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USGS Studies Show Extent of Sediment Contamination and Saltwater Impacts on Charles River

Release Date: 03/30/2001
Contact Information: Amy Miller, Press Office, 617-918-1042 USGS Robert Breault, 508-490-5076 USGS Peter Weiskel, 508-490-5026

BOSTON - The U.S. Geological Survey today issued two new reports detailing sediment contamination problems and saltwater impacts on the Charles River Basin. The studies, based on hundreds of sediment and water samples collected over a 12-month period, show high levels of metals and organic pollutants in the lower basin as well as significant saltwater intrusion, which also contributes to compromised water quality.

Results from the two reports will be closely analyzed by the U.S. Environmental Protection Agency's New England Office, which has set a goal of making the Charles River safe for fishing and swimming by Earth Day 2005.

"These reports are bad news in some respects, but the good news is that we will have a much better understanding of the problems and therefore be better equipped to find the right solutions," said Ira Leighton, acting regional administrator of EPA's New England Office, which has spearheaded the Clean Charles 2005 Task Force, a joint collaboration of more than 25 communities, environmental groups, citizens groups and many government agencies. "In the months ahead, we'll be looking at a number of options for mitigating both of these situations, all with an eye towards making the river safe for fishing and swimming."

Both of the EPA-funded studies focused on an eight-mile section of river known as the Charles River Basin, which runs from the Watertown Dam down to the mouth of the river near the Museum of Science in Boston. The mouth of the river is separated from Boston Harbor by a dam.

The sediment report, based on 147 sediment samples collected in July and August 1998, showed high concentrations of inorganic pollutants (lead, cadmium and other metals) and organic compounds (including PCBs, poly-aromatic hydrocarbons and pesticides). Median concentrations ranged from 1 to 35 times higher than median concentrations of these constituents from rivers in similar urban settings across the United States. The study was conducted in cooperation with EPA, the Massachusetts Department of Environmental Management and the New England Interstate Water Pollution Control Commission.

Robert Breault, USGS hydrologist and senior author of both reports, said the contamination likely results from numerous factors.

"It is partly the result of the basin's low water flow (compared to its large volume), a lack of natural flushing that once occurred from the normal tide cycle, or a lack of uncontaminated sediment from upstream that can help dilute these urban sediments," he said. "An oxygen-poor, sulfide-rich zone within a salt wedge that forms as a result of present-day dam operations may also be a factor."

The study area included four potential public beaches - Daly Field in Newton, Magazine Beach in Cambridge, Herter East Park in Brighton and the Esplanade Ponds in Boston. The organic compounds were generally detected in the lowest concentrations in areas of low sediment deposition, such as near Magazine Beach and the Esplanade Ponds. Larger contaminant concentrations were found in areas where sediments tend to be deposited, such as Daly Field and Herter East Park.

The USGS issued a second report today detailing the effects that saltwater from Boston Harbor has on the lower Charles. Although cut off from the harbor by a dam, the USGS study found that the opening and closing of locks has resulted in a significant saltwater wedge in the basin, particularly in the dry summer months when water flows from upstream are low and the locks are open more often due to increased boating traffic. (The term salt wedge is named for the shape that the saltwater takes as it moves upstream.)

Data on the distribution, variability and chemistry of the saltwater entering the lower Charles River was collected from June 1998 to July 1999, and highly detailed maps of the river bottom were constructed. The maps portray water depths, as well as the extent and distribution of salinity in the basin during the study.

In the high spring runoff period and during major storms, freshwater flows from the upstream Charles River can flush the salt wedge completely out of the basin, as occurred during an eight-inch rainstorm in mid-June 1998. (To prevent flooding, the dam is equipped with large pumps that allow the operators to lower the water level of the basin in anticipation of large upstream flow.) After the June 1998 storm, the salt wedge returned as boat traffic intensified, especially over the July Fourth holiday. By mid-August 1998, anoxic conditions (no oxygen) had developed in the wedge; such conditions are harmful for most organisms. The salt wedge continued to expand through most of 1999 when flows decreased due to near-drought conditions were experienced in the Boston area.

"A greater understanding of the salt wedge dynamics will help managers to mitigate its negative effects and possibly prevent or control its formation," Breault said.

Salt water intrusion into the Charles River Basin has long been an issue of concern. The original dam built in 1908 helped solve one of Boston's major sanitary problems - the accumulation of untreated sewage on the tidal flats of the Charles River estuary during low tide. But, by building the dam and opening the locks for boaters, salty harbor water was introduced to the basin, causing fish kills and odors in the basin. In 1975, the Metropolitan District Commission concluded that the fish kills and odors were likely the result of occasional mixing of deep, sulfide-rich saltwater with the overlying freshwater.

Another dam was built in the late 1970s to replace the old dam and was designed to significantly reduce saltwater intrusion into the basin. However, salt water intrusion has increased through the dam as the number of lock cycles increased in response to increasing boat traffic, and as the dam has aged. At the time of the USGS study, lock operations were found to be the major factor leading to the formation of the salt wedge.

The saltwater report, titled "Spatial Distribution, Temporal Variability, and Chemistry of the Salt Wedge in the Lower Charles River, Massachusetts, June 1998 to July 1999", by R.F. Breault, L.K. Barlow, K.D. Reisig, and G.W. Parker, is published as a USGS Water Resources Investigations Report 00-4124.

The sediment report, "Distribution and Potential for Adverse Biological Effects of Inorganic Elements and Organic Compounds in Bottom Sediment, Lower Charles River, Massachusetts," By R.F. Breault, K.D. Reisig, L.K. Barlow and Peter K. Weiskel, is published as a USGS Water Resources Investigations Report 00-4180.

Both reports are available for inspection at the USGS, Massachusetts-Rhode Island District Office, 10 Bearfoot Road, Northborough, MA 01532. The reports and fact sheets can be purchased at U.S. Geological Survey, Information Services, Box 25286, Denver, CO 80225-0286 (telephone: 303-202-4700).

As the nation's largest water, earth and biological science and civilian mapping agency, the USGS works in cooperation with more than 2,000 organizations across the country to provide reliable, impartial scientific information to resource managers, planners, and customers. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, contribute to sound economic and physical development of the nation's natural resources, and enhance the quality of life by monitoring water, biological, energy, and mineral resources.