3/27/08
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Groundwater and Geology
This week– Sediments
• Unconsolidated clasticsediments
• Semi- consolidatedsediments
• Lithified sediments
– Sandstones
– Carbonates
– Igneous & MetamorphicRocks
• Extrusives
• Intrusives
• Metamorphic
– Fractures
2(Schwartz & Zhang, 2003)
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http://capp.water.usgs.gov/gwa/
http://nationalatlas.gov/natlas/Natlasstart.asp
Click here
Click here
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Unconsolidated Clastic Sediments
Permeable
lenses of sand
and gravel within
glacial till show
awide variation in
bed thickness,
grain size, and
sorting of grains.
North Dakota.(USGS)
(Ritzi,WSU)
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(Schwartz & Zhang, 2003)
Blanket Sand and Gravel AquifersFluvial Deposits: Riverine Alluvial Aquifers:
Meandering River: Braided River:
NASA: MadagascarNASA: Indus River, July 2003
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Braided-stream Deposits
Coarse, braided-stream deposits showing disconnected sand lenses (S) and a
variety of cobble-dominated facies ranging from poorly-sorted massive units
(Gm), to moderately-sorted horizontally-bedded units (Gh) and trough
crossbedded units (Gt). Heavy lines identify bounding surfaces between
depositional sequences. Prime Earth quarry northwest of Boise, Idaho. For
scale, quarry face is approximately 12 m high.Boise State Center for Geophysical Investigation of the Shallow Subsurface
http://kihei.boisestate.edu/hydrogeophysical_research_site.htm
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(~50% of total groundwater pumpage)
BA
Sand/
Silt SandSilt, Clay
BA
Point bar
deposits
Natural levees
Backswamp
River
Gravel
(sand)
Alluvial River Valleys
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Fluvial systems - Meandering rivers
Allen & Allen (1990)
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Deposition builds up the river and
eventually it breaks through the
natural levee and changes
course—channel avulsions
Usually a wide variety of sediments are found in
any borehole—complex layering of high and low K
deposits
Buried channel gravels will provide best well yields
Alluvial River Valleys
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(Fitts, 2002)
Alluvial River Valleys
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Often in the Midwest:
Pleistocene
Coarse Sand and Gravel
(glacial outwash)
Holocene alluvium
mixed deposits
Alluvial River Valleys in the Midwestern US
Mix of materials is good—sand, gravel give good
T,Sy, clay, silt give good S, so drawdowns are low.
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Example: Lower Mississippi River Valley
Overbank clays
Outwash sands and gravels Filled braided channels
Meandering channel depositsRiver
Loess
silts
Alluvial River Valleys in the Midwestern US
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Evolution of Mississippi River fill through the late Quaternary
Allen & Allen (1990)
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Alluvial River Valleys
Water quality
– usually good— Si and K can be high
• SiO2 15 - 30 mg/L
• K 5 – 10 mg/L
– If buried swamp deposits, reduced conditions
cause high Fe2+, Mn, H2S
– May have high TDS in arid regions with
evaporite minerals
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Alluvial River Valleys
• Water Development Considerations– Advantages of wells in alluvial valleys
• Ease of drilling
• Shallow water tables
• Highly productive wells
• Induced infiltration from rivers and wetlands
– (esp. Midwest and Southeast)
• Shallow wells near rivers provide “free” treatment of water.
• Good water quality
– Disadvantages• Ease of pollution
• Induced infiltration (water rights issues in the West)
• Doctrine of conjunctive use
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www.windows.ucar.edu/.../sed_alluvial.html
(Schwartz & Zhang, 2003)
Fluvial Deposits: Alluvial Fans
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http://ktwu.washburn.edu/journeys/
High Plains (Alluvial Fan) Aquifer
http://ktwu.washburn.edu/journeys/
Statement from US Senator Jeff Bingaman:
“Currently, the Ogallala Aquifer is being mined at a much
higher rate than it is being recharged, and is showing
alarming declines in many areas. In just the last two decades,
large portions of the aquifer show drops - between 10 to 40
feet - in the water table. That kind of drop reduces the
productivity of wells and greatly increases pumping costs. It
also poses a serious threat to the long-term viability of the
agricultural economy served by the aquifer.”
http://www.saveourwatersupply.org/ogallala/index.html
(Schwartz & Zhang, 2003)
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(Fitts, 2002)
Basin-fill Aquifers (Western US)
3/27/08
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Closed Basin-fill Aquifers
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Closed Basin-fill Aquifers
• Alluvial fan deposits coarse at basin margins;toward the basin center, fan deposits grow finer
• Faults can act as ground water barriers
• Water quality generally good, but can have poorquality due to evaporation
• Buried stream channels form best water sourcestoward center of basin; playa deposits in basincenters have low K
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Open (riverine) Basin-fill Aquifershttp://capp.water.usgs.gov/gwa/ch_i/I-reg_aq_systems6.html
Northern Rocky Mountains Intermontane Basins aquifer system
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Rio-Grande -
both open and closed basinshttp://capp.water.usgs.gov/gwa/ch_c/C-text4.html
USGS
NASA
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Glacial-Deposit Aquifers
(Schwartz & Zhang, 2003)
(Schwartz & Zhang, 2003)
24(Fitts, 2002)
Glacial-Deposit Aquifers
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Mahonet Sand: Buried Alluvial Aquifer
(Schwartz & Zhang, 2003)
(Ritzi,WSU)
(Ritzi,WSU)
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Semiconsolidated Clastic Sediments
NASA: Mid-Atlantic Coastal Plain
http://capp.water.usgs.gov/gwa/ch_l/L-northatl.html
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(Schwartz & Zhang, 2003)
http://capp.water.usgs.gov/gwa/ch_e/E-text6.html
http://capp.water.usgs.gov/gwa/ch_e/E-text7.html
Texas Coastal Aquifer System
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Large sedimentary basins Typical rocks:
-Sandstone
-Siltstone
-Shale
-Limestone
Lithologic units, individually, are typically quite uniform and are
extensive. Locating good water bearing units is not difficult, nor is
identifying confining units
.
Oil well geophysical data is quite useful.
Consolidated Sediments: Sedimentary Rockshttp://capp.water.usgs.gov/aquiferBasics/sandstone.html
http://capp.water.usgs.gov/aquiferBasics/sandcarb.html
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(Schwartz & Zhang, 2003)
Black Hills
Sandstone Aquifers: the Dakota SS
J.E. Williamson, USGS
Madison Limestone
KGS
Dakota Sandstone
D. Mayer
Cretaceous Seaway
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Sedimentary RocksOne major control on permeability is the degree of
cementation and consolidation. Medium-grained sand will
have a K of 1 to 30 cm/s, while typical corresponding
sandstone will be 0.001 to 0.5 cm/s, a reduction of 3 orders
of magnitude!
Well-log descriptions such as “well-indurated” or “friable” can be very important.
(J. Wilson, NMT)
Permian Sandstone Capping the Sandia Mountains, NM
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Sedimentary Basins
Water Quality (Distance down flow line !) :
– Typical anion sequence (Chebotarev Sequence)
HCO3- ! SO4
2- ! Cl-
– Low TDS ! High TDS (higher than seawater)
Contributing factors
– Relative solubilities of CO32-, SO4
2-, and Cl-
minerals
– Common ion effect
– Ion exchange
– Ion filtration-
-
shaleIon filtration:
Negative ions retained
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SO42-
Cl-
HCO3-
Rapid flow
•Much flushing
•Soluble minerals are
dissolved
Soil CO2 gives low pH
dissolution of CaCO3
Slow flow
Moderately soluble
minerals present
CaSO4 ! Ca2+ + SO42-
HCO3- + CaSO4 !
Ca2+ + SO42- + HCO3
- !
SO42+ + H+ + CaCO3
CO2 + H2O + CaCO3
! Ca2+ + 2HCO3-
CH2O + !H2O !
!CH4 + !HCO3 + !H+
CH4 is due to bacterial
fermentation of organic
matter
Very slow flow
•Very soluble minerals
may be presentNaCl ! Na+ + Cl-
•Leakage of ions from
shale layers assumes
more importance
Reduction of sulfate2CH2O + SO4
2- + H+ ! HS- + 2CO2 + 2H2O
FeS
Common ion effect
reduces HCO3
organic matter
Cl-
SO42-Cl-
Chebotarev Sequence
(see Freeze & Cherry, 1979)
The water quality of old
groundwater is another issue to
take into account. Generally speaking,
the longer the residence time, the higher
the concentration of dissolved ions ingroundwater.
Groundwater tends to evolve chemically toward the composition
of sea water during the course of flow. It was observed by
Chebotarev in the Great Artesian Basin of Australia.
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Sedimentary Basins
Water supply considerations:– Advantages:
• Hydrogeology (depth to aquifer, T distribution) frequently simple and predictable.
• Wells frequently flow (at least when first drilled)
• Absence of pollution
– Disadvantages:• Depth to aquifer is frequently great and the rocks are
relatively hard (large drilling cost)
• K is usually fairly small (a long well screen is needed)
• T and S are usually both fairly small (rapid drawdown and high pumping costs)
• The water quality at considerable depths is usually poor (high TDS, Na+, F+, H2S, or Fe3
+)
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Carbonate Rocks & Aquifer Systems
(Schwartz & Zhang, 2003)
http://college.hmco.com
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Limey shale overlaid by limestone.
Cumberland Plateau, Tennessee Limestone in the Sandia Mtns, NM (J. Wilson)
Fractured Carbonate Rocks
(Schwartz & Zhang, 2003)
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(Schwartz & Zhang, 2003)
Carbonate Aquifers
Develop wells in upper 7.5m of carbonate, where solution weathering (pavement
karst) has enhanced K. K diminishes with depth; below 15-30m the aquifer dies out.
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Carbonate Aquifer Systemshttp://capp.water.usgs.gov/aquiferBasics/carbrock.html
Karst Systems including Carbonates
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Floridan Aquifer
http://capp.water.usgs.gov/aquiferBasics/floridan.html
(Schwartz & Zhang, 2003) http://sofia.usgs.gov/publications/papers/pp1403a/index.html
TDS (mg/L)
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Edwards-Trinity Aquifer System
http://www.ci.austin.tx.us/watershed/bs_aquifer.htm
http://capp.water.usgs.gov/gwa/ch_e/E-edwards_trin2.html
(Schwartz & Zhang, 2003)
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(Schwartz & Zhang, 2003)
Carbonate & Karst
Dye tracer experiment, Croft Spring, Tennessee
http://www.dyetracing.com/dyetracing/dy05005.html
http://geoscape.nrcan.gc.ca
Spring Mill Lake Drainage Basin, Indiana
http://igs.indiana.edu/survey/projects/springmill/
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Carbonates
Primary porosity can vary greatly– Occasionally will have large,
interconnected pores or vugs(coquina, limestone breccia) —these are excellent aquifers:
– Frequently will have high porosity,but very low K (chalk)—these arepoor aquifers unless secondaryporosity (eg, fractures) is present:
– Mud limestone is very dense andwell cemented, low n and K—these are poor aquifersbut good dimensional stone:
www.see.leeds.ac.uk
(K. Zehnder, ETHZ)
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Carbonates
Secondary porosity very
important
– Due to a combination of fracturing
and solution
– Extreme case is karstic terrain
– The largest springs in the world
all issue from karstic limestone:
Syria, 35 to 40 m3/s
– Secondary porosity can make
carbonate rocks good aquifers
without full karstic development.
– Degree of fracturing and solution
tends to decrease away from
outcrop areasSimulated flow in an open fracture chalk
system with porous and permeable
matrix. Red-yellow – high flow (fractures),
green-blue - low flow (matrix).
www.see.leeds.ac.uk
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Carbonates
Water development considerations
– Well success is highly variable
• Wells close to each other may be either dry or
excellent producers.
• Traces or faults and fracture zones are good clues
to well success, especially intersections of fracture
zones.
Compression
Compressi
onFractures
Fractures
Structural
effects
http://www.truenorthenv.com
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Carbonates
More water development considerations
– Water quality is usually good
• Low TDS
– Although water is very hard (mCa/mMg > 1 in LS, " 1 in dolomitic rock)
– And it can have severe pathogenic pollution
problems due to flow in fractures and
conduits, and a lack of filtering
(sinkhole landfill problems)
Hard water is water that contains
cations with a charge of +2,
especially Ca2+ and Mg2+.
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Volcanic Rocks
Smithsonian
Composite Volcano
Typically the best
aquifers are
provided by
interflow breccias.0.200.001 – 0.01n
10-8 - 10-510-11 – 10-8K (m/s)
InterbedsDense Basalt
Red Point Breccia, Grand Manan
Island, New Brunswick
J. McHone, Auburn U.
With time, weathering reduces
K of interbeds.
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Volcanic Rocks, NM
(H. Guan, NMT)
(J. Wilson, NMT)
Andesite, Magdelina Mtns., NM
Tuff, Jemez Mtns., NM Fractured Tuff, LANL., NM
(J. Wilson, NMT)
Columnar
and other
vertical
jointing can
also provide
directional
conductivitywww.tropix.co.uk /
M.Helena Afonso
Porto Santo Is.,
Madeira
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Dike Impounded GW
http://www.hawaii.gov/dbedt/czm/wec/html/mountain/water/index.htm
http://capp.water.usgs.gov/gwa/ch_n/N-HItext3.html
Most of the water resources
on the Hawaiian Island of
O‘ahu are a result of the
interaction between O‘ahu's
high mountains and the high
rainfall of the tropics
This is the
bulkhead in
the dike.
Behind here
is ground
water. The
door is rarely
opened.
(McCoy, UoH)
(Schwartz & Zhang, 2003)
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Volcanics
Water Quality
– Generally very good
• Usually has high SiO2 due to solution of
amorphous silica (~50 mg/L)
• Frequently high F and K
• Occasionally high As in hydrothermal areas
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Fractured Crystaline Rocks
(C. Cleveland, INSTAAR, CU) (J. Wilson, NMT)
Fractured Granite, Colorado Fractured Metamorphic Rock, NM
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Crystalline Rocks
• Primary Porosity– Primary porosity is very small (< 1%)
– Primary K is very small (<10-10 m/s)
• Secondary Porosity– Most porosity is due to expansion joints
and weathering near the surface.
– Most fractures and joints close within100 ft of the surface (if a well is a failure,drilling deeper generally will not help)
– Faults can provide deep fracturing.
• Storage is usually small even if K is high
• Yields are usually small (10 – 25 gpm), even for goodwells
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Crystalline Rocks
Water Quality
– Generally excellent
• Usually Ca, Na, HCO3- water
• HCO3- is from soil CO2
• Ca and Na is from incongruent dissolution of
aluminosilicates
• SiO2 is moderate
– May have pollution problems due to shallow
water table, fracture flow
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Crystalline Rocks
slope
2
flat upland
3
ridge crest
4
valley
1
Likelihood of well success: 1 > 3 > 2 > 4
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Fractured Consolidated Sedimentary,
Igneous, and Metamorphic Rocks
(Schwartz & Zhang, 2003)
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Fracture Flow
(Schwartz & Zhang, 2003)
“Cubic Law in a single fracture”Fracture Network & Connectivity
REV??
(Pollard and Aydin, 1988).
National Research Council, Rock Fractures and Fluid Flow: Contemporary Understanding and Applications (1996)
http://fermat.nap.edu/books/0309049962/html/R1.html
Q’ = b*(b2/12)*!gJ/µ " b3
(Shapiro and Hsieh, 1994)
Mirror Lake, NH
Mirror Lake, NH
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Fractured Rock
(Schwartz & Zhang, 2003)
Dual Continua: Double Porosity
Double Permeability Models
(Storage in matrix and in fractures)
(Flow in the fracture only)
(Flow in the fracture and the matrix)
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Trends of (Fractured) Rock Properties with Depth
(Schwartz & Zhang, 2003)
Fracture Apertures Close with Depth
Conductivity depends on
fracture frequency (&
connectivity) and
aperture.
Effect of weathering and
exfoliation (stress relief)
decrease with depth
Note clustering
0
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Trends of Well Yield with Depth
(Schwartz & Zhang, 2003)
