ABSTRACT
Elevated levels of naturally occurring radionuclides in ground water are associated with uranium enrichment in the Newark Basin of New Jersey. The factors controlling the concentration, distribution, and migration of these radionuclides in ground water are being studied by the U.S. Geological Survey, in cooperation with the New Jersey Department of Environmental Protection, Division of Water Resources. Ground water from 260 sites in the basin was analyzed to determine the distribution of gross alpha-particle radiation. High levels of gross alpha radiation (greater than the 15 picocuries per liter maximum contaminant level established by the U.S. Environmental Protection Agency) were found predominantly in ground water near the contact of the Lockatong and Passaic Formations along the southeastern part of the basin, and in the Hopewell and Flemington fault blocks, where these formations are repeated.
The source of the radioactivity has been determined by borehole geophysical testing and analysis of lithologic cores. Natural gamma-ray logs of wells near the Lockatong-Passaic contact depict thin but laterally extensive zones of high radioactivity. Analysis of lithologic cores of these zones indicates that uranium is concentrated in black mudstones that contain 48abundant pyrite mineralization. The color and mineralogy of the radioactive beds suggests that the uranium was deposited in a reducing environment. This is consistent with the geochemical behavior of uranium precipitating in reducing environments and mobilizing in oxidizing environments.
The uranium-bearing black mudstones, which are common in the Lockatong and lower Passaic Formations, are the primary source of radionuclides in the ground water of the basin. The upper part of the Passaic Formation, which is composed primarily of red shale and sandstone, contains ground water with relatively low concentrations of radionuclides. Localized and widely scattered occurrences of elevated radioactivity in ground water are found in the sandstone of the Stockton Formation. Ground water from the basalt and diabase aquifers in the basin contains low levels of radionuclides.
