the central portion of the mound as 

 well as along the flanks. 



Box 3.18 "Evidence of Contaminants 



Migrating Through Cap?" 



If a sand cap is in place, it will be 

 easy to distinguish the boundary 

 between the cap and the contaminated 

 material visually. The two layers 

 should be separated and sectioned 

 vertically, properly labeled, and sent to 

 the laboratory for analysis. If there is 

 not a distinct grain-size discontinuity 

 (e.g., when a silt/ clay cap is used on 

 contaminated muds), vertical sections 

 ("10 cm) should be made starting at the 

 top of the core and working down to 

 the bottom. 



One has arrived at Box 3.18 because 

 the initial post-disposal monitoring has 

 shown anomalous recolonization, no 

 detectable physical explanation, and a 

 toxic sediment response to laboratory 

 bioassays or because the same 

 sequence of events occurred after more 

 mature successional stages were not 

 found on the mound following one or 

 more years. The only two possibilities 

 are that the cap had been breached 

 (contradicting the results of Box 3.1 if 

 it occurs as a result of the immediate 

 post-disposal monitoring), or an errant 

 disposal event has deposited 

 contaminated material on top of the 

 surface capped layer. The underlying 

 assumption is that the cap material is 

 chemically distinct from the 

 underlying contaminated material; the 

 unstated null hypothesis being tested 



H : There is no gradient in 



contaminant levels between the 



contaminated and capped layer. 



Acceptance of the null hypothesis 

 would force you to conclude an errant 

 disposal event had occurred and lead 

 you to Box 3.19; rejection of the null 

 hypothesis would lead to Box 3.22 and 

 require further capping material be 

 placed on the mound. 



Because it is unknown what 

 compound(s) is(are) responsible for the 

 toxic bioassay response, one would be 

 forced to analyze each separate vertical 

 section of sediment for the maximum 

 number of contaminants possible 

 within budgetary constraints, 

 presumably the same standard suite 

 that has been tested repeatedly to this 

 point (again, assuming there are no 

 unique organic and inorganic 

 compounds that can be used as a 

 tracer for the underlying contaminated 

 sediment; if these tracers are present, 

 then these compounds are the only 

 ones for which the vertical sections 

 need to be analyzed). 



Sources of Uncertainty: Because 

 the only time zero chemical levels 

 collected at this point are just surface 

 contaminant levels, the surface 

 interval is the only comparison one 

 will be able to make with time zero 

 levels. All the other data from the 

 subsurface intervals in the piston or 

 gravity core can be considered only 

 baseline data at this point against 

 which future evaluations can be 

 compared. It is also quite likely that if 

 there is evidence of contaminant 

 migration, it will not be a uniform 

 pattern that all compounds will follow; 

 more than likely, the data will display 

 the same variability as surface 



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



