Statistical evaluation was conducted on the ten most common organic compounds found in Nassau County groundwater during 1987. The three most common chemicals found in the groundwater were tetrachloroethylene, trichloroethylene, and 1,1,1-trichloroethane. Few samples were found to contain chloroform in Nassau County (3% of drinking water samples, and 6% of non-drinking water samples). Surprisingly, bromoform was found more frequently than chloroform (11% of the drinking-water samples). However, the concentrations of bromoform were very low, usually less than 5 ppb, well below the allowed limits of 50 ppb in New York state. In addition to the frequency of occurrence of organic pollutants found in the water samples, the profile of concentration range was also studied. A possible source for bromoform and its related compounds is discussed.