Geology of Regional Aquifers
Focusing on the Northeast
Aquifer types by geologic
material
• Sand and gravel (unconsolidated and semiconsolidated)
• Sandstone
• Interbedded sandstone and carbonate
• Carbonate (limestone and dolostone)
• Volcanic rocks (usually basalt)
• Crystalline bedrock (granite, gneiss, etc.)
Unconsolidated sand and gravel
•
•
•
•
•
•
•
•
generally unconfined.
high hydraulic conductivity.
susceptible to contamination.
Quaternary coastal plain deposits.
fluvial deposits.
basin-fill deposits.
glacial outwash.
lowland blanket deposits.
Semi-consolidated sand and gravel
• Developed along Atlantic and Gulf coastal plains.
• Unconfined updip (landward), confined downdip (seaward).
• Interbedded with clay-rich confining units forming stacked.
confined aquifer systems.
• Moderate to high hydraulic conductivity.
Sandstone
•
•
•
•
•
Developed in strata of depositional basins.
Gently dipping to horizontal, very widespread.
Generally confined.
Mostly secondary porosity in fractures and joints.
Low to moderate hydraulic conductivity.
Sandstone and carbonate
• Interbedded sandstone and carbonate - marine shoreline
deposits.
• Solution cavities in carbonates provide high yields of water.
• Hydraulic conductivity is moderate to high.
Carbonate Rock (marble, limestone and dolostone)
• Generally confined to the eastern US.
• Widely variable hydrologic characteristics, depending on
development of secondary porosity due to solution.
Volcanic Rock (generally basalt)
• Generally confined to the western US.
• Widely variable hydrologic characteristics, depending on
development of secondary porosity.
• Basalt is usually most productive, due to development of
columnar joints during cooling.
columnar jointing
Other Rock (generally low permeability rock)
• Sedimentary strata = siltstones, shales, muddy sands.
• Crystalline strata = igneous and metamorphic bedrock.
• Crystalline strata may form important low-yield aquifers for
rural regions.
• Secondary porosity
Aquifers in the northeastern US
• Surficial aquifers - Glacial deposits
– Valley-fill glacial deposits
– Morainal glacial deposits
• Coastal plain aquifers
• Consolidated bedrock aquifers
– sandstone
– carbonate rock
– crystalline bedrock
Glacial Deposits
Surficial Aquifers
Surficial Aquifers
Glacial Valley Fill
Created by glacial ice flowing
and then melting in valleys.
Deposits:
• Ground moraine till
• Ice contact deposits
• Outwash - stratified drift
• Meltwater lake clays
Aquifers are limited in size and
locally confined by lake clays.
Recharge by overland flow and
baseflow from upland streams.
Corning
Valley-fill
Aquifer
Corning Valley-fill Aquifer
Corning Valley-fill
Aquifer
Well yields Corning Aquifer
Surficial Aquifers
Moraine Deposits
•
•
•
•
•
•
Long Island
Cape Cod
Till
Outwash
Marine clays
Lake clays
Cape Cod
Terminal moraine
Stratified drift (outwash delta), Caumsett State Park, Long Island
Coastal Plain Aquifers
• Cretaceous to Pleistocene sedimentary layers.
• Gently seaward dipping.
• Alternating sand / gravel and clay deposits
formed through transgressions and
regressions.
Deposition
Subsidence
Coastal Plain
Coastal Plain
Transgression
Deposition
Shoreline moves
Shoreline
landward moves
landward
Sea Level
Sea Level
Rise
Rise
Crust Subsides
Bedrock Aquifer Regions