1.0 INTRODUCTION 



The Massachusetts Bay Disposal Site (MBDS) is located in the northeast portion of 

 Massachusetts Bay, approximately 18 nmi east-northeast of the entrance to Boston Harbor 

 and 10 nmi south-southeast of Gloucester, Massachusetts (Figure 1-1). The disposal site 

 consists of a 2 nmi diameter circle centered at 42° 25.700' N and 70° 34.000' W. Ambient 

 water depth at the buoy location is approximately 90 m. As part of the Disposal Area 

 Monitoring System (DAMOS), Science Applications International Corporation (SAIC) has 

 conducted six monitoring surveys at MBDS, from 1985 to 1992. These studies mapped the 

 distribution of dredged materials, monitored the formation of the disposal mound, evaluated 

 the benthic environment, provided information on the physical parameters of the site, and 

 determined the extent of chemical contamination. Assessment techniques for the surveys 

 have included precision bathymetry, side-scan sonar, REMOTS® sediment-profile 

 photography, current meter and transmissometer deployments, conductivity, temperature, 

 depth, and dissolved oxygen (CTD/DO) monitoring, and sediment and benthic sampling for 

 physical and chemical analyses. The 1985 survey also included observational cruises using 

 manned submersibles, fish collections, and the implementation of the Benthic Resources 

 Assessment Technique (BRAT). 



A major construction project underway in the Boston area, the Central Artery/Third 

 Harbor Tunnel (CA/THT) project, has increased disposal activity at MBDS. MBDS has 

 received 289,588 m^ of dredged sediments since the last bathymetric/REMOTS® surveys m 

 August 1990; 81% of this volume originated with the CA/THT project and consisted 

 primarily of Boston Blue Clay. Disposal of sediments from the CA/THT project began with 

 one barge load of material in August 1991 (2,280 m^) and did not begin again until January 

 1992. Disposal of Boston Blue Clay at MBDS had been occurring for three months at the 

 time of the survey. Boston Blue Clay is a relatively homogeneous, light greenish-gray to 

 medium gray clay which was deposited in a nearshore marine environment that existed m the 

 Boston area during an interglacial period about 18,000 years ago. Results of the grain size 

 analyses indicate some variability in the Boston Blue Clay which is a natural feature resulting 

 from the environmental changes during deposition: the gravel content ranged from 0.3 to 

 16.9%, sand ranged from 0.8-14.7%, silt ranged from 3.1-73.2%, and die clay content 

 varied from 25.7-65.3% (Camp, Dresser, and McKee, Inc. 1993). In general, the clay can 

 be characterized as having a large proportion of fmes, generally greater than 40%. The 

 remaining 19% of the dredged sediments deposited at MBDS were a mix of sands, silts, and 

 clays determined suitable for open water dredged material disposal from the Hingham, Nut 

 Island, JFK, Manchester Harbor, and Gloucester State Pier projects. These sediments, with 

 the exception of 1,064 m^ from the State Pier Project, were deposited before mid- July 1991. 

 Based on the barge logs, dredged material was released within 350 m of the "MDA" buoy, 

 centered at 42° 25.086' N and 70° 34.457' W. 



Monitoring Cruise at the Massachusetts Bay Disposal Site, March 31 - April 4, 1992 



