44 



value used for the volume of a single barge load was 2000 m 3 , and the grain size distribution 

 was kept constant at 20% sand, 40% silt, and 40% clay, with a density of 1.45 g/cc. 



The Capping Model predicted that 1-3 m of Quinnipiac River material (190,000 m 3 ) 

 would overlie a base of 0.5-2 m of Mill River material (70,000 m 3 ). Bathymetric analyses 

 following deposition of Mill River sediments (April 1982) generally agreed with the modelled 

 results. Two bathymetric surveys were conducted following deposition of Quinnipiac River 

 sediments and before New Haven/Black Rock Harbor deposition, in June 1982 and 

 December 1982. Bathymetric results from the June 1982 survey indicated that the 

 Quinnipiac sediment layer was thinner ( < 1 m) than predicted by the Capping Model, 

 assuming no consolidation of Mill River sediments. The December survey, however, 

 indicated that both Mill and Quinnipiac River sediments had settled approximately 0.5 m in 

 the period between June and December, suggesting a maximum total consolidation of Mill 

 and Quinnipiac River sediments from bathymetric estimates of approximately 2 m. 



Modelling the disposal of point-dumped (operational radius of 50 m) Black Rock 

 Harbor sediments (67,000 m 3 ) following the combined disposal of Mill and Quinnipiac River 

 sediments (260,000 m 3 ) resulted in a thickness of Black Rock sediments of 2-4 m. No 

 bathymetric survey was conducted following deposition of Black Rock Harbor material. In 

 addition, the Capping Model was used to predict the thickness of a 3,000 m 3 layer of Black 

 Rock material deposited following final capping of New Haven material. The result was that 

 the hypothetical thin layer of Black Rock was indistinguishable from the huge mound of 

 material below it. 



New Haven Harbor sediments were disposed not as a taut-wired point-dumping 

 operation, but rather as a widely distributed LORAN-C controlled disposal operation for 

 more comprehensive coverage of cap material. Ten disposal points were concentrically 

 arranged, one in the center, three at 80 m, and six at 120 m from the center. The Capping 

 Model predicted a thickness range of 1.5-3.5 m of New Haven sediments (400,000 m 3 ) 

 overlying the cumulative sum of the other units within a 300 m radius of operations. 

 Bathymetric observations, obtained after deposition of both Black Rock and New Haven 

 sediments (June 1983), resulted in a minimum total post-Mill and Quinnipiac River sediment 

 thickness of 1-2 m (again assuming no postdepositional settling). These results are consistent 

 with a New Haven cap of 1.5 meters recovered in the cores. The recovery of ambient 

 material below this interval in MQR-6, however, indicates that at least this core was 

 recovered from the mound flanks, where the total thickness of dredged material is thinner 

 than at the center of the mound. 



The differences in the modelled thicknesses and those measured by bathymetric 

 volume-difference analyses are a function of sediment consolidation and the diameter of 

 disposal operations. Much of the material is dispersed in the flanks around the mound and is 



Sediment Core Chemistry Data Summary from the MQR Mound, August and December 1991 



