Occurrence of dissolved organic carbon in selected ground-water samples in the United States

A study of nonvolatile DOC (dissolved organic carbon) in ground water was conducted to establish base levels of naturally occurring dissolved organic materials. Samples of ground water were obtained at 100 sites in 27 States. Samples were pressure filtered at the time of collection and immediately frozen on dry ice. DOC concentrations were determined by wet oxidation of organic carbon to carbon dioxide which was measured by an infrared analyzer. The DOC concentrations ranged from less than the 0.1 mg/l limit of detection to 15 mg/l. Concentrations of DOC were directly correlated with specific conductance and alkalinity, but did not correlate with pH. The DOC mean concentration was 1.2 mg/l; however, the DOC median value was lower at 0.7 mg/l. Differences in DOC concentration for various types of consolidated rock aquifers were slight; for example, median DOC values for sandstone, limestone, and crystalline rock aquifer types ranged from 0.5 to 0.7 mg/l. No difference was found in the median DOC concentration between shallow (<200 ft; 61 m) and deep (>200 ft) sand and gravel aquifers.