Presentation is loading. Please wait.

Presentation is loading. Please wait.

Aquifers of the U.S. Fractured RockAquifers of the U.S.

Similar presentations

Presentation on theme: "Aquifers of the U.S. Fractured RockAquifers of the U.S."— Presentation transcript:

1 Aquifers of the U.S. Fractured RockAquifers of the U.S.

2 Fractured Systems Crystalline rock; Piedmont, Shield, Batholiths Carbonates; FL, Valley and Ridge, Mid- continent, MT, NV, TX Basalts; Columbia River Plateau, Snake River Plateau, Hawaii Felsic volcanics; Basin and Range Sandstone; Mid-continent, CO Plateau, VandR Till (confining unit); mid-continent

3 Important Information Background: Location, Lithology, Tectonic history Fracture and matrix characteristics Storage and transmission properties Flow system Distribution of major fluxes (Recharge, Baseflow, ET, Precip, Stormflow, Runoff) Water Quality

4 Piedmont and Blue Ridge Crystalline rocks with glacial cover

5 Paleozoic history of southern Piedmont From Hatcher Penobscottian Taconic Acadian Alleghanian






11 Metamorphic and igneous rock Sandstone and diabase in rift basins Limestone Folded and faulted sedimentary rock


13 Fault zone, tectonic Thrust fault, tectonic Sheet joints, young Fabric=bedding + tectonic Includes complex folds Faults and joints; tectonic + young? Topography and weathering Fabric and fractures


15 Transition Fractured metamorphic and igneous rock Saprolite

16 Gneiss, schist bedrock Granite or other intrusive bedrock Distinct transition Gradational transition

17 Storage and transmission properties High porosity S y ? porosity Low storage 10 -7 10 -6 m/s

18 Saprolite sampled at different depths. Measure density and chemical composition. S.G. decreases from 2.1 in rock to 1.6 in shallow saprolite. S.G. decreases as minerals are altered and mass is removed. 0.5 gm/cc removed during weathering. Chemical concentrations indicate S.G. change largely due to weathering of feldspar to kaolinite as a two-stage reaction.


20 Red clay, mica, quartz. Local lenses of quartz and mica. Relic foliation absent (bioturbation?). to 1-3 m depth. Original fractures healed with clay infilling, new frx possible—dessication, tree roots, burrows. High lateral stress from surface processes. B-horizon Clay, quartz, mica. Relic fabric expressed =saprolite Pervasive alteration of feldspar and FeMgs. Volume decrease due to removal of material during weathering Major fractures filled with clay, Fe+Mn oxides Chemical alteration penetrating wall rock of hydrologically active fractures. Fresh rock common. Fractures in fresh rock. Some minerals deposited in fractures, minor alteration of fracture walls. Feldspar, quartz, mica, amphibole as gneiss and schist. Max. compression horizontal--deep origin of rock. Reactivity of pore water decreases Most feldspar and FeMg altered Volume change. High lateral stress from parent rock relaxes. Max compression vertical? Apparent fracture toughness depends on degree of saturation and clay content (increases above water table).  Importance of water table position in weathering? Moderate alteration, some feldspar and FeMgs present. Open fractures common. Horizontal fractures common. Dipping frx present Most fractures, least weathering = highest K. 5-15 m to w.t w.t. +/- 0.5-2 m seasonal 15-30 m to intact rock, based on drilling



23 Saprolite thickness Typically 50 ft, but variable 10-100 ft w.t. 20-60 ft bgs Frx zones in valleys Flat-lying frx


25 Saprolite thickness Greatest over valley or highland? Could be either

26 Groundwatersheds





31 Exception to the Conceptual Model

32 What about other exceptions? Hydrogeological conceptual model = guide, not gospel

33 Lineaments

34 Specific capacity Characterizing the effects of lineaments on well performance How to characterize performance?

35 Effects of lineaments on well yields in the Piedmont Other effects of location on well yield Factor of 2 to 7 difference in yield Factors from 3 to 25 between valley and upland

36 Well yields in different rock types and regions in the Piedmont 15-30 gpm typical Roughly 20 gpm

37 Effects of well depth and diameter on yield in the Piedmont. Based on Daniels


39 Crystalline Rock Triassic Rift Basins Fractured sedimentary and volcanic rock Carbonate Aquifers Major Ion Content


41 Glaciated crystalline rocks in northern Appalachians

42 Other Hydrogeologic Settings in the Piedmont



45 Stockton Fm. Lockatong Fm. Passaic Fm. Orange Mt. Basalt Feltville Fm. Preakness Basalt Towaco Fm. Hook Mt. Basalt Boonton Fm. Conglomerates Palisade sill


47 Newark Basin, NJ Mesozoic Basins Sandstone aquifers Shale confining units Redbeds in the Hartford Basin, Conn Conglomerate Basalt Arkose



50 Carbonate rock aquifers

51 Water quality in Crystalline Rock aquifers

52 Crystalline rock Triassic Basin Carbonate rock meq/L

53 SC, GA, Al =100 mgpd



Download ppt "Aquifers of the U.S. Fractured RockAquifers of the U.S."

Similar presentations

Ads by Google