20 



this location since November 1985. "Fresh" dredged material appeared to be present within 

 800 m west, 500 m south, 400 m east, and 500 m north of the center of the disposal site. 



The apparent "fresh" dredged material contained chaotic sedimentary fabrics and 

 anomalous grain size distributions (Figures 3-6, 3-9). Gravel, very coarse, and coarse sands 

 ( < 1 phi) were present at the center of the disposal site and within 200 m of the center. 

 Penetration by the camera was limited at stations 200N, 200S, and 100E due to over- 

 consolidated clay clasts and occasional rock rubble at the sediment surface (Figure 3-10). At 

 other stations, the dredged material consisted of sand over mud and appeared to be less 

 consolidated, exhibited more stratification, and allowed deeper penetration by the camera 

 (Figure 3-9). Dredged material was not apparent at the reference stations. 



Steep gradients in the depth of the RPD were measured between the disposal site, 

 where most RPD values fell between 2 and 4 cm, and the three reference areas, where most 

 values were > 5 cm (Figure 3-11). The frequency distribution of mean apparent RPD 

 depths for the disposal site stations indicated a major mode of 3.0 cm while the distribution 

 of RPD depths for the reference areas showed a major mode at 6 cm (Figure 3-12). 

 Reference area RPD values were significantly deeper (Mann-Whitney U-test, p < 0.05). 



The spatial distribution of infaunal successional stages, as inferred from REMOTS® 

 photographs, showed that all reference stations and all disposal site stations (with the 

 exception of station 100 E) supported Stage EQ taxa (Figure 3-13). In general, the dominant 

 infaunal successional stage was Stage I on Stage III at both reference and disposal site 

 stations. Only 75% of the January 1989 disposal site stations showed evidence of Stage HI 

 taxa. Reference station replicate photographs indicated the presence of Stage I, Stage U on 

 Stage HI, and Stage HI communities. 



Past mapping experience has shown that Organism-Sediment Index (OSI) values 

 < +6 indicate bottom disturbance by either chemical or physical means. Only 3 stations 

 had median OSI values < +6 and included 500SW, 400W, and 300N (Figure 3-14). This 

 indicated an improvement in benthic conditions in comparison with results from the 1989 

 REMOTS® survey in which 9 stations immediately surrounding the disposal site center had 

 mean (vs. median) OSI values of < +6. OSI values were greater generally in August 1990 

 and ranged from 6 to 11 compared with November 1988 values of 2 to 11. These higher 

 values ( > +6) are indicative of undisturbed, high-diversity benthic communities. Reference 

 station (1990) OSI values were significantly greater than values at disposal site stations 

 (Mann- Whitney U-test, p<0.05). The OSI frequency distribution for the disposal site 

 stations showed a major mode of 10 and 11 at the reference stations (Figure 3-15). 



Monitoring Cruise at the Massachusetts Bay Disposal Site, August 1990 



