2. FACTORS OF GROUNDWATER QUALITY
3. CHANGES IN GROUNDWATER QUALITY
4. OVERVIEW OF MONITORING POINTS
6. DATA SUMMARIES
1. Maps of groundwater basins
2. Summary data by groundwater basin
3. Box plots by groundwater basin
4. Summary data by geologic unit
5. Selected analyte trends for basins in southeastern Pennsylvania
This report summarizes groundwater quality data collected under the Pennsylvania Department of Environmental Protections (DEP) Fixed Station Network (FSN) and Ambient Survey groundwater monitoring program. The report covers data collected from 1985 to 1997 for selected groundwater basins, most of which are located in southcentral and southeastern Pennsylvania. Groundwater basins were selected based on a 1985 prioritization of basins. Monitoring points were typically homeowner wells or springs, and occasionally included untreated water from public water supplies and industrial wells.
Groundwater samples from 1,089 wells and springs were analyzed for 27 different analytes including basic inorganic constituents, nutrients and metals. Nearly 10,000 sample results were reviewed and compared to existing groundwater quality standards such as maximum contaminant levels. Water quality data from 940 of the monitoring points were analyzed based on lithology, land use types, and additional information such as well depth and geographic location. Land use descriptions and well depths for 149 monitoring points in the southwestern region of Pennsylvania were not collected.
Trend analysis was performed on water quality data from 475 monitoring points that were located in southcentral and southeastern Pennsylvania. The Kendall Tau nonparametric test was used to test for trends at the 95 percent confidence level.
The geographic extent of the sampling has been limited to selected basins in the southern half of the state. In general, the highest priority basins were sampled, based on the 1985 prioritization of Pennsylvanias 478 groundwater basins. The groundwater samples that were analyzed represent some of the top 100 priority basins. These basins were ranked as deserving a higher concern regarding groundwater quality.
Results indicate that groundwater quality is typically good. This is despite the sampling of high priority basins, which likely biases the data and presents a more negative picture of the overall groundwater quality of Pennsylvania. Some exceedances of drinking water standards are the result of naturally elevated concentrations of substances such as iron, total dissolved solids (TDS) and manganese or low pH. Concentrations and trends of some parameters such as nitrate, chloride and total hardness suggest that groundwater is being affected by human activities.
For pH, TDS, nitrate, iron, manganese and turbidity, 10 to 25 percent of the samples analyzed for each constituent exceeded groundwater quality (drinking water) standards. For the metals cadmium and lead, two to three percent of the samples exceeded their respective standards. For nitrite, chloride, sulfate, arsenic, barium, chromium, copper, zinc and mercury, less than one percent of the samples for each constituent exceeded an associated drinking water standard.
Groundwater quality is most obviously related to geology and land use. Other factors probably exert lesser influences that are often difficult to discern. Box plots were generated that show the range of concentrations by groundwater basin for each analyte.
The trend analyses suggest that groundwater quality is undergoing some change. Although natural shifts probably can account for some of the variation, it is most likely that human activities are affecting the groundwater quality on a regional scale. Analytes with upward trends at more than 10 percent of the 475 monitoring points that underwent trend analysis included alkalinity, TDS, nitrate, total hardness, calcium, magnesium, sodium, potassium and chloride. Analytes with downward trends at more than 10 percent of the 475 monitoring points included pH, nitrate, magnesium, chloride and sulfate.
Exact causes of the groundwater quality trends are difficult to determine. Different areas of the state are obviously under different stresses and only general inferences can be made from the data. The presence of natural shifts in groundwater quality (from precipitation trends or cycles) may have a background presence on some of the changes in groundwater chemistry. Nevertheless, notable downward trends in nitrate and sulfate at many monitoring points may be the result of the reduction in sources of nitrate from agricultural areas (fertilizers), onlot septic systems and atmospheric deposition. Increases in TDS, chloride, calcium, potassium, total hardness and sodium at many monitoring points may be the result of increased nonpoint source pollution such as road salting and sprawling paved developments and suburbs.
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