living in that region. It had more diffuse effects throughout the United States and even, with some attenuation, in other parts of the world, with some increase in focus in areas like southwestern Florida, the northern and southern California coasts and New England—all of which were especially sensitive because they were facing lease sales. There were obviously impacts on New York and Houston, where Exxon's headquarters are located, and so on. The magnitude of impacts may be widely dispersed in this era of instant communication and social amplification must be considered in its assessment.

There are several temporal aspects of impacts, two of which are noted here. There is, first, as already noted under magnitude above, the matter of duration, occurring on a continuum from evanescent to everlasting. Second, some effects are continuous, perhaps rising and falling through time; others are intermittent. In cases in which possible effects are intermittent there are the further questions of whether periodicity is regular or irregular, and what the frequencies are.

Some impacts pass away leaving, soon after their termination, few if any marks of their occurrence (e.g., the impact of exploration that has not succeeded in discovering gas or oil, for example); the effects of other activities can accumulate. This is obviously the case for some physical events (oil deposition in wetland fish spawning grounds), but also can be characteristic of more purely sociocultural impacts. Thus, the repetition of confrontations between local citizens' groups and government agencies may cumulatively abrade public trust in government.

The effect of accumulation does not always conform to expectations derived from simple arithmetic. For example, the impact of one offshore support vessel working out of a small harbor might be slight; the impact of a second might double it but still be slight. After some increase in the number of vessels, however, qualitative changes can begin. New docks, new fuel delivery routes, and changes in the proportions of persons employed in the petroleum versus the fishing industry and in their consequent places in the local economies and political arena could result.

Some impacts may be self-limiting and self-correcting. Given enough time, a fishery could recover from the effects of a spill even if no remedial action is taken. Other effects can be offset or

Front Matter (R1-R10)

Executive Summary (1-10)

Introduction (11-22)

The Human Environment (23-28)

A Framework for Organizing OCS Socioeconomic Studies (29-44)

Analysis of the Program (45-60)

Conclusions and Recommendations (61-66)

References (67-82)

Appendix A: Commission on Physical Sciences, Mathematics, & Resources (83-86)

Appendix B: The Human Environment (87-106)

Appendix C: The Evolution of the Federal OCS Program: National and Regional Perspectives (107-142)

Appendix D: Social and Economic Studies Technical Reports, Alaska OCS Region, MMS (143-153)