Carlton D. Hunt

Plume tracking and dilution of effluent from the Boston sewage outfall.

Field surveys were conducted on the Boston sewage outfall plume to test and certify the outfalls initial dilution in the near field and to investigate its dispersion in the far field. Rhodamine WT dye was added to the effluent at the treatment plant at a constant concentration over a 6-h period and tracked offshore over three days. During the near-field surveys, the current was flowing closely parallel to the diffuser, resulting in the wastefield spreading laterally as a dynamic density current at a rate that was closely predicted by theoretical equations. The plume was submerged by the oceanic density stratification, with a minimum initial dilution of about 102 within a few tens of meters from the diffuser. The initial dilution and the other near-field characteristics were in good agreement with predictions of mathematical models and with the physical model study on which the diffuser design was based. After a travel time of 24h, the dye patch was still intact and oceanographic mixing and dispersion had increased dilution by a factor of about two to more than 200:1. After 48h, the plume had broken into large patches, and most dilutions considerably exceeded 400 with an average dilution of order 1000. For the approximately 52h that the dye patch was followed in the far field, mixing was due to lateral diffusion; vertical mixing was negligible. This slow vertical mixing is due to the stable density stratification in the water column. The outfall is performing as designed. The field surveys provided a strong confirmation of the ability of small-scale laboratory model studies to replicate and predict the near-field characteristics of ocean wastewater outfalls. They also increase the confidence that mathematical models can be used to reliably estimate initial dilution under other effluent flows, oceanographic conditions, and stratification regimes.

Long-term monitoring using resident and caged mussels in Boston Harbor yield similar spatial and temporal trends in chemical contamination

Measurements of chemical contaminants in caged (transplanted) and resident mussel populations have become a routine tool for monitoring and assessing the status and trends of coastal water quality. However, few long-term data sets are available to assess the comparability and efficacy of these two monitoring approaches. Three long-term independent data sets exist for Boston Harbor: the National Mussel Watch program has analyzed resident blue mussels (Mytilus edulis) from the Boston Harbor/Massachusetts Bay region for over twenty years, the Massachusetts Water Resources Authority has annually deployed caged (transplanted) mussels (M. edulis) to assess bioaccumulation potential of sewage effluent discharged under its NPDES permit for over fourteen years, and the GulfWatch program has analyzed resident blue mussel populations for over twelve years. Together, these data provide consistent and comparable information on temporal and spatial changes in chemical contamination in Boston Harbor as steps were taken to reduce contaminant loading. The data also demonstrate the complementary nature of resident and caged (transplanted) mussels for assessing contaminant trends even when the basic approaches and sampling frequency differ. These fifteen-year data sets demonstrate contaminant concentrations in mussels from Boston Harbor are similar and with few exceptions have significantly decreased since the early 1990s. The observed trends also demonstrate broad scale improvements to the quality of Boston Harbor and expand understanding of the response of coastal systems to interventions that reduce the load of chemicals to the ocean.

Field and Model Studies of the Boston Outfall

Near- and far-field oceanographic measurements of the plume from the Boston outfall were made over two days in April 2001. The results were consistent with the original physical model studies on which the diffuser design was based. New laboratory experiments were run to simulate the actual conditions at the time of the field tests using three-dimensional laser-induced florescence (3DLIF) to measure dilution. The 3DLIF results were very close to the field observations and provided considerable additional insight into the near-field mixing processes: the plumes from each port of the multiport risers merge, first with other ports on the same riser, and then with similar plumes from adjacent risers; mixing transverse to the current direction then gradually erases any vestiges of lateral concentration variations. The field results were consistent with predictions of the mathematical model NRFIELD. Measurements were also made in the far field on the second sampling day. For the observed travel times of up to 24...

Transport of Sewage Sludge From the 106-Mile Site - Results From an October Survey

Abstract Approximately 8 million tons of sewage sludge were disposed of annually at the 106-Mile Deepwater Municipal Sludge Dump Site (106-Mile Site) between 1987 and 1990. Beginning in 1988 and continuing to the present, the focus of monitoring at the 106-Mile Site moved towards improved understanding of the fate of the sludge. A survey conducted in October 1989 was designed to (1) detect the presence of any sludge particles that settle rapidly following disposal, (2) determine if sludge could be detected in the surface waters at locations away from the immediate disposal site, and (3) determine if water quality was degraded, by assessing whether the Environmental Protection Agencys marine water quality criteria were being exceeded. The survey showed that the sludge does have a rapidly settling component composed of organic floc. mineral grains, and other heavy, gritlike particles, all of which are relatively large. These particles may settle at rates of between 8 and 180 m h−1 and may reach the sea flo...

Boston Harbor Sediment Quality Responds to Cleanup

Today, unlike a generation ago, the discharge of sewage into Boston Harbor, plays a small role in the loading of contaminants to Boston Harbor. The investment in state-of-the-art facilities, which effectively remove contaminants from the waste stream, has enabled Boston Harbor to recover from the past contaminant loading. Evidence of the improvements are found in contaminant load reductions, downward trends in sewage tracers and contaminant concentrations in surface sediments, and improvements in sediment quality

Fish and Shellfish Monitoring in Boston Harbor and Massachusetts Bay - 1992 Through 2005

The long-term biomonitoring for fish and shellfish in Boston Harbor and Massachusetts Bay provide data to assess potential environmental impacts from the diversion of effluent into Massachusetts Bay in September 2000. Condition of the indicator species (i.e., winter flounder, lobster, blue mussels) are characterized in terms of length, weight, biological condition, the presence of external or internal disease, and inorganic and organic contaminant tissue concentrations. The key findings of the fish and shellfish monitoring program are the documented improvements in tumor incidence and bioaccumulation of contaminants in fish and shellfish taken from the bays, and the limited response to the diverted effluent in the organisms collected in Massachusetts Bay to date.

A novel biofouling control technology for capillary flow cells

Prevention of biological fouling is critical to maintenance of optimal function and extended life for equipment and materials deployed in aquatic and marine settings. We established the efficacy of copper plus a proprietary antifouling treatment to prevent biofouling in glass capillary tubes using in situ epifluorescent microscopy and single-photon confocal microscopy to visualize biofilm formation in capillary flow cells exposed to filtered ambient seawater. The capillary cells were subjected to a series of biofouling control treatments with filtered seawater flowing at a rate of approximately 1 mL per minute. A screening study addressed three potential biofouling control concepts for application to development of the Submersible FlowCAM®, a new in situ instrument that can identify and enumerate both phytoplankton and small zooplankton species. The second addressed the effective exposure under a similar flow system using single-photon confocal microscopy as an end-point analysis. Control cells appropriate to each test were included. The first study demonstrated that biofouling in the control cells (no protection) was sufficient to stop flow after 60 days. Flow cells tested with only copper showed bacterial accumulation at 28 and 49 days. In contrast, very little (and in some cases, no) bacterial biofilm accumulation was observed in any of the proprietary or proprietary plus copper treatments throughout the entire 63 day test period. The second test demonstrated that the Cu plus proprietary treatment was highly effective at preventing biofilm formation in capillary flow cells across a range of treatment exposures under a constant copper concentration in the seawater. Copper treatment alone was not sufficient to prevent biofilm formation.