46 



contaminants are analyzed as those in 

 Box 3.1 and comparison is made with 

 the time zero levels. Sediment 

 samples collected from the disposal 

 mound and in the reference area are 

 compared with the following null 

 hypothesis in mind: 



H„2: Contaminant concentrations in 

 surface sediments are not 

 higher than at time zero levels. 



If the H 1 null hypothesis is accepted, 

 the logic returns us to Box 3.10. If the 

 H 1 null hypothesis is rejected, H 2 

 becomes important as a potential 

 explanation for the observed increase 

 in tissue contamination. If 

 contaminant concentrations in surface 

 sediments are higher than time zero 

 levels (H 2), the source of this 

 contamination is explored in Box 3.16. 

 If the surface sediment is not higher 

 than at time zero, an alternative 

 explanation is required (Box 3.15). 

 Because of the high costs associated 

 with field collection of biomass (it can 

 sometimes take a full day to collect 

 sufficient biomass of infauna at a 

 single station) and subsequent 

 laboratory analysis, usually sufficient 

 biomass for three replicate samples is 

 collected from only one general 

 location on the disposal mound and 

 compared with three replicates from 

 the ambient seafloor. Regarding 

 sediment sampling, a sufficient 

 number of replicates must be collected 

 to detect at least a 50% difference in 

 time zero levels; this number of 

 replicates can be determined by 

 calculating power levels for the 

 statistical model used (Cohen, 1977; 

 Bernstein and Zalinski, 1983). Once 

 again, unless there was a unique 



chemical signature in the underlying 

 contaminant material, the same suite 

 of contaminants analyzed during 

 permit evaluation (8 metals, PCB's, 

 total PAH's) would be the same ones 

 being tested at this point. See the 

 discussion accompanying Box 1.7 in 

 Section 2 for further considerations at 

 this point. 



Underlying Assumptions : One 

 assumes that if contaminant levels are 

 detectable and different from time 

 zero levels, then they will be greater. 

 These is a possibility for contaminant 

 levels to be less than those measured 

 at time zero because of the 

 phenomenon described earlier (fine 

 sediment being winnowed from the 

 apex of the disposal mound). Because 

 most contaminants are associated with 

 fine-grained sediments, as the mound 

 loses fines, surface contaminant levels 

 could decrease. One can guard against 

 this by not collecting sediment from 

 winnowed areas; these areas would be 

 identified by the earlier REMOTS® 

 monitoring. 



Another assumption in this step of 

 the monitoring protocol is that the one 

 organism collected for laboratory 

 analysis is a good representative of the 

 majority of infauna present at the 

 disposal mound. It also is assumed 

 that non-polar organic compounds are 

 the main contaminants of concern; 

 polar organics are not tested at any 

 step of the way. 



Sources of Uncertainty: 

 Sometimes, time zero levels of 

 sediment contaminants are lower than 

 ambient levels (hence the need for 

 collecting sediment at the reference 



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



