There are other environmental problems connected with offshore oil besides oil pollution, many of them a routine part of operations. In drilling an offshore well, operators customarily discard overboard their drill cuttings with some un-separated 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. Localized shortterm impacts have been detected as a result of these discharges. Routine discharges like these, together with chronic low-level oil leaks, present 'considerable environmental risk,' the Council on Environmental Quality concluded in its report on OCS oil and gas.
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 marshes and estuaries is usually damaging to the young fish, shellfish, and other organisms residing there. They may not be able to tolerate the higher salinity or they may be decimated by invading predators with an affinity 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. From the air, the changes in Louisiana's wetlands from offshore oil activity are striking. For mile after mile in the vast coastal lowlands, the curving, free-form marshes are penetrated by geometrically straight channels-narrow ones for pipelines, broader ones for drill barges and rigs. Spoil from the dredging is piled in ridges on the channel banks, altering the natural drainage from dozens of winding streams. Altogether, the study concluded, dredging, filling, and channelization in the Gulf of Mexico may have caused more damage 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 the:A. causes 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. ways in which offshore oil drilling affects the water quality in a region
E. effects of offshore oil drilling on marine life
2. The passage implies that the natural region most vulnerable to damage due to offshore oil drilling is:A. beaches
B. the ocean floor
C. coastal plains
D. marshlands
E. the waterfront
3. Each of the following is mentioned in the passage as an environmental problem associated with offshore oil drilling EXCEPT:A. pollution from oil leaks
B. seawater intrusion into wetlands
C. pollution of the air by drilling-rig machinery
D. increased levels of mineral salts in coastal waters
E. increased population of certain marine predators