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From The Home Front To The River Front, USGS Updates Water-Quality Information

April 16, 1998

The results of two U.S. Geological Survey water-quality studies in the Lower Susquehanna and Potomac River Basins provide a message that hits close to home for rural residents that drink water from private wells: Owners of rural wells in these two basins, part of the Chesapeake Bay watershed, need to ensure their water supplies are safe to drink.

The USGS studies found high levels of nitrate and high counts of bacteria in ground water from wells used for household supply in several rural areas. The study results underscore the need for awareness that untreated ground water may not always be safe to drink.

There was good news, however, about these same rural wells. Concentrations of pesticides and other organic contaminants in the water from the wells did not exceed levels established by Federal and State agencies as drinking-water standards.

Of the well-water samples in which a pesticide was present, nearly 70 percent contained more than one detectable pesticide. This is a significant new finding from the USGS studies.

"Human activities on the land surface, such as application of fertilizers and manure on croplands, have a significant effect on the concentration of nitrogen that ends up in the ground water or streams," said Scott Ator, USGS Hydrologist and principal author of the Potomac River Basin report. Ator's colleague, Bruce Lindsey, USGS Hydrologist and principal author of the Lower Susquehanna report, added, "Animal manure, used as an agricultural fertilizer, and commercial fertilizers are major sources of nitrogen and phosphorus in the Chesapeake Bay watershed. We now have good baseline data to measure changes as the new Pennsylvania law for nutrient management goes into affect this year."

"The old adage `Too much of a good thing' applies in certain areas," Lindsey said. Nitrogen in manure and fertilizers added to agricultural land is essential for plant growth; however, a concentrated animal operation can produce more manure than the crops grown on that farm can use. The numbers of concentrated animal operations are increasing in the basins.

Moving from the home front to the river front, the studies also provide an extensive baseline of information against which planners and water managers can measure the success of strategies for reduction of nutrients and toxics in tributaries to Chesapeake Bay. Fish, streambed-sediment, and water samples were used to assess the occurrence of contaminants.

Contaminants in streambed sediment at some sites were detected at levels potentially harmful to aquatic life. Trace metals and long-banned organic contaminants are present in streambed sediment in the Lower Susquehanna and Potomac Rivers and their tributaries and have been incorporated into the food chain. These metals and contaminants were detected in clam and fish tissues. The use of PCBs, DDT, and chlordane has been banned or restricted for nearly 20 years, but these contaminants are still being detected in rivers and streams. The USGS cautioned that the fish were collected and analyzed to determine if contaminants were present, not to determine if the fish were safe to eat.

Being more specific, Ator said, "Mercury contamination from an industrial source near Waynesboro, Va., has led to measurable concentrations of mercury in sediment as far as 170 miles downstream on the Shenandoah River near Harpers Ferry, W. Va., even though the use of mercury at the Waynesboro site ended in 1950."

The studies of the Lower Susquehanna and Potomac River Basins, two of the largest watersheds that drain into Chesapeake Bay, were conducted by the USGS National Water-Quality Assessment (NAWQA) Program. The full-color reports summarize USGS studies that began in 1992 and are written to convey the technical findings to a wide audience including water managers, policy makers, other scientists, and the public. Details on the results of the studies and information on how to obtain copies of the reports are provided in the attached background statement.


The full-color reports summarize USGS studies that began in 1992 in the Lower Susquehanna and Potomac Basins. Single copies of the reports, Water Quality in the Lower Susquehanna River Basin, USGS Circular 1168, and Water Quality in the Potomac River Basin, USGS Circular 1166, can be ordered free of charge from:

U.S. Geological Survey
Branch of Information Services
Box 25286
Denver Federal Center
Denver, Colorado 80225-0286
Telephone: (303) 202-4700

A limited supply is available at the USGS office in the Harrisburg area at 840 Market Street, Lemoyne, Pennsylvania 17043; telephone (717) 730-6900 and the USGS office in Baltimore at 8987 Yellow Brick Road, Baltimore, Maryland 21237; telephone (410) 238-4200.

For additional information about USGS programs and activities in Pennsylvania, Maryland, and other states in the Chesapeake Bay watershed, please visit our web site at:

Highlights of USGS Circulars 1166 and 1168:

  • Assessing the occurrence of nitrogen, phosphorus, and a broad suite of pesticides was a major focus of the Lower Susquehanna and Potomac River studies.

  • Concentrations of nitrate, a form of nitrogen, are of particular concern where large amounts of manure or other fertilizers are applied to areas that are underlain by limestone. Limestone areas comprise about 18 percent of the land area in the Lower Susquehanna and Potomac Basins. Forty percent (48 of 119) of water samples from wells in agricultural areas underlain by limestone contained nitrate concentrations that exceeded the U.S. Environmental Protection Agency's Maximum Contaminant Level for drinking water of 10 milligrams per liter. The limestone bedrock has features such as large fractures, caverns, and sinkholes that allow nitrate to move rapidly from the land surface to the ground water. In limestone areas, ground water from springs made up a large part of the water in streams. Thus, high nitrate concentrations were found in spring-fed streams.

  • Streams in agricultural areas underlain by limestone, like many streams in Lancaster County, Pa., and in the Great Valley of Virginia, West Virginia, Maryland, and Pennsylvania, have some of the highest concentrations of nutrients when compared to 18 other NAWQA studies across the country. Mill Creek in Lancaster County and Bachman Run in Lebanon County, Pa., were two streams studied in the Lower Susquehanna Basin that have high concentrations of nitrate. Overall, in limestone and non-limestone areas, 21 percent (58 of 274 wells) of the wells and 11 percent (31 of 272 stream samples) of the streams sampled had nitrate concentrations greater than 10 milligrams per liter.

  • Concentrations of nitrogen and phosphorus have changed over the past 10 to 20 years in the rivers where they flow into Chesapeake Bay. The amount of nutrients delivered to Chesapeake Bay is dependant upon the amount of rainfall. For example, 1996 was an exceptionally wet year and flood waters from these two rivers in 1996 carried large amounts of nutrients and suspended sediment to Chesapeake Bay. Therefore, the reported trends were adjusted for these types of variations in streamflow. Despite an estimated 44-percent increase in population in the Potomac River Basin from 1970 to 1990, total-phosphorus concentrations in the Potomac River at Washington, D.C., have decreased since 1979 and nitrogen concentrations have apparently stabilized. There are downward trends in both total-phosphorus and total-nitrogen concentrations for the Susquehanna River at Conowingo, Md. Different forms of nitrogen, however, show differing patterns in long-term trends in both rivers. Nitrate shows no change or upward trends for the Susquehanna and Potomac, respectively.

  • In addition to the nitrogen and phosphorus results, the USGS researchers conducted the most extensive surveys to date of pesticides in the Chesapeake Bay watershed. On the basis of analyses of about 1,100 samples collected from nearly 300 wells and 300 streams, pesticides commonly were detected in water, streambed sediment, and tissue from fish or clams from streams draining urban and agricultural lands. An urban stream, Accotink Creek in the Potomac Basin near Annandale, Va., had pesticide concentrations among the highest of all sites sampled in 20 NAWQA studies across the country. Pesticides were found more frequently in streams than in ground water, but concentrations were generally very low in both. Pesticide degradation products were frequently detected as well. One or more of the herbicides atrazine, metolachlor, and simazine were detected in 9 out of 10 streams and 5 out of 10 wells.

  • Concentrations of pesticides in water from the wells and streams sampled rarely exceeded levels established as drinking-water standards. For many of the pesticides that were found, human-health criteria standards have not yet been set. The information derived from the USGS studies on the occurrence of individual pesticides and the occurrence of mixtures of pesticides and their breakdown products are important to managing pesticide use and understanding how these chemical compounds occur in the Bay watershed.

  • Contaminants have been incorporated into the food chain. Fish can accumulate and concentrate contaminants that are very hard to detect in samples of water. Selected species of fish were collected and analyzed to determine if contaminants were present, not to determine if the fish were safe to eat. USGS methods examined whole fish, not fillets that people eat. Concentrations in the whole body of fish and the edible portions (fillets) are not directly comparable. Nevertheless, the levels for total chlordane, total DDT, or total PCBs that must be exceeded in the edible portion before consumption advisories are issued were not exceeded in the whole-body tissues at any of the sampling locations.

  • Very few volatile organic compounds (VOCs) were detected in water from wells based on studies of ground-water quality in the Lower Susquehanna Basin. The VOCs detected are present in commonly used industrial solvents and degreasers or are components of gasoline. The good news is that none of the concentrations of the VOCs detected in samples from 129 wells used as drinking-water supplies exceeded the Maximum Contaminant Levels or Lifetime Health Advisory Levels established by the U.S. Environmental Protection Agency. The investigation in the Great Valley near Harrisburg, Pa., showed that VOCs were detected more frequently in an urban area compared to an agricultural area.

  • Bacteria in water from wells used for rural household supply is an important water-quality issue related to human health. A reconnaissance study of bacteria in well water was completed for the Lower Susquehanna Basin study. Total coliform bacteria were detected in water from nearly 70 percent of the household wells sampled, indicating that the water should not be used for drinking without treatment. Fecal coliforms and Escherichia coli, bacteria that indicate contamination by human or animal feces, were found in water from 25 and 30 percent, respectively, of the wells tested. Few household wells from which water was sampled were grouted, and few had sealed, sanitary caps at the top of the casing. Lack of these protective features can enable the entry of bacteria into well water. With annual testing recommended by county extension agents, owners of rural wells should keep an eye on the bacterial quality of their well water. Follow-up to this reconnaissance is needed; it is uncertain whether bacteriological contamination of well water is caused by inadequate protection of wells from surface runoff, septic-system failure, application of animal manure to fields, or a combination of these and other causes.

* * * USGS * * *

US Geological Survey

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