WATER-QUALITY CONDITIONS IN A NATIONAL CONTEXT

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Seven major water-quality characteristics were evaluated for stream sites in each NAWQA Study Unit. Summary scores for each characteristic were computed for all sites that had adequate data. Scores for each site in the Lower Susquehanna River Basin were compared with scores for all sites sampled in the 20 NAWQA Study Units during 1992-95. Results are summarized by percentiles; higher percentile values generally indicate poorer quality compared with other NAWQA sites. Water-quality conditions at each site also are compared to established criteria for protection of aquatic life. Applicable criteria are limited to nutrients and pesticides in water and semivolatile organic compounds, organochlorine pesticides, and PCBs in sediment. (Methods used to compute rankings and evaluate aquatic-life criteria are described by Gilliom and others, in press.)

EXPLANATION

RANKING OF STREAM QUALITY RELATIVE TO ALL NAWQA STREAM SITES--Darker colored circles generally indicate poorer quality. Bold outline of circle indicates that one or more aquatic life criteria were exceeded.

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Surface-water long-term monitoring sites and subunit numbers

NUTRIENTS in water

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Comparisons of scores based on nitrate, phosphorus, and ammonia concentrations in streams showed that the agricultural and urban sites were among the highest of all NAWQA Study-Unit sites (above the 75th percentile). Animal manure and fertilizer are the primary sources of the nitrogen. The The forested site was above the 25th percentile nationally, which may be related to atmospheric deposition of nitrogen or the small part (less than 15 percent) of the basin in nonforested land use.
 

PESTICIDES in water

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The scores based on total herbicide concentrations and total insecticide concentrations were higher than the national median at the two agricultural sites. The score for total herbicides and total insecticides was slightly lower than the national median at the urban site.
 

ORGANOCHLORINE PESTICIDES and PCBs in streambed sediment and biological tissue

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TRACE ELEMENTS in streambed sediment

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Scores based on trace-element concentrations in streambed sediments at the five long-term monitoring sites where sediment was collected were above the national median for all NAWQA Study Unit sites. The concentrations of trace elements in sediment were not well correlated with concentrations in fish liver tissue for 8 of the 11 trace elements, indicating that the elements in the sediment may not have been bioavailable.
 

SEMIVOLATILE ORGANIC COMPOUNDS (SVOCs) in streambed sediment

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STREAM-HABITAT DEGRADATION

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Stream-habitat scores at six of the seven sites were ranked between the 25th and 75th percentile nationally. Bachman Run had the poorest stream-habitat score because of high bank erosion and minimal vegetative bank stability; it was ranked as one of the most degraded of all NAWQA Study-Unit sites.
 

FISH-COMMUNITY DEGRADATION

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Fish communities at five of the seven sites were ranked between the 25th and 75th percentile nationally. East Mahantango Creek exhibited a diverse and healthy fish community and was ranked as having one of the least degraded fish communities of all NAWQA Study-Unit sites. The fish community at Mill Creek scored poorly because of the high percentage of pollution-tolerant and omnivorous species and the high incidence of anomalies; it ranked among the poorest of all NAWQA Study-Unit sites.

CONCLUSIONS

In the Lower Susquehanna River Basin Study Unit, compared to the other NAWQA study units:

• Nutrient concentrations in streams are high and, in agricultural areas, often would exceed drinking-water standards if the water was not filtered and treated before use as a public-water supply.
• Pesticide concentrations are near the national median but would rarely exceed drinking-water standards.
• Concentrations of PCBs and organochlorine pesticides in fish tissue at some sites are among the highest; however, an interagency work group concluded that no human-health advisories for fish consumption were warranted.

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Five major water-quality characteristics were evaluated for ground-water studies in each NAWQA Study Unit. Ground-water resources were divided into two categories: (1) drinking-water aquifers, and (2) shallow ground water underlying agricultural or urban areas. Summary scores were computed for each characteristic for all aquifers and shallow ground-water areas that had adequate data. Scores for each aquifer and shallow ground-water area in the Lower Susquehanna River Basin were compared with scores for all aquifers and shallow ground-water areas sampled in the 20 NAWQA Study Units during 1992-95. Results are summarized by percentiles; higher percentile values generally indicate poorer quality compared with other NAWQA ground-water studies. Water-quality conditions for each drinking-water aquifer also are compared to established drinking-water standards and criteria for protection of human health. (Methods used to compute rankings and evaluate standards and criteria are described by Gilliom and others, in press.)

All of these subunits represent both shallow ground-water areas and drinking-water aquifers. For national comparison purposes, these subunits were compared to the summary scores from other drinking-water aquifers.

RANKING OF GROUND-WATER QUALITY RELATIVE TO ALL NAWQA GROUND-WATER STUDIES--Darker colored circles generally indicate poorer quality. Bold outline of circle indicates one or more standards or criteria were exceeded.

(14,603 bytes) Ground-water subunits for Land-Use Studies and Subunit Surveys

RADON

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Radon activities in limestone and crystalline subunits in the Piedmont Physiographic Province were among the highest of all NAWQA Study Units. Activities in the remaining subunits were slightly above the 50th percentile when compared to other subunits representing drinking-water aquifers in all NAWQA Study Units.

NITRATE

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Nitrate concentrations in agricultural areas underlain by limestone bedrock were among the highest of all NAWQA Study Units, and numerous drinking-water samples exceeded the drinking-water standard for nitrate. Ground water in the subunits underlain by crystalline bedrock also had high nitrate concentrations. Ground water in the urban subunit and the subunit underlain by sandstone and shale had nitrate concentrations closer to the median when compared to all subunits representing drinking-water aquifers in all NAWQA Study Units.

DISSOLVED SOLIDS

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Scores based on concentrations of dissolved solids were above the 50th percentile for all of the subunits underlain by limestone. The subunits underlain by crystalline bedrock and the subunit underlain by sandstone and shale had scores for dissolved solids that were among the lowest of all the subunits representing drinking-water aquifers in all NAWQA Study Units.

VOLATILE ORGANIC COMPOUNDS (VOCs)

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Scores based on the frequency of detections of VOCs in the Great Valley limestone urban subunit and the Piedmont limestone agricultural subunit were among the highest of subunits representing drinking-water aquifers in all NAWQA Study Units; however, the frequency of detection was much higher in the urban subunit. No VOCs were detected in the subunits in the Appalachian Mountains, which is the more rural part of the Study Unit. The Piedmont crystalline subunit and Great Valley carbonate agricultural subunit also had scores that indicated a low frequency of detections of VOCs when compared to national data.

PESTICIDES

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Pesticides were detected frequently in all the subunits except for the Appalachian Mountain sandstone and shale subunit. The limestone agricultural, limestone urban, and crystalline agricultural subunits were ranked as having some of the highest pesticide-detection frequencies of subunits representing drinking-water aquifers in all NAWQA Study Units; however, none of the detections of pesticides in water from any of the wells sampled exceeded drinking-water standards.

CONCLUSIONS

In the Lower Susquehanna River Basin Study Unit, compared to the other NAWQA study units:

• Nitrate concentrations in waters from household wells in agricultural subunits underlain by limestone are some of the highest and represent a human-health concern.
• The number of pesticide detections was high for subunits underlain by limestone and crystalline bedrock. Pesticide concentrations did not exceed USEPA MCLs for drinking water.