SUMMARY OF IMPORTANT FINDINGS 
Barium (present in barite, a major constituent of drilling mud) has 
increased by a factor of 5.9 in bulk (unfractionated) sediments 200 m 
from the drill site in block 410 as a result of drilling. The maximum 
barium concentration (172 ppm) was within the range of predrilling 
concentrations (28 ppm-300 ppm) measured at other sampling stations of 
this program. Because of the low toxicity of barium in the form of 
barite (BaSO,), no adverse chemical stress to bottom-dwelling organisms 
is expected from these measured increases in barium concentrations. This 
prediction is being tested by the biological studies conducted within the 
Monitoring Program (Battelle-WHOI, 1984). No drilling-related changes in 
the concentrations of chromium or of other metals have been observed in 
bulk sediments from any of the locations sampled in this program. 
Of the barite discharged to the ocean waters while drilling in Block 312, 
we estimate that 25 percent was present in the sediments within 6 km of 
the well at the time of the fifth monitoring cruise which was conducted 
4 weeks after drilling was completed. 
The inventory of barite, which accumulated as a result of drilling in 
Block 312, has decreased steadily for almost a year during the period 
following drilling with a “half-life” of 0.34 years. A much slower rate 
("half-life” 3.4 years) is estimated for the period between cruises 8 and 
12. At the time of cruise 12, the Ba inventory between 0.5-2 km from the 
well site was approximately 12 percent higher than the predrilling value. 
The barite from drilling mud is associated with the fine sediment 
fraction in low concentration and is widely distributed. Its fate is 
closely linked to the energetic sediment transport processes 
characteristic of this region. We found evidence for Ba transport and 
67 
