before source removal, and a few years later in November 1994. The concentration contours were developed from numerous monitoring wells and multilevel groundwater samplers. By the later time, much of the region between the source removal area and transect B contained less than 10 μg/liter naphthalene, which is below the New York State Department of Environmental Conservation drinking water standard. Phenanthrene—another dissolved constituent from coal tar—has a similar fate. By November 1994, no phenanthrene was detected in any of the monitoring wells.

Four types of evidence indicate the involvement of microorganisms in the attenuation of naphthalene and phenanthrene:

1. depletion of oxygen at the center of the plume, where naphthalene concentrations were highest, and an inverse relationship between oxygen and phenanthrene concentrations throughout the plume;

Excavation operations that successfully removed the source of coal tar waste contamination in South Glens Falls, New York. After the source was delineated, the subsurface was stabilized with sheet pilings, excavated, and filled with clean sandy material. SOURCE: Courtesy of Dr. E. F. Neuhauser, Niagara Mohawk Power Corp.