USING AQUIFER TEST SIMULATIONS TO INVESTIGATE HETEROGENEITY AND GROUND-WATER FLOW IN FRACTURED SEDIMENTARY ROCKS AT THE NAVAL AIR WARFARE CENTER, WEST TRENTON, NJ

The former Naval Air Warfare Center (NAWC), West Trenton, NJ, is underlain by northwest dipping fractured mudstones within the Triassic Lockatong Formation of the Newark Basin. The subsurface geology has been extensively characterized using geophysical logs from about 70 boreholes, coring, and drill cuttings. This characterization has enabled construction of a three-dimensional geologic framework consisting of cyclic sequences of four mudstone types: thin black fissile mudstone beds, thin grey laminated beds, thick grey massive beds, and thick red massive beds. The framework delineates 44 distinct beds bounded by a southeast dipping fault contact. Water level data, hydraulic testing, and the distribution of dissolved chlorinated solvents suggest that: bedding plane fractures within the fissile and laminated mudstones are the primary pathways for ground-water flow, cross-bed fractures also might be important flow paths, and the fault behaves as a flow barrier. Numerical models of a 72-hour aquifer test are used to examine these hypotheses. During the test, one well was pumped at a constant rate and drawdowns were measured at 24 observation wells open to one or a few mudstone beds at various depths. The test is simulated using the USGS MODFLOW-2000 code, with model layers aligned with dipping beds. Simulations and calibrations are used to determine hydraulic property distributions that are consistent with the geologic framework (e.g., permeability variation by mudstone type) and that produce a reasonable fit to the aquifer test data. In models that meet these criteria, simulated and hypothesized flow paths are compared, to check and as necessary refine hypotheses about the permeability distribution and ground-water movement. The improved insight gained through these simulations about hydrogeologic controls on ground-water flow is an important step in ongoing research at NAWC to understand transport and remediation of chlorinated solvents in fractured-rock aquifers.