Bedding‐plane partings, particularly those enlarged by stress relief, tend to provide principal ground‐water flow pathways which are often overlooked. In order to identify them, the use of a proper conceptual model of the bedrock aquifer system and appropriate methods of hydrogeologic characterization are necessary. Several pervasive bedding partings were identified at a study site located within a dipping sequence of mudstone and shales, typical of the Passaic Formation in the Newark Basin of New Jersey. These bedding fractures constitute the discrete aquifer units of a multiunit, leaky bedrock aquifer system. One such unit of exceptional transmissivity (the “Raritan unit”) was identified and selected for a detailed characterization. Results of three short‐duration pumping tests verified the continuity and relatively uniform transmissivity of the Raritan unit over distances exceeding 1,500 feet. Significant hydrochemical differences between the various aquifer units at this 100‐acre site were found to be consistent with the multiunit structure of the bedrock aquifer system. A similar pattern can be observed in regional hydrochemical data recently published by others. The principal finding, that a few bedding fractures dominate ground‐water flow at many sites in the region, has a major implication on hydrogeologic characterization requirements for the water supply, well‐head protection, and aquifer remediation projects in the Newark Basin and similar areas of sedimentary bedrock.

Fractured shales of the Brunswick Formation provide a major aquifer in the most industrialized region of New Jersey. Numerous cases of ground water contamination have been documented in this formation. However, effectiveness of monitoring and remediation efforts is often hampered by the use of inappropriate concepts regarding ground water flow controls in this complex aquifer system. One such concept presumes that near‐vertical fractures parallel to the strike of beds provide principal passages for the flow and produce an anisotropic response to pumping stress. Field evidence presented in this paper confirms that the Brunswick Formation hosts a gently dipping, multiunit, leaky aquifer system that consists of thin water‐bearing units and thick intervening aquitards. The water‐bearing units are associated with major bedding partings and/or intensely fractured seams. Layered heterogeneity of such a dipping multiunit aquifer system produces an anisotropic flow pattern with preferential flow along the strike of beds. Within the weathered zone, the permeability of the water‐bearing units can be greatly reduced. The commonly used hydrogeologic model of the Brunswick as a one‐aquifer system, sometimes with vaguely defined “shallow” and “deep” zones, often leads to the development of inadvertent cross‐flows within monitoring wells. If undetected, cross‐flows may promote contaminant spread into deeper units and impair the quality of hydrogeologic data. Hydrogeologic characterization of the Brunswick shales at any given site should be aimed primarily at identification of the major water‐bearing and aquitard units. Recommended techniques for this characterization include fluid logging and other in‐well tests.

Under‐exploration of complex hydrogeologic settings may lead to the occurrence of short‐circuiting internal flows in monitoring wells. Susceptible settings include fractured formations with large thickness and monotonous lithology. The occurrence of internal flow may distort flow pattern and induce contaminant migration. Monitoring data from the affected wells may be misinterpreted if the flow is unaccounted for. In order to identify and measure well bore flow in several deep monitoring wells at a site, a technique of in‐well tracing was used. The vertical movement, dispersion, and dilution of an injected saline slug was tracked by periodic electrical conductivity logging. Combining internal flow measurements with baseline conductivity and temperature logs provided estimates of the quality and origin of water entering well bores from major transmissive fractures. Identified locations of these fractures coincided with locations of larger fractures seen on video logs; only a few fractures were significant for the flow. Relative distributions of heads and fracture permeabilities in a well with internal flow could be evaluated easily, but determination of their absolute values would require measurement of static heads. In data quality, cost, and feasibility, the in‐well slug tracking compares favorably with conventional fracture characterization methods, such as coring, packer permeability testing, flowmeter and other specialized geophysical logging.

Down‐hole temperature and electrical‐conductivity probes are attractive logging devices for use in monitoring wells, because they are readily available, relatively inexpensive, and allow for rapid measurements. Benefits of such logging are illustrated by examples from several small sites in complex hydrogeologic settings. Interpretation of the logs provided information on the effectiveness of well purging, aquifer heterogeneities and the rates of ground water movement, leaks and cross‐flows within wells, and locations of transmissive fractures in bedrock wells. Thus the logs offered an inexpensive means of acquiring valuable field information to supplement the geologic, potentiometric and chemical data collected during construction or subsequent investigation of the wells.

A large subsurface pool of waste solvent product, consisting primarily of 1,1,1‐tichloroethanc and carbon tetrachloride, was encountered during investigations at an industrial site in northern New Jersey. In the 1950s the product was discharged through a settling chamber directly below the shallow water table. Eventually the product accumulated within elongated depressions of erosional surface of varved clays at depths 10 to 15 feet below grade. The host sediment, line to medium sand, was overlain by line sand and silt. The delineated area of pooled DNAPLs covered 2750 feet2, and the maximum pool thickness exceeded 3 feel. The primary recovery involved pumping product from nine wells. Each recovery well was equipped with a sump extending into the clay, which enabled the system to keep the product pumping level below the bottom of the pool. A total of 3495 gallons of solvent product was recovered over two years. Nearly half of this volume was produced by two wells placed at the lowest points of the pools. Postpumping sampling of the former pools indicated that 43 to 94 percent of the pooled solvent mass was removed during the primary recovery. Average initial product salutation within the pool was estimated at 53.2 percent of the total porosity measured at 31 percent. Average residual saturation after the primary product recovery was 3.7 percent of the total pore volume. To test the feasibility of residual product recovery, an experimental secondary recovery was undertaken. Using sheet piling, a 506 feet2 lest cell was constructed inside the former DNAPL pool. The cell featured a central recovery well, six peripheral wells, and monitoring probes. I he selected sequence of secondary operations included partial dewatering. hot water injection, final dewatering, and thermally enhanced vapor extraction (TVE). During six weeks of the secondary recovery operations. 87.9 gallons of product were removed, of which 72 percent was from TVE. 25 percent from hydraulic mobilization effects. and 3 percent from dissolution of residuals. Confirmatory soil sampling showed an average reduction of residual contamination by 93.4 percent in comparison to the concentration of residuals prior to the secondary recovery. For the lest cell, a combined total solvent recovery of 99.6 percent was achieved. This high recovery exceeded DNAPL recoveries expected or achieved in other field‐scale attempts.