BACKGROUND

Boston Harbor has been the traditional focus of New England maritime activities. For over 300 years it has been the principal port of call for both commercial and pleasure vessels. It is a full dayís sail closer to Europe than other American ports giving it a distinct competitive advantage. The local economy has benefited greatly through the creation of jobs and increased commerce both in the shipping and fishing industries. As an example, Massport has estimated that every 1,000 tons of cargo generates 7.8 jobs and an economic impact of $1,120,000. In 1994 a total tonnage of 1,313,000 moved through the port, generating and estimated 10,240 jobs and $1.47 billion in value (USACOE, 1995).

Like most harbors, Boston Harbor experiences silting or sediment deposition in the navigation channels. Sediments are generally deposited in two ways: (a) from fine solids in rivers and streams settling out of the water column in the slower moving harbor and (b) from current and wave action washing solids in from the ocean as well as redistributing and eroding shorelines and channel boundaries. In addition, Boston Harbor receives deposits of organic material from the MWRA sewer outfalls. Over time this sediment accumulates to the extent that dredging of the navigation channels is necessary to provide for the safe passage of ships. During the first half of this century dredging projects increased the depth of the broad sound North Entrance Channel and the Main Ship Channel to -35 MLW (Mean Low Water). In 1974 portions of the Main Ship Channel were deepened to -40 MLW to accommodate larger tankers and container ships. Most vessels now operating in the port draw at least 36 to 37 feet of water (USACOE, 1995).

Several factors led to the implementation of the Boston Harbor Navigation Improvement Project (BHNIP). The first is the current trend in shipping towards larger, more efficient container vessels, which require a 40 foot channel depth. The second is the recent requirement that all oil tankers are doubled hulled, a requirement that increases a vesselís draft. In order to maintain New Englandís valuable petroleum deliveries an increased channel depth is needed to accommodate these new tankers. The third factor is the need to improve navigational efficiency. In the highly competitive shipping industry, companies are unwilling to wait for tide changes or light load their vessels to allow for safe transit because it puts them at an economic disadvantage.

The Navigation Improvement Project (BHNIP) will dredge three tributary channels and two portions of the Main Ship channel to -40 ft. MLW, thereby allowing for the safe transit of newer, larger vessels into the Inner Harbor berthing areas and will reduce the need to wait for high tide or light load vessels. This project will generate 1.0 million cubic yards (cy) of contaminated silt (maintenance), 1.8 million cy of the underlying parent material (mainly blue clay) and .1 million cy of rock. The contaminated maintenance material will be disposed of under the Least Environmentally Damaging Alternative (LEDA) of in-channel disposal (in channel disposal is the creation of borrow pits within the boundaries of the navigation channel. See Figure 1) under a three foot sand cap and will require the removal of an additional 1.8 million cy of parent material. The total 3.4 million cy of clean parent material will be disposed of offshore at the Massachusetts Bay Disposal Site (MBDS). The total cost of this project is approximately $66 million (USACOE, 1997).

Figure 1. Disposal Cell Schematic

(click on picture for a larger, better quality image)

It is estimated that over the 50 year project life a total of 7.1 million cy of sediment will accumulated and need removal. See Table 1 for a breakdown of quantities by area (USACOE, 1995). While improvements to the local sewage systems and reductions in other pollutant flows are expected to improve water and sediment quality it is not expected that a large quantity of this 7.1 million cy of maintenance material will be suitable for offshore disposal. Accordingly, alternative disposal sites must be sought.

Table 1. Maintenance Material Quantities by Site

MAINTENANCE DREDGING AND DISPOSAL OPTIONS

While the in-channel disposal option chosen for the BHNIP is an effective solution to the disposal of dredged material it is a one time option. Once contaminated sediments have been placed and capped that area is no longer available for disposal use. Accordingly, to conserve this valuable resource the Army Corps of Engineers has directed its contractors to dredge the in-channel borrow pits as deep as possible. However, it is not anticipated that any significant area will remain in the BHNIP dredging areas for disposal of future maintenance material. Possible future options might include the creation of borrow pits in the Main Ship Channel or President Roads Anchorage.

In the Final EIR/EIS the Corps identified 24 possible disposal sites and designated 17 as being a Least Environmentally Damaging Alternative. This included the three in-channel disposal sites. Refer to Table 2 for a listing of sites and capacities. Of the upland sites, all of the landfills are scheduled to close by the year 2000 and are thus not considered to be viable alternatives for the placement of future maintenance material. The remaining upland sites have limited capacity and unresolved issues concerning permits, dewatering, and monitoring of contaminated sediments. Because of these reasons it would seem that all the upland sites are not suitable for disposal of future maintenance material. The remaining aquatic sites are only able to accommodate 1.8 million cy of material; approximately 25% of the needed capacity. It should be apparent after looking at Table 2 that based on the analysis of the FEIR/S the most promising long term options are subaqueous borrow pits or open ocean disposal. Only these options approach the needed capacity for maintenance material disposal and, in addition, have some of the lowest disposal costs. However, there are some remaining issues that need to be resolved before such sites can be considered.

Table 2. Disposal Site Capacities (without in-channel sites)

First, open ocean disposal at sites such as the MBDS is contingent on successfully demonstrating the containment of contaminated sediments in deep water (> 100 ft.), whether with capping or geotextile containers. The Army Corps of Engineers is interested in pursuing a demonstration project with capping at the MBDS, but requires that a close source of suitable (clean) project material is available. At this time, the Corps isnít planning a local demonstration project with geotextile containers because of the perceived cost and size limitations of the technology but is monitoring tests with the containers in other regions.

Second, issues regarding the siting of subaqueous borrow pits need to be addressed. These sites were not designated as LEDA because of concerns that the sites were too shallow or exposed (Subaqueous B, E, Spectacle Island) or were located in prime lobster and fish habitat (Meisburger 2,7). While the use of borrow pits looks to be promising much needs to be done to identify better sites.

It should be noted that other options, such as treatment technologies, may become feasible in the future. However, at the present time these technologies are impractical due to the costs and volume of material involved and it would be imprudent to depend on their development to solve the problem of dredged material disposal.

PROPOSED PLAN

While the subaqueous and open ocean disposal sites look to be likely future disposal areas much work needs to be done in three distinct areas. The first area is demonstrating the feasibility of capping in deep water. The second is the identification of future in-channel disposal sites. Third is developing a method for siting subaqueous disposal sites.

Until the feasibility of open ocean disposal with capping for contaminated sediments is demonstrated in-channel disposal and borrow pits remain the best options. As mentioned before, the in-channel method will not be available in the improvement dredging areas in the future. In addition, none of the subaqueous or borrow pit sites were designated as LEDA due to concerns such as the depth or the sites, wave and tidal motions, and the presence of lobster and finfish communities. Until methods are developed that avoid, to the furthest extent possible, these siting problems the current navigation improvement project is in jeopardy of being rendered ineffective in a few decades due to a lack of disposal alternatives for the accumulating silt.

It is felt that the best long term sustainable management plan for disposal of contaminated dredged material will result from a comprehensive study of the harbor environment with the goal of identifying likely sites for the location of borrow pits, whether in a navigation channel or in the surrounding harbor.

Specifically, the use of GIS (Geographic Information Systems) technology will be studied with the aim of developing a method for siting in-channel and subaqueous borrow pits. It is anticipated that individual layers of critical factors such as shellfish habitat, depth, sediment quality, etcÖ will be mapped. Using GIS technology these layers can be overlaid and combined to aid in the identification of prime locations for the siting of borrow pits. In addition, it is anticipated that an easy to use PC or Internet based interface will be developed to allow all the stakeholders to vary the importance of the various factors and to see how the various tradeoffs involved in these siting decisions affect the final selections of disposal sites. It is felt that this will improve public participation in the planning process and allow all stakeholders and participants to have a common platform for discussion of the issues and tradeoffs involved in siting disposal areas.

The Commonwealth of Massachusetts has already developed a statewide GIS system (MassGIS) using the Arc/INFO system that has many layers such as topographic charts, transportation networks, anadromous fish runs, hydrography, etcÖ This plan of study will build on that system using spatial data from NOAA, MWRA, U.S.G.S., and other organizations that are concerned with the quality of Boston Harbor and Massachusetts Bay. Currently, the following data layers have been or will be gathered.

• Bathymetry

• Sediment Depositional / Erosional Areas

• Nautical Line Charts (shipping lanes, cables areas, pipelines)

• Barrier Beach Locations

• Coastal Barrier Resource Units

• Shellfish Production Areas

• Anadromous Fish Runs

• Areas of Critical Environmental Concern

• Eelgrass Beds

• Currents

• Marinas

• Dive Sites

• Lobster Catch

• Recreational Fishing

In effect, this project is simply combining existing data with the intent to provide a meaningful method for analyzing it in a holistic manner.

Data on sediment quality and contamination levels is still being sought. The U.S.G.S. in Woods Hole should be releasing this data on CD-ROM in the near future. It should be noted that this list is not complete. This is due to the lack of data on such features as finfish or benthic habitat. It is not anticipated that this type of data will be available in time to be included in this project.

During the beginning of the new year, efforts will be directly at developing a user interface to the data to allow for the weighting and manipulation of datalayers. If the resources are available efforts will be made to develop a system to serve up the data and allow for its manipulation online through the World Wide Web. It is expected that several demonstration meetings will be given during February to gather feedback about the system and to evaluate the relative merits of its development and to determine if further design should take place. These demonstrations will involve scientists, regulators, engineers, environmental groups and members of the public. Finally, during the month of March, a Masterís thesis will be written that will document the entire project and outline the results and future development of this system.

This information and improved access to it should help improve the decision and regulatory process for the long term management of dredge materials and disposal sites. It is anticipated that the development of new GIS layers will not only benefit decision makers but will benefit decision makers but will also be of aid to future researchers. This should help us improve our understanding of disposal options and allow us to manage dredge materials more effectively in the future.

REFERENCES

Dolin, Eric and Pederson, Judith, CZM Technical Report: Marine-Dredged Materials Management in Massachusetts: Issues, Options and the Future (December 1991)

Governorís Commission on Commonwealth Port Development, Final Report (October 1994)

U.S. Army Corps of Engineers and Massport, Final Environmental Impact Report and Final Environmental Impact Statement: Boston Harbor, Massachusetts Navigation Improvement Project and Berth Dredging Project (June 1995)

U.S. Army Corps of Engineers, Boston Harbor, MA, Navigation Improvement Project Summary Sheet (June 1997)