58 



incorporated and expanded as a 

 tiered monitoring program 

 (Germano et al. 1994). 



• REMOTS® data have shown that, 

 in general, disposal activities do not 

 prevent the reestablishment of 

 normal benthic conditions. 



3.3 Chemical Characteristics 



Capping of dredged material was 

 initiated to isolate sediments contaminated 

 with inorganic (heavy metals) and organic 

 constituents from the environment 

 designated for disposal. In marine 

 environments, metals and most organic 

 chemicals are usually strongly bound to 

 particulates. The particles that dominate 

 waters and surface sediments in coastal 

 areas are a complex mixture of dead plant 

 and animal matter, clay particles, and 

 living microorganisms. These "organic- 

 mineral aggregates" provide complexation 

 sites for the chemicals carried by rivers, 

 rain, and wind into coastal waters. Once 

 chemicals are bound to particles, their fate 

 is frequently determined by the movement 

 and deposition of the particles. 



Many compounds are cycled through 

 marine sediments, and most of this activity 

 is biologically mediated. Organic 

 compounds and metals used as nutrients 

 are actively mobilized and chemically 

 modified by the feeding, burrowing, and 

 oxygenation of surface sediments (Aller 

 1978, 1980). Other compounds are sorbed 

 passively by organisms and can move 

 through the food chain. Because the 

 contaminated dredged material in capped 



mounds is assumed to be isolated from 

 biological activity, it has also been 

 assumed that the contaminants are not 

 mobile. Unlike terrestrial landfills, 

 subaqueous capped mounds do not 

 experience leaching from ground water 

 movement. For this reason, chemical 

 monitoring has been limited to "assurance" 

 monitoring, i.e., routine analyses of 

 surface sediments to assess contaminant 

 levels. 



The geochemical processes within 

 marine sediments are complex and strongly 

 influenced by biological activity, pore 

 water mobility, and availability of oxygen. 

 Although no detailed studies of 

 geochemical processes within capped 

 mounds have ever been conducted, the 

 extensive surveys of contaminant levels in 

 surface sediments strongly support the 

 assumption that subsurface contaminants 

 are not reaching the surface. 



3.3.1 Methods 



In the evaluation of chemical 

 characteristics of capped mounds to 

 determine whether or not capping was 

 successful in isolating contaminants, the 

 DAMOS Program has emphasized 

 monitoring of the composition of surface 

 sediments forming the cap layer. Smith- 

 Mclntyre grab samples have been analyzed 

 on an intermittent basis since the beginning 

 of the program (Appendix C). The results 

 of these analyses are stored within the 

 DAMOS database. 



The contaminants of concern which 

 were routinely measured in the beginning 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



