47 



stations both at time zero and now) 

 and will increase over time due to 

 natural deposition of fine grained 

 material. If levels are higher, there is 

 still a distinct possibility that it is due 

 to an errant disposal event and not 

 migration of chemicals through the 

 cap (hence the need for the next tier 

 for verification). If both the disposal 

 mound and the ambient seafloor show 

 similar levels of increase, the most 

 parsimonious explanation is that it is 

 due to regional deposition of 

 contaminated detritus. 



As far as sources of uncertainty for 

 interpreting the results from the 

 infaunal body burden analyses, in 

 addition to the appropriate ones listed 

 under Box 1.7 in Section 2, there are a 

 number of potential unknowns that 

 could affect the interpretation of the 

 final results: 



• The final data are species- 

 specific; the relevance to other 

 species can always be 

 questioned, and the inability to 

 collect the same species at the 

 same locations in subsequent 

 years may hinder long-term 

 trend monitoring. 



• It is difficult to account for 

 seasonal variation in lipid 

 content (which has a direct 

 effect on body burden levels of 

 contaminants); unless all 

 individuals are in the same 

 stage of ontogeny and 

 reproductive maturity at all 

 locations and at each 

 subsequent sampling time, any 

 variation is not necessarily due 

 to contaminants leaching 



through the cap. 



There are no regulatory criteria 

 established for the majority of 

 invertebrate species or for 

 contaminants (the FDA has set 

 action limits in seafood for 

 PCBs, a few pesticide 

 compounds, and methyl 

 mercury, but not for PAHs and 

 any other metals of concern), so 

 trigger levels are arbitrary. 

 Attempts to find "meaningful" 

 levels of change are often 

 confused with statistically 

 "significant" levels of change. 

 Given enough of an intensive 

 sampling effort, a very small 

 change can be statistically 

 significant. Because of our lack 

 of knowledge about "normal" 

 invertebrate biochemical levels 

 and metabolic pathways, any 

 trigger level at which we choose 

 to reject the null hypothesis is 

 arbitrary. This is without a 

 doubt the most serious flaw in 

 this whole procedure; because 

 of the large variability which 

 typically exists in tissue 

 contaminant levels, we define 

 an order of magnitude 

 difference between the disposal 

 mound and reference as being 

 "significant" enough to reject the 

 null hypothesis. 



If the null hypothesis (H 1) is 

 accepted, there is still the 

 possibility that some unknown 

 chemical (not being analyzed in 

 the tissue) that will exert a 

 chronic, deleterious impact on 

 invertebrate species is still 

 bioaccumulating but simply not 



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



