Figure IV.D.1-2: Diagram showing the general location and trend of the Western Boundary Undercurrent (from Emery and Uchupi, 1972)

features, even though the current was measured at 20 cm/sec. They report, however, that the sediment cover in the area (at an approximate depth of 2,000 m) was very loose and, upon disturbance by the submersible or by animals, was carried away rapidly and dispersed in the water. Features such as the lower Continental Rise Hills (found at a depth of about 5,000 m) have been ascribed to these currents, but this is still being debated.

Asquith (1979) has suggested that the WBUC occasionally picks up and entrains fine-grained material which has flowed onto the rise from the submarine canyon distributory channel systems, carries them in a westerly direction and redeposits them in other areas as they fall out of suspension. This current, therefore, could be a possible mechanism for resuspension and transport of sediment on the continental rise.

IV.D.2. Formation Waters

During oil and gas production, formation water (i.e. produced water) is recovered as well. Formation water is interstitial water present in a water-bearing formation under natural conditions. This water must be removed during resources production and, if not reinjected or injected into disposal wells, discharged to the marine environment after treatment. The discharge of these waters is subject to EPA NPDES permit (Best Practicable Control Technology) regulation.

The amount of formation water recovered depends upon the method of recovery and the nature of the formation. In some formations, water is recovered in the early stages of production, while in others it may not be recovered until the final stages of a reservoir's production or not at all. Daily discharges from platforms are generally less than 1,590 m3 (10,000 bbl), although discharges from facilities handling a number of platforms are usually larger; daily discharges of 27,800 m3 (175,000 bbl) have been reported for a central facility in the Gulf m3 of Mexico, and 9,858 m3 (62,000 bbl) for the Trading Bay facility in Alaska (Menzie, 1982). Overall, however, smaller amounts of formation water are produced during the initial production phase, while maximum recovery occurs near the end of a given reservoir's life. According to USGS records for the Gulf of Mexico, an average of 0.8 barrels of formation water are produced for every barrel of oil recovered (Regional FEIS, Gulf of Mexico, 1983). For Sale No. 111 a total of 160 million barrels of formation water would be discharged (Section IV.E.1.c).

Formation waters contain dissolved inorganic salts in concentrations that vary widely, depending on the formation, but are usually several times greater than that of seawater. The total mineral concentration commonly found ranges from a few ppm to approximately 300,000 ppm for a heavy brine, with typical concentrations ranging from 80,000 to 100,000 ppm (Menzie, 1982). The formation water properties of most concern, however, which may adversely affect the marine environment are entrained oil or petroleum hydrocarbons, high trace metal concentrations, and low dissolved oxygen concentrations. Review data on the composition of formation waters can be found in Koons et al. (1977).

Petroleum hydrocarbons are present in formation waters at concentrations which vary widely with geographic region and production stage of the formation. However, the EPA requires that before discharge, formation waters must be treated so that the concentration of oil does not exceed 72 mg/1 (ppm) for any one day nor exceed

an average 30-day concentration of 40 mg/1 (40 CFR 435). U.S. EPA statistical analyses show an average formation water oil content of 25 ppm for the Gulf of Mexico (Regional FEIS, Gulf of Mexico, 1983). Treatment usually consists of processing the water through an oil separation system.

Tillery (1980) reported that concentrations of trace metals in formation waters from the Buccaneer Field in the Gulf of Mexico were higher than the receiving water and that they varied with time (Table IV.D.2-1). Mercury, strontium, and thallium exceeded seawater concentrations by factors less than 10, while barium, cadmium, chromium, and manganese exceeded seawater concentrations by factors of 10 to 100, and iron by factors of 560 to 2,340, although these iron measurements have been disputed (Menzie, 1982).

Table IV.D.2-1.

Ranges in Mean Concentration of Metals in Produced Water
and Seawater from the Buccaneer Field During Summer and
Winter 1979 Sampling Period

Formation water is characteristically low in dissolved oxygen or anoxic and somewhat warmer (30° to 40° C temperature in the Gulf of Mexico) than the water surrounding the platforms (Galloway, 1981). Due to rapid dilution both dissolved oxygen and temperature gradients would likely be rapidly diminished (Koons et al., 1977).

A study reported by Rose (1981) from the Buccaneer Oil Field in the Gulf of Mexico demonstrated low toxicity of formation water concentrations in the water column surrounding an outfall. Lagrangian (exposure--time-dependent) assessments of aquatic hazards showed concentrations of formation waters to be 4 orders of magnitude lower than bioassay-based limiting permissible concentrations. Forty-eight hours after discharge, concentrations of formation water in the water column were about 0.1 ppm to 0.001 ppm, while limiting permissible concentrations were held to be 50 ppm. Consequently, it was concluded that the discharge of formation water does not represent an unacceptable toxicological hazard to planktonic organisms. Eulerian (exposure--time-independent) assessments showed concentrations of formation waters to be approximately 4 ppm at 140 m from the platform, indicating that toxicity-related hazards to nonplanktonic organisms is unlikely to exist beyond 100 m from the outfall, and may occur only within a few meters.

IV.D.3. Other Discharges or Sources of Pollution

Deck drainage includes all effluents resulting from platform washings, deck washings, and run-off from curbs, gutters, and drains including drip pans and work areas. Constituents of concern in effluents are oil and grease. NPDES permit regulations specify there should be "no discharge of free oil" in deck drainage which would cause a film or sheen or a discoloration on the surface of the water or cause a sludge or emulsion to be deposited beneath the surface of the water (40 CFR 435). In compliance with this requirement, contaminated deck drainage is collected by a separate drainage system and treated for solids removal and oil/water separation. The oil is then held for shore disposal.

Domestic waste (from sinks, showers, etc.) and sanitary (sewage) wastes are
discharged from offshore oil and gas facilities. It is estimated that 6,000
gallons per day of domestic/sanitary wastes are discharged from a typical
exploration vessel and 5,000 gallons per day from a development platform
(FEIS OCS Sale No. 49).

Sanitary discharges are regulated by the EPA and are also addressed under OCS Order No. 7. The EPA requires that the effluent be treated prior to discharge into the ocean such that it not contain any constituent in concentrations which exceed EPA's marine water criteria (U.S. EPA, 1976b), and that it have a minimum chloride residual of 1.0 mg/l, maintained as close to this concentration as possible (40 CFR 435). Accordingly, the potential exists for the generation of trace quantities of chlorinated compounds.

Pipeline installation by burial causes the resuspension of sediments into the overlying water column. The composition of resuspended sediments is sitespecific. However, from the large extent of sandy substrate in the mid-Atlantic region it can be assumed this would be the primary component entering the water column. Because of high erosion problems association with trenching through sandy substrates, it is estimated that up to 28,000 cubic yards of sediment per mile of pipeline could be disturbed during installation.

Breaks or ruptures of gas pipelines would release light molecular-weight hydrocarbons ((C2 to C5) into the water column. These ruptures would also suspend sediments locally. The gases, however, would eventually evaporate into the overlying atmosphere.

IV.E.

Alternative 1: Hold the Sale as Proposed and Cumulative Impacts

For the purpose of assessing the impacts of the proposed action on the total environment, a number of assumptions have been made in order to estimate the logical consequences of the proposed sale. These assumptions are described in detail in Appendix B. They include estimates on the amount of recoverable oil and gas, and the most likely transportation routes and locations for processing and refining OCS resources. In addition, the number of estimated oil spills resulting from the proposed action, namely one, and the potential risk of contact to marine and coastal resources have been examined and quantified in Appendix C. Therefore, the levels of impact addressed under the proposed action are based primarily on the assumptions and analysis contained in Appendices B and C. The definitions of negligible, minor, moderate, and major impacts used in this section are given in Section II.B.6.

Cumulative impacts are the impacts on the environment which result from the incremental impact of the proposed action when added to other past, present and reasonably foreseeable future actions regardless of what agency (Federal or non-Federal) or person undertakes such other actions. Activities which are likely to cause cumulative impacts with proposed Sale No. 111 include previous OCS lease sales in the region, the transporting of imported (domestic and foreign) petroleum products through the region, and activities in other areas or regions which may affect migratory species using the lease sale area. Previous OCS lease sales in the mid-Atlantic region include Sales 40, 49, 59, RS-2, and 76. The most likely number of oil spills greater than 1,000 barrels projected as a result of proposed Sale No. 111 and from previous sales is two. Existing tanker transportation of imported crude oil and refined petroleum products in the mid-Atlantic is expected to result in approximately 27 oil spills greater than 1,000 barrels each over the production life of the fields. To the extent that OCS oil replaces imported oil, the risk associated with the transportation of OCS oil would be substituted for the risks associated with the transportation of oil imports. All oil that might be produced in the mid-Atlantic is assumed here to replace an equivalent amount of imported crude oil.