Summary of major issues and findings--
Lower Susquehanna River Basin Study Unit
Water from 30 percent of the wells sampled and about 20 percent of the streams sampled would exceed the U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Level (MCL) for nitrate-nitrogen of 10 mg/L as N (milligrams per liter as nitrogen) if not properly treated before use as drinking water (p. 8).
- Water from wells in agricultural areas underlain by limestone and crystalline bedrock commonly exceeded the USEPA MCL for nitrate in drinking water. Water from wells in urban areas underlain by limestone bedrock and in forested and agricultural areas underlain by sandstone and shale had nitrate concentrations that seldom exceeded the MCL.
- Streams in agricultural areas underlain by limestone had nitrate concentrations that, if not lessened by appropriate treatment before use as drinking water, commonly would exceed the USEPA MCL. Streams in other areas did not.
- The highest nitrate concentrations in streams were generally in the winter and spring.
Nitrate concentrations in the Susquehanna River at Harrisburg were generally less than 2 mg/L, which is considerably below the MCL for nitrate in drinking water of 10 mg/L (discussed above) (p. 8).
Concentrations of nitrate at these levels, when multiplied by the large flows of the Susquehanna River, contributed large amounts of nitrate to the Chesapeake Bay when compared to other rivers entering the bay.
Streams from agricultural areas underlain by limestone bedrock contributed large amounts of nitrate per unit area to the Lower Susquehanna River when compared to streams in areas with other land uses and bedrock types.
The main nitrogen source in the Study Unit is animal manure used as an agricultural fertilizer (p. 9).
The data collected in this study provide a baseline to evaluate the effectiveness of the Pennsylvania Nutrient Management law, which requires concentrated animal operations to develop and have approved nutrient-management plans by 1998.
Manure-application rate may be the most important factor controlling nitrate concentrations in streams in agricultural basins underlain by limestone.
The concentration of total nitrogen in the Susquehanna River's inflow to the Chesapeake Bay has decreased in the 1985-96 time period (p. 11).
- The concentration of nitrate (one component of total nitrogen) has remained unchanged during this period.
- The specific environmental circumstances that would explain the lack of change in nitrate concentration during a time of downward trends in total nitrogen could be related to the nitrate in streams that originates in ground water or to other nonpoint sources.
Concentrations of pesticides in water from the wells and streams sampled rarely exceeded levels established as drinking-water standards (p. 12-14).
- Although drinking-water standards, human-health advisory levels, and aquatic-life criteria were rarely exceeded, these criteria have not been established for many of the pesticides that were sampled for. In addition, mixtures and degradation products were not considered in developing the human-health criteria. Therefore, only a limited range of potential effects of the occurrence of pesticides in drinking water has been assessed.
- On the basis of analyses of 577 samples collected from 169 shallow wells and 155 streams, pesticides were frequently detected in ground water and streams; usually, more than one pesticide was detected at a time. More than 60 percent of well-water samples in which pesticides were present contained more than one detectable pesticide.
- The most commonly detected pesticides were the herbicides used primarily on corn: atrazine, metolachlor, simazine, prometon, alachlor, and cyanazine.
- Detections of pesticides in water were related to pesticide use, pesticide-leaching potential, and bedrock type. Pesticides were most likely to be detected in samples from agricultural and urban areas. Limestone areas were far more likely to have pesticides in well water than areas underlain by sandstone and shale.
- Seasonal variations in pesticide concentrations in water from streams are affected by the timing of pesticide application and the type of bedrock. The highest concentrations of pesticides in streams were seasonal pulses lasting up to several months.
- Concentrations of pesticides in the Susquehanna River were generally less than 1 part per billion. The pesticides detected in the Susquehanna River were similar to those detected in water from streams in agricultural areas throughout the Lower Susquehanna River Basin.
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 (p. 15).
Fecal coliform and Escherichia coli, bacteria that indicate contamination from human or animal feces, were detected 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. 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 other causes.
- The presence of bacteria in water from rural wells is one of the most important water-quality issues related to human health in the Study Unit.
None of the concentrations of the volatile organic compounds detected in samples from wells used as drinking-water supplies exceeded the MCLs or Lifetime Health Advisory Levels established by the USEPA (p. 16).
- In the Great Valley near Harrisburg, Pa., volatile organic compounds were detected more frequently in an urban area than in an agricultural area.
Radon, a product of the radioactive decay of uranium, is present in ground water throughout the Lower Susquehanna River Basin (p. 17).
- Radon activities in 86 percent of the 165 ground-water samples tested for radon were greater than a previously proposed standard, now under review by the USEPA, of 300 pCi/L (picocuries per liter, a measurement of radioactivity).
- More than 30 percent of the 165 ground-water samples tested for radon contained radon at activities greater than 1,000 pCi/L. The area of the Study Unit underlain by crystalline rocks of the Piedmont Physiographic Province had the highest median ground-water radon activities, but variation in radon activities within most subunits is large.
Correlations were found between the concentrations of trace elements in streambed sediments and the concentrations in livers of bottom-feeding fish for only 3 of 11 elements regarded as common contaminants (p. 18).
- The highest concentrations of arsenic, beryllium, cadmium, cobalt, iron, manganese, nickel, selenium, and zinc in streambed sediments were at sites affected by mine drainage.
No organic contaminants were detected in whole fish at levels considered harmful to human health; however, some contaminants in streambed sediment were detected at levels harmful to aquatic life (p. 19-21).
- Organic compounds were detected in whole-body fish tissue and streambed sediment at all 20 sites sampled, which represented a variety of settings. Of the 28 compounds analyzed for, 12 were detected. Although some of the detected compounds are known human health risks, an interagency work group on fish-tissue contaminants reviewed the data collected by the USGS, compared the data to U.S. Food and Drug Administration action levels, and concluded that no public health advisories were warranted for the fish species (white sucker or smallmouth bass) collected at any of the sampling sites.
- PCBs in fish tissue were associated with urban and industrial land use. DDT and chlordane and their degradation products in fish tissue showed an association with agricultural land use.
- The fish-tissue data indicate that DDT and chlordane have degraded over time and that no recent influx of these compounds has occurred. At four sites, concentrations of total DDT or total chlordane in streambed sediment exceeded USEPA Tier 1 guidelines for protection of aquatic life. Tier 1 guidelines for total PCBs were not exceeded at any of the sites.
- Concentrations of semivolatile organic compounds in streambed sediment exceeded the USEPA Tier 1 guidelines for protection of aquatic life at 4 of the 21 sites.
Fish communities inhabiting the seven streams in long-term monitoring basins were related to the bedrock type (p. 22-23).
- The habitat characteristics that proved most influential in defining fish communities were mean channel width, mean water temperature, mean canopy angle, and suspended sediment.
- Fish populations were healthier in the three freestone streams than in the four limestone streams. The fish population was influenced by agricultural activity in the agricultural settings, but the influence of agriculture on fish communities is related to habitat degradation rather than nutrients in the water.