48 



being measured. One could 

 argue this is highly unlikely, 

 because if unknown or 

 "mystery" chemicals can leach 

 through the cap, chances are the 

 same route of transport would 

 be available to those chemicals 

 which are being measured in 

 the tissues and would show up 

 as abnormally high levels. 



Because of the expense 

 associated with bioaccumulation 

 studies, the number of samples 

 analyzed is typically small (3 

 replicates from the mound are 

 compared with 3 replicates from 

 the ambient seafloor). Different 

 levels of variability are 

 associated with different 

 contaminants; the most 

 notoriously variable are the 

 organics. Some compounds 

 (e.g., PCB's) have demonstrated 

 such a high coefficient of 

 variation in samples collected to 

 date that as many as 20 

 replicates would need to be 

 collected to detect a 50% 

 difference at an alpha level of 

 0.05 (DAMOS database, 

 unpublished). If contaminants 

 that will trigger management 

 actions have inordinately high 

 variability, then explicit 

 computation of power relative 

 to a small sample size (e.g., 

 Cohen, 1977) should be carried 

 out before further sampling is 

 performed. Such computations 

 often lead to the realization that 

 there is no point in doing the 

 study unless the sample size is 

 doubled or quadrupled. If the 

 resources do not exist, there is 



no point in collecting only a 

 fraction of the data needed to 

 make a defensible statement; 

 studies deficient in statistical 

 power result in a large 

 proportion of invalid rejections 

 of the null hypothesis (Overall, 

 1969). 



Box 3.15 "Seek Alternate Explanation " 



One can reach this box via Box 3.14 

 or 3.21. In either case, one has arrived 

 at this point because bioaccumulation 

 may have occurred (via Box 3.13) and 

 surface sediment contaminant levels 

 may (via Box 3.21) or may not (via Box 

 3.14) be higher than time zero levels. 

 If the increase in invertebrate tissue 

 contaminant levels is due to either an 

 errant disposal event or regional 

 deposition, then there is no need to 

 supply additional capping material to 

 the mound or re-evaluate the current 

 capping management protocol. This 

 will force you back to Tier 1 in Box 

 3.10. 



52 2 Tier Two: Mound Chemical Profiling 

 and Related Management Decisions 



Boxes 3.16 & 17 



"Determine Source of 

 Contamination..... " 



Once you have arrived in Tier 2, all 

 indications are pointing toward the 

 cap being breached. Results of the 

 physical monitoring program become 

 important at this point to help identify 

 locations and sources of cap breaching. 

 Piston, gravity, or vibra-core sampling 

 will need to be done at several 

 locations (3-5) through the mound into 

 the underlying contaminated 

 sediment. Samples should be taken at 



An Integrated, Tiered Approach to Monitoring and Management of Dredged Material Disposal Sites 



