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This article describes the use of kriging for optimizing data collection and utility in a regional ground‐water investigation of the Potomac‐Raritan‐Magothy aquifer system in central New Jersey. Kriging was used to (1) estimate the altitude of an aquifer surface, (2) estimate hydraulic conductivities from point data, and (3) estimate the associated kriged errors. The selection of locations for additional data collection, based on the kriged errors, was effective in terms of improving the aquifer surface data base. In another application, hydraulic conductivity values were kriged, first using equal weights, then unequal weights to account for the reliability of the data. The weighting values that were used for unequal weighting were estimated by an analysis of variance. Although inclusion of the data reliability in the kriging will increase the kriged errors, the accuracy of the range of uncertainty in the interpolated values also increases.

Solutes were determined for 26 pore‐water samples extracted from Tertiary and Cretaceous core material from a 1,320‐foot‐deep test borehole at Freehold, New Jersey. The cored materials are sediments that form a multilayered aquifer system of seven aquifers and eight confining units in the New Jersey Coastal Plain. The sediments are of marine origin in the upper 650 feet of the core and primarily nonmarine below 650 feet. Total concentrations of silica and major anions (SO4‐2 and Cl‐) and cations (Ca+2, Mg+2, total Fe, Mn+2, Na+, and K+) in the pore‐water samples varied with depth. Three core intervals are defined by water‐ chemistry variations, the environment of deposition (marine or nonmarine), and the degree of alteration (weathered or unweathered) of the units. Calcium, magnesium, sulfate, and total‐ion concentrations were greater in the midcore (unweathered marine) interval than in the upper (weathered marine) and lower (fluviodeltaicsilicate) intervals of the core. Generally, pore‐water chemical types in confining units were distinct from those found in aquifers–particularly in the midcore interval. In this interval, observed variations in pore‐water chemistry in part reflect carbonate dissolution and cation exchange reactions common in Coastal Plain sediments. However, high concentrations of sulfate in unweathered marine sediments indicate novel processes may be important factors influencing pore‐water chemistry in confining units.

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Sediment and pore‐water samples from Tertiary and Cretaceous strata in the New Jersey Coastal Plain were collected from cores from Freehold Township, Monmouth County; Howell Township, Monmouth County; and from Clayton Township, Gloucester County. These strata form a multilayered aquifer system in which upper units are marine origin and lower units are predominantly nonmarine. Concentrations of major constituents in pore‐water samples from confining units and aquifers were highly variable: calcium (1.7–660 mg/I), magnesium (0.3–140 mg/l), sulfate (1.52200 mg/l), and dissolved inorganic carbon (9–290 mg/l); with large differences between marine confining units and aquifers. Where the aquifers are unconfined and oxic, well waters in the Potomac‐Raritan‐Magothy aquifer system in the northern Coastal Plain have higher concentrations of nitrate, chloride, and dissolved oxygen. In areas where the aquifer system is confined and anoxic, there are higher concentrations of sulfate and bicarbonate. Differences in bicarbonate concentrations between two wells (12 and 67 mg/l) along a regional flow path can be caused by mixing of water in a nonmarine aquifer with leached sulfate‐enriched, marine confining‐unit water, and subsequent reduction of sulfate. Bacterially mediated organic carbon oxidation, iron reduction, and sulfate reduction, and ion‐exchange reactions may explain constituent variations. Bacteriological assays of core sections from the Howell and Clayton Township coreholes showed viable sulfate‐reducing bacteria as deep as 558 feet below land surface. Sediments from a depth of 210 feet showed populations of sulfate‐reducing bacteria of 103–l06 organisms per gram of soil.