Occurrence and concentrations of volatile organic compounds in shallow ground water in the Lower Susquehanna River Basin, Pennsylvania and Maryland

This report presents the results of a regional assessment of volatile organic compounds (VOC's) in ground water from six sampling areas within the Lower Susquehanna River Basin. The sampling areas, selected to represent aquifers where ground water is used as a drinking water supply, include four areas underlain by limestone, one area underlain by crystalline bedrock, and one area underlain by interbedded sandstone and shale. The land use is rural in five areas and urban in one area. Samples were collected in 1993-95 from 118 wells ranging from 30 to 226 feet deep.

Analyses for 60 VOC's at detection levels ranging from 0.05 to 0.2 mg/L (micrograms per liter) reveal the presence of 24 compounds. The compounds were present in water from 32 of the 118 wells. Methyl tert-butyl ether was the most commonly detected compound. Concentrations of methyl tert-butyl ether, found in 16 of the 118 wells, ranged from 0.11 to 51 mg/L. Chloroform was the second most commonly detected compound. The highest concentration detected in a water sample was 61 mg/L of chloroform. None of the detections in samples from wells used as drinking water supplies exceeded the Maximum Contaminant Levels or Lifetime Health Advisory Levels established by the U.S. Environmental Protection Agency. However, the 51 mg/L of methyl tert-butyl ether, detected in water from a monitoring well, is in the 20 to 200 mg/L range proposed for a Lifetime Health Advisory Level.

The occurrence of VOC's in limestone aquifers in the Great Valley near Harrisburg, Pa., is influenced by land use. VOC's occur more frequently in the urban area than in the agricultural area. Within the urban area, analyses of samples from wells, springs, and a spring-fed stream show contaminated ground water discharging from springs and flowing into the stream.