Hydrogeology and Groundwater Occurrence
What the exam tests
Hydrogeology questions connect New Jersey's physiographic provinces to well yield, water levels, and contamination risk. You need to read a site's geology and predict how a well will behave.
Provinces and aquifers
- Valley and Ridge (northwest): folded sedimentary and carbonate rocks; karst in limestone yields large but unpredictable wells.
- Highlands: fractured crystalline bedrock; yields come from fractures, not rock matrix. Wells are sensitive to drought and to nearby pumping.
- Piedmont: red shale, sandstone, and basalt; the Brunswick and Lockatong formations yield modest domestic supplies; the Passaic Formation is a common target.
- Coastal Plain: layered sand, silt, and clay; confined aquifers such as the Kirkwood-Cohansey, Englishtown, and Mount Laurel-Wenonah are major supplies. Saltwater intrusion is a coastal risk.
Core concepts
Porosity is storage; permeability and transmissivity describe flow. A confined aquifer has a potentiometric surface and a lower storage coefficient than an unconfined aquifer. Pumping creates a cone of depression; specific capacity (gpm per foot of drawdown) is a quick productivity index. Recharge in the Coastal Plain comes largely from precipitation on the outcrop area, not through confining layers.
Worked example
Two domestic wells are 400 feet apart in the Highlands. Well A pumps 10 gpm and Well B's water level drops 15 feet. The observation is interference, not a new fracture. A 24-hour pump test in A shows specific capacity falling from 0.8 to 0.3 gpm/ft, suggesting limited fracture storage. The fix is not to drill deeper by default; it is to evaluate fracture intersections and set the pump to avoid pulling the water level below the producing zone.
Traps
Equating depth with yield in bedrock. Confusing a confined aquifer's potentiometric surface with the water table. Ignoring saltwater intrusion near the coast when increasing pumping. Treating a single water-level measurement as a baseline without barometric and pumping corrections.