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ligy0925

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There are other environmental problems connected with offshore oil pollution, many of them a routine part of operations. In drilling an offshore well, operators customarily discard overboard their drill cuttings with some unseparated drilling mud ( which is not actually mud but a combination of clay and chemicals). A typical 15,000-foot well usually produces more than 1,000 tons of drill cuttings. In addition, mineral salts, which may have distinctly harmful effects on some forms of marine life, are released from geological formations and are regularly discharged after treatment in the course of production.
Routine discharges like these, together with chronic low-level oil leaks, present “considerable environmental risk,” the Council on Environmental Quality concluded in its report. Digging channels for service ships and barges, building docks and other structures at the waterfront, and, to a lesser extent, laying pipeline cause another kind of environmental disruption. Instead of poisoning marine creatures, these activities tend to bury them, choke them, or cut off the light which is essential to their whole food chain. Most important, dredging and filling change drainage patterns of estuaries and wetlands and can lead to erosion or saltwater intrusion. Increased salinity of the water in marsh and estuary is usually damaging to the young fish, shellfish, and other organism residing there. They may not be able to tolerate the higher salinity. They may be killed by those sea animals with a taste for saltier waters.
Dredging for oil development was responsible for about one-quarter of the loss of 500 square miles of Louisiana marsh in 30 years through 1972, according to studies made at Louisiana State University. The big changes in Louisiana’s wetlands from offshore oil activity are striking. For mile after mile in the vast coastal lowlands, the curving, freeform marshes are penetrated by geometrically straight channels. Altogether, the study concluded, dredging, filling, and channelization in the Gulf of Mexico may have cause more damages than pollution from oil.
Finally , the sheer physical numbers of drilling rigs, production platforms with their multiple wells, service ships, barges, and 10,000 miles of underwater pipeline present something of a hazard to navigation in the Gulf of Mexico. Ships coming through must keep to prescribed two-mile-wide fairways, and wells may not be drilled into the shipping lanes (though they may be drilled underneath, in the ocean floor, at a slant).
(1)The primary purpose of the passage is to describe____.
A) cause of oil pollution in and around offshore drilling sites
B)impact of offshore oil drilling on the geography of a region
C) environmental risks associated with offshore oil drilling
D)effects of offshore oil drilling on marine life
(2) All the following are mentioned as environmental problems associated with offshore oil drilling EXCEPT_____.
A) found in the drill cuttings discarded during offshore operation
B) normally found in the ground near offshore oil drilling sites
C) a common by-product of the oil refinement process
D) produced in large quantities by oil drilling equipment
(3) It can be inferred from the passage that the normal salt levels of estuary waters______.
A) serve as a barrier to saltwater marine sea animals
B) tend to discourage population growth of the marine animals
C) are necessary for breeding for most offshore-dwelling shellfish
D) prevent the growing of the smaller organisms that normally reside there
(4) The word “ salinity” (line 10. Para. 2) can be explained as “__________”.
A) salt containing               B) chemical
C) medicine                    D) poison
词汇：
dredging n 挖泥
estuary n 河口
drilling rig  钻探平台
fairway n 航路