STRUCTURAL CONTROL AND GROUNDWATER DEVELOPMENT IN THE NEW JERSEY HIGHLANDS

A cooperative effort between New Jersey Geologic Survey personnel, a geophysical/geologic consulting firm and a geotechnical engineering firm has provided an informed utility director with high-yielding wells in crystalline rocks in an area of New Jersey not really known for its over abundance of groundwater.

Schooley’s Mountain is a northeasterly-trending ridge of the New Jersey Highlands underlain by crystalline metamorphic rocks of Middle Proterozoic age. Utilizing a Very Low Frequency (VLF) Electromagnetic (EM) method, potential fracture zones were mapped by orienting the VLF traverses essentially perpendicular to existing geologic structures based on available and recently-updated geologic information.

Sites for drilling test production wells were selected on the basis of interpreted fracture zones that were identified close to the mapped projections of several regional geologic structures, using both published and unpublished data. The Reservoir and Turkey Brook faults essentially bracket the Schooley’s Mountain area and enclose an area underlain by rocks of granitic affinity. These pyroxene granites are quartz-poor and tend toward quartz monzonite. VLF data have been previously used by the authors to “fine-tune” the available geologic information at sites that were still available in a fast-growing, up-scale suburban area.

Data are presented in regard to the results of short-term aquifer tests in a number of the recently-drilled test wells. Yields ranging from 120 to 300 gallons per minute (gpm) and specific capacities ranging from 0.75 to 3.3 gpm per foot of drawdown have been obtained. Comparisons are made to hydrogeologic data from comparable lithologies away from structural boundaries.

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[1] Geoscience Services, 3 Morristown Rd., Bernardsville, NJ 07924 (geoserv@hotmail.com).

[2] Advanced Geological Services, 3 Mystic La., Malvern, PA 19356 (d_jagel@advancedgeo.com).

[3] Washington Twsp. Mun. Utilities Auth., 46 E. Mill Rd., Lang Valley, NJ 07853 (pcostic@wtmua.org).