Use of Habitat Equivalency Analysis (HEA) to Determine the Environmentally Superior Project Alternative

Abstract

Abstract Project alternatives for environmental projects are often difficult to compare and rank because each alternative may have different magnitude and types of impacts to multiple habitats over varying time scales (e.g., short-term, long-term). Habitat Equivalency Analysis (HEA) is a methodology developed by the National Oceanic and Atmospheric Administration (NOAA) that can quantify and compare the net environmental effects on affected habitats, including the short-term and long-term effects of project alternatives and compensation measures. It can be used to rank the alternatives according to their relative net environmental impact, which helps project teams and decision executives identify the alternatives with the most favorable (or most adverse) environmental effects. The use of HEA proved critical to identifying the environmentally superior alternative proposed to regulatory agencies for the disposition of the Chevron 4H Shell Mounds. The 4H Shell Mounds are drill cuttings (and associated drilling fluids) piles, covered by several feet of shell hash, off the coast of California that were left following removal of the 4H platforms. As part of a California Environmental Quality Act process, Chevron was requested to propose a project for the final disposition of the 4H Shell Mounds. Chevron evaluated four project alternatives: leave in place with offsite compensation in the form of enhancement of a nearby salt marsh, enhancing with an artificial reef, capping, and removal by dredging. A HEA was performed that compared the net environmental impacts of the four project alternatives on an important marine biological resource (i.e., fish habitat value). The HEA demonstrated that leaving the mounds in place with enhancement of a nearby salt marsh (i.e., offsite compensation) provides the greatest gain in fish habitat value while averting significant and unavoidable impacts to the local marine environment associated with mounds removal. Besides this demonstrated use of HEA to identify the environmentally superior alternative within an environmental impact assessment (EIA) process, HEA should prove equally valuable for scaling the actions necessary to mitigate environmental impacts.