18 



2.2.1 STNH Disposal Operations 



Two taut-wired, moored buoys were 

 deployed marking the locations of the 

 selected Stamford-New Haven North 

 (STNH-N) and South (STNH-S) disposal 

 points (Figure 2-1). Clamshell dredging of 

 the east branch of the Stamford Harbor 

 channel began 25 March 1979, and 

 material was transported to the disposal 

 area using hopper barges. Initial disposal 

 was confined to the southern buoy location 

 in predisposal water depths of 

 approximately 22-23 m. Between 25 

 March and 22 April approximately 

 38,000 m 3 (disposal barge log estimate) of 

 Stamford sediment was deposited at the 

 southern buoy. 



On 23 April, the primary disposal 

 point was shifted to the northern buoy 

 location, in water depths averaging 

 approximately 19 m. Between 23 April 

 and 16 June 1979, approximately 

 31,000 m 3 (disposal barge log estimate) of 

 Stamford material was deposited at the 

 northern disposal point. Harbor dredging 

 was terminated in mid- June to avoid any 

 potential impacts on spawning species. 



Dredging of New Haven Harbor silts 

 to provide a cap for the southern site 

 deposit began on 1 May 1979 and 

 continued until 15 June 1979. Clamshell 

 and associated hopper barge techniques 

 were used to dredge and transport 

 approximately 110,000 m 3 (disposal barge 

 log estimate) of silts to the southern 

 capped mound. Sand-sized material to 

 provide a cap for the northern disposal 

 project was dredged by the USACE hopper 



dredge Essavons from the mouth of New 

 Haven Harbor during the period 16 to 21 

 June 1979. The latter dredging resulted in 

 the placement of a total of approximately 

 112,000 m 3 (disposal barge log estimate) 

 of sand capping material, 65,000 m 3 near 

 the center of the mound and the rest 

 approximately 100 to 300 m from the 

 center. 



Initial bathymetric surveys at STNH-N 

 and STNH-S were conducted before 

 disposal, after disposal of Stamford 

 material, and after disposal of New Haven 

 capping material (Appendix C). The 

 results of this monitoring are fully 

 discussed in Section 3.1.2. 



On completion of the postdisposal 

 surveys, additional "clean up" dredging 

 was conducted in Stamford, resulting in 

 the placement of an additional 6,000 m 3 of 

 material at the STNH-S during the period 

 of 26 September through 18 October 1979. 

 This sediment subsequently was capped 

 with material dredged from New Haven 

 Harbor during the period of 29 January 

 through 3 June 1980. According to 

 disposal barge log records, this latter 

 dredging resulted in the placement of an 

 additional 110,700 m 3 of sandy silts to 

 supplement the cap at STNH-S. Disposal 

 volume estimates for the Stamford-New 

 Haven project resulted in cap-to- 

 contaminated-material ratios of 1.3:1 for 

 STNH-N (sand cap) and 5:1 for STNH-S 

 (silt cap) based on available disposal barge 

 estimates (Table 2-4). The cap: mound 

 ratio estimate for STNH-S is relative 

 because of the 6000 m 3 of Stamford 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



