Sediment traps also were deployed 6 km east of the drilling rig in 
block 312 while drilling was in progress (ST426) and after completion of 
drilling in this block (ST513 and ST515). The Ba concentrations of these 
sediments are also higher than those of predrilling samples. Some of the 
material contributing to the elevated Ba concentrations measured in these 
samples may have originated from the four drilling rigs operating between 5 
and 45 km to the south or east of these trap locations. Alternatively, storm 
and tidal currents could have transported material eastward. 
There is a weak but positive indication that drilling mud was transported 
in measurable concentrations to the expected depositional site at the head of 
Lydonia Canyon (fig. 14, table 3C). Drilling began during the second period 
in which sediment traps were used to collect suspended sediment (fig. 14). 
The concentration of Ba in the fine fraction of trap sediments from the head 
of Lydonia Canyon increases slightly from the first deployment until the 
fourth deployment and ret oscace to increase more dramatically at the time 
of the fifth deployment, which includes the period when four wells were 
finishing drilling activity on the bank (fig. 14). On the basis of these 
increases in Ba concentration, which were measured in traps at two levels in 
the water column (10 m and 20 m above bottom), we suggest that a small 
drilling mud signal was present in the suspended matter in Lydonia Canyon. No 
such indication is apparent from the analysis of the bulk sediment-trap 
material--for which the Ba concentrations during the period of drilling are 
generally within one standard deviation of the concentrations determined in 
predrilling trap samples (table 3A, B). 
Trace-metal variations with depth in sediment 
During the second and third year of monitoring, sediment cores and grab 
samples (appendix table 4D, and Bothner and others, 1983) were subsampled as a 
48 
