The Georges Bank Monitoring Program 1985: 
Analysis of Trace Metals 
in Bottom Sediments During the Third Year 
of Monitoring 
By M. H. Bothner, R. R. Rendigs, Esma Campbell, 
M. W. Doughten, C. M. Parmenter, C. H. O’Dell, G. P. DiLisio, 
R. G. Johnson, J. R. Gillison, and Norma Rait 
ABSTRACT 
Of the 12 elements analyzed in bulk (undifferentiated) 
sediments collected adjacent to drilling rigs on Georges Bank, 
only barium was found to increase in concentration during the 
period when eight exploratory wells were drilled (July 1981 until 
September 1982). The maximum postdrilling concentration of 
barium (a major element in drilling mud) reached 172 ppm in 
bulk sediments near the drill site in block 410. This concentra- 
tion is higher than the predrilling concentration at this loca- 
tion by a factor of 5.9. This maximum barium concentration 
is within the range of predrilling concentrations (28-300 ppm) 
measured in various sediment types from the regional stations 
of this program. No drilling-related changes in the concentra- 
tions of the 11 other metals have been observed in bulk 
sediments at any of the locations sampled in this program. 
We estimate that about 25 percent of the barite discharged 
at block 312 was present in the sediments within 6 km of the 
rig, 4 weeks after drilling was completed at this location (drill- 
ing period was December 8, 1981-June 27, 1982). For almost 
a year following completion of this well, the inventory of barite 
decreased rapidly, with a half-life of 0.34 year. During the next 
year, the inventory decreased at a slower rate (half-life of 3.4 
years). The faster rate probably reflects resuspension and sedi- 
ment transport of barite-rich material residing at the sediment 
surface. Elevated barium concentrations in postdrilling 
sediment-trap samples from block 312 indicate that such 
resuspension can occur up to at least 25 m above the sea floor. 
As the remaining barite particles are reworked deeper into the 
sediments by currents and bioturbation, removal by sediment- 
transport processes is slower. 
The barite discharged during the exploratory phase of drill- 
ing is associated with the fine fraction of sediment and is widely 
distributed around the bank. We found evidence for barium 
transport to Great South Channel, 115 km west of the drilling, 
and to stations 2 and 3, 35 km east of the easternmost drilling 
site. Small increases in barium concentrations, present in the 
fine fraction of sediment only, were measured also at the heads 
of both Lydonia and Oceanographer Canyons, located 8 and 39 
km, respectively, seaward of the nearest exploratory well. 
INTRODUCTION 
This study was designed to establish the con- 
centrations of trace metals in sediments prior to 
drilling on Georges Bank and to monitor the 
changes in concentrations that could be attributed 
to petroleum-exploration activities. Some of the 
specific questions addressed were (1) Where do 
discharged drilling muds accumulate on Georges 
Bank? (2) How much do trace metals increase as 
a result of accumulating drilling mud? and (3) In 
areas where drilling-mud components increase, 
how long do these components remain at an 
elevated concentration after the drilling is 
completed? 
This U.S. Geological Survey (USGS) study 
supports the main thrust of the Georges Bank 
Monitoring Program; that is, to evaluate poten- 
tial adverse effects of drilling effluents on bottom- 
dwelling organisms. The other studies (and con- 
tractors) within the Georges Bank Monitoring Pro- 
gram include (1) the analysis of benthic infauna 
(Battelle New England Laboratories and the 
Woods Hole Oceanographic Institution), (2) the 
analysis of hydrocarbons in bottom sediments and 
the analysis of hydrocarbons and trace metals in 
benthic fauna (Scientific Applications, Inc.), and 
(3) the analysis of previous benthic infauna 
samples from Georges Bank (Taxon, Inc.) (Michael 
