The distributions of common dissolved constituents, trace metals, and volatile organic compounds in ground water near Philadelphia, Pennsylvania, and Camden, New Jersey, are influenced by local geology and land use. Many common dissolved constituents are more concentrated in ground water beneath urban and industrial areas than in water beneath suburban and undeveloped and agricultural areas. Industrial and urban land uses commonly are situated in the outcrop of the aquifer where vulnerability of ground water to contamination is increased by the lack of overlying confining strata. Ground water beneath undeveloped and agricultural lands is least affected by trace metal or volatile organic contamination, but differences in water quality as related to other land-use categories are less clear and vary according to the chemical constituent considered.
Only about 20 percent of all water samples contained detectable concentrations of trace metals or volatile organic compounds; as a result, determinations of relations between water quality and land use are difficult. Variations in detection limits further complicated data interpretation. The proportion of water samples in which concentrations of constituents were below detection compared to water samples in which concentrations were present in detectable amounts is the most useful statistic in determining relations based on trace-metal or volatile organic-compound data. Iron and Manganese concentrations are elevated in water throughout the Coastal Plain aquifer in Pennsylvania, but the elevated concentrations cannot be adequately explained on the basis of land use alone.