28 



Disposal Site and placed at the MQR buoy 

 located near the southwestern corner of the 

 CLIS site (Figure 2-1). Water depths in 

 this area ranged from 20 to 21 m. This 

 location was selected to minimize 

 interference with the previous capped 

 mounds. Disposal barge logs indicated 

 that approximately 42,000 m 3 of high- 

 water-content Mill River sediment was 

 placed prior to the initiation of Quinnipiac 

 River dredging. This latter operation, 

 beginning in early May 1982 and 

 completed prior to the first of June, 

 resulted in the placement of approximately 

 133,200 m 3 of silts as a cap layer over the 

 Mill River sediments, resulting in a 

 disposal barge log cap: mound ratio 

 estimate of 3.2:1. 



Dredged material volume estimates 

 obtained by comparing bathymetric 

 profiles before and after disposal of each 

 unit disagree substantially with the disposal 

 barge log values. Volume calculations 

 based on depth differences were 

 approximately 70,000 m 3 of sediment 

 dredged from the Mill River and 

 190,000 m 3 from the Quinnipiac River, 

 resulting in a 2.7:1 capping ratio (Table 2- 

 4; Morton et al. 1984a). 



Given the variations in sediment water 

 content and compaction induced by the 

 dredging operation, it is not surprising to 

 find substantial differences between 

 disposal barge estimates and measured in- 

 place volumes. These characteristics have 

 been discussed by several investigators 

 (e.g., Tavolaro 1984). Normally, 

 however, this combination of factors 

 results in in-place volumes that are less 



than disposal barge volumes (Section 3.1). 

 The volume calculation data, based on 

 depth differences for the Mill River 

 dredging, show in-place volumes to be 

 significantly larger than those detailed on 

 the NED log. This in part may be a result 

 of the unique textural quality (i.e., wood 

 pulp) of the disposed material. In 

 addition, incomplete records confound 

 estimates of disposal barge volumes. 



Clamshell dredging of Black Rock 

 Harbor and subsequent disposal at Mill- 

 Quinnipiac (MQR) began on 9 March 1983 

 and continued through 18 April 1983. 

 Dredging of New Haven Harbor began on 

 29 March and was completed on 17 May. 

 NED disposal barge logs indicated that 

 approximately 67,000 m 3 of Black Rock 

 sediment was placed at the MQR mound 

 and capped with approximately 400,000 m 3 

 of additional New Haven material, which 

 resulted in a 6:1 cap ratio for this second 

 layer of MQR (Table 2-4). 



This ratio is again misleading and 

 somewhat compromised by the fact that 

 the periods of deposition of Black Rock 

 and New Haven material overlapped to 

 some extent (Figure 2-8). The majority of 

 Black Rock material was disposed before 

 New Haven. Subsequent to the final New 

 Haven cap deposition, however, two barge 

 loads of Black Rock material 

 (approximately 3,000 m 3 ) were deposited 

 at MQR. This disposal sequence 

 complicated evaluation of this project and 

 may have resulted in a thin layer of Black 

 Rock material at the surface. A more 

 complete discussion of monitoring results 

 of this capped mound is included in 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



