IV.E.1. Impacts on Water Quality Existing (baseline) water quality conditions and general water circulation patterns within and proximate to the proposed lease sale in the Mid-Atlantic were presented in Sections III.A.5 (Chemical Oceanography and Water Quality) and III.A.2 (Physical Oceanography). Water quality within the proposed lease sale area appears to be generally good. Notably, there is no evidence of unusual or elevated levels of petroleum in either the water column or bottom sediments. Some limited water quality degradation results from ocean dumping (at the formerly-designated 106-Mile Ocean Waste Disposal Site area) and along the shelf as the heavily contaminated inner New York Bight area is approached. In accordance with the mean resource estimates it is projected that 20 exploratory, 8 delineation, and 45 production wells will be drilled within the lease sale area. To recover (produce) the resources, 4 platforms and 2 subsea complexes will be required. a. Oil Spills The most severe impacts on marine water quality would result from large, acute oil spills as usually associated with well blowouts and tanker accidents (see Section IV.B, Oil Spills in the Mid-Atlantic Marine Environment, for sources of oil input). However, smaller spills (usually less than 50 barrels) during routine operations are more likely to occur. It is difficult to apply findings of one oil spill to predict actual effects of another, as every spill incident is unique. For a spill within the proposed sale area, a major factor would be the assimilative capacity of the ecosystem. Also important would be the oceanographic and meteorologic conditions when the spill occurred (such as wind, wave action, turbulence, currents, turbidity, temperature, salinity, and pH), as these would affect the behavior and weathering of the spilled oil, and thus the degree and duration of water quality degradation. Also, in assessing the impacts of an oil spill, it is important to consider not only the amount of oil present at the time a particular region is affected, but also the chemical state of the oil as well. This would depend on the nature of weathering (see Section IV.B.). During oil recovery and transportation from Sale No. 111 the assumed number of large oil spills (greater than 1,000 barrels) is one (Section IV.B.3, 011 Spill Risk Analysis). Oil, if spilled within the proposed lease area, would most likely result in a surface layer (slick) which would decay in the deeper (greater than 60-m depth) offshore area. Oil Spill Risk Analysis Model (OSRAM) simulation results indicate an 88 percent probability that oil spilled (>1,000 barrels) in the lease area would remain (without contacting shore) within the model's study area (seaward boundaries of 42°30′ N, 65°30'W, and 33°00' S - Figure 1, Appendix C) for 30 days--the number of days after which the spill is presumed to be no longer detectable. There is an 11 percent probability that this spilled oil would contact land and a 1 percent probability that it would be carried eastward, beyond the study area toward the open ocean, within the 30-day period. The impact on water quality in the deeper offshore/ open ocean (most of proposed lease area) by a large, acute spill could be severe although likely temporary in nature. Physical oceanic processes would assist in breaking up the resulting oil slick and would contribute to weathering the oil with photochemical oxidation and biological degradation aiding these processes. If an oil spill occurred within the inner or middle shelf area (less than approximately 60 m depth), or if oil from a deeper area were carried onto the shelf and toward the shallower coastal areas, the effects on water quality may be considerably more serious. Oil, in this case, would be more likely to get dispersed throughout the water column, may get entrained in suspended particles and bottom sediments and possibly re-released into the water column from the sediments due to physical forces such as tides, currents and waves. However, the likelihood of a large (greater than 1,000 barrels) spill occurring or being carried to inside the shelf break and close to shore, as measured by "land" contact using the OSRAM model, is small. During the 30-year expected production life from lease Sale No. 111, the probability of such a spill occurring and contacting land within 30 days is 7 percent (Table 12, Appendix C). Small oil spills (less than 50 barrels) resulting from accidents, such as spillage during fuel transfer or overflow of deck drains, during routine operations are very likely to occur. Of the 7,107 recorded (1964 to 1981) oil spills in the Gulf of Mexico OCS, all but 176 spills were less than 50 barrels in volume (Regional FEIS, Gulf of Mexico, 1983). These spills, relative to larger volume spills, are great in number but comparatively insignificant in terms of oil released. These periodic (possibly chronic) spills would have very limited (localized) impact on offshore water quality. Operational discharges of oil from ships are the routine and intentional discharges, primarily resulting from bilge water pumping and tank cleaning and ballasting, during normal operating procedures. Preliminary results indicate that oil inputs into the east coast waters (3 to 200 miles offshore) from operational discharges in most years far outweigh those from accidental spills (NOAA, 1984). However, with regard to transport of oil resulting from the proposed sale, the effects of operational discharges on water quality are anticipated to be very limited. Only 56 tanker trips per year (mean estimate for peak year) are projected for the Sale No. 111 related transport of oil (Table II.B.1-1). Also, recent stricter regulations now address operational discharges from vessels (e.g. discharges permitted only 50 miles beyond land) further limiting potential water quality impacts. b. Drilling Muds and Cuttings The volumes of drilling muds and cuttings expected to be discharged during operations resulting from the proposed action are given in Table IV.E.1-1. Discharges would occur over an assumed exploration and development drilling period of 11 years within the approximately 20.3 million acres of the proposed lease area. The initial dispersion and deposition of drilling discharges within the proposed lease area would most likely occur as previously observed in the rig-monitoring studies discussed in Section IV.D.1.b. Two factors in particular, currents and water depth, would be significant in determining for a particular case the actual dispersion of the materials from the point of discharge. Generally, however, because of the relatively small volume of this component compared to the large volume of receiving water, the rapid settling and dispersion of materials to background levels within approximately 1,000 meters, and because discharges would be spaced over a large area and long period of time (a total exploration and development * All figures based on water depth of 3,800 feet. Assuming well depth ** Cutting volumes include various washout factors which vary (depending on the section of the hole) and a bulking factor of 1.2. The bulk of discharged drilling materials would decrease rapidly around the point of discharge by settling of the heavier materials (e.g. most cuttings) and dispersal of the lighter mud components. The only time concentrations of whole muds in the water column would approach laboratory bioassay 96-hour LC-50 values (10,000 to 100,000 ppm) is when the discharge is actually occurring and then only in the immediate vicinity of the discharge pipe (Ayers, 1981). Depending on the rate of discharge and on local hydrographic conditions, the remaining suspended solids concentrations could be reduced to 0.01 percent or less, from less than 1 to 10 ppm, within 100 meters of the discharge. This is far below. the concentration range of 100 to 1,000 ppm that most investigators have noted as having sublethal effects on marine biota (Ayers, 1981). As a result of continued settling and dispersion, and depending on hydrographic conditions, suspended solids would normally be expected to attain background levels in the column within 1,000 meters downcurrent from the discharge (Ayers, 1981). Rig monitoring studies conducted in the mid-Atlantic, Gulf of Mexico, and off California have shown that suspended solids reached background levels within 200 to 1,000 meters from the discharge, depending on discharge rate and hydrographic conditions (EG&G, 1982; Ayers et al., 1980; Ray and Meek, 1980). Light transmittance values would reach background levels at a slightly greater distance from the discharge than suspended solids due to the presence of colloidal particles in the water column. Transmittance values have been observed to reach background at 800 to 1,000 meters downcurrent in the mid-Atlantic (EG&G, 1982) and up to 1,500 meters from high rate (1,000 bbl/hr) tests in the Gulf of Mexico (Ayers et al., 1980b). Soluble components would undergo the same general dispersion characteristics as the fine particulate fractions of the discharge and would become well mixed in the water column within a few hours of discharge. Dilution ratios for soluble components have been estimated to be two orders of magnitude lower than those of the solids components (Ayers et al., 1980b). Trace metals dilution rates, as measured by suspended solids concentrations, have been shown to be similar to that of whole muds. Elevated trace metal concentrations in the water column are usually limited to within 1,000 m of the discharge point. In the 1,000 bbl/hr discharge test in the Gulf of Mexico, barium, chromium and aluminum concentrations all approached background levels within 1,100 m of the discharge point (Ayers et al., 1980b). Comparing the estimated concentrations of trace metals in drilling muds after 10,000-fold dilution (100 meters downcurrent from the discharge point) with EPA criteria for saltwater aquatic life (Table IV.E.1-2) shows all estimated metal concentrations being below the EPA criteria levels (within "safe" levels). A few generalities can be made in predicting and contrasting the fate of discharged drilling materials and associated water quality impacts within the major sub-areas (shelf, slope, rise) of the Sale No. 111 area. In all these sub-areas the lighter particulate and soluble discharge components associated with the surface plume would be dispersed/diluted to ambient levels within approximately 200 to 2,000 meters of the discharge point, this varying with water currents an discharge rate. Thus, impact on background water quality would be limited (localized) and minor. The heavier drilling discharges released on the shelf within the sale area would likely accumulate in the general vicinity of the drilling rig. In the shallower (less than 60 m depth) areas of the inner and mid-shelf regions, these initial accumulations would be resuspended and transported elsewhere as a result of storm-related currents (see Section IV.D.1.c, Resuspension and Transport of Drilling Muds and Cuttings). In contrast, settled drilling discharges on the outer shelf would not be so dispersed due to the low energy bottom environment, as was noted in the Mid-Atlantic Block 684 studies (EG&G, 1982). In the slope and rise, bottom accumulations of drilling discharges are not likely to occur due to the increased settling distance afforded by the greater depth there. There is some concern that the boundaries of the "cold band" may reduce Table IV.E.1-2. Comparison of Estimated Trace Metals Concentrations in SOURCE: EPA, 1981 NPDES Permit Determinations (Georges Bank/Atlantic Ocean), |