Water Quality in the Connecticut, Housatonic, and Thames River Basins, Connecticut, Massachusetts, New Hampshire, New York, and Vermont, 1992-95

Table of contents || Previous section

Summary of Major Issues and Findings

Toxic contaminants have accumulated in some Study Unit streambed sediments and fish.

Concentrations of polychlorinated biphenyls (PCBs) in streambed sediments and fish in the Housatonic River were among some of the highest detected in NAWQA Study Units across the Nation. Concentrations of trace elements and organic contaminants in streambed sediment and fish were highest in the southern part of the Study Unit (Massachusetts and Connecticut). Because of the presence of these contaminants, fish consumption advisories have been issued for a number of rivers and lakes throughout the Study Unit. These advisories recommend limiting the number of fish of certain species that should be consumed by people, particularly by children and pregnant women.

Nutrient (nitrogen and phosphorus) concentrations are a concern for surface-water quality.

The large amount of nitrogen entering Long Island Sound from streams, precipitation, and coastal communities has stimulated algal blooms. Decay of the algae then produces low dissolved-oxygen conditions in the Sound, creating poor habitat for fish and other marine animals. Nitrogen and phosphorus concentrations are highest in urban streams, primarily because of wastewater discharges from sewage-treatment facilities.

Pesticides were frequently detected in Study Unit streams.

The herbicides atrazine, metolachlor, prometon, and simazine, and the insecticides diazinon and carbaryl were the most frequently detected compounds. Concentrations of atrazine, metolachlor, and simazine were highest in surface water draining from agricultural areas. Concentrations of prometon, diazinon, and carbaryl were highest in surface water draining from urban areas. However, current drinking-water standards were not exceeded. None of the pesticides were detected at concentrations greater than the U.S. Environmental Protection Agency's maximum contaminant level (MCL) or the health advisory limit (HAL), and few pesticide concentrations exceeded 1 microgram per liter (1 µg/L). Current drinking-water standards, however, do not include some detected pesticides (or breakdown products), and do not include consideration of more than one pesticide in the water. Thus, the actual health concern posed by these results is somewhat uncertain.

Several classes of contaminants were detected in ground water.

These contaminants included pesticides, volatile organic compounds (VOCs), and nitrate. Twenty-four different pesticides (or their breakdown products) were detected in shallow ground water beneath the Study Unit. Atrazine, prometon, and simazine were the most commonly detected pesticides in ground water. VOCs were detected in 70 percent of the shallow ground-water samples collected in urban areas. Methyl tert-butyl ether (MTBE), a gasoline additive, was the most frequently detected VOC, and chloroform, a byproduct of water disinfection, was the second most frequently detected. Median nitrate concentrations in shallow ground water beneath agricultural fields (3.8 mg/L) were nearly 30 times higher than background concentrations (0.14 mg/L).

Some contaminant MCLs were exceeded in ground water.

The pesticides atrazine and ethylene dibromide were detected at concentrations greater than their MCLs in a few samples collected from agricultural areas. The VOCs--tetrachloroethene, trichloroethene, benzene, and naphthalene--exceeded their MCLs in some samples collected from urban areas. Nitrate concentrations exceeded the MCL in 15 percent of the samples of shallow ground water collected in agricultural areas.

Radon is present in ground water across the Study Unit.

Radon is a naturally occurring, colorless, odorless radioactive gas derived from uranium. Exposure to radon has been recognized as a health risk, primarily as a cause of lung cancer. Radon concentrations exceeded the previously proposed limit of 300 picocuries per liter in 97 percent of water samples collected from bedrock supply wells, and 88 percent of water samples collected from the shallow monitoring wells in the Study Unit.

U.S. Geological Survey Circular 1155

Table of contents || Previous section

Suggested citation:
S.P. Garabedian, J.F. Coles, S.J. Grady, E.C.T. Trench, and M.J. Zimmerman, 1998, Water Quality in the Connecticut, Housatonic, and Thames River Basins, Connecticut, Massachusetts, New Hampshire, New York, and Vermont, 1992-95: U.S. Geological Survey Circular 1155, on line at <URL:>, updated August 23, 1998 .

This page is a subpage of <URL:>
Email questions and comments to
Last modified: Sun Aug 23 17:37:01 1998