New Jersey Water Science Center
Great Falls of the Passaic River at Paterson, N.J.
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Aquifer Flow and Chemistry
Project Title: NJ13701 Aquifer Flow and Chemistry
Based on previous findings, the emphasis is:
1. Pore-water from confining unit clay: (10 samp) FOCUS: Sr, Cl? isotope
2. Aquifer water: (6 samp) FOCUS: age dating for recharge computations
3. Solids in core material: (6 samp) FOCUS: role of iron in redox cycle
Statement of Problem
Water-quality problems (radium, mercury) in southern NJ in the unconfined Kirkwood-Cohansey aquifer increase needs for high quality water from confined aquifers. The Piney Point aquifer is the shallowest confined aquifer in the area. Effects of increased pumpage on water quality are not known. Sodium bicarbonate-chloride type waters dominate the confined aquifers of the NJ Coastal Plain. Recent studies of the confining units in the NJ Coastal Plain demonstrate that the confining units contain Ca-Na-SO4 type waters, providing SO4 to the aquifers. The reduction of SO4 and the resulting H+ (acid) production drives shell dissolution and divalent cation-exchange which produce NaCO3-type water in the aquifer. Demonstration of this principle in NJ provides indirect chemical evidence that pore water from confining units is leaking into the aquifers as suggested by regional flow models. More direct proof is provided by analysis of Sr isotopes of confining unit and aquifer waters and solids, showing solutes in the aquifer originate from confining units. These observations have generated important questions for aquifers where head has significantly declined. The questions include: 1) Does leakance increase with declining heads? Over what time frames? Can change in leakance be monitored via changes in water quality? 2) How can our geochemical understandings improve our understanding of regional hydrology? Can Sr isotopes (or other isotopes: C, Cl, O and H) be used to understand flow paths or determine the length of time it has taken water to arrive from land surface (age dates)? 3) Iron concentration varies widely in both confining units and the aquifers. Does iron mineralogy in confining units explain variation in aquifer and pore water quality?; and 4) Is there a source of Cl in confining units?
Strategy and Approach
The installation of borehole and observation wells throughout Southern NJ provides opportunity to study the chemical evolution of water in both aquifers and confining units. The upcoming drilling programs offer opportunity to study aquifers where significant drawdown has occurred: the Piney Point and the PRM aquifers. The aquifers cannot afford degradation of water quality because of the limited availability of water for supply. The boreholes and regional sampling programs allow for documentation of chemistry of the confining units - major elements, isotopes, and sedimentary chemistry -coupled with that of the confined aquifers.