This chapter describes each alternative and summarizes the potential environmental impacts of the alternatives in comparative form. The summary describes the primary impacts and is based on the detailed analysis of all potential impacts presented in chapter IV. The impact analysis is based on scenarios for the alternatives that are described in detail in chapter IV. These consist of assumptions that are developed for analytical purposes. The scenarios are not predictions of future events. The 4 OCS Regions are divided into 26 OCS planning areas (Figure 2-1). Only eight of the planning areas are being considered for leasing in the proposed program. This alternative proposes the adoption of a schedule of sales indicating, as precisely as possible, the size, timing, and location of those sales consistent with the requirements of Section 18 of the OCS Lands Act, as amended, for the period of mid-1997 through mid-2002. It provides for no more than 16 sales (Table II-1). The proposal consists of annual, area-wide sales in the Western and Central Gulf of Mexico (Figure 2-2), and one sale of approximately 672 blocks in the western-most portion of the Eastern Gulf of Mexico (Figure 2-3). It also proposes two sales in the Beaufort Sea, a small, focused sale of approximately 335 blocks in the central, shallow-water section of the planning area (Figure 2-4), and a second, more extensive sale of approximately 2,317 blocks which extends the width of the planning area (Figure 2-5). This alternative also contains a combined sale in the Chukchi Sea and Hope Basin with a combined total of approximately 6,647 blocks (Figure 2-6), and one sale each in the Cook Inlet (approximately 376 blocks) (Figure 2-7) and Gulf of Alaska (approximately 1,174 blocks) (Figure 2-8). Except in the Central and Western Gulf of Mexico, the areas to be considered for leasing have been restricted to specific portions of the planning areas, referred to as "program areas" (Table II-2). The primary impact producing factors associated with offshore oil and gas activity are the placement of infrastructure, operations, and accidental events. The analyses in the EIS assume the implementation of all mitigation measures required by statute, regulation, or lease stipulations. A measure that prohibits surface stuctures within 6 miles of the Alabama coastline could be included for any sale in the Eastern Gulf of Mexico to reduce impacts on scenic quality. The protection afforded by these measures is present in the analysis of the resources being mitigated. The analysis presents the environmental consequences of the alternatives with the applicable mitigation. The impact-causing factors for this alternative include the placement of an offshore infrastructure such as rigs, platforms and pipelines, and onshore facilities such as support bases and processing plants. Operational impacts include bottom disturbance from platform and pipeline placement, local water quality changes from discharging drilling fluids and air and noise emissions from platforms, supply boats and air traffic. The accidental event of principal concern is oil spills. Table II-1. Timing of Leasing Activity for Alternative 1, The Proposal This alternative could result in the placement of offshore platforms after successful exploration and development of an area. The number of platforms ranges from 1 to 2 for the single sale in the Gulf of Alaska to 70 to 210 for the five sales in the Central Gulf of Mexico. Although no major impacts from OCS-related oil spills have been observed for more than 20 years, environmental degradation that might result fromspills continues to be one of the greatest causes of concern about OCS development. Based on past experience, damaged or broken pipelines would be the most likely cause of a large oil spill. Each planning area on the leasing schedule is assumed to advance to the production stage so that the analyses include the possibility of an oil spill of any size occurring. The statistical probability of one or more oil spills of 1,000 barrels or larger occurring ranges from 0-to-18 percent in the Eastern Gulf of Mexico, to 76-to-99.5 percent in the Beaufort Sea; however, these probabilities are extended over the 30to 40-year span of exploration and production. The Western and Eastern Gulf of Mexico areas could experience up to one spill, the Central Gulf of Mexico around 1 or 2 spills, over the 34-to 40-year span of exploration and production. Should the maximum amount of anticipated oil production for the Beaufort Sea occur, up to 5 spills of 1,000 barrels or greater could occur in the Beaufort Sea with an additional 3 spills possibly taking place along tanker routes carrying Beaufort Sea oil to the West Coast. In the Chukchi Sea, as many as 3 oil spills could occur, with up to 2 tanker spills of Chukchi oil taking place elsewhere. The Cook Inlet and Gulf of Alaska could also each experience around one oil spill over the 30-year life of the production resulting from this proposal. a. Impacts on Water Quality Offshore drilling discharges could cause a measurable change in one or more ambient water quality parameters up to several hundred meters from the discharge source for several weeks in marine and coastal waters. In Alaska, pollutant concentrations are not likely to exceed EPA water-quality criteria outside a 100-m radius around each drill site or production platform. Discharges could reduce water quality on considerably less than one percent of the area. This would exist only during periods of drilling and should rapidly dissipate on completion. If oil is spilled, water quality in up to several thousand square kilometers could be reduced by hydrocarbon contamination for a short period of time. In the Gulf of Mexico, there could be minor, long-term changes in water quality around existing navigation channels, pipeline canals, and onshore support complexes primarily within the Texas and Louisiana coastal zone. These changes are not expected to preclude current uses of the waters affected, except during short-term |