Table 3.6. Expected oil spillage due to non-catastrophic incidents (vessel not sunk) 

 involving seagoing vessels in superport region (Bryant 1974). 



Table 3.7. Pipeline spillage incidents and volume 

 for the United States and its territories 

 during 1971 and 1972 (Bryant 1974). 



Perhaps a more serious long-term hazard of 

 mineral production within the inland wetlands is the 

 chronic spilling of small quantities of oil over a period 

 of many years. Some of this oil finds its way into the 

 sediments of the surrounding wetlands, as shown by 

 hydrocarbon analyses (Bishop et al. 1976). The sedi- 

 ments appear to act as a sink for the liydrocarbons, 

 releasing them slowly to the bottom waters in oil 

 field canals (Milan and Wlielan 1978). 



Impoundment s: Leveed pits are created for 

 confinement of brine associated with mineral ex- 

 traction. The volume of brine disposed of in this 

 fashion in the Chenier Plain is small relative to other 

 disposal means (table 3.5). The number of these 

 leveed pits is small and total area is insignificant, 

 although the local impact may be important. 



Probably a more important activity is the in- 

 advertent creation of impoundments as a result 

 of canal dredging. Spoil banks from crisscrossing 

 canals or from canals along natural ridges may effec- 

 fively cut off an area from nomial water flow. The 

 number and area of impoundments due to mineral 

 extraction activities alone are difficult to quantify. 

 Impoundments are discussed further in parts 3.3 

 and 3.4. The effect of impoundments on biota is 

 discussed in part 4.0. 



Water Based Construction : The Chenier Plain 

 has an overall density of about 0.33 well/km^ (0.85 

 well/mi^) (Louisiana Department of Conservation 

 1977); the Calcasieu Basin has the highest density- 

 0.72 well/km^ (1.86 wells/mi^). Probably the major 

 impacts of well construction are disturbances of the 

 site. Construction of pipeUnes is another activity 

 associated with mineral extraction. The direct con- 

 struction effects are small compared to the major 

 impact of the resulting canals. 



Canal Dredge and Spoil. The major long-term 

 iinpact of mineral production on basins is tlie con- 

 struction of canals and their associated spoil banks 

 through shallow water bodies and wetlands. Table 

 3.8 shows the length and area of these canals (plates 

 5A and 5B). The majority of canals provide access 

 for navigation, although road embankment canals 

 become increasingly important toward the west 

 end of the Chenier Plain. Most pipeline canals are 

 back-filled, but many later become shallow-water 

 hnear features because of compaction and erosion. 

 (See part 3.3 for a discussion of impacts of canals.) 

 Oil field activity canals cover about 6.700 ha (6,556 a) 

 of tlic Chenier Plain. Associated spoil banks cover 

 anywhere from two to three times as mucii area as 

 the canals (Craig etal. 1979). Using a conservative 

 factor of twice the canal area for spoil banks, the 

 total land permanently impacted by canals and spoil 

 banks is about 20,000 ha (49,421 a). This type of 

 modification is discussed in part 3.4. 



32 



