velocities of individual or flocculated particles cause vertical motion 

 within the plume. The motion is dependent on the particle grain sizes 

 and may be negligible for the fines, but it does lead to a sorting of 

 the material in the plume. 



Ayers et al. (1980b) described the distribution of drilling muds 

 in the water column for a well being drilled in 1978 in the nearshore 

 gulf. In two experiments, 250 barrels (bbl) of mud were discharged at a 

 rate of 275 bbl/hr t and 389 bbl of mud were discharged at a rate of 

 1 ,000 bbl/hr. The mud was a chrome lignosulfonate-clay type having a 

 bulk density of 2.09 g/cc . Water samples were taken at the bottom, 

 top, and most dense portion of the discharge plume using a rosette 

 sampling array suspended from a helicopter. This novel sampling 

 technique allowed rapid and almost continuous sampling of the plume. 

 Transmittance, dissolved oxygen, temperature, and salinity were 

 monitored as a function of depth and distance from the source using 

 instruments suspended from the helicopter. Divers took samples and 

 underwater photographs of the discharge plume close to the discharge 

 source. Water samples were analyzed for solids content, barium, 

 aluminum and chromium concentrations. 



During both discharges, the mud formed a lower plume and an upper 

 plume. The lower plume contained the bulk of the discharged material 

 and descended quickly to the sea floor. As the lower plume descended, 

 an upper, near-surface plume was generated by turbulent mixing of the 

 lower- plume with seawater. The upper plume was several meters thick, 

 existed in the water column at the thermocline for a much longer time 

 than the lower plume, and drifted away from the source with the current. 

 All sampling and hydrographic measurements were made on the upper plume. 

 Suspended solids and metal tracer concentrations in the plume reached 

 background levels about 500 m from the discharge source during the 275 

 bbl/hr test and about 1,000 m from the discharge source during the 1,000 

 bbl/hr test. Transmittance was the only hydrographic variable affected 

 by the discharge. All other hydrographic variables remained unchanged 

 from ambient conditions within the monitored interval (40 to 1,500 m 

 from the discharge point). 



A comparison of these results with a previous experiment (Ayers et 

 al. .1980b) at lower discharge rates indicated that transport time 

 (distance/current velocity) required for suspended solids to reach 

 background levels increased with discharge rate; however, even at high 

 discharge rates background levels are reached in about 100 min. It was 

 shown that most of the drilling mud settles rapidly and the material 

 remaining in the water column (estimated to be 5% to 7$ of the 

 discharged material) had a minimal effect on ocean water quality. 



Drill cuttings do not accumulate on the bottom in areas of high 

 current velocity because they are either entrained within the shifting 

 sediment or dispersed over a large area (Dames and Moore 1978; ECOMAR, 

 Inc. 1978; Environmental Devices Corporation 1976). In areas of low 



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