HYDROGEOLOGIC FRAMEWORK BASED ON VAN HOUTEN CYCLIC STRATIGRAPHY, TECTONICS, AND WEATHERING, NAVAL AIR WARFARE CENTER, TRENTON, NEW JERSEY

The former U.S. Naval Air Warfare Center (NAWC), Trenton, New Jersey, is within the early Mesozoic Newark rift basin and is underlain by northwest dipping strata of the Nursery Road, Byram, and Ewing Creek Members of the Lockatong Formation. Parts of the site are highly contaminated with trichloroethylene. Clay, silt, and organic matter were deposited during the Triassic in about 15 Van Houten cycles. A full cycle is composed of a basal carbon-rich mudstone, middle laminated dark-gray mudstone, and upper massive red or light gray mudstone. Strata within each cycle responded differently to postdepositional diagenesis, tectonics, and weathering. The geologic events selectively cemented the sediment to varying levels of competency and then formed non-hydraulically conductive, faults, partings, and joints in the deeply buried rock. Offloading preferentially allowed the fracture features to open thus creating multiple water-bearing and semi-confining units. The thin, black, carbon-rich, mudstone was rheologically the weakest strata and the locus of regional strata-bound fracturing during Jurassic compressional tectonics. Similarly, laminated, dark gray, mudstone was prone to develop bedding partings and closely spaced joints whereas the massive red and gray mudstone formed more widely spaced joints. Uplift and offloading removed lithostatic pressures to permit the bedding faults in the black mudstone to be hydraulically active at depths of about 200 ft below land surface and progressively more hydraulically active at shallower depth. Weathering from land surface downward preferentially converted the fracture rock hydrology to porous media hydrology. The black and dark gray mudstone weathered much more completely to form clay semi-confining strata. The light gray and red massive mudstone are less weathered, therefore, they form a network of vertical and bedding fractures giving the shallowest strata the hydraulic appearance of a porous media. Detailed knowledge of the geologic and hydrogeologic framework of the NAWC site enables a better understanding of pathways for movement of water and contamination in the secondary porosity; storage and release of contaminates from the primary porosity; and an improved understanding of the bio-geo-chemical aspects of the site.