20 



The areal extent of the deposits at MBDS, 

 Elliott Bay, and Port Gardner, although 

 well defined, is larger than deposits 

 measured at shallower sites. Deposits at 

 WLIS and CLIS, formed at less than 30 m 

 depth, measured approximately 200 meters 

 in diameter for disposal volumes of 



128.000 m 3 and 62,624 m 3 , respectively. 



3.1.1 Massachusetts Bay Disposal Site 



Sequential surveys conducted from 

 1985 to 1992 have documented the 

 development of a distinct disposal mound 

 at MBDS. The volumes of dredged 

 material released at MBDS annually since 

 1985 are listed in Table 3-1. Prior to 

 1985, disposal operations at MBDS were 

 conducted using a conventionally moored 

 buoy with a wide scope or only LORAN-C 

 navigation. Acoustic bathymetric surveys 

 at that time were unable to detect any 

 dredged material mound (Bajek et al. 

 1987). In November 1985, a taut- wired 

 buoy was deployed at a previously unused 

 location in MBDS. An acoustic 

 bathymetric survey conducted at the same 

 area in 1987 still did not indicate any 

 topographic features related to disposal. 

 The REMOTS® sediment-profiling system, 

 however, showed a large pancake-like 

 deposit of dredged material (SAIC 1988). 

 In 1988, a comparison of the 1988 and the 

 1987 bathymetric surveys was able to 

 discern a layer of dredged material 0.3 m 

 thick and 150 m in diameter (Figure 3-3). 

 The REMOTS® survey detected flank 

 deposits less than 20 cm thick at the edges 

 and up to 900 m in diameter. A 

 comparison of the 1990 bathymetry and 

 the 1988 data indicated an additional 

 thickness of 0.8 m and a diameter of 



420 m (Figure 3-4). The REMOTS® 

 survey in 1990 recorded fresh dredged 

 material up to 800 m west of the buoy 

 location (Germano et al. 1993). The barge 

 release locations from 1987 to 1990 

 indicated that most disposal points were 

 400 m from the buoy (Figure 3-5). From 

 1990 to 1992 the dredged material 

 thickness increased by 2 m west of the 

 buoy and covered an area 200 by 400 m 

 (Figure 1-5). The barge release locations 

 from 1990 to 1992 indicated that disposal 

 locations again were within 400 m of the 

 buoy location (Figure 3-6). 



The SAIC DAMOS capping model was 

 used to predict the height and lateral extent 

 of a mound that would be formed under 

 the disposal conditions that have existed at 

 MBDS since 1987. Based on REMOTS® 

 observations, the MBDS dredged material 

 was estimated to be silty clay with some 

 sand (30% sand, 35% silt, and 35% clay). 

 The amount of material deposited at 

 MBDS from 1987 to 1992 was 

 approximately 836,148 m 3 over a 450 

 meter radius. The mound that the model 

 predicted for these parameters was 4.22 m 

 high and 600 m in radius. The actual 

 mound formed at MBDS between 1987 

 and 1992 was approximately 2.4 m high 

 just west of the buoy location. Because 

 the location of the peak of the dredged 

 material mound varied slightly from 1987 

 to 1992, the cumulative amount of material 

 at any one location was less than that 

 predicted by the model. The excess mound 

 height predicted by the model is due to the 

 random distribution pattern inherent in the 

 model. Excess height in the modeled 

 dredged material mound may also be due 

 to overestimation of the amount of 



Deep Water Capping 



