Introduction

The United States Geological Survey (USGS) has conducted a multidisciplinary research program in Massachusetts Bay since 1989. The long-term goal of this project is to understand the fate and transport of contaminants that are adsorbed by suspended and bottom sediments. Studies have been conducted with a particular emphasis on monitoring oceanographic, chemical, and geological conditions during the $4 billion Boston Harbor cleanup effort. A major step in the harbor cleanup was completed on September 6, 2000 when the discharge of 380 million gallons per day of treated sewage effluent was switched from the harbor mouth to the new Massachusetts Bay Outfall located approximately nine miles offshore. Components of the USGS study have included geologic mapping, circulation and sediment transport observations, evaluation of heavy- metal contamination, and modeling of ocean circulation and tidal exchange. A summary of the entire program is presented at the following web site: http://woodshole.er.usgs.gov/project-pages/bostonharbor/

This report summarizes the time-series analyses of grain size distribution and the abundance of organic-mineral aggregates in surface sediments at two monitoring stations near the Massachusetts Bay Outfall. Sediments, especially the finer fractions, can adsorb contaminants from sea water and exert a strong influence on the transport and ultimate distribution of contaminants. Therefore, it is important to know the extent to which sediment characteristics in Massachusetts Bay can change in response both to natural events, such as storms, and to the start of the new sewage outfall.