Post on 11-Jan-2016
Piedmont and Blue Ridge
Crystalline rocks with glacial cover
Paleozoic history of southern Piedmont
From Hatcher
http://geoweb.gg.utk.edu/Geology/Faculty/Hatcher/Hatcher.html
Metamorphic and igneous rock
Sandstone and diabase in rift basins
Limestone
Piedmont
Chimney rock
Blue Ridge Province
flow through fractures
Transition
Fractured metamorphic
and igneous rock
Saprolite
Gneiss, schist bedrock
Granite or other intrusive bedrock
Distinct transition
Gradational transition
Storage and transmission
properties
High porosity
Sy?
porosity
Low storage
10-5 10-4 cm/s
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.
PorositySpecific
yieldK
cm/sec
Granitic Gneiss 0.015 0.007 3.47E-08
Mica Schist 0.028 0.017 1.74E-09
Hornblende-feldspar gneiss 0.007 0 1.74E-09
Quartzite 0.022 0.012 1.39E-09
Amphibolite 0.02 0.017 1.39E-09
Laboratory determinations of properties of crystalline rocks.
from Randall and others 1966
Saprolite thickness
Typically 50 ft, but variable 10-100 ft
w.t. 20-60 ft bgs
Frx zones in valleys
Flat-lying frx
Saprolite thickness
Greatest over valley or highland? Could be either
Ground watersheds
Open Hole
Multi-level completion
Important: Exception to the Conceptual Model
Specific capacity
Well Performance and Lineaments
Lineaments
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 hill
Well yields in different rock types and regions in
the Piedmont
15-30 gpm typical
Roughly 20 gpm
Effects of well depth and diameter on yield in the Piedmont. Based on Daniels
Glaciated crystalline rocks in northern
Appalachians
Other Hydrogeologic Settings in the Piedmont
Stockton Fm. Lockatong Fm. Passaic Fm. Orange Mt. Basalt Feltville Fm. Preakness Basalt Towaco Fm. Hook Mt. Basalt Boonton Fm. Conglomerates Palisade sill
Newark Basin, NJ
Mesozoic Basins• Sandstone aquifers• Shale confining unitsRedbeds in the Hartford Basin, Conn
Conglomerate
Basalt
Arkose
Carbonate rock aquifers
Water Chemistry Reminder
• Major Cations: Na+, K+, Ca2+, Mg2+
• Major Anions: HCO3-, Cl-,SO4
2-
• TDS: Total Dissolved SolidsMCL= 500 mg/l Values: Fresh < 1000 mg/l; brackish 1000-10,000; saline; 10,000-100,000 mg/lSeawater: 35,000 mg/l
• Hardness: Ca and Mg scaled to Ca on a meq basis– Soft water < 60 mg/l total hardness– Use water softener= 80-100 mg/l– Very hard >150 mg/l
Milliequivalent
• Charges/volumes
Conc mgmillimol
e valence charge meq millimole charge
literMole weight mg liter
Water quality in Crystalline Rock aquifers
Crystalline rock Triassic BasinCarbonate rock
meq/L
Crystalline Rock
Triassic Basins
Carbonate Aquifers
SC, GA, Al =100 Mgpd