130 



The direct observations of the surface sediments of the Seawolf Mound in the 

 REMOTS® images were consistent with the predictions from modeling, direct physical 

 oceanographic measurements and past observations (Waddell et al. 2001). There was 

 evidence of winnowing of no more than 3 cm of fine-grained cap material and no evidence of 

 storm-induced winnowing (characterized by dense layers of pebbles and shells with no 

 bioturbated layer). Armored shell lag surfaces were mixed with decaying tube mats, 

 indicating sufficient stability to induce settlement and growth of dense amphipod tube mats 

 with eventual senescence (Figure 4-1 lb). The available sand fractions show some evidence 

 of transport over silt layers without winnowed interfaces (this process can be difficult to 

 distinguish from sand layers directly deposited by disposal barges onto previously deposited 

 silt layers). This visual evidence strongly supports the conclusion that depth difference results 

 are due to consolidation not erosion of sediments from the surface of the Seawolf Mound. 



In 1998, surface sand overlying fine-grained sediment (sand-over-mud stratigraphy) 

 was noted for most REMOTS® photographs collected from the Seawolf Mound. The depth 

 of the sand layer was usually less than 5 cm. Both the core samples and REMOTS 

 photographs indicated fine-grained sediments over the apex and plateau of the mound. Very 

 fine sand was observed on the apron of the mound similar to observations of sediments at 

 the reference areas. Many replicate photographs also showed evidence of shell lag. 

 Although there was no obvious spatial pattern of boundary roughness values, several stations 

 were identified as winnowed (Figure 4-12). If at least one replicate contained evidence of 

 winnowing, shell lag, or disturbed amphipod mats the station was identified as winnowed. 

 All of the surface types were common across the mound. The presence of shell lag tends to 

 limit the process of further erosion through armoring of the surface sediment. Similar to the 

 Seawolf Mound, the reference area sediments were affected by tidal processes. Sand-over- 

 mud stratigraphy and shell fragments at the surface were common, as well as disturbed tube 

 mats. These results, combined with bathymetric results, demonstrate that while minor 

 surface transport of sediments is characteristic of the area surrounding NLDS, the cohesive 

 sediments that comprise the bulk of the material in the Seawolf Mound have remained in 

 place throughout the period of this study. This finding is consistent with the observations of 

 stable disposal mounds at NLDS over a period of at least twenty years (SAIC 2001). 



4.2.4 Sediment Chemistry of the Seawolf Mound 



To provide a basis for comparison with cores collected from the Seawolf Mound, the 

 results of chemical testing of sediments in the Thames River prior to dredging were 

 reviewed. Data from pre-dredged sediments indicated an overlap in chemical concentrations 

 between the material classified as UDM and CDM (Maguire Group 1997). In general, the 



Monitoring Cruise at the New London Disposal Site, Seawolf Mound 1995 - 1998 



