(in the United States, usually the Minerals Management 

 Service of the Department of the Interior) around offshore 

 platforms. The objective of these monitoring programs was 

 to assess the impacts of drilling mud and cuttings 

 discharges on the benthic environment. Accumulation of 

 drill cuttings and of some drilling mud ingredients, 

 particularly barite, in sediments has been detected near 

 offshore exploratory rigs and production platforms. On 

 Georges Bank, elevated concentrations of barite derived 

 from drilling mud discharges were detected in sediments 

 near two exploratory rigs. The excess barite was washed out 

 of the sediments and diluted to background within one to 

 two years after cessation of drilling. 



On the Mid-Atlantic outer continental shelf, but not on 

 Georges Bank, accumulation of drilling mud and cuttings 

 solids was accompanied by changes in benthic community 

 structure. Such benthic impacts, when they have been 

 detected, usually were restricted to a radius of about 200 

 meters from an exploratory rig from which only one well was 

 drilled. In the North Sea, impacts on the benthos around 

 multi-well development platforms sometimes extended out to 

 1000 to 3000 meters from the platform. Impacts were much 

 more severe if oil-based drilling muds were used and oily 

 cuttings were discharged (not permitted in U.S. waters) 

 than if water-based muds were used and discharged. Recovery 

 of benthic communities impacted by solids from water-based 

 drilling muds usually began within one or two years after 

 completion of drilling. 



B-12 



