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 Pennsylvania's 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. 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.