Groundwater in the Newark basin aquifer flows mainly through discrete zones that maintain water parallel to strike and bed dipping, while flow perpendicular to strike is restricted, imparting anisotropy to the flow field of groundwater. The SUTRA finite element model was used to represent the structure of the mother rock in the aquifer by spatially varying the orientation of the hydraulic conductivity tensor to reflect variations in strike and bed immersion. The directions of maximum and average hydraulic conductivity were oriented parallel to the bed, and the direction of minimum hydraulic conductivity was oriented perpendicular to the bedding. Groundwater flow models were prepared to simulate local flow in the vicinity of the Spring Valley field well and regional flow through the Newark basin aquifer.
The Newark basin contains sedimentary rocks deposited as alluviums during the Upper Triassic and is one of a series of basins that developed when the Mesozoic rifting of the supercontenite Pangea created the Atlantic Ocean. The westward dipping basin is filled with intercalated facies from coarse grain to fine-grained rocks that were intruded by diaasses associated with Jurassic volcanism. The aquifer of the Newark basin is bounded to the north and east by the Palisades threshold and to the west by the Ramapo fault. Although the general immersion of the bed is towards the fault, the mapping of the conglomerate beds indicates that the rocks are bent in wide and sinclinal anticlines. An alternative and more uniform pattern of regional structure, based on interpolated strike and dive measures from various sources, has also been proposed. Two models of groundwater flow (A for the first type of mother rock structure and B for the latter type) were developed to represent these alternative representations of the rock bed structure.
Transient simulations were calibrated to reproduce the measured water level recoveries in a 9.3 mi2 area surrounding the Spring Valley well field during a 5-day aquifer test in 1992. The models represented a rock mass of 330 feet thick vertically divided into 10 equally spaced layers and calibrated by non-linear regression. The results of the B model improved the observed water level recoveries with an estimated hydraulic conductivity of 9.5 ft / day, specific storage of 7.6 x 10-6 ft-1 and Kmax: Kmin anisotropy ratio (parallel hydraulic conductivity to bed: perpendicular to bed) of 72: 1. The error of the model was 50 percent greater in model A because the assumed structure did not coincide with the actual bed strike in this area.
The steady-state simulations of the regional flow through the modeled extension 85.4-mi2 of the Newark basin aquifer represented both the alluvial aquifer under the Mawah River and the fractured rock bed. The rock mass was divided into two aquifer units: an upper unit 500 feet thick divided into 10 equidistant layers through which most of the groundwater is assumed to flow and a lower unit divided into 7 layers with increasing thickness. The models were calibrated by non-linear regression to mean water levels measured in 140 wells from August 2005 to April 2007. Simulated water levels using the two models were similar and generally coincided with those observed, and the average Estimated recharge with both models was 19 inches per year for the simulated period. The estimated transmissivity parallel to the bed strike (1,100 ft2 / d) was uniform in two transmissivity zones (T) in model A, but in model B the transmissivity of a high zone T (1,600 ft2 / d), delineated from the aquifer, was slightly higher than in a low T zone (1,300 ft2 / d). The anisotropy of Kmax: Kmin was estimated at 58: 1 in model A and 410: 1 in model B, so the flow rate perpendicular to bed is lower in model B than in model A.
The groundwater age distributions simulated with models A and B are similar and indicate that the majority of surface groundwater (225 feet below the surface of the rock) is between 5 and 20 years old, with younger water ( 5 years or less) water (over 100 years) in lowland discharge areas near the Hackensack River and Saddle River. The two simulated distributions differ in some areas where younger water is simulated with model A. Effective porosity (2 x 10-2) was estimated by comparing simulated groundwater ages with those previously estimated on the basis of tritium dating / helium (3H / 3He). The wellfield capture zones delineated for main well fields are generally elongated parallel to the presumed strike of the bed layers and are affected by the simulated potentiometric surface, the current channel drainage network and the catch zones of adjacent well fields. Capture zone sizes range from 1.9 mi2 (1,200 acres) for well fields with the highest average withdrawal rates (1,300 gal / min) to less than 0.04 mi2 (25 acres) for well fields with the lowest rates of 80 gal / min. Grassland flows in the Pascack stream and the Nauraushaun stream have probably been reduced due to groundwater withdrawals because the catchment areas of several well fields overlap with these watersheds.
The effects of annual and monthly changes in recharge and groundwater withdrawals in water levels and streams were assessed using two-period transient flow simulations: a period of 47 years from January 1960 to December 2006 and a three year period from January 2000 to December 2003. The simulations included a range of order of magnitude in specific storage (Ss) and saturated and variably saturated conditions. Simulated monthly water levels with the smallest Ss value (7.6 x 10-6 ft-1 of the Spring Valley water level recovery trial simulation) fluctuate at about 15 feet in the lowlands and 85 feet in the highlands and at about 3 feet and 20 ft using the largest Ss value, while measured water levels fluctuated by 7 feet and 13 feet, respectively. Hydrographs of annual simulated groundwater levels indicate a tendency to decrease groundwater levels from 1960 to 2006 in upland areas where water levels decreased by 15 to 20 feet. Although the groundwater flow models described in this report are accurate enough to estimate the water budget and to delineate the wells that are being pumped, larger scale models of smaller scale would be needed to more accurately simulate the movement of contaminants, the interference between adjacent wells and the local pumping effects in the discharge of current.