were low compared to their average concentration in crustal rocks and that 
they were characteristic of uncontaminated coarse-grained sediments. We found 
the variability in trace-metal concentrations from station to station to be 
closely correlated with the content of fine-grained material and organic 
carbon in the sediments, as commonly occurs (Crecelius and others, 1975). Pb 
values higher than average crustal abundances were measured only at the 
location south of Martha's Vineyard where fine-grained sediments are 
accumulating and where previous studies (Bothner and others, 1981) have 
suggested tetraethyl lead from gasoline as a source of the elevated Pb found 
in this area. 
Throughout the three years of monitoring, the concentrations of Ba in 
bulk sediments from the upstream control stations (transect I, stations 1-3) 
were fairly consistent with time (fig. 4, appendix table 4A). On the basis of 
these data, we judge that no increase in Ba had occurred at these stations. 
We found no increases in the concentration of other metals as a result of 
drilling at these upstream locations during the three years of monitoring. 
In contrast, there were some measurable changes in the concentration of 
Ba in block 410 (stations 16, 17, and 18, fig. 5). Drilling began in this 
block immediately after the first sampling cruise in July 1981 and continued 
(with some interruptions) until March 31, 1982. The mean current flow on this 
part of the Continental Shelf is to the west, although tidal and storm 
currents can reverse the mean flow (Butman and others, 1982a). Relative to 
the mean current flow, stations 17 and 18 are upstream and downstream of the 
rig position, respectively (fig. 5). 
At station 16, located within 200 m of the drill rig in block 410, 
average Ba concentrations apparently increased steadily from a predrilling 
concentration of 32 ppm to the maximum concentration of 1/72 ppm measured on 
26 
