NSWC/WOL/TR 76-161 



a residue of carbon floating on the water, which is unsightly 

 though not harmful to the environment. The results are shown in 

 Table 3.7. The weights are probably accurate to + 10% or better. 

 However, as in the evaluation of chemical concentrations, the 

 major problem is one of obtaining representative samples when the 

 distribution in the pool, and also in the ambient water, is not 

 uniform. 



Visual examination in a microscope showed the presence of 

 sediment in the background sample and both sediment and carbon in 

 the pool samples. Although the water was relatively deep, sediment 

 was present because of the proximity of shallow water and the 

 relatively strong current in the river. At 50 and 70 seconds carbon 

 particles with diameters up to about 260 microns were present. At 

 90 seconds, the largest observed were about 130 microns, and, at 

 110 seconds, the largest were about 45 microns in diameter. However, 

 by this time, the majority were of the order of 5 microns. The 

 last sample, taken at 130 seconds after the shot was predominantly 

 sediment with only fine (<5 microns) carbon particles remaining. 

 There was a tendency for sediment and carbon to agglomerate into 

 clusters. 



The extent of fish kill could not be determined visually from 

 the barge, but gulls were observed feeding about 300 meters from 

 the shot point. Observers in the boat stated that about 1000 fish 

 were slowly floating up to the surface. The surface trawl was 

 placed in the water about 8 minutes after the shot and was towed 

 through the dye patch. The patch, including the dead fish, moved 

 away from the barge at about 0.4 m/sec, and the trawl was towed 

 at about 1 m/sec. The trawl was in the water for 12 minutes, but 

 the time in the dye was only about 5.5 minutes. It was noted that 

 the fish were in patches in the pool of dye. 



About 1.2 kg of menhaden were collected in the first trawl. 

 The levels of damage are shown in Table 3.8. 



Following the first trawl, a series of samples was taken with 

 a dip net. The data are summarized in Table 3.9. The distances 

 shown were determined with a range-finder. However, they represent 

 the locations of fish after transport by the current. The original 

 positions are not known. 



It was noted that fish were still floating to the surface, 

 and a second surface trawl was started 65 minutes after the shot 

 and was terminated 9 minutes later. The boat was too far away from 

 the barge for accurate tracking with the eguipment available. The 

 trawl net collected 0.77 kg of menhaden; the data are shown in 

 Table 3.10. 



Table 3.11 presents a comparison of the overall results of 

 the three sampling efforts. In terms of percentage, the differences 

 are minor, though more specimens were collected with the dip net. 



20 



