1 are very low concentrations of background suspended solids. The general 



2 pattern is that you have rapid dilution and within an hour or so you are 



3 back down to virtually background concentrations of drilling fluids. 



4 So this, again, you might say is field-validation of the 



5 calculations that you do have rapid dilution of the drilling fluids. 



6 As I say, the muds may not cause problems in the water column 



7 because of the rapid dilution, but on the bottom they tend to accumulate 



8 and not dilute, at least initially. One of the major concerns about 



9 accumulations of drilling fluids on the bottom is that they do contain 



10 elevated levels of several metals and that these metals could be a 



11 toxicological problem to resident biota. 



12 This is the concentration range of various metals in drilling 



13 fluids and this is taken from a fairly large database, and compare it to 



14 the range of "background concentration" of metals in natural marine 



15 sediments. 



16 There is no such thing as the concentration of a metal in 



17 sediments, as Mike Bothner, I am sure, can tell you. There are wide 



18 ranges, for instance, natural levels of 8,000 ppm barium have been 



19 detected in apparently clean sediments. 



20 If you look across horizontally here at all these, what you find 



21 is that in drilling fluids in general, barium is nearly always higher in 



22 concentration in the drilling fluid than in the sediments. 



23 Chromium very often is, especially if chrome-1 ignin-sulphonate is 



24 used as the defloculant or thinner, you can get very high concentrations 



25 of chromium, though chrome-1 ignin-sulphonates are being outlawed in 



26 several areas, they are not permitted for offshore discharge. 



27 Occasionally copper is higher, though some natural sediments have 



28 very high copper. The other two metals potentially posing a problem are 



29 lead, as you can see we can have very high concentrations of lead 



30 occasionally in drilling fluids, and zinc. Again, zinc is naturally 



31 high in most marine sediments, but it can be much higher in drilling 



32 fluids. 



33 Most of these metals that I just mentioned, copper, lead, and 



34 zinc, in addition to cadmium and mercury, which are sort of on EPA's hit 



92 



