Study Set Flashcards
order of ionic loss of a rock as it weathers
CO32-, Mg2+, Na+, K+, SiO2−, Fe2+/3+, and finally Al3+
Goldich Dissolution Series
method of predicting the relative stability or weathering rate of common igneous minerals on the Earth’s surface, with minerals that form at higher temperatures and pressures less stable on the surface than minerals that form at lower temperatures and pressures.
Most common and abundant mineral group in the earth’s crust
Plagioclase
The Ca endmember in the plagioclase series
Anorthite
The Na endmember in the plagioclase series
Albite
The order of plagioclase minerals from Ca to Na endmembers
Anorthite, Bytownite, Labradorite, Andesine, Oligoclase, Albite
Mohs hardness of all plagioclase
6 to 6.5
Liquidus of plagioclase
1,215 °C (2,219 °F)
Perthite
Used to describe the intergrowth of two feldspars that are formed through exsolution (homogenous mixture of two different kinds of atoms)
Miscibility Gap
Where a mixture exists as two or more phases (coexistence), the constituents are not completely miscible.
Area of Influence
The area within which the potentiometric surface is lowered by withdrawal or raised by injection, of water through a well
Aquifer
A geologic unit that is saturated and sufficiently permeable to transmit significant economic quantities of water to wells and springs.
Capillary Fringe
The lowest part of the vadose zone, immediately above the water table, where water is under pressure that is less than atmospheric pressure.
Confined Aquifer
An aquifer overlain by a confining layer of low permeability.
Connate Water
Water trapped in the pores of a sedimentary rock at the time of deposition; fossil water.
Darcy
A unit of intrinsic permeability = 9.87 x 10^-9 cm^2.
Darcy’s Law
The basic equation describing groundwater flow put forth by darcy: Q=KiA (K = hydraulic conductivity i=hydraulic gradient A is cross-sectional area of aquifer through which flow occurs (w x b, ft^2))
Discharge Area
An area where subsurface water is discharged to land, bodies of water or the atmosphere.
Effective Porosity
The percentage of the total volume of a soil or rock that consists of interconnected pore space. The term is sometimes used analogously to specific yield.
Field Capacity
The quantity of water held by the soil or rock against the pull of gravity Field capacity is dependent on the length of time the soil or rock has been undergoing gravity drainage, while specific retention is not.
Flow Net
Two-dimensional representation of flow lines and equipotentials.
Ghyben-Herzberg Principle
The principle that states that the depth to which fresh water extends below sea level is approximately 40 times the height of the water table above sea level.
Head
A measure of the potential energy of a fluid at any given point with respect to a given datum. In practice, it is the elevation to which water rises at a given point as a result of reservoir pressure.
Hydraulic Conductivity (K)
The capacity of a porous medium to transmit water. The rate at which fluid can move through a permeable medium depends on properties of the fluid (Viscosity and specific weight) and properties of the medium (intrinsic permeability).
(K)
Hydraulic conductivity
Hydraulic Gradient (I)
Rate of change in total head per unit of distance of flow in a given direction.
(I)
Hydraulic Gradient
Intrinsic Permeability (Ki)
A property of the porous medium that measures the relative case with which a fluid can be transmitted through it under a hydraulic gradient. It is dependent upon the pore size and is measured in darcys.
(Ki)
Intrinsic Permeability
Juvenile Water
Water that is derived directly from magma and is thought to have come to the Earth’s surface for the first time.
Meinzer
A unit of hydraulic conductivity in gpd/ft^2. Rate of flow in gallons per day through a cross section of 1 square foot under a unit hydraulic gradient at 60 degrees F.
Perched Groundwater
Unconfined groundwater separated from an underlying body of groundwater by an unsaturated zone.
Permeability
The property of a porous rock or soil for transmitting a fluid. It measure the relative ease of flow under unequal pressure.
Porosity (n)
The percentage of the bulk volume of a rock or soil that is occupied by void space.
(n)
Porosity
Potentiometric Surface
A surface that represents the total head of groundwater and is defined by the level to which water will rise in a well.
Recharge Area
An area where water infiltrates downward into the saturated zone.
Runoff (R)
That part of precipitation appearing in surface streams.
Specific Retention (Sr)
Ratio of the volume of water a soil or rock can retain against gravity drainage to the total volume of the soil or rock, usually stated as a percentage.
Specific Storage (Ss)
Amount of water per unit volume of a saturated formation that is stored or expelled from storage due to compressibility of mineral skeleton and pore water per unit change in head. Units are ft^-1.
Storativity or Storage Coefficient (S)
Volume of water that a permeable unit releases from or takes into storage per unit surface area of the aquifer per unit change in head. In an unconfined aquifer, storage = specific yield.
Specific Yield (Sy)
Ratio of the volume of water that drains from a saturated soil or rock due to gravity to the total volume of soil or rock, stated as a percentage.
Transmissivity (T)
The capacity of an aquifer to transmit water of the prevailing kinematic viscosity. T=Kb, where b = saturated thickness of the aquifer Dimensions are gpd/ft or ft^2/day.
Unconfined Aquifer
An aquifer having a water table.
Underflow (U)
Groundwater that flows beneath the bed or alluvial plain of a surface stream, especially in arid regions.
Vadose Zone or Zone of Aeration
A subsurface zone containing water under pressure that is less than atmospheric pressure. It is measured from the ground surface to the water table.
Water Table
The surface within unconfined groundwater at which the hydraulic pressure is equal to atmospheric pressure.
Watershed
The region drained by a stream or body of water, or a drainage divide.
Sustainable Yield
Can be defined by equating recharge rates to pumping rates in a way that pumping rates do not exceed recharge rates.
Macro Pore Flow
Occurs along worm holes, root holes or fracture
Funneled or Focused Flow
Occurs along lenses that may concentrate and deflect the direction of flow
Unstable Flow
Flow that breaks through interfaces and creates fingers that become more conductive to water flow, as compared to adjacent areas that are dry.
Angular Unconformity
Unconformity between two groups of rocks that are dipping at different angles. The older rocks below are often dipping more steeply than the rocks above.
Disconformity
A type of paraconformity in which the rocks above and below are essentially parallel but the unconformity surface is not parallel to the bedding.
Nonconformity
sedimentary deposits rest upon older igneous or metamorphic rocks
Paraconformity
Unconformity is parallel to the strata above and below it.
Eon
Four subdivisions of time on Earth: Three Eons - hadean, Archean, and Proterozoic - Cover almost half the time on Earth; The fourth eon - Phanerozoic - incorporates the Paleozoic, Mesozoic and Cenozoic eras.
Epoch
Subdivisions of the Tertiary and Quaternary periods.
Era
Subdivisions of the Phanerozoic: Paleozoic, Mesozoic and Cenozoic.
Ga
Abbreviation for Giga-annum; one billion years.
GIS
Geographic Information System, a computer-based tool used for mapping, analyzing and visualizing geographically referenced data.
GPS
Global Positioning System, a radio navigation system that determines the exact location, time and velocity from triangulation.
Ka
Abbreviation for Kilo-annum; one thousand years
Key Beds
A well-defined, easily identified strata that is distinctive enough to be useful in correlation in mapping.
Ma
Abbreviation for Mega annum/ one million years
Magnetic Declination
The angle between true North and magnetic North.
Period
Subdivisions of the three eras: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian in the Paleozoic, Triassic, Jurassic, and Cretaceous in the Mesozoic, and Tertiary and Quaternary in the Cenozoic.
Rule of V’s
Outcrop pattern of a formation or fault as it crosses a valley.
State Plane Coordinate System
A two dimensional coordinate system developed by the National Geodetic Survey for use in states and counties. There are 130 zones in the U.S. defined by county, state, and international boundaries. Convenient for local use, however cannot be used in large regions and coordinates need to be converted to latitude and longitude.
Township and Range
A surveyed unit of the Public Land Survey System that forms a 6 mile by 6 mile square and is divided into 36 sections (identified by number) that each have 16 individual 40 acre parcels (identified by letter). Townships are measured in rows north and south of a Baseline and Ranges are measured in columns east and west of a Principal Meridian.
Periods of the Paleozoic Era
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
Periods of the Mesozoic Era
Cretaceous
Jurassic
Triassic
Epochs of the Cenozoic
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
Holocene
Periods of the Cenooic
Tertiary
Quaternary
Start of the Mesozoic Era
65.5 Ma
Start of the Paleozoic Era
251 Ma
Beginning of the Paleozoic Era
542 Ma
Period known as Age of Man
Quaternary
Period known as Age of Mammals
Tertiary
Period known as Age of Reptiles
Cretaceous - Triassic (Mesozoic)
Period known as Age of Amphibians
Permian - Carboniferous (Pennsylvanian and Mississippian)
Period known as Age of Fish
Devonian - Silurian
Period known as Age of Invertebrates
Ordovician - Cambrian
Subperiods of the Tertiary
Neogene and Paleogene
Subperiods of the Carboniferous
Pennsylvanian and Mississippian
Law of Initial Horizontality
Assumes the sequence of layers was deposited horizontally. The oldest layer is on the bottom and the youngest layer is on the top.
Law of Superposition
States that the oldest layer is on the bottom and the youngest layer is on the top. Assumes that the layers have not been overturned during deformation.
Another Way of stating is that the beds become younger in the direction of dip. Applies to any layered rock sequence such as sedimentary units or extrusive igneous rocks.
Cross-Cutting Relationships
feature that is cut is older than the feature that cuts across it.
Lateral Continuity
Implies there are sedimentary layers that when deposited covered a large area extending laterally in all directions. Rocks would be considered laterally continuous even though they may be separated by uplift or erosion.
Faunal and Floral Evolutionary Age Relations
Evolutionary development of fossils can suggest a sequence of age. Older and more primitive fossils are usually found below younger fossils. Extinctions may break the pattern and new patterns may emerge. Fossils can be used to correlate with stratigraphic sequences in other areas.
Law of Inclusions
inclusions in a rock signify that the inclusions are older than the rocks in which they are included. Inclusions may also provide clues of the provenance at the time of formation.
Metamorphism Age Relations
Metamorphosed beds are younger than the rock as it existed before metamorphism.
Sole Marks
Coarse sand or silt layer is deposited onto mud. Erodes pits and scars into the mud layer and then the depressions are in-filled with the more coarse material.
Physical continuity
strata are generally continuous unless eroded, interrupted by faulting truncated by an unconformity, shaped as a lenticular body, or deposited locally.
Lithology correlation
Distinctive units can be used to correlate with a high degree of confidence.
Sequence of strata correlation
Rock units may repeat in an orderly fashion allowing a correlation of the entire sequence to be made.
Rock Property Correlation
Strata may be correlated by means of their electrical or radioactive properties as measured on a well log.
Index fossil correlation
appearance of a fossil, evolution through time and finally its disappearance yields valuable information which could then be correlated to similar rocks in other areas.
Fossil Assemblage Correlation
Groups of several fossil species are more useful for correlations because there is a greater opportunity for the assemblage to be present than a single species. Assemblages may also permit a more detailed correlation where stratigraphic ranges overlap.
Unconformity
Time break in a sequence of beds
Rule of V: Horizontal Bedding
V upstream parallel to topography
Rule of V: Dip Upstream
V upstream, outside topography
Rule of V: Vertical bedding
Straight lines cutting across valley topography
Rule of V: Dip downstream greater than valley gradient
V downstream
Rule of V: Dip downstream equals valley gradient
Parallel lines along valley sides
Rule of V: Dip downstream less than valley gradient
V upstream inside topography
Downwarp
Synform - can’t be assumed to be a syncline unless the ages of the units are known.
Upwarp
Antiform - can’t be assumed to be a anticline unless the ages of the units are known.
Anticline plunge
In the direction of the closure of the U
Syncline plunge
Opposite direction of the closure of the U
Juxtaposition of noncontiguous sedimentary facies
Sedimentary facies that do not usually occur next to each other may be moved laterally by strike slip faults
Sag Pond
a body of fresh water collected in the lowest parts of a depression formed between two sides of an active strike-slip, transtensional or normal fault zone.
scarplet
a fault only a few inches to a foot high.
Triangular Facets
A triangular face having a broad base and an apex pointing upward; specif. the face on the end of a faceted spur, usually a remnant of a fault plane at the base of a block mountain. A triangular facet may also form by wave erosion of a mountain front or by glacial truncation of a spur.
Slickensides
naturally polished rock surfaces that occur when the rocks along a fault rub against each other, making their surfaces smoothed, lineated, and grooved.
Grooving
A striation created by a geological process, on the surface of a rock or a mineral.
Drag
a minor geological fold produced in soft or thinly laminated beds lying between harder or more massive beds in the limbs of a major fold
Gouge
a filling material such as silt, clay, rock flour, and other kinds of geological debris in joints, cracks, fissures, faults, and other discontinuities in rocks
Breccia
is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. A breccia may have a variety of different origins, as indicated by the named types including sedimentary breccia, tectonic breccia, igneous breccia, impact breccia, and hydrothermal breccia.
Megabreccia
a breccia composed of very large rock fragments, sometimes kilometers across, which can be formed by landslides, impact events, or caldera collapse.
Mylonite
a metamorphic rock formed by ductile deformation during intense shearing encountered during folding and faulting, a process termed cataclastic or dynamic metamorphism. This process involves nearly complete pulverisation of the parent rock so the original minerals are almost completely broken down and recrystallise as smaller grains which are tightly intergrown, forming a dense, hard rock. As a result of the shearing encountered during formation, recrystallised minerals grow preferentially along planes of foliation parallel to the direction of shear.
Silicification
the replacement of original skeletal material accomplished through the concurrent dissolution of calcium carbonate and precipitation of silica. The processes is aided by the nucleation of silica to organic matter which surrounds the mineral crystallites within the shell. It is far more common in Paleozoic than younger deposits, is more likely to occur in organisms with low magnesium calcite shells, in carbonate sediments, and in environments with elevated dissolved silica.
Fenster
An erosional feature through he overlying thrust sheet into the block underlying the fault, creating a “window”.
Klippe
An outlier of the overlying thrust sheet that has been isolated from the rest of thte thrust by erosion.
Concordant Features
Consistent with bedding planes
Sill
a concordant feature, that is, they are emplaced along zones of weakness and geographically restricted
Dike
parallel-sided, generally of constant thickness, and are relatively restricted in areal extent. Discordant features, cutting across many lithologic units
Discordant Features
Cut across other lithologic units
Xenolith
Rock fragment that becomes enveloped in a larger rock during the latter’s development and solidification. Almost exclusively used to describe inclusions in igneous rock entrained during magma ascent, emplacement and eruption.
Large igneous intrusions
forcefully emplaced, forma circular shape, have foliation parallel to the margins, and lack xenoliths of country rock. Country rock dips away from the intrusive contact. Folds and faults are usually present.
Hornfells
a dark, fine-grained metamorphic rock consisting largely of quartz, mica and particular feldspars. It was subjected to the heat of contact metamorphism at a shallow depth. Since pressure does not play a significant role, it is often made up of mineral grains that are equidimensional in shape and without a preferred orientation.
Contact Metamorphism
Rocks are formed with concentric bands around the boundaries of intrusive igneous rocks. The bands or rings are superimposed on other stratigraphic and structural boundaries.
Regional metamorphism
laterally extensive, covering the entire map. Rocks are slate, phyllite, schist, gneiss, migmatite and eclogite.
Cataclastic metamorphism
identified by faults that have a zone of breccia, cataclasite, or mylonite associated with them.
Slate
is a fine-grained, foliated metamorphic rock that is created by the alteration of shale or mudstone by low-grade regional metamorphism. Slate is composed mainly of clay minerals or micas, depending upon the degree of metamorphism to which it has been subjected. The original clay minerals in shale alter to micas with increasing levels of heat and pressure. Slate can also contain abundant quartz and small amounts of feldspar, calcite, pyrite, hematite, and other minerals.
Tectonic environment that forms slate
usually a former sedimentary basin that becomes involved in a convergent plate boundary. Shales and mudstones in that basin are compressed by horizontal forces with minor heating. These forces and heat modify the clay minerals in the shale and mudstone. Foliation develops at right angles to the compressive forces of the convergent plate boundary to yield a vertical foliation that usually crosses the bedding planes that existed in the shale.
Phyllite
These are almost always convergent plate boundary environments involving continental lithosphere. Phyllite forms in areas of regional metamorphism where where beds of sedimentary rocks have been subjected to moderate heat and compression by the colliding of continental plates and mountain-building events. Both slate and phyllite form in sedimentary basins that are deeply buried, or in accretionary wedges above subduction zones. a foliated metamorphic rock that is made up mainly of very fine-grained mica. The surface of phyllite is typically lustrous and sometimes wrinkled. It is intermediate in grade between slate and schist
schist
is a foliated metamorphic rock made up of plate-shaped mineral grains that are large enough to see with an unaided eye. It usually forms on a continental side of a convergent plate boundary where sedimentary rocks, such as shales and mudstones, have been subjected to compressive forces, heat, and chemical activity. This metamorphic environment is intense enough to convert the clay minerals of the sedimentary rocks into platy metamorphic minerals such as muscovite, biotite, and chlorite. To become schist, a shale must be metamorphosed in steps through slate and then through phyllite. If the schist is metamorphosed further, it might become a granular rock known as gneiss. a metamorphic rock with well-developed foliation. It often contains significant amounts of mica which allow the rock to split into thin pieces. It is a rock of intermediate metamorphic grade between phyllite and gneiss.
gneiss
Gneiss usually forms by regional metamorphism at convergent plate boundaries. It is a high-grade metamorphic rock in which mineral grains recrystallized under intense heat and pressure. Gneiss can form in several different ways. The most common path begins with shale, which is a sedimentary rock. Regional metamorphism can transform shale into slate, then phyllite, then schist, and finally into gneiss.
During this transformation, clay particles in shale transform into micas and increase in size. Finally, the platy micas begin to recrystallize into granular minerals. The appearance of granular minerals is what marks the transition into gneiss.
migmatite
place holder
7.5 minute quad scale
1:24,000
15 minute quad scale
1:62,500
30 x 60 minute scale
1:100,000
1 degree x 2 degree scale
1:250,000
metamorphic rocks
have been modified by heat, pressure and chemical processes, usually buried deep below Earth’s surface. These extreme conditions have altered the mineralogy, texture and chemical composition of the rocks.
Foliated metamorphic rocks
have a layered or banded appearance that is produced by exposure to heat and directed pressure. Examples slate, phyllite, schist, gneiss.
Examples of Non-foliated metamorphic rocks
Hornfels, Marble, Novaculite, Quartzite and Skarns.
Anthracite
Highest rank of coal. It has been exposed to enough heat and pressure that most of the oxygen and hydrogen have been driven off, leaving a high-carbon material behind. It is bright, lustrous and breaks with a semi-conchoidal fracture. Often referred to as “hard coal”.
Gneiss
A foliated metamorphic rock that has banded appearance and is made up of granular mineral grains. Typically contains abundant quartz or feldspar minerals.
Hornfels
a fine-grained non-foliated metamorphic rock with no specific composition. It is produced by contact metamorphism. Hornfels is a rock that was “baked” while near a heat source such as a magma chamber, sill or dike.
Lapis Lazuli
Famous blue gem material, formed through contact metamorphism or hydrothermal metamorphism, where limestone or marble has been altered.
Marble
Non-foliated metamorphic rock that is produced from the metamorphism of limestone or dolostone. Primarily composed of calcium carbonate.
Mariposite
Metamorphic rocks that contain enough green mica to impart a green color, although major constituents are quartz, calcite, dolomite, ankerite or barite. These rocks have been altered by hydrothermal activity, and usually thought to have a serpentinite protolith. Mariposite was sometimes a host rock of gold.
Novaculite
a dense, hard, fine-grained, siliceous rock that breaks with a conchoidal fracture. It forms from sediments deposited in marine environments where organisms such as diatoms (single-celled algae that secrete a hard shell composed of silicon dioxide) are abundant in the water.
Quartzite
a non-foliated metamorphic rock that is produced by the metamorphism of sandstone. It is composed primarily of quartz.
skarn
a rock characterized by its formation rather than its mineral composition. It often forms when carbonate rocks near a magma body are altered by contact metamorphism and metasomatism. Various minerals, gems, and even precious metals can sometimes be found in skarn.
Soapstone
a metamorphic rock that consists primarily of talc with varying amounts of other minerals such as micas, chlorite, amphiboles, pyroxenes, and carbonates. It is a soft, dense, heat-resistant rock that has a high specific heat capacity. These properties make it useful for a wide variety of architectural, practical, and artistic uses.
one degree of latitude scale in feet (miles)
364,000 ft (69 miles)
one minute of latitude scale in feet (miles)
6068 ft (1.15 miles)
one second of latitude scale in feet
101 Ft
Large-scale maps are useful for…
1:24,00 (1” = 2000’)
1:1,200 (1” = 100’)
1:600 (1” = 50’)
Engineering planning and geologic mapping in developed areas or areas where more detail is needed. A 1:1,200 or 1:600 scale map is usually private surveys, fault investigations, locating utilities or roads, housing developments or other jobs specific to small areas.
Intermediate-scale maps are useful for…
1:50,000
1:62,500
1:100,000
County-wide or regional planning and land management.
Small-scale maps are useful for
1:250,000
1:500,000
1:1,000,000
Often state wide data, typically include the major features such as state and national parks, cultural boundaries, airports, major roads and railroad lines.
Clarke’s ellipsoid
the first ellipsoid of the earth and first established in 1866. The horizontal data based on this ellipsoid was NAD27.
NAD83
Horizontal datum that is based on the geodetic reference system (GRS80).
Chlorite
Common sheet silicate minerals that form during the early stages of metamorphism. Most often found in rock environments where minerals are altered by heat, pressure, and chemical activity, with low temperatures a few miles of earth’s surface. Also found as retrograde minerals in igneous and metamorphic rocks that have been weathered. Rocks that commonly contain abundant chlorite include greenschist, phyllite, chlorite schist and greenstone.
Physical properties of chlorite
Green in color, have foliated appearance, perfect cleaveage, and an oily or soapy feel. Variable chemical composition gives them a range of hardness and specific gravity.
Physical properties of chlorite
Green in color, have foliated appearance, perfect cleavage, and an oily or soapy feel. Variable chemical composition gives them a range of hardness and specific gravity.
Cataclasite
a cohesive granular fault rock that has been formed through brittle deformation mechanisms containing pieces of the fractured pre-existing rock type.
Karst
a term that is applied to the topography of a region which is underlain by limestone, dolomite, gypsum, or other rocks which can be affected by dissolution.
Karst Topography
is characterized by surface depressions in which water is intercepted and diverted into underground caverns and passageways.
Four conditions necessary for karst development
1) a soluble rock, preferably limestone, at or near the surface
2) a dense rock, highly jointed and thin-bedded
3) Entrenched valleys below uplands underlain by soluble and well-jointed rocks
4) a region of moderate to abundant rainfall
Four most important U.S. regions for karst
Florida, southern Missouri, southerly trending belt from south-central Indiana into central Tennessee, and in the Appalachians from Alabama to Pennsylvania.
dripstone
travertine deposits that result from the calcium carbonate-rich water dripping from the ceiling of a cave or cavern.
Stalactites
downward protrusion of dripstone deposit.
stalagmites
upward protrusion of dripstone deposit.
sinkholes
most commonly observed feature of karst terrain. Sinkholes are circular depressions that are commonly funnel-shaped and can be a few feet to a hundred feet in diameter.
Compound Sinkhole
when sinkholes enlarge and combine with adjoining sinkholes.
solution sinkholes
occur when rainwater comes into contact with carbonate bedrock either directly or through a thin covering of soil. Water moves through joints, fractures and bedding planes and dissolves the carbonate, forming small depressions at the surface. The depressions subsequently may focus the accumulation of surface water or debris that settles in the depressions. The resultant landform is gently undulating with shallow depressions and mounds.
Cover-subsidence sinkholes
Form where sand overlies the carbonate bedrock. As water moves thorough the sand and into the joints and fractures of the bedrock, it carries some of the sand with it. Additional sand fills the vacated space, eventually forming a depression at the surface.
Cover-collapse sinkholes
Develop where there is a thick layer of clay above the soluble bedrock. The water moves through the clay and starts dissolving the bedrock below. As the cavity grows in the bedrock the cohesive clays above bridge the opening and eventually the cavity roof collapses and breaches the ground surface in catastrophic fashion. Often these sinkholes are steep-sided chimney-like structures, but until they fail abruptly there is little evidence of their existence at the surface.
Helictite
An irregular twiglike deposit that forms in a cavern where there is not enough water to form drips but where the surface remains damp allowing the calcium carbonate to grow in any direction.
Travertine
A deposit of calcium carbonate precipitate that can be found in limestone caverns coating the cavern walls, floors and ceilings.
blind valley
A valley that ends at a swallow hole due to a prolonged period of upstream erosion above the sinkhole.
Cavern
Large caves that may extend in any direction, have one or several levels, and are created by solution of limestone along joints and bedding planes.
Hum
Isolated hill remnants due to erosion by solution in karst terrain.
Karst Window
A hole in the ground in which one can observe an underground stream flowing from one cavern to another. A hole in a cavern which breaks to the surface.
Lapies
Grooved or fluted surface resulting from the solution of limestone at or near the surface in an area of high relief. The grooves range in width from a few millimeters to more than a meter in width and commonly result in knifelike ridges.
Natural tunnels & bridges
Features produced by the underground flow of water in karst terrain. When the tunnel sections collapse leaving only small segment, bridges are formed.
Polje
An elongated basin with a flat floor and steep walls formed by solution of a previously faulted or folded structure. This feature can be 30 miles or more in length.
Sink
The point at which a sinking creek ends, often in an observable swallow hole.
Sinkhole or karst plain
A limestone plain exhibiting sieve-like characteristics resulting from numerous sinkholes intercepting any surface water and diverting them to subsurface channels.
Sinkhole pods or karst lakes
A pond or lake resulting from the clogging by clay of a doline sinkhole that perches water above the water table.
Sinking creeks
Any surface creek or stream which disappears underground in karst terrain; many disappear in a swallow hole.
Solution Valley or Karst Valley
A transitional feature between surface and subsurface drainage in an area of clastic rocks. Valley forms because of extensive collapse and karst development. A special type of blind valley.
Solution-subsidence trough
A non-tectonic feature, up to 10 miles in length, resulting from concurrent subsidence and solution along joints or faults.
Swallow hole
A hole in the bottom of a sinkhole which allows surface water runoff or streams to flow into the subsurface.
Terra rossa
A red clayer (CL-CH) soil found mantling the ground surface and extending into joints or fractures resulting from surface or near surface solution, usually found on moderate to gentle slopes.
Uvala
An elongated karst window that has occurred by the collapse of a extensive portion of a subsurface waterway. These features can extend from 1000 feet to a mile or more.
Conditions to classify snow or ice field as a glacier
1) Must be a large accumulation or mass of ice and snow.
2) It must be located on or principally on land.
3) Must be formed by compaction and recrystallization of snow.
4) Must be evidence of past or present movement
5) Glacier remains from year to year.
Glacial movements
Continental - outward in all directions due to the weight of the snow.
Alpine - directional controlled by the topography.
Drift
All rock and associated material that has been carried by and deposited by a glacier, glacial ice, or water running from a glacier. This term is a general term and includes all those depots that can be further described by the terms till, stratified till, and deposits of glacio-fluvial, glacio-lacustrine, glacio-eolian, and glacio-marine origin.
Drumlin
An elongated ellipsoidal feature which can be composed of a wide variety of materials ranging from till to relatively large rock fragments; some even have a bedrock core. These streamlined hills are usually clustered and are found near the terminal or recessional moraines. Many are thought to be deposited after the ice passes around an obstacle.
Esker
These serpentine shaped stratified deposits develop as the load arrived by the streams flowing beneath, within, and above the glacier , once it has become stagnant, is dropped. They have the appearance of inverted stream channels, often with branching, and they may join the outwash plain at the glacier margin.
Kame and Kame Terrace
A small hummock or terrace of ice-contact drift that has resulted from the deposition of sediment either in crevasses at the surface of the glacier, on the irregular surface of stagnant glaciers, or often from streams flowing at the edge of the glacier along the contact of the ice with the valley wall. The materials are typically stratified and contain poorly sorted sands (SW) and gravels (GW).
Kettle
A depression in the postglacial terrain formed by the melting of a large stagnant ice block which allows for the settlement of the overlying glacial drift. In some area the outwash plains pitted with may kettles. This could results fr4om the stagnation of a laterally extensive sheet of ice with varying thickness.
Arcuate Terminal Moraine
An arcuate moraine that has been deposited at the terminus of the glacier, marking the furthest progression of the glaciation. Older terminal moraines that are not the maximum extent of glaciation are typically destroyed by subsequent glacial advances incorporating the older moraine material with the younger.
Ground Moraine
Often used interchangeably with till plain. Can be composed of both the material contained within the glacier as well as that being moved along at its base.
End Moraine or Terminal Moraine
The end moraines found at the maximum extent of a continental glaciation are similar to those found in alpine glaciation though they tend to be much more extensive and often have less steep slopes, occasionally making it difficult to distinguish between the ground moraine and the end moraine materials.
Recessional moraine
Moraines that have formed during a temporary hiatus in the retreat of the ice sheet. There are often many recessional moraines that form as the retreat occurs.
Outwash Plain
A broad plain composed of outwash: stratified debris that is carried by meltwater streams both in front of and beyond the terminal or end moraine. The outwash plain is typically comprised of coarser grained materials (SW, GW) closer to the terminus of the glacier grading to finer materials with increased distance.
Swell and Swale Topography
Till deposits rich in clay may result in a gently undulating surface which often is also found in areas that have had multiple glaciations.
Till
An unsorted, unstratified glacial deposit composed of a heterogeneous mixture of clay (CL), silt (ML) , Sand (SW), gravel (GW), and boulders. It is usually unconsolidated and deposited directly by a glacier without having been reworked by meltwater.
Till plain
Also called ground moraine, deposition by an ice cap of glacial till forming a relatively flat to undulating surface which covers an extensive area and buries the preglacial topography.
Ice-scoured plain
An assemblage of erosional landforms on exposed bedrock resulting from the flow of an ice cap. It exhibits may of the same surficial features that are found in areas of alpine glaciation such as striations, grooves and polished surfaces, as well as the development of roche mountonnees or mammillated surfaces.
Roche moutonnee
An elongated bedrock knob which is oriented parallel to the direction of glacial flow and has a smooth rounded upstream end and usually a steep rough downstream end where the glacier plucked out the rock as it moved away.
Streamlined topography (mammillated surface)
A series of smooth rounded erosional rock mounds alternating with parallel valleys resulting from the smoothing off of a mountainous region by the ice cap.
Knob and basin topography
Also called knob-and-kettle topography, hummocky landscape consisting of knolls or mounds of glacial drift in an area also interspersed with basins or kettles. The basins often contain water. (Alpine Glaciation)
Lacustrine plains
A plain that has formed by the filling of a lake with lake sediments and alluvium which has been deposited along the margin of the glacier. Characterized by very flat valley bottoms in hilly terrain. (Alpine Glaciation)
Moraines
A mound or ridge composed of accumulated glacial drift or till deposited directly by the glacier. Moraines are composed of a heterogeneous collection of unsorted and unstratified clay (CL), silt (ML), sand (SW), gravel (GW) and boulders. Many of the larger clasts are faceted and have striations or polish due to the abrasion during the movement of the glacier. (Alpine Glaciation)
Lateral Moraine
A linear moraine located along the edge of a valley glacier and composed of materials deposited on the glacier from the valley walls. (Alpine Glaciation)
Medial Moraine
A linear moraine paralleling the valley walls which occurs when two valley glaciers merge joining the two inside lateral moraines from the two or more tributaries as they flow into the more major drainage. (Alpine Glaciation)
Valley Train
A long, narrow deposit of outwash (sand and gravel), deposited by glacial meltwater, which begins at the end moraine and extends down valley (Alpine Glaciation)
Arete
A jagged sharp sawtooth-like ridge that results form the growth of cirques on opposite sides of a mountain ridge by alpine glaciation.
Cirque
A horseshoe-shaped hollow high on a mountainside that was created by the erosive action at the head of a glacier. (Alpine Glaciation)
Col
A narrow sharp-edged pass or sag between cirque head and side walls along an arete. (Alpine Glaciation)
Fjords, Fiards (Fjards)
A submerged glacial trough or valley at its seaward end resulting from the raising of sea level as the glaciers melted. The fiard is a shallower and shorter, but often broader, feature than the fjord. (Alpine Glaciation)
Glacial polish
A smooth surface produced on bedrock by abrasion by the movement of a glacier. (Alpine Glaciation)
Glacial steps or stairway
A series of cross-valley steps extending down from the cirque, these steps are characterized by a relatively flat floor or with a slight up valley slope broken by steeper sections stepping down valley. (Alpine Glaciation)
Glacial trough (U-shaped valley)
A steep-sided valley that extends down from the cirque in which glacial action has widened and deepened an existing valley. (Alpine Glaciation)
Hanging valley
A U-shaped glacial tributary valley truncated by a deeper U-shaped glacial main valley leaving a valley whose mouth is relatively high on the main valley wall. The discordance is due to the greater erosive power of the main glacier. (Alpine Glaciation)
Horn
A jagged sharp peak at the high point in an arete which has been sculpted by the erosional action of three or more cirques. This pyramidal feature is the remainder of the original mountain summit in a region modified by alpine glaciation.
Monuments (tinds)
A horn that has been isolated by the lateral interstation of cirques. (Alpine Glaciation)
Paternoster lakes
A series or chain of lakes occupying the glacial steps. (Alpine Glaciation)
Striations
Lines scrapped into the bedrock by rocks being carried along at the base of the glacier. Striations generally indicate the direction of glacier movement. Larger rocks create grooves or grooved rock that can be as big as a valley. (Alpine Glaciation)
Tarn
A small deep lake formed in a cirque basing. (Alpine Glaciation)
Trough lakes
Similar to fjords in that they consist of a long glacial trough and contain water but are found above sea level. (Alpine Glaciation)
Truncated or faceted spur
A ridge in a pre-glacial valley that has been truncated by the abrasion of glacial action as it straightened the valley. Varying degrees and shapes of truncation are possible, and in some cases may mimic faceted spurs caused by faulting and uplfit. (Alpine Glaciation)
Base Level
The lowest level beyond which a stream cannot erode its bed.
Bed Load
heavier particles (boulders, pebbles, gravel and sand) that travel along the bottom of a channel by bouncing (saltation) or traction. They are not carried continuously in the water column.
Runoff
The portion of precipitation appearing in streams.
Sheet Flow
Unconcentrated laminar overland flow that contributes ot the development of the valleys, valley systems and slopes.
Sheetwash
the material transported by sheetflow
Suspended sediment
primarily fine inorganic particles of clay and silt (typically < 0.063 mm. It also may include fine sand (0.63-0.250 mm) and particulate organic matter suspended in the water column.
GW
Well-graded gravels, gravel-sand mixtures, little or no fines (Clean Gravels - Less than 5% fines)
GP
Poorly-graded gravels, gravel-sand mixtures, little or no fines (Clean Gravels - Less than 5% fines)
GM
Silty gravels, gravel-sand-silt mixtures (Gravels with fines - More than 12% fines)
GC
Clayey gravels, gravel-sand-clay mixtures (Gravels with fines - More than 12% fines)
SW
Well-graded sands, gravelly sands, little or no fines. (Clean Sands - Less than 5% fines)
SP
Poorly graded sands, gravelly sands, little or no fines (Clean Sands - Less than 5% fines)
SM
Silty sands, sand-silt mixtures (Sands with fines - More than 12% fines)
SC
Clayey sands, sand-clay mixtures (Sands with fines - More than 12% fines)
ML
Inorganic silts and very fine sands, rock flour, silty or clayey fine sands or clayey silts with slight plasticity
CL
Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays
OL
Organic silts and organic silty clays of low plasticity
MH
Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts
CH
Inorganic clays of high plasticity, fat clays
OH
Organic clays of medium to high plasticity, organic silts
PT
Peat and other highly organic soils
Silts and clays - Liquid limit less than 50%
L Classificaltion
Silts and clays - Liquid limit 50% or greater
H Classification
Alluvial Fans
Alluvial fans develop when the stream gradient becomes too flat as it exits the hilsl and the water becomes too slow to carry the sediment load. The sediment load is deposited at the exit from the hills where the stream intersects the lowland valley bottom. Alluvial fans are created where torrential rainfall occurs in arid environments. In general, fans consist of a wide range of sand (SW) and gravel (GW) grain sizes. The larger sies are found at the entrance to the valley and finer grains are found farther away from the hills.
Bajadas
Coalescing alluvial fans
Deltas
When streams enter lakes or seas the flow branches out and sedimentation takes place because of the change in gradient. The coarser grains settle quickly into forest beds sloping offshore. .The turbulence at the point of entry allows the suspended load to be carried further offshore and to be deposited horizontally as bottomset beds. As the forest beds progress offshore the fine grained materials in suspension can drop out as nearly horizontal topset beds overlying them. The topset and bottomset beds consist of deposits of finer grained silts (ML) and clays (CL).
Gravel Bars (Sand Bars)
Gravel bars (GP) and sand bars (SP) can develop midstream when the flow velocity of the water declines where it borders with a higher velocity flow in the stream. These bars are usually linear in the flow direction. Often these are relatively well sorted or poorly graded deposits.
Point Bars
When sediment is deposited at the bend in a stream, inside of the turn and are called a Point Bar.
Natural Levees
Form when flood stage has been reached and as the river recedes. The water velocity declines dropping some of the sediment load parallel to the shore. The river moves more toward mid channel as the water drops making the levee higher towards the main channel and lower towards the shore. These levees are generally formed of sand and coarse silts (SW-ML)
Braided Streams
In channel deposition of sands (SW) and gravels (GW) in a braided pattern is due to changes in the velocity of the water within the channel. Increased erosion overloads the stream’s capacity to carry the bed load. When the water is blocked up by deposition it moves to a place where the water is traveling faster, thus moving the bed load around. The materials are eroded or deposited intermittently depending on water velocity. Erosional braiding can occur in bedrock channel bottoms when the resistance to erosion of the bedrock is not uniform.
well sorted =
poorly graded
well graded =
poorly sorted
Free Meanders
Free meanders form in valley bottoms on flat flood plains and can change course by eroding river banks and depositing material.
Incised Meanders
Form on initially flat surfaces but if flow increases or the underlying materials are soft, the stream erodes downward creating a deeper meander that no longer allows the water to move out of the channel.
Ripple Marks
There are two types of ripple marks. Asymmetrical ripple marks indicate directional current. The symmetrical ripple marks are indicative of oscillating water.
Peneplains
Broad, relatively flat to gently undulating surfaces that are created as a result of a variety of erosional processes acting over a long period of time, including marine abrasion or sheetwash.
Pediments
slightly inclined planar surfaces. They meet the mountains generally at an abrupt angle on the upper part of the slope and grade into the valley bottom. They are frequently rock floored or have a thin veneer of alluvium. They are often found in arid regions and are prominent in the Basin and Range Province.
Inselbergs
A prominent isolated remnant of a mountain surrounded by a pediment surface.
Stream channel development occurs through what three processes:
Deepening (vertical), Widening(lateral) and lengthening.
Stream channel deepening occurs…
Dominately due to hydraulic action and scouring of the bottom of the valley through the action of the bed load. In mature streams.
Stream channel widening occurs…
Through currents undercutting the channel walls which eventually causes the banks to collapse. It is also caused by runoff and gullying as well as by incoming tributaries.
Stream channel lengthening occurs…
Lengthening can occur as erosion migrates upstream, downstream if there has been uplift or sea level changes, or by expanded meander loops in flat terrain.
Colluvial Stream Profile
Sediments are from hillslope, and debris flows. There is little transport - little deposition
Cascades Stream Profile
Sediments are from stream flow, debris flows and hillslope. There is high transport - low deposition.
Step-pool
Sediments are from stream flow, debris flows and hillslope. More transport of fines and gravels during normal to moderately high flows with little deposition except in low flow conditions
Plane-bed
Sediments are from stream flow bank failure, debris flows. Channels that have a surface that is armored has higher transport than deposition but those unarmored stream bottoms tend to transport.
Pool-riffle
Sediments are from stream flow, bank failure. Deposition limited in that grains eroded from one reach generally are deposited in the next and generally the stream is more transport limited than plane-bed profiles.
Dune-ripple
Sediments are from stream flow, bank failure. Generally fine grained with relatively flat gradients so transport is steady.
Order of Channel Morphology
Bedrock (Steep), Colluvial (>0,1), Cascades (>0.065), Step-pool (0.3 to 0.065), Plane-bed (0.015 to 0.03), Pool-riffle (<0.015), Dune-ripple (<0.015)
Channel Morphology that is debris flow dominated
Bedrock, Colluvial, Cascades
Channel Morphology that is fluvial dominated
Cascades, Step-ppol, Plane-bed, Pool-riffle, Dune-ripple
Channel Morphology where scour occurs
Bedrock, Colluvial, Cascade, Step-pool
Riffles
erosional habitats with fewer deposited fine particles between substrates.
Step pools
Series of pools separated by near-vertical steps that repeat at a frequency of one to four channel widths.
Meander Stream Pattern
form in areas with relatively flat bedding and terrain. Often found within a floodplain. Once a meander is established and if uplift occurs then the meander can become incised.
Oxbow lakes
When a meander cuts through to create a cutoff meander.
Parallel Stream Pattern
Develops on relatively young, steep slopes with a relatively uniform gradient such as found in newly uplifted terrain. This type of terrain is found along the west coast which is tectonically active and exhibits an emerging coastline.
Dendritic Stream Pattern
Common pattern that develops where there is uniform resistance to erosion and no control by structural or lithologic elements. Tributaries branch irregularly with most if not all stream confluences occurring at angles less than 90 degrees. The pattern often indicates relatively horizontal bedding to shallow dip and is found where the slope is gentle to moderate.
Radial Stream Pattern
Radial patterns are similar to parallel patterns in that they both develop on steep slopes that are relatively uniform. The radial pattern is simply a series of roughly parallel stream channels that have developed on a conical shaped hillside such as a volcanic cone or dome causing them to form the radiating appearance.
Deranged Stream Pattern
Have no predictable pattern resulting from irregular surfaces such as are found in glacial or karst terrain where there is no prominent drainage direction. Streams that flow in and out of small bodies of water that occupy low areas and swampy or boggy areas are characteristic.
Braided Stream Pattern
Found in streams that have alternating flooding and dry periods, When it is flooding there is a lot of sediment being carried as suspended and bed loads. As the flooding declines the volume of sediment being carried declines because the energy of the flow has decreased. This deposited sediment creates an irregular stream bottom and the water has to find its way around the deposited material giving it a braided pattern.
Trellis Stream Pattern
Develop where there is strong lithologic controls and are found where there is bedding structure. This is prevalent in the Appalachians where the folded beds create dipping resistant rock formations that make hogbacks with softer formations making the valleys. The nearly right angle tributaries result from cutting across the resistant layers.
Rectangular
Right angle jointing or faulting creates the rectangular pattern. These joints and faults develop in a weakened rock which allows the streams to accentuate the erosion more rapidly as the unjointed rocks are more resistant. This type of drainage is prominent in the Adirondack Mountains.
Annular
Annular drainage patterns form on an eroded upwarped dome or down dropped basin. The ring like pattern develops from erosion of the softer rocks causing the stream to follow the rocks that are softer and more easily eroded. Similar to trellis, only in an enclosed pattern.
Reynolds Number
Calculated to determine whether the flow is laminar or turbulent. Incorporates hydraulic radius (Cross sectional area of the stream divided by the length of the boundary from side to side where water is in contact with the channel), flow velocity, and the ratio between the fluid density and viscosity. Reynold numbers less than 500 represent laminar flow, between 500 to 2000 both laminar and turbulent flow, and greater than 2000 turbulent flow.
Laminar Flow (streamline flow)
fluid travels smoothly or in regular paths. The velocity, pressure and other flow properties at each point in the fluid remain constant.
Turbulent Flow
fluid undergoes irregular fluctuations and mixing.
Advanced or Emerging Coastlines
The west coast, as it is continuing to experience uplift as a result of it being in a tectonically active region of the U.S. This results in a higher energy environment with steep cliffs and many erosional features. The extent to which these features develop is related to the relative resistance of the rocks to erosion.
Characteristics that influence the rate of marine erosion include
Rock Type and strength, joint and fracture patterns, shape of the coastline, tide swing, and the extent and depth of the continental shelf.
Retreated or submerging coasts
The east and Gulf coasts are , in general, submerging coastlines, with a lower energy environment, resulting in mostly depositional features.
Spit
Develop from a wave train that is oblique to the shore causing the sand to be deposited longitudinally projecting from the protruding point on the shore. Attached to the shore at one end. A hook results when the waves swing around, particularly in high seas.
Estuary
partly enclosed coastal body of water in which river water is mixed with seawater. In a general sense, the estuarine environment is defined by salinity boundaries rather than by geographic boundaries.
Tombolo
One or more sandbars or spits that connect an island to the mainland.
lagoon
An area of relatively shallow, quiet water situated in a coastal environment and having access to the sea but separated from the open marine conditions by a barrier. The barrier may be either a sandy or shingly wave-built feature such as a sandbar or a barrier island or coral reef.
Wave Cut Bench / Platform
have been eroded into gently sloping surfaces at the surf level by the waves and the abrasion of the rock debris
Marine Terrace
A wave-cut platform that has been exposed onto land by uplift or a lowered sea level.
Sea Cliff
Sea cliffs are scarp-like features found at the seaward side of marine terraces and are caused by erosion from wave action, frequently from undercutting.
Headlands
The cliffs and upland areas remain in areas where more resistant rocks remain following the erosive action of the waves.
Sea Arches, Caves
Arches and caves develop along headlands or sea cliffs where the waves attack from more than one direction. Caves that continue to be eroded can become arches.
Stacks, Chimneys, or Skerries
These are created when resistant portions of the headlands become separated from the shore by wave action erosion but are located on the wave cut platform. Stacks and chimneys are exposed at high tide whereas skerries are only exposed when the side recedes.
Beaches
composed of well-sorted (poorly-graded) materials that are constantly being broken down by the wave action. Young beaches are often made up of coarser grained materials (gravel). The variation of the intensity of the waver action can cause the beach deposits to move onshore or offshore
Bars
Submerged sand ridges develop when the waves, which are short and steep, break closer to the shore, drawing the sand offshore where it deposits to create a sand bar. This wave type occurs most often in the winter and during storms. Sand bars may then disappear in the summer when the waves are quieter.
Barrier Beaches, Islands
When sand bars become big enough they can become a barrier beach that runs parallel to the shore. If the sand is above the water at high tide long enough, sand dunes develop through wind-borrne transportation, and eventually plants can begin to take hold. If this continues long enough and gets well enough established then a barrier island is formed. Barrier beaches (islands) often form shallow quiet water areas called lagoons on the shoreward side of the beach.
Barrier Island Chains
Several barrier islands running parallel to the shore end to end.
Fault Scarp
caused by the fault movement itself
Fault-line scarp
caused by differential erosion or weathering along the fault causing the scarp to recede from the location of the fault.
Graben
are down dropped blocks that present as valleys.
Horst
Horst are relatively higher blocks that can erode to make triangular facets
Reverse faults form in what type of environment
result from a compressional structural environment in an area that has brittle rocks.
Thrust faults
Reverse fault that has a dip of less than 45 degrees and often are on the order of 20 degrees or less.
Blind Thurst
When a fault does not reach the ground surface.
Nappe
formed by tectonic plate collisions where material has been thrusted on top of the underlying material as much as a mile or two.
Landslide geomorphology is highly dependent on what three variables
Slope
Underlying Geology
The presence of water
Head scarp
The break in slope that marks the uppermost portion of the slide mass where it has broken away from the in-place hillside. Frequently cracks form above the scarp that can be an incipient scarp.
Crown
The undisturbed in-place material above the head scarp of a slide.
Hummocky terrain
A bumpy, irregular ground surface that contains numerous high spots and low spots, which are small closed basins where water can be retained, due to the downslope movement of the landmass.
Transverse cracks
Cracks that form transverse to the slide movement where the slide mass moves over a high spot or ridge under the slide material.
Radial Cracks
Cracks that form parallel to the slide movement at the toe of the slide mass as the material spreads where it is not contained.
Transverse Ridges
Ridges that form transverse to the direction of the slide movement from the compression or thrusting of the upper slide material on the lower part of the slide.
Toe
The lowest part of the slide mass that usually has an arcuate shape where the slide material has moved over original ground.
Foot
The downslope extension of the slide mass beyond the rupture plane in the subsurface.
Rupture surface (slide plane)
The demarcation between the in-place ground and the slide mass.
Speed of Fall Landslide Movement
Rapid
Speed of Topples Landslide Movement
Rapid
Speed of Flow/Avalanche Landslide Movement
Rapid
Speed of Slide (Rotational/Translational) Landslide Movement
Slow
Speed of Lateral Spreads Landslide Movement
Slow
Speed of Creep Landslide Movement
Very Slow
Falls - Common Trigger
Freeze thaw in rocks
Topples - Common Trigger
Freeze thaw in rocks
Flows/Avalanches - Common Trigger
Supersaturated soils
Slides (Rotational) - Common Trigger
Rising Groundwater
Slides (Translational) - Common Trigger
Rising groundwater or shaking
Lateral Spreads - Common Trigger
Rapid under earthquake conditions
Creep - movement observation
So slow that tree trunks will bend upward making a J-Shape
Most prominent and well known form of eolian features
Sand Dunes
Barchan Dune
Crescent-shaped, tails to leeward, rarely vegetated
Leeward
Direction Wind is blowing
Windward
Direction wind is blowing from
Parabolic Dune
Crescent-shaped, tails to windward, often associated with some vegetated cover
Transverse Dunes
Perpendicular to the wind, exhibits the traditional gentle windward slope and the steep slip face nearing the angle of repose. (Both Barchan and Parabolic dunes are a variety of transverse).
Longitudinal Dune (Seif)
Parallel to the wind, thought to develop in areas in which the prevailing wind causes the dunes to lengthen in the direction of the wind but the dune height increases due to the cross winds during periods of irregular wind flow.
Star Dunes
Have 3 or more arms and form from multi-directional winds. These make the tallest dunes because the sand collets in the center.
Blowout
a depression caused by deflation in an area where either migrating dunes exist or a small break develops in the surficial integrity of a stabilized windblown deposit or in some causes the underlying material is composed of a poorly to non-indurated material. (Erosional Landform)
Desert Pavement
Sometimes called desert armor, is a name applied to the relatively flat residual surface of closely-packed, wind-polished stones. This type of condition is the result of the removal of the fine-grained particles by wind and sheetwash. Often these remaining stones are somewhat cemented in place. (Erosional Landform)
Pedestal rocks
Commonly called balanced rocks, these formations are a result of a combination of wind and water erosion (deflation) in an area where there are resistant rocks capping weaker more easily eroded rocks. (Erosional Feature)
Ventifacts
Stones that have been abraded by the wind on at least one side so they are polished or faceted. They are usually only found in unique environment of no vegetation, strong wind and plentiful sand. (Erosional Feature)
Yardang
A long, jagged, sharp-edged ridge between troughs, oriented with the direction of the prevailing winds, in an arid region which is underlain by relatively weak materials. (Erosional Feature)
Soil Profile is dependent on what two factors
Climate and Environment. Breakdown of the organic materials that are deposited on top of the ground and the chemical breakdown of the underlying bedrock.
O-Horizon
The upper most layer of the soil profile. Organic layer which consists principally of relatively undecomposed plant matter.
Zone of Eluviation
A-Horizon - Downward percolation of water through soil horizons that transports soil content from upper layer sto lower levels
A-Horizon
Surface soil (biomantle or zone of eluviation) - This top layer of the soil horizon contains a mixture of organic and mineral materials. Soluble constituents such as iron, aluminum, clay and organic compounds have been leached out. It tends to be darker in color and most of the biological activity such as worms, fungi, bacteria and nematodes are concentrated here.
Zone of illuviation
B-Horizon - Accumulation of dissolved or suspended soil materials in one area or layer as a result of leaching (percolation) from another.
B-Horizon
Subsoil (Zone of illuviation) - The iron, aluminum, clay and organic compounds accumulate in this zone, there is no organic matter, and it has a distinctly different soil structure. The color of this horizon is brighter and stronger or has higher chroma.
C-Horizon
Substratum - Soil forming processes have had little effect on these soils. They lack properties of the other horizons but may accumulate soluble compounds that have passed through the B-Horizon. In saprolites the original rock structure may still be present.
Saprolite
formed by decomposition of rocks that has remained in its original site.
Regolith
The layer of unconsolidated rocky material covering bedrock. Includes all of the weathered material within the profile.
Solum
The altered layer of soil above the parent material that includes the A and B horizons.
Weathering
the in-place alteration of rocks and minerals. defined as the physical and chemical decomposition and/or disintegration of the mineral constituents of a rock mass by the natural processes of oxidation, reduction, hydration, solution, carbonation, or freeze-thaw.
Two types of weathering
mechanical and chemical
Mechanical weathering
breaks down the rock by either freeze-thaw action or changes in temperature of pressure. As chemical weathering turns minerals to clay, they can absorb enough water to expand and put pressure on the rocks, physically breaking them apart.
Chemical Weathering
alters the internal structure of minerals by the processes of oxidation, carbonation, or hydration. As the surface area of an exposed rock increases through mechanical weathering the opportunities for chemical weathering increase/accelerate.
Hardpan
A hardened impervious layer, typically of clay occurring in or below the soil and impairing drainage and plant growth. Found in the B-Horizon.
What happens when feldspar (the most abundant mineral in the Earth’s crust) reacts with water and weak acids
It decomposed into clay minerals.
What is the main determinant of the products produced by chemical or mechanical weathering
Climate
Dominate weathering in Artic Climate
Frost weathering (mechanical weathering) dominates. Feldspars in granitic rocks are reduced to coarse angular fragments, similar to what you might find in mountainous topography or in tectonically active areas.
Dominate weathering in temperate to semi-arid climates
Mechanical weathering dominates, leaving feldspar-rich sands and a clay fraction of montmorillonite ( a member of the smectite group of expansive minerals) and illite.
Dominate weathering in humid, tropical climates
Chemical weathering dominates. Feldspar is reduced to kaolinite, iron and aluminum hydroxides, and dissolved ions of K, Na, Ca, and Mg (laterite). Pyroxenes and olivines may dissolved completely. Intensely weathered clays from silicates may have lost all silica leaving accumulations of aluminum hydroxides that form bauxites.
Laterite
a clayey soil horizon rich in iron and aluminum oxides, commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red because of the high iron oxide content.
Bauxite
a metalliferous laterite where aluminum is concentrated.
Weathering of pyrite FeS2
is based upon the Eh (oxidation or reduction potential) and pH (the measure of acidity or basicity of a solution) relationship.
Eh is measured how
in the environment in volts using an electrode and comparing it to a theoretically calculated value.
What do Eh and pH indicate?
Eh indicates the ability of the environment to supply electrons, while pH indicate the environment’s ability to supply protons.
Stability of minerals under weathering
Halite
Calcite
Olivine
Anorthite
Pyroxene
Amphibole
Albite
Biotite Mica
Orthoclase
Muscovite Mica
Clay Minerals
Quartz
Aluminum Hydroxides (Gibbsite)
Iron Oxides (Hematite)
pH dependent bacteria that can accelerate the weathering process of pyrite
Thiobacillus ferroxidans
Oxidizing environment
adds oxygen and removes hydrogen and loses electrons through the process.
Reducing environment
oxidation is prevented by removal or oxygen and other oxidizing gases or vapours, and may contain actively reducing gases such as hydrogen, carbon monoxide and gases such as hydrogen sulfide that would be oxidized by any present oxygen.
Dunes
Sand that is piled up as a result of transportation by the wind of sand-sized particles. Often found in back beach areas or desert climates where the topography is relatively flat and the surface sand is dry. Most dunes are composed of a well-sorted sand (SP).
Ripple and ridges
Small-scale features that are usually found on the surfaces of sand deposits resulting from the flow of wind or water over the surface. The shape of the ripple mark can be an indicator of the direction of flow of the wind or water or the depositional environment.
Sand shadows and sand drifts
These two features are similar in that both form as a result of an obstruction in the path of migrating sands. The sand shadow forms behind the obstruction where the velocity of the wind declines causing the sand to drop. Sand drifts develop in the lee (downward side) of a gap where the velocity of the wind declines after passing through the gap.
Sandsheets
Extensive flat areas covered with a coarse-grained sand that does not form dunes, but typically are covered with ripple marks.
Whaleback or sand levees
A very large hill or ridge of sand elongated parallel to the prevailing wind. In general whalebacks do not migrate and can be over 100 miles long, a couple of miles wide and 150 feet high. Undulations are smaller whalebacks.
Loess
Wind-blown silt (ML) that is calcareous, homogeneous, and permeable. Loess covers extensive area s in the Pacific Northwest and Mississippi Valley regions.
API Units
A unit of measurement of gamma rays. API stands for American Petroleum Institute.
ASTM
American Society of Testing and Materials International. ASTM develops numerous standards by consensus and publishes them annually.
Auger
A screwlike boring tool used in relatively unconsolidated near-surface materials. Soil that sticks to the auger gives a good indication of the soil type encountered at the depth penetrated.
Azimuth
For radar images, the dimension parallel to the flight path.
Borehole Geophysics
The science of recording and analyzing measurements of physical properties made in wells or test holes.
Caliper Log
A well log that shows the variations with depth in the diameter of an uncased borehole.
Casing
A heavy metal pipe lowered into a borehole and cemented in place to prevent cave-in, loss of drilling fluid, and unwanted fluids from entering the borehole.
Cone of Depression
A depression in the potentiometric surface of groundwater that has the shape of an inverted cone and develops around a well from which water is being withdrawn. It defines the area of influence of a well.
Cone Penetrometer
A tool consisting of a cone-shaped tip on the end of a hollow steel rod that is pushed into the ground to record resistance to insertion.
CPT
Cone Penetration Test. The test measures the resistance of the cone to penetration and the friction on the rod. Can be correlated to soil type and density in both cohesionless and cohesive soils. Sandy soils have a high cone resistance and low friction ratio; clayey soils have a low cone resistance and high friction ratio.
Drawdown
The amount the water level in a well is lowered due to withdrawal of water.
Dutch Cone
A specific type of Cone Penetrometer.
Gamma Ray Log
The radioactivity log curve of the intensity of natural gamma radiation emitted from the rocks in a borehole. It is commonly used to differentiate between shale (with a high gamma reading) and other sedimentary rocks.
Gravity Survey
A series of measurements made by a gravimeter at a number of different locations in the field to determine the density distribution by evaluating the gravitational pull.
Ground-Penetrating Radar
The application of radar or radio waves to the subsurface using a radar impulse as the source and a receiver. Transmits high frequency radio waves into the ground that are recorded back at the antenna to get an image of subsurface structures or conditions.
Low frequency antennas examine the subsurface at great depths while the higher frequencies are used near the surface.
Ground-penetrating radar can see as deep as 100 feet.
InSAR
Interferometric Synthetic Aperture Radar. A remote sensing method that is sued to study ground deformation, particularly in subsidence, volcanic and fault studies.
Invaded Zone
A transitional zone in a borehole located between the flushed zone and the uninvaded zone. It refers to the degree to which the mud filtrate penetrates the formation fluids, resulting in a transition from the mud filtrate saturation to the formation water saturation.
LiDAR
Light Detection and Ranging. A remote sensing method using laser beams to record topographic changes.
Lysimeter
A device for collecting water from the pore spaces of soils to determine the soluble constituents removed by drainage. It consists of a porous ceramic cup (to withdraw soil pore water) a tube to act as a reservoir and a vacuum assembly to retrieve the sample.
Neutron Log
A radioactivity log curve of the intensity of radiation produced when the rocks in a borehole are bombarded by neutrons. It indicates the presence (but not type) of fluid. It is often used in association with the gamma ray log to distinguish porous and nonporous formations.
Normal-Resistivity Log
A log that makes measurements of the resistivity of formations using 4 electrodes set up in a standard 16- or 64-inch spacing.
are used to determine water quality and to find the saltwater-fresh interface in coastal aquifers.
Are subject to errors unless corrections are made for bed thickness, borehole diameter, mudcake thickness, and fluid invasion.
Packer Test
An aquifer test in which two inflatable seals (or packers) are set in an open borehole to prevent movement of groundwater in the test section while the permeability of the isolated rock is determined.
Percolation (Perc) Test
An in-situ test that determines the suitability of a soil for a sewage disposal system (leachfield). This test made by digging a hole, filling it with water, wand measuring the rate of decline of the water table.
Piezometer
A device that measures in situ pore water pressures, often an open standpipe to monitor water levels in permeable materials, or an enclosed electronic pressure transducer used in impermeable soils.
Pumping Test
A test made by pumping a well for a period of time and observing the change in hydraulic head in the aquifer.
Range
For radar images, the dimension perpendicular to the flight direction.
Resistivity Log
A log that makes quantitative measurements of the specific resistance of a material to the flow of an electric current.
Rippability
The ease with which soil or rock can be excavated mechanically. Initially was based solely on seismic velocity, now parameters such as uniaxial tensile strength, weathering, abrasiveness and spacing of discontinuities are considered to obtain a more representative assessment.
Rotary Drilling
The chief method of drilling deep wells. A drill bit grinds a hole in the rock, and lubrication and cooling are provided by continuously circulating drilling mud which brings the well cuttings to the surface.
Rock Quality Designation (RQD)
A measure of the intactness of rock core, relating to the percentage of intact core to the total core run. defined as the total combined length of all the pieces of intact core that are longer than twice the diameter of the core recovered during the core run divided by the total length of the core run.
Seismic Reflection
A survey method that utilizes the travel times of seismic waves that are reflected back from deep formations giving a detailed picture of subsurface structures.
Shelby Tube
A thin-walled, push-tube sampler that obtains undisturbed samples of cohesive soils. Some level of cohesion is required. Hard, cemented or gravelly soils, or soils too soft or wet, cannot be sampled with this type of sampler.
Single-Point Resistivity Log
A log that measures the resistivity using two electrodes and having a limited area of investigation of from 5 to 10 times the electrode diameter.
Widely used for making lithologic interpretations.
Slug Test
An aquifer test made either by pouring a small charge of water into a well or by removing a slug of water from the well. The removal of water from the well is also called a bail-down test. Used to determine hydraulic oncductiivty and transmissivity, reliability of storage coefficient value is questionable.
Split-Spoon Sampler
A thick-walled barrel sampler that obtains disturbed soil samples and that is used in the Standard Penetration Test.
Spontaneous Potential (SP) Log
A log of the difference in DC voltage between an electrode in a well and an electrode at the surface. The difference in voltage is mostly a result of the electrochemical potentials that develop between borehole fluid, formation water and the surrounding rock materials.
Standard Penetration Test (SPT)
A standardized soil sampling procedure in which a 140-pound hammer is dropped 30 inches, drilling a two-inch split-spoon sampler 18 inches. The blow count to drive the sampler through the last 12 inches is correlated with the soil conditions. The number of blows is related to the density or strength of the soil. Recorded blow counts are affected by the overburden pressure with deeper soils showing greater resistance to being driven and therefore a higher blow count.
Tensiometer
A device sued to measure soil matric potential (soil water suction, or the ability to draw water into the pore spaces). Used to determine irrigation needs and water consumption by plants.
Test Pits
A pit easily dug with a backhoe to obtain bulk samples and to identify subsurface materials in situ. They are useful to differentiate between large boulders and bedrock, to detect soil cracks or fissures, and to determine thickness of shallow units and suitability of borrow materials. Frequently used for fault and landslide investigations.
Only useful for shallow surveys 12 to 15 feet deep.
Well efficiency
The ratio in percent of theoretical drawdown to actual drawdown measured in a well.
Well log
A graphic record of the measured physical characteristics of the subsurface encountered in a well plotted as a function of depth.
Remote Sensing
general term for the collection of images using methods that are not in direct physical contact with the object or location being observed. (Aerial imagery, satellite imagery, infrared detectors, thermal, laser, and radar systems)
Stereo-Paired Low-altitude Aerial Photography (black & white, color) Advantages/Disadvantages
Gives more detailed view of a smaller area. Images may only be taken on clear days, either early or late, to provide shadows to assist in interpretation. Relatively low cost.
Principally used for engineering geologic and environmental investigations; landslides, faults, site histories.
Scale 1:40,000 or larger
High Altitude Aerial Photography (black & white, color) Advantages/Disadvantages
Images don’t show as much detail as they have less resolution, they are much smaller in scale so are only usable for regional studies. Fewer photographs are required to cover an area. Relatively low cost.
Used to map topography, soils, gross geologic features like plunging anticlines, and crop inventories.
Scales 1:80,000 to 1:120,000
Infrared Photography “False Color” (black & white, color) Advantages/Disadvantages
Images will show stressed vegetation as pink to blue before it is visually apparent. Healthy vegetation appears red. Images provide higher contrast and greater resolution than visible color photos.
Used to study landforms, health of vegetation, environmental pollution, and effects of human activities; not to be confused with thermal infrared which takes images at longer wavelengths.
Scales: 1:58,000 to 1:120,000
SLAR - Side-looking Airborne Radar Advantages/Disadvantages
Capable of obtaining data day or night and through the clouds, but the shadows produced may obscure areas.
Often used in areas in which cloud cover is common.
SRTM - Shuttle Radar Topography Mission / SIR - Shuttle Imaging Radar Advantages / Disadvantages
High resolution data available from the USGS for input into GIS. Data control points were precisely located by geodetic surveying. There are voids where data was not collected.
Elevation data used to generate 3-D visualizations of the Earth’s surface show changes due to flooding, erosion, landslides, earthquakes, weather, and climate change. Military uses them for mission planning, rehearsal, modeling, and simulation.
InSAR - (Interferometric Synthetic Aperture Radar) Advantages/Disadvantages
Surveys can be done quickly and cover a large area at a good resolution. Errors can be introduced by atmospheric conditions as well as varying topography. There is no U.S. satellite dedicated to InSAR.
Used for measuring deformation and hazard monitoring such as fault and landslide movement, volcanic activity, and subsidence. Additional uses are tracking ice sheets and groundwater movements.
Landsat (formerly Earth Resources Technology Satellite - ERTS) Advantages / Disadvantages
Open source imagery available in digital format. Uniform prices and priorities.
Samples 11 electromagnetic bands.
Map soils, geology, and the effects of precipitation and evaporation upon the occurrence and character of groundwater.
SPOT (Satellite Pour I’Observation de la Terre also known as Systeme Probatoire d’Observation de la Terre) Advantages / Disadvantages
While expensive, there is a quick turnaround for images (the satellite can be tasked to provide custom images). Resolution is available at various levels down to 2.5 m.
Images are used for different purposes ranging from stereoplotting and detailed radiometric studies, photointerpretation, standard cartographic projection (digital elevation models), thematic studies, and surveillance.
LiDAR (Light Detection and Ranging) Advantages / Disadvantages
It penetrates the canopy and can be used for obtaining details in remote areas. It cannot be used on cloudy or rainy days. Uses a near infrared laser to map topography, while green light is used to measure bathymetry.
Used to collect elevation data as an alternative to field surveys and photographic techniques and is used for fault studies.
NDOP Imagery
Provides complete coverage of the U.S. The intention of the program is to update digital orthoimagery every 3 to 10 years.
NHAP Imagery (National High Altitude Program)
Started in 1978 and ended in 1987. It was run through a number of Federal agencies; their goal was to provide consistent and systematic aerial photograph coverage in the U.S. for the widest variety of users. Two images were taken at 2 different scales, 1:58,000 CIR and 1:80,000 black and white, simultaneously.
NAPP Imagery (National Aerial Photography Program)
Began in 1987, replacing NHAP, with the objective of acquiring complete uniform photo coverage of the conterminous U.S. over a 5 to 7 year cycle. The photography has a scale of 1:40,000 and can be provided in either the black and white or color infrared format.
NRCS Imagery (Natural Resource & Conservation Service) or USFS Imagery (Forest Service (FS) or USFS)
Photos are not generally rectified for scale accuracy. The scales of the negatives range from 1:6,000 to 1:80,000; not all scales are available for all areas. Most of the FS photography is available in color or color infrared. Most of the NRCS imagery is B/W.
NAIP Imagery (National Agriculture Imagery Program)
Aerial imagery is acquired during the growing season. The goal is to make digital orthophotography available to both the public and government agencies within a year. These “leaf-on” photos are taken to provide an indication of the growing conditions. This imagery is used as a base layer for GIS programs.
Electromagnetic Spectrum
light and energy emitted by the sun. Commonly divided into seven regions from shortest to longest wavelengths:
Gamma Rays,
X-rays,
Ultraviolet,
Visible,
Infrared,
Microwave,
Radio.
Visible Light
approximate wavelengths of 400 to 700 nanometers.
Violet has the shortest and red has the longest
ROY G BIV
Blue Light - reflected by water
Green Light - reflected by chlorophyll
Red Light - reflected by iron rich rocks and soils
Infrared Light
Divided into Near Infrared (NIR), Shortwave Infrared (SWIR), Midwave Infrared (MIR), and Longwave or Thermal Infrared (LWIR or TIR). Approximate wavelengths are from 700 nanometers to 15,000 nanometers
Near Infrared (700 to 1100 nanometers)
absorbed by water which highlights land-water boundaries. Plants reflect these wavelengths; the healthier reflect more strongly than stressed plants. This method can penetrate the haze so it is more useful in hot and humid areas.
Shortwave Infrared (1100 to 3000 nanometers)
is useful to distinguish between cloud types and between clouds, snow and ice. The more water there is at the surface and in the soils, the darker the image will appear. Newly burned land reflects well in this wavelength. In Addition, geologic maps can be made based on the different reflected characteristics of the rocks.
Midwave Infrared (3000 to 5000 nanometers)
is used to measure thermal radiation at night, sea surface temperatures, and fires.
(Unnamed) Infrared (6000 to 7000 nanometers)
can track water vapor in the atmosphere, so it is useful for weather forecasts.
Thermal or longwave Infrared (8,000 to 15,000 nanometers)
Images digitally record emitted heats (not reflected heat). As a result, these wavelengths can be detected both day and night. In a black and white thermal image the areas or objects that have a lighter grey or white are warmer than those that are darker or black in the image. Metallic objects, granite, or snow have a low emissivity and so appear cool or dark whereas cement, asphalt, basalt have a higher emissivity and will show up as a lighter tone.
Things that influence emissivity of thermal images
Color (dark images absorb heat have a higher emissivity)
roughness of the surface (rough surfaces absorb heat better)
Moisture content
soil compaction
angle of observation
Common Uses of Aerial photographs
Historical uses of sites for environmental evaluations
Interpreting landslides features and mapping, faults, joints and lineations.
Examining drainage and erosional characteristics for potential impact on engineered structures.
Mapping surficial deposits for potential borrow areas.
Geologic mapping of rock lithology
Delineating soil patters and distributions.
Examining small-scale structural features to determine the presence of traps for petroleum.
Determining general lithology, structure, and physiography for locating ore deposits.
Passive Remote Sensing Technique
rely on sensors to record the energy reflected back from the Earth’s surface. They do not introduce a source of energy such as light or microwaves.
Active Remote Sensing Technique
Introduce a source of energy or light and sensors capture the reflected energy.
(e.g. LiDAR, Radar, SLAR, SRTM, InSAR)
Radar Images
Acquired by sending microwave pulses and the return energy is recorded. Can operate day or night and in all weather, with the ability to penetrate clouds.
Determination of scale
scale =
Focal Length (f) /
Flying height (H)
H
Seismic Refraction
to determine the seismic velocities of the subsurface materials, generally at relatively shallow depths based on the refraction of the waves that occurs at the interface between the different geological materials. The refraction angle is based Snell’s Law relating the angle of incidence and the angle of refraction to the seismic velocities of the two subsurface materials at the interface between the two materials.
Seismic Refraction - Seismograph Geophones
Planted in a linear fashion, at regular intervals with shot points made at each end and sometimes in the middle. Geophones detect the seismic waves triggered at the shot points and the travel time information of the travel time information of the direct wave is transmitted to a seismography to be recorded.
Geophones array should be 4 to 5 times the depth of interest and geophones should be equally spaced. Seismic waves can be generated by hitting a metal plate, dynamite, or dropping a heavy ball.
Ideally the lithologic interfaces are roughly horizontal and there are 3 or fewer interfaces having increasing seismic velocities with depth.
Seismic Refraction - Uses
Engineering geology investigations
determination of shallow subsurface conditions
depth to bedrock
characterize rock type and degree of weathering
locate faults and fractures
stratigraphic mapping
calculate individual subsurface layer depths and thickness
landfill delineation
foundation investigations
rippability surveys
Economic geology investigations
mineral exploration
Mining investigations
petroleum exploration
determining near surface corrections for deep refection investigations
Hydrogeology investigations
depth to water table
hazardous waste site investigations
locating buried channels
Seismic Reflection
to determine the seismic velocities of the subsurface materials, generally at relatively deep depths based on the reflection of the waves at the interface between two rock types. The reflection angle is the same as the angle of incidence.
Direct Wave
the first arriving wave in a seismic refraction survey
Seismic Reflection - Seismogrpah Geophones
method uses a short shot to geophone spacing and can record many interfaces to thousands of feet in depth. Seismic sources and recording devices are similar to seismic refraction surveys though the shot signal is larger due to the depths involved. Shallow work can be done by at much greater expense.
Seismic units of measurement
velocities, feet/sec, or meters/sec
Seismic Reflection Uses
Economic
Petroleum exploration - defining structures at great depth, often under oceans
Ground Penetrating Radar units of measure
MHZ (megahertz)
Ground Penetrating Radar Antenna
Usually in contact with the ground. Transmits short pulses of radio waves into the ground to detect subsurface objects, voids, fractures and a change in geologic units.
The electrical conductivity of the subsurface materials and transmitting frequency limit the applicable depth. Lower frequencies can penetrate deeper, however high frequencies provide better resolution.
Depth penetration reaches a maximum of 30 m in dry sandy soils or massive dry materials such as granite, limestone and concrete,. Clays or high conductivity materials (such as saline groundwater) restrict penetration of the waves from only a few centimeters to 3 m.
Usually mounted on a sled or lawnmower device that can be pushed or towed.
Ground Penetrating Radar Uses
Engineering geology investigations
locate karst-related voids in the subsurface
map geological strata (bedrock)
fractures and voids
site stratigraphy
examine the structural integrity of roads, bridges, and buildings
locate and map re-bar in concrete structures
profile lake and river bottoms
Hydrogeology/environmental investigations
locate and delineate subsurface features
underground storage tanks
buried drums
metallic and nonmetallic utilities and pipes
map landfill boundaries and previously excavated and backfilled areas
delineate and map groundwater table
General geology
identify drilling locations.
Electrical Resistivity Survey
Ability to transmit electrical current through the ground is related to the resistivities of the subsurface materials and the resistivity of the groundwater.
Most minerals, except metallic ores are essentially nonconductive so the measurements are of the pore water characteristics.
Ideal for delineating electrolytic contaminant plumes but can also be sued for locating bulk waste or buried drums, trench limits and locating or following buried utilities.
Electrical Resistivity Survey - Electrical or Direct Current Methods
Measure the bulk resistivity of the subsurface to determine geologic structure and/or physical properties of the geological materials.
Groundwater fluids in saturated or nearly saturated ground regulate the resistivity of the subsurface materials. Freshwater has a higher resistivity while water with a high value of TDS is conductive (low resistiviyt).
Apparent Resistivity
Is the bulk average resistivity of all soils and rock that influence the flow of current.
Electrical Resistivity Survey - Current Source
Electrodes Data acquisition System. The electrodes are planted in the ground linearly at a spacing that is dependent on the lateral extent required and the depth of interest. The wider spaced the electrodes the deeper the view. An additional probe is planted through which the electrical current is transmitted.
An electrical current is introduced directly into the ground through current electrodes. The voltage potential difference is measured between a pair of potential electrodes.
Wenner Array
Electrical Resistivity Survey method used most frequently for engineering and environmental investigations.
Electrical Resistivity Survey - Uses
Engineering geology investigations
map faults
karst voids
Hydrogeology/environmental investigations
characterize subsurface hydrogeology
determine depth to groundwater
map stratigraphy
map clay aquitards
map salt-water intrusion
map vertical extent of certain types of soil and groundwater contamination
estimate landfill thickness
map lateral extent of conductive contaminant plumes
delineate disposal areas
aid is siting wells.
Magnetic Surveys
Measures variations in the magnetic field by determining the magnetic character of the ferromagnetic minerals in terms of the intensity and orientation of the magnetization in the Earth’s field.
Records both remnant magnetization from the existing magnetic filed (flux) and the strength of induced magnetism from an external magnetic filed.
Usually more pronounced in igneous rocks; sedimentary rocks are generally not magnetic.
Magnetic Survey - Unit of measure
The unit of measure for magnetic anomaly maps is the nT or nanoTesla, which is the magnetic flux density.
Magnetic Survey - Uses
Allows evaluation to a greater depth for ferrous objects, makes an ideal tool to detect steel barrels in the subsurface.
Hydrogeology/environmental investigations
locate buried steel drums and tanks
Economic geology investigations
geologic features
mineralized bedrock fractures
igneous intrusions
ore bodies
locating rails in abandoned mines
Gravity Surveys
Gravity measurements detect changes in the earth’s gravitational field caused by variations in the density of the soil or rock or engineered structures. Useful for mineral and petroleum exploration, regional geophysical surveys, and measurement of the geoid.
Bouguer Anomaly
the difference between the observed gravity measurement’s and the theoretical gravity.
Gravity surveys require a number of corrections to obtain the Bouguer Anomaly
Bouguer anomaly basic equation
= observed gravity - latitude correction + free air correction - terrain correction
Free Air Correction
compensates for the altitude of the recording device above sea level. Gravitational attraction decreases with elevation.
Bouguer Correction
Corrects for variations in density of the Earth’s materials. A correction is applied using a constant and applying it to the specific graivity of the rock and the difference in elevation between the topography and sea level.
Latitude Correction
Corrects for the shape of the Earth. The earth is not round and the gravity increases with higher latitudes because of diameter of the Earth is greater at the equator than it is at the poles.
Topographic (Terrain) Correction
Corrects for the decrease in gravitational attraction due to the distance form the center of the Earth and greater density of materials that make up the higher elevation areas. This is computes using a planar base with mountains causing a positive correction and valleys causing a negative correction.
Tidal Correction
Corrects for the variations in background values related to the pull associated with the relative positions of the Earth, sun and moon.
Gravimeter Unit of measure
milligals ( the unit acceleration of gravity of 1 cm/sec^2 is called a gal, a milligal (mgal is one thousandth of a gal)
Gravity Surveys - Uses
Engineering geology investigations
locate and characterized buried bedrock channels and bedrock structural features
detect voids, caves, and abandoned mines or tunnels
geological mapping - used on a regional scale for mappin the subsurface geology
geotechnical studies - mapping subsurface cavities
Economic geology investigations
petroleum exploration - used on a regional scale for mapping sedimentary basins
coal exploration - mapping of coal beds within sedimentary basins
mineral exploration - reconnaissance and direct indication of deposits
Hydrogeology/environmental investigations
mapping of groundwater
Spontaneous Potential - Units of measure
millivolts, measured increases to the left, run together with resistivity
deflections are negative to the left and positive to the right.
Spontaneous Potential - Uses
determining correlating lithology
establishing or confirming bed thickness
determining salinity of formation water
Resistivity - Units of measure
Ohm - Meters, increases to the right, run together on the same tool as SP
Resistivity - Uses
making lithologic interpretations
identifying water quality
locating the fresh water - salt water interface in coastal aquifers
determining hydrocarbon saturation in oil and gas wells
Neutron - Units of measure
% porosity, measured as increases to the left
Neutron - Uses
measuring porosity in petroleum and hydrogeology investigations
Gamma - Units of measure
API, measures naturally occurring radioactivity, increases to the right
Gamma - Uses
Determining shale content of formation
correlating stratigrpahy and lithology
evaluating of radioactive deposits
Density (Gamma-Gamma) - Units of measure
grams/centimeter^3 or kilograms/meter^3 or porosity units
Density (Gamma-Gamma) - Uses
measuring density of the rocks and is used to determine porosity
Sonic - units of measure
milliseconds/ft, acoustic logs
Sonic - Uses
Measuring the transit time of the formation to determine porosity
correlating units and facies analysis
mineral exploration for iron, hydrocarbons and potassium
Spontaneous Potential Curve Deflection (standard case)
Negative to the left and positive to the right. When the formation water is more saline than the drilling mud the deflection is to the left, if the relationship is reversed deflection is mirror image to the right.
Shale line or baseline
A line drawn through the extreme positive deflections on the SP curve for standard salinity relationships
Sand line
A line drawn through the extreme negative deflections
Electrical Resistivity
The ability of a substance to impede the flow of electrical current through itself. The greater the porosity and amount of formation water, the lower the resistivity.
Resistivity is the inverse of conductivity.
In most rocks the porosity and chemistry of the water filling the pores is of greater importance to the resistivity value measured than the composition of the rock matrix.
Most important factor in determining resistivity
The salinity of the water in the pores.
Values of R for evaporites and coal
Can be greater than 1000 ohm-meters because they are impervious and have very low porosity.
Why Tertiary Age sediments have anomalously high Resistivity
These sediments were deposited mainly in fresh water.
What are does a short-normal probe investigate
invaded zone
What are does a long-normal probe investigate
the invaded zone and formation water
How to differentiate between Coal and limestone on log curve
SP/Res curve is not a good answer since both exhibit low SP and very high resistivity. Therefore a density log would show a difference since coal is not very dense and limestone is extremely dense.
A mineral is defined as
a solid inorganic substance of natural occurrence
How are minerals defined
by means of their physical or chemical characteristics. Physical characteristics are a direct result of their chemical composition.
Physical characteristics that can be used to identify a mineral
crystal habit and symmetry
cleavage
fracture
crystal twinning
specific gravity
color and streak
luster
luminescence
radioactivity
magnetism
How are silicate minerals classified
on the basis of the configuration of anions in the mineral structure.
Shape of the silicate molecule
tetrahedron with four large oxygen atoms surrounding a silicon atom.
What are the seven types of silicate minerals?
Nesosilicates
Sorosilicates
Cyclosilicates
Inosilicates
Inosilicates
Phyllosilicates
Tectosilicates
Nesosilicates
Contains SiO4; composed of an isolated tetrahedral
includes zircon, olivine, and garnet
Sorosilicates
Contains Si2O7; isolated double or linked tetrahedral
includes lawsonite and hemimorphite
Cyclosilicates
Contains SiO3
Includes beryl group and tourmaline
Inosilicates (single-chain)
contains Si03
includes pyroxene group and pyroxenoid group
Inosilicates (double-chain)
Contains Si4O11
Includes amphibole group
Phyllosilicates
Contains Si2O5; forms sheets
includes biotite, talc and chlorite
Tectosilicates
Contains SiO2 and Si3O8; forms frameworks
includes feldspar and zeolite groups
Igneous Rocks - modes of occurrence
intrusive (plutonic) or extrusive (volcanic), or hypabyssal
Intrusive Rocks
Coarse grained rocks that are formed by slowly cooling magma far below the earth’s surface
Extrusive rocks
Smooth and fine-grained rocks that are formed by faster cooling magma at or above the earth’s surface
Hypabyssal Rocks
Less common rocks that are formed only slightly below the earth’s surface.
Igneous Rocks Texture Classification
Phaneritic or Aphanitic
Phaneritic
Igneous rock in which crystal structure can be identified megascopically (by the naked eye).
fine-grained < 1mm
medium-grained 1mm - 5mm
Generally intrusive
Aphanitic
Fine-grained igneous rocks in which mineralogy cannot be determined megascopically (by the naked eye)
Generally extrusive
Discontinuous reaction series
Olivine
Mg pyroxene
Mg-Ca pyroxene
Amphibole
Biotite
Potassium Feldspar
Muscovite
Quartz
Sedimentary Rocks can be deposited
physically, chemically or biologically
Three main categories of sedimentary rocks
-Detrital sedimentary rocks, consisting of loose materials derived from erosion
-chemical and biochemical rocks, made up of precipitated minerals
-diagenetic sedimentary rocks, formed as a result of recrystallization, replacement, or other chemical modifications of the original sediments.
How much of the continental surface do sedimentary rocks cover?
comprise less than 10% of the earth’s crust by volume, but cover 75% of the continental surface.
What is the most abundant sedimentary rock
Mudrocks, making up 65% of all sedimentary rocks.
Percent breakdown of sedimentary rocks
Mudrocks, making up 65%
Sandstones make up to 20 to 25%
Carbonate rocks make up 10 to 15%
Diagenesis
Any change occurring within sediment after its deposition and during and after its lithification, exclusive of weathering. Includes the processes of compaction, cementation, replacement, and crystallization, under normal surficial conditions of pressure and temperature.
What are not considered diagenetic processes
Weathering and metamorphism as they do not occur between 100 and 300 C
Cementation
Process by which coarse clastic sediments become lithified or consolidated into hard, compact rocks, usually through deposition or precipitation of minerals in the spaces among the individual grains of the sediment
Replacement
Change in composition of a mineral or mineral aggregate, presumably accomplished by diffusion of new material in and old material out without breakdown of the solid state.
Facies
Broad term referring to such aspects of rock units as rock type, mode of origin, composition, fossil content, or environment of deposition.
facies chagne
refers to a lateral or vertical variation in the lithologic or paleontologic characteristics of contemporaneous sedimentary deposits. It is caused by, or reflects, a change in the depositional environment.
Make occur vertically with time or laterally over as a result of changing environments with distance at the same time.
Difference between conglomerate and breccia
Conglomerates are made up of 50% or more rounded pebbles, cobbles, or boulders whereas sedimentary breccias are made up of 50% or more angular pebble, cobble, or boulder sized fragments
Detrital Rock Examples
Conglomerates, breccias, sandstones, siltstones and claystones
Dolomite
known chemically as CaMg(CO3)2, forms when the porewaters in limestone are enriched through evaporation which causes magnesium to be subsequently exchanged for calcium in the atomic structure.
Diatomite
a light-colored soft friable siliceous sedimentary rock consisting chiefly of diatoms, occurs through thick accumulations of diatomaceous material
Chert
a hard, dense, dull to semivitreous, microcrystalline or cryptocrystalline sedimentary rock, consisting dominantly of interlocking crystals of quartz. Chert may also contain amorphous silica (opal)
Clastic Limestone
Made up of calcium carbonate fragments that were deposited in place or were transported from elsewhere withihn the basin in which they formed.
Classification of chemically and biologically precipitated particles
Oolites are from 0.2 to 2.0 mm, pellets are particles <2.0 mm, and fossils with no size.
Calcirudites
is a type of limestone that is composed predominantly, more than 50 percent, of carbonate grains that are larger in size than sand (2 mm in diameter). The grains can consist of either fragments of fossils, fragments of older limestones and dolomites, other carbonate grains, or some combination of these.
calcarenites
is a type of limestone that is composed predominantly, more than 50 percent, of detrital (transported) sand-size (0.0625 to 2 mm in diameter), carbonate grains. The grains consist of sand-size grains of either corals, shells, ooids, intraclasts, pellets, fragments of older limestones and dolomites, other carbonate grains, or some combination of these.
calcilutites
also known as cementstone, is a type of limestone that is composed of predominantly, more than 50 percent, of either clay-size or both silt-size and clay-size detrital (transported) carbonate grains. These grains consist either of fossil fragments, ooids, intraclasts, pellets, other grains, or some combination of them.
Nonclasstic limestones
Consists of chemically or biologically precipitated calcite or aragonite material that has not been transported since original deposition.
Aragonite
is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, CaCO3.. It is formed by biological and physical processes, including precipitation from marine and freshwater environments.
stromatolite
reef limestone, that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). These microorganisms produce adhesive compounds that cement sand and other rocky materials to form mineral “microbial mats”. In turn, these mats build up layer by layer, growing gradually over time. A stromatolite may grow to a meter or more. Although they are rare today, fossilized stromatolites provide records of ancient life on Earth.
Three major subclasses of metamorphic rocks
Dislocation Metamorphism
Contact Zones around igneous intrusions
Metamorphosed regionally during mountain building
Contactites
Form when hot magma is intruded into relatively cooler host rocks, heating and metamorphosing the surrounding country rock.
Dislocation Metamorphism
concentrated along narrow belts of shearing or crushing without an appreciable rise in temperature (fault Zones)
Nearly all gamma rays are emitted by what
K40, U238 and Th232
The amount of radiation increases by rock type
anhydrite gypsum < gabbro and basalt < coal < limestone and dolomite < sandstone < shale < arkose < granite
Coal, limestone and dolomite may contain uranium deposits and thus have a higher gamma ray count than expected. Formations with volcanic ash will also give a higher reading.
What is a gamma ray log generally used for?
to determine the shale content of the formations, because radioactive elements tend to concentrate in clays and shales.
Name of the probe used by gamma ray log
scintillation detector - a laboratory grown crystal that produces flashes of light when radiated. These light pulses are used to determine gamma radiation. The more pulses of light the more gamma radiation.
In groundwater applications, gamma rays are measured how?
In counts per second, counts per minute or pulses.
Gamma Ray area of investigation
6 to 12 inches from the borehole wall, area of investigation is also dependent on the energy of radiation measured, density of material, and the probe design.
Neutron log interactions are due to…
the amount of hydrogen present which in turn is due to the water content of the rocks. The greater the hydrogen content, the smaller the volume of investigation of the probe.
Radioisotope when exposed to a neutron source
Will emit alpha particles which bombard the source and produce neutrons.
Most common neutron source
a mixture of beryllium and americium
Three types of neutorn detectors
lithium-iodide crystals
helium-3 tubes
sodium-iodide crystals
Epithermal neutrons energies
0.1 to 100 electron volts, and as energy is lost even further they become thermal neutrons (0.025 electron volts)
Loss of neutron energy
is called moderation and the elements that cause that loss are called moderators
hydrogen is the most effective element in moderating neutrons because it has the same mass as a neutron.
Calibration of all neutron logging equipment
is based on marble and limestone in a pit in Houston, Texas
Neutron logs are affected by…
variations in borehole diameter
thickness of mudcake
salinity of borehole and interstitial fluids
weight of the drilling mud
casing thickness and cement
temperature and pressure
composition of the rock matrix
Neutron log for gypsum or coal
not diagnostic, a neutron log will produce large deflections in the neutron curve to the left, hydrogen in coal is not in the form of water and the gypsum has water of crystallization.
Caliper probe
has three arms that are spaced 120 degrees apart and coupled together and attached to a potentiometer.
Potentiometer
measures changes in resistance which re recorded as voltage changes. The change in resistance is proportional to the average borehole diameter. The caliper probes are calibrated so that 1 inch of chart = 1 inch of borehole.
What does the seismic method indirectly examine
Strength of rocks and their suitability for foundations, pressure zones and discontinuities within the rock. It can often be used to locate the depth to bedrock and to provide a preliminary assessment of the rippability of earth materials.
Revised rippability classification
Uses 5 Classes with 1 being less than 5. A class 1 classification requires light machinery while a class 5 will require blasting.
Snell’s Law
= v1/v2 = sin a / sin b
=
Ground Penetrating Radar
a nondestructive and cost-effective method used to measure changes in the dielectric properties of subsurface materials. It can be used in a variety of subsurface materials including rock, soil, and ice along with engineered materials such as pavement or concrete to detect buried objects, changes, in the subsurface materials and voids
Similar to seismic reflection, except electromagnetic energy is used instead of acoustic energy.
Flux
is proportional to the ferrous mass, ambient magnetic field, magnetic susceptibility and remnant magnetization.
gravimeter
Measures density variations which conform to changes in the earth’s gravitational field.
Relative gravimeter
The most common and is used for gravity surveys conducted by airplanes or ships covering a large area, is compact and contains a spring carrying a weight that is shifted out of equilibrium when gravity changes.
Absolute gravimeter
Measures the force needed to return a falling mass to equilibrium.
Annulus
The space between the pipe and the borehole wall; a ring shape.
Blowout
Uncontrolled flow of gas or fluids from a well.
Fracing or Facking
Using high pressure fluids to fracture in-place rocks to allow for more permeability in tight formations to withdraw oil and gas.
Packer
An expanding device used to isolate particular areas in a well for testing.
Tremie
A pipe used to place grout underwater.
Tripping
The act of removing the drilling rod from the borehole and putting it back in (a round trip)
Shallow boreholes are useful for…
determining soil types, soil thickness, or depth to shallow groundwater.
Flight Augers
mechanically driven augers that are rotated and pushed downward into the earth and do not stay in the hole during sampling. This results in disturbed samples/ therefore strength or compressibility test cannot be performed.
Hollow-stem augers
allow a soil sampler to be inserted through the middle of the rod for sampling without removing the augers. These samples may be sent to a lab for a variety of test such as shear strength, composition, and Atterberg limits. Since drilling fluids are not generally used there is no interference with the groundwater.
Rotary-wash drilling
A method that relies on the rotation of the drilling bit and removal of cuttings from the hole by circulating drilling fluid. Soil classification is done by visual inspection of the cuttings as well as by equipment and drilling rate changes.
Montmorillonitic Clay (bentonite)
used to prevent cave-in of loose cohesionless soils or soils below the water table
Air Rotary
Air or foam is used through the drill stem to bring the cuttings to the surface around the outside of the drill stem.
Can be used to depths of 1000 feet or more and the hole can be advanced quickly.
Problematic for contaminant investigations when foam is added because it introduces foreign materials.
Mud Rotary
Water or drilling mud circulated through the drill stem is used to bring the cuttings to the surface in the annular space between the borehole wall and drill wall.
Used for boreholes in which a geophysical log needs to be run, get rock core samples and can be drilled to great depths.
Advantage is that the hole will remain open after the drill stem has been removed, while a drawback is that the drilling fluid can penetrate the formations changing the groundwater chemistry.
Reverse Rotary
Drilling fluids are added to the borehole through the annular space between the borehole wall and the drill stem and then suction draws the cuttings up the drill stem.
Has an advantage over mud rotary due to the velocity in which the cuttings are brought to the surface through the suction pump. Requires little if any drilling additives and a minimum borehole diameter of 12 inches.
Much more expensive than air or mud rotary methods.
Shutter Ridge
a ridge which has moved along a fault line, blocking or diverting drainage. Typically, a shutter ridge creates a valley corresponding to the alignment of the fault that produces it. Shutter ridges occur exclusively at strike-slip faults.
Bucket Auger
A large-diameter bucket (18 to 48 inches) collects material that is excavated using a auger-type bit that fills the bucket with material. The bucket is then brought to the surface and dumped, leaving an open hole. Works best in clayey formations as materials must be able to stand in an open hole.
Percussion Drilling Methods / Cable Tool
Borehole advancement is accomplished by using cable to drive the bit. the cable lifts and drops a heavy drill string or a hammer type of device called drilling jars to break up the subsurface materials. After the soil and rock materials are broken up they are removed with a bailer. If the hole is above the water table, water must be added to make a slurry for the bailer to work. Casing is installed as the hole is advanced. “The oldest drilling method, Slow and expensive because it is labor intensive”
Sonic Methods
Borehole advancement and continuous sampling of disturbed samples is through a process where the rod and sampler are vibrated through the ground at frequencies between 50 and 180 Hz. It is useful for a wide range of soil types including soils with large particles that are very difficult to sample. Can drill at any angle and drilling fluids can be used but are not required.
Piezocone (CPTU)
A standard penetrometer with the ability to measure porewater pressures.
Electric Conductivity Cone
A device that measures the conductivity of the subsurface materials. Use to evaluate the thickness of the capillary fringe, depth to the water table and more importantly the degree of contamination. The dissolved solids and the acidity (pH) indicate the presence of contaminants such as nitrates, sulfates, Ca, Mg, Na, Cl, and Fe as well as heavy metals.
Environmental Cone
A device with a cavity that collects and tests water in a nitrogen environment. Determines pH, re-dox potential and temperature.
Hydrocarbon Cone
A cone with a UV light source that detects fluorescence by a photomultiplier tube. Hydrocarbons fluoresce in the presence of UV light allowing free prodcut to be detected.
Cone Pressuremeter
Has an inflatable section that is implmented during a pause in the advancement of the cone to determine the shear modulus. Measures soil strength and stiffness, undrained shear strength in clays, relative density in sands, and shear modulus of the subsurface materials.
Gamma Cone
Measures naturally occurring radiation. Because of the variations of radiation occurring in the various subsurface materials this tool is instrumental in lithologic mapping and stratigraphic correlation.
Seismic Cone
Measures shear wave velocity and gives the strain shear modulus and constrained modulus, used in conjunction with a seismography and a seismic wave generating device. Analysis of the moduli allows the prediction of ground surface motions from earthquakes, evaluation of the impact on foundations by the use of vibrating equipment and anticipated deformation adjacent ot excavations, and the impact of wave loading on offshore structures.
Soil moisture probe (SMP)
A device located above the CPT device that consists of 2 isolated electrodes and an electric circuit that records the characteristics between the electrodes. Can obtain soil moisture properties like electrical conductance and therefore resistivity, capacitance, the dielectric properties. NAPL’s have dielectric properties different from water and can be differentiated using this device.
Purpose of using drilling fluids
-Bringing cuttings up
-Preventing borehole collapse / accumulation of cuttings on the borehole wall
-Preventing or reducing fluid loss or gain to or from the formation
-Reducing interactions of the drilling fluids with the formation
-Prevent swelling
-Keeping the drill bit and rod cool and lubricated
-Controlling the downhole pressure heads to prevent heaving or blowouts
Seal the formation
Using drilling fluids to prevent or reduce fluid loss or gain to or from the formation
What is colloidal clay?
Bentonite
Polymer (revert) drilling mud weakness
Low gel strength so cuttings drop out faster. Some polymers can’t be used in particular situations due to bacteriological problems or chemical interactions.
What is barite and its use case?
Barium sulfate adds substantial density to drilling fluids to prevent the borehole from collapsing or taking on water from the formation.
Calcium carbonate as a drilling fluid additive
a bridging agent
Calcium chloride/sodium chloride as a drilling fluid additive
may be used to add weight but is also used when temperatures are below freezing. Weakness is that it will cause a viscosity loss in bentonite fluids.
Calcium chloride / potassium chloride as adrilling fluid additive
inhibits reactions with shale
Oil or synthetic based mud
Used principally for petroleum drilling.
What are the appropriate conditions for a split spoon sampler for (SPT) (Driven Sampler)
Saturated or unsaturated soft to stiff clay, silt and sand. Results in a disturbed soil sample.
What are the appropriate conditions for a Shelby Tube sampler (push sampler)
Saturated soft clay and interbedded silts and sands, superior for firm clays that are either unsaturated or saturated. Results in an undisturbed sample.
What are the appropriate conditions for a Osterberg (Hydraulically) or Hvorslev (Mechanical) push samplers?
Designed for both saturated and unsaturated cohesionless sands and soft wet clays such as bay muds or lake bed deposits. Results in undisturbed soil sample.
Difference between Osterberg and Hvorslev sampler?
Osterberg - Hydraulically activated piston
Hvorslev - Mechanically activated piston
What are the appropriate conditions for the Pitcher Barrel sampler? (Modified push drill samplers, double tube sampler)
Acceptable in all saturated and unsaturated soil materials except gravels and superior in interbedded silts and sands. Results in an undisturbed soil sample.
What are the appropriate conditions for the Denison sampler? (Modified push-drill samplers, double tube sampler)
Acceptable in both saturated and unsaturated silts and sands, superior in clays. Results in an undisturbed soil sample.
Driven Samplers
Widely available since sampler is compatible with commonly used drilling rod diameter. Can yield disturbed and undisturbed soil samples depending on barrel sample wall size and diameter. Undisturbed samples are obtained by samplers with thin walls and high ratio of inside diameter to wall thickness.
Sample is removed by splitting the barrel or removal of a liner.
What can a disturbed sample be used for?
General characterization, grain size distribution, or attenberg limits.
What can undisurbed sample be used for?
Shear strength, compressibility, compaction and consolidation characteristics.
Three ways to obtain an undisturbed soil sample
Thin-walled or push-tube samplers (Shelby Tube)
Piston Samplers
Double-tube samplers
Thin-walled push-tube samplers size
normally have a 3-inch or 5-inch o.d. and thickness of 14-gauge or 11-gauge, respectively. The thinner the wall, the better the samples obtained. (e.g. shelby tube). The sample is removed by hydraulically pushing it out.
What should you do after recovering a push-tube sampler?
Measure the length and compare to the length of push to determine percent recovery and determine if consolidation or sloughing occurred during sampling. If the sample length is shorter than the push length, the soil may have been compressed or fell out during removal of the sample. If longer the then the sample may have sloughed into the borehole.
Fixed-Piston Samplers
A thin-walled cylindrical tube is forced into undisturbed soil in a continuous push without rotation. Pressure is applied throughout the drill stem to push the inner sample head and sample tube. When sampling has fully penetrated the soil the pressure is relived and the sampler is rotated to shear off the sample at the bottom of the tube. Drilling mud and fluids are maintained at the top of the hole to maintain suction and successful sample recovery. Sample tubes are generally 3 in i.d. by 3 3/4 in o.d. or 5 in i.d. by 5 3/4 in o.d.
What are fixed-piston push samplers primarily used for?
To take samples below the water table. They work best in cohesionless sands and soft wet soils. Hard, cemented or gravelly soils are too hard to penetrate using the piston sampler. Also lots of moving parts which complicates sampling.
What are two types of fixed-pistons push samplers?
Mechanically activated types (Hvorslev and Butters)
Hydraulically activated types (Osterberg and modified Osterberg)
Double-tube Core Barrel Samplers
Used to sample fine-grained, uncemented, or slightly cemented soils. If drilling is performed carefully in slightly cohesive soils, an undisturbed sample is possible. The samplers are not suitable for gravelly soils, cohesionless sands with low unit weights and loose silts below the water table, very soft and plastic cohesive soils, or materials that are fractured or fissured.
Two main types of double tube samplers
Denison
Pitcher
Denison sampler
Has an outer barrel with cutting teeth on the bottom, an inner barrel with a smooth cutting shoe, a spring core catcher, and a liner. The outer barrel rotates around the stationary inner barrel and advances the sampler. The liner has an i.d. of 5 7/8 in and is 24 inches long. Its purpose is to hold the sample and assist in transport. Drilling fluid circulates through vents in the inner barrel. The sampler can obtain samples of hard or cemented soils.
Pitcher sampler
the inner barrel extends ahead of the bit and is loaded with a spring that allows it to conform to the soil stiffness. If the soil is too hard to be penetrated, the spring retracts the inner barrel and the bit moves down even with the end of the tube and cuts as the tube fills. The barrel is rotary driven and the inside diameter of the sample is from 4 to 6 inches.
What is the ASTM test procedure for the SPT
ASTM D-1586
What do 0-4 SPT blows tell about a sand and silt soil type?
Very Loose
What do 30-50 SPT blows tell about a sand and silt soil type?
Dense
What do 0-2 SPT blows tell about a clay consistency?
Very Soft - Easily penetrated a few inches with fist.
What do 15-30 blows tell about a clay consistency?
Very stiff - Readily indented with thumb nail.
Boring Log minimum requirements
- A location sketch, including notes and distances to map, and the ground surface elevation at the hole.
- The job location, name, date, number and boring number.
- The drilling company, drillers’ names, and type of drill rig.
- Type of sampler used, hammer weight and fall for driven samples or pressures required to obtain push samples, and sample condition.
- Water levels when first encountereed, measured daily during the hole dvancement, and upon completion.
- Completion status indicating grout intervals, backfill materials and method, monitoring equipment installed and perforation intervals.
- A detailed soil or rock description.
What should a soil boring log include
detailed soil description with color, soil classification using the Unified Soil Classification System (USCS) symbol, moisture content, strength, and structure.
What is soil strength?
consistency or relative density
How should soil color be described?
at the natural moisture content and in comparison to some commonly used standard color char such as the Munsell Soil Color Chart.
Field estiamtes of the moisture content
Are approximate and use the following general terms - Dry, Moist, Wet, Saturated.
How is soil strength (relative density or consistency) estimated?
Relative to the blow count from a SPT. Relative density is used for all coarse-grained soils and term consistency is sued for all fine-grained soils.
Field measurement for coarse-grained soils
100% of the sample passes the 3-inch sieve and less than 50% passes the #200 sieve.
Field measurement for fine-grained soils
more than 50% passes the #200 sieve
Homogenous Soil characteristic
uniform properties throughout
Heterogeneous Soil Characteristic
Dissimilar properties
Stratified Soil Characteristic
Alternating layers of different types or colors of soil
Laminated Soil Characteristic
Alternating layers less than 1/8 to 1/4 inch thick
Fissured Soil Characteristic
Tendency to shear along definite fracture planes with little resistance; fractures may be a result of shrinkage and are often filled with fine sand or silt.
Honeycombed Soil Characteristic
Contains many holes
Slickensided Soil Characteristic
Soils which are slick, glossy, polished, and/or grooved on the surfaces of fractures or soil particles, generally constituting planes of weakness.
Blocky Soil Characteristic
Easily broken into small angular lumps which are difficult to further break down
Lensed Soil Characteristic
Containing thin, discontinuous beds or small pockets of different material.
Caliche Soil Characteristic
Secondary calcium carbonate forming a horizon that is typically very hard or well cemented.
Useful soil material descriptors
-estimates of percentages of gravel, sand and fines
-the maximum size of the particles
-grain shape of coarse-grained component (angularity)
-coating or staining of particles
-plasticity
-organic content
-type and degree of cementation
Useful observations about drilling operations
-drilling methods used
-pressures recorded
-color of return circulation
-grain or loss circulation
-drilling difficulties
-overnight slough
-morning water levels
-drillers’ comments
What are useful drilling comments when completing a hole
-total depth
-reason for stopping the hole and completion status
-installation of water monitoring or pump equipment
-backfill grout and any open hole testing
Rock coring
utilizes a rotary-wash drilling method and performed when it is necessary to obtain continuous samples. Similar to the Pitcher barrel sampler and is drilled into the rock with special core samplers made from hardened steel alloys, or diamond chip bits.
Standard Drill bit size from small to large
EW - 13/16 Core Diameter 1 1/2’ Hole Diameter
AW - 1 3/16 Core Diameter 1 7/8’ Hole Diameter
BW - 1 5/8 Core Diameter 2 3/8’ Hole Diameter
NW - 2 1/8 Core Diameter 3” Hole Diameter
2 3/4 x 3 7/8 - 2 11/16 Core Diameter 3 7/8” Hole Diameter
HW - 3 Core Diameter 3 7/8” Hole Diameter
First Letter designates size of the hole and second letter indicates the group of compatible drill rods, casing, etc.
Rock Boring Logs
necessary to make an accurate interpretation, we need to identify sections with poor recovery which will require an interpretation of the subsurface geology.
Rock descriptions include
detailed rock type, color, hardness, mineralogy, textural and structural features and any other features that might aid in correlation and/or interpretation of the geology.
Also run length, recovery and Rock Quality Designation (RQD)
Fugitive data
data which would be lost if not documented during the drilling process. Would include drilling rate, drilling methods, drilling pressures, color of return fluid, loss or gain of circulation, drilling difficulties, drillers’ opinions, rig actions, bit changes, drilling muds (types and quantities) etc.
Lightness
range from light or white to dark or black
Chroma
the color saturation which would range from a very pale to vivid
Hue
the color, Munsell Rock Color Chart helps ensure consistency of color names
Hardness categories for rock boring logs
Soft - plastic material
Friable - easily crumbled or reduced to powder by the fingers
Low Hardness - can be gouged deeply or carved with a pocket knife
Moderately Hard - Can be readily scratched by a knife blade, scratch leaves heavy trace of dust
Hard - can be scratched with difficulty, scratch produces little powder and is faintly visible
Very Hard - cannot be scratched by a knife blade
porphyritic
a type of texture occurring in volcanic and intrusive igneous rocks defined by the presence of larger crystals, called phenocryst
can be intrusive or extrusive
phenocryst
an early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of an igneous rock
Modified Wentworth Scale
Used to differentiate sedimentary rock grain sizes.
Gravel - 2mm - >256 mm (conglomerate/ breccia rock
Sand - 1/16 - 2 mm (sandstone)
Mud - < 1/256 - 1/16mm (siltstone, claystone, mudstone, shale)
lineation
the arrangement of grains may show a preferred orientation
Foliation
a general term used to describe platy, layered or planar fabric metamorphic rocks.
Quantitative terms used in describing layered sedimentary rocks
Massive - Very thick bedded > 4 ft
Blocky - thick bedded 2-4 ft
Slabby - thin bedded 0.2-2 ft
Flaggy - very thin bedded 0.05 to 0.2 ft
Shaly or Platy - laminated 0.01 to 0.05 ft
Papery - thinly laminated < 0.01 ft
Terms for angularity and roundness
very angular, angular, sub-angular, sub-rounded, rounded and well rounded. These are the assumed weathering pathways from the original discoidal, prismatic, or spherical shapes.
Textural features used to describe rock specimines
- Grain or crystal size
- Grain or crystal shape
- Lineation
- Bedding and foliation
- Grading/sorting
Grading
refers to the range of particle sizes
Sorting
refers to the degree to which the particle sizes are differentiated
How do engineering geologists and geotechnical engineers describe rock and soil?
In terms of grading
Fresh - weathering descriptor
rock shows no discoloration, loss of strength or any other effect due to weathering.
slightly weathered - weathering descriptor
the rock is slightly discolored, but not noticeably lower in strength than fresh rock
Moderately Weathered - weathering descriptor
the rock is discolored and noticeably weakened, 2-inch diameter core can’t usually be broken by hand across the rock fabric.
Deeply Weathered - weathering descriptor
the rock is usually discolored and weakened to such an extent that the 2-inch diameter core can be readily broken across the rock fabric.
Extremely Weathered - weathering descriptor
rock is discolored and is entirely changed to a soil but the original fabric of the rock is usually preserved. Soil properties depend on the composition and structure of the parent rock.
Fractures
include joints, shears, faults or other continuous breaks in the rock and tend to reduce the overall mass hardness and strength of the rock.
Joints
fractures along which there has been no relative movement of the rock on either side of the fracture.
Quantity of fractures are expressed how
in terms of fractures per foot
How are fracture surfaces described
planar, undulating or stepped and rough, smooth or slickensided.
Fracture Spacing
Described as crushed, intensely fracture, closely fractured, moderately fractured, little fractured or massive fractured.
RQD designations
0-25% - Very Poor
25-30% - Poor
30-75% - Fair
75-90% - Good
90-100% - Excellent
Vane Shear tests
measured using a device with 4 flat metal blades fixed at 90 degrees to each other attached to a metal rod that is pushed into the soil and rotated. The rotational torque values at soil failure indicate the in-situ undrained shear strength and sensitivity of cohesive fine-grained soils.
ASTM D1556
Sand Cone Density Test
Sand Cone Density Test
An apparatus consisting of a gallon jug and cone that measures the volume of a small hole which can be compared to the weight of the soil material removed and dried to determine the moisture content. This value is then compared to the compaction cure developed in the lab to get a relative compaction.
Nuclear Density Test ASTM Number
ASTM D6938 - 17a
Nuclear Density Test
Using a nuclear density gauge a probe that emits gamma rays into the subsurface is inserted into the ground and measurements are recorded of the backscattered rays which are proportional to the density. After drying a sample of the tested material the moisture content is determined. The calculated dry density is then compared to the lab generated compaction cure.
how is compaction % calculated
dry density / maximum dry density
Inclinometer
A device that measures the inclination from the horizontal of a special casing by measured of a downhole wireline. Slope vs. depth data is recorded.
Often used to monitor landslide or slope movements over time.
Manometer
A liquid column instrument used to determine minor changes in atmospheric pressure (Potentiometric levels)
Used for floor level measurements for monitoring embankment settlement, and measuring liquid levels in tanks.
Magnetometer
Measures strength or orientation of magnetic field.
Used for mineral and oil exploration, as drill guidance systems, locating hazards for tunnel boring machines, in Plate tectonic research, mapping geological structures, detecting geologic hazards in coal mines, or detecting subsurface materials with magnetic characteristics such as toxic waste drums.
Datalogger
An electronic logging device that measures temperature, pressure, humidity, and water levels.
Used to record soil moistures, water levels, water flow, pH, conductivity and monitor deformation.
Piezometer Uses
Monitors natural ground-water levels or to measure and monitor changes in ground-water levels resulting from loading at the surface due to construction or the effect of raising the water level in a reservoir.
Lysimeter Uses
Used to sample water chemistry in the vadose zone, measure deep percolation and evapotranspiration.
Steel Casing
Most commonly used, good structural integrity, stainless steel varieties extend life of the well and offer more protection against corrosion.
Cement casing
Used in deep wells, often for oil and gas wells, different types of cement are used according to specifications, often fails if not placed correctly
Plastic (ABS, PVC)
Best in shallow wells up to 8’ diameter, not as good for deep wells because of cost and limited strength.
Fiberglass casing
Used in corrosive water, shallow to medium depth wells, costly.
Conductor Casing
The casing that is the largest, drilled and set first to prevent the sides of the hole from caving.
Wire Wrap or continuous slot
Developed for use in non-gravel pack wells in glacial deposits. The shape of the openings reduces clogging and a smaller aperture is possible to achieve 90% retention. The large surface area of openings has a greater intake area, exposing it to corrosion and incrustations, leading to lower collapse strength. It is more difficult to develop with mechanical methods.
Bridge Slot
Vertical slots arranged in a staggereed pattern give a high surface area of openings. It has a low production cost, and a lower strength because many openings may lead to collapse.
Shutter Screen
Originally designed for gravel pack wells. Felxibility for different surface openings and patterns make it more customizable. It has a high collapse strength. Development is easier.
Entrancce Velocity
Frictional head losses as the water enter the well screens should be minimized. Proper selection of screen size accomplishes this by maintaining entrance velocities between 1 to 5 feet per second.
Screen length in Homogeneous Unconfined, less than 150 feet thick aquifer
Screen bottom 1/3 to 1/2 of aquifer.
Screen length in nonhomogeneous Unconfined aquifer
Screen the most permeable part of the lower aquifer at up to 1/3 aquifer thickness
Screen length in confined aquifer
Screen 80-90% of aquifer length
Filter pack goal
to optimize well yield of the well but allow only 10% of the fines to enter the well
How do you determine wether or not to use filter pack
Grain size distribution, fine grained materials need filter pack. Filter pack also acts to stabilize the annulus.
Procedure for determining filter pack
- Run grain size analysis and select the grading of the sample on the basis of the finest material.
- Plot the grain size analysis percent passing curve on semi-log paper.
- Plot another curve multiplying the formation size by four times and another curve of 1/6 the formation size, representing the uniformity coefficient d60/d10.
- The filter pack gradation will fall between the curves plotted in step 3.
Multipliers up to 10 may sometimes by used if the material is coarser and nonuniform.
Select a filter material composed of clean, well-rounded siliceous grains of uniform gradation. Calcareous compositions are not desirable. - Select a screen slot size that will retain 90% or more of the filter pack.
Setting the pump
30% safety factor = industry guideline, equivalent to 70% of available drawdown.
Specific Capactiy
is a measure of the pumping rate in gpm divided by drawdown in feet of the well after a 24-hour test.
= Pumping Rate (Q) / drawdown
What is one of the most important indicators of corrosive or incrusting groundwater?
The pH
Corrosion occurs when the following conditions exist:
pH ,< 7
TDS > 1000 mg/L
Dissolved oxygen >2 mg/L
CO2 > 50 mg/L - reacts with rainwater, forms carbonic acid, lower pH
H2S < 1 mg/L - changes electric potential, pits steel
Chloride > 500 mg/L
Incrustation occurs under the following conditions:
pH > 7.5
Iron Precipitation > 0.5 mg/L
Lowered solubility of CaCO3 which forms as incrustations and scale.
Manganese precipitation if oxygen present, >0.2 mg/L.
Baylis Curve
Shows relatively small range of values of pH and alkalinity that allows for quality drinking water. Scale forming vs. Corrosive
Iron bacteria are present in groundwater when
enough iron and/or manganese, dissolved organic material, bicarbonate, or carbon dioxide co-exist. Iron bacteria may also be introduced from the subsoil or during well construction. A pH less than 3 keeps dissolved iron in solution an thus will act as the source of iron for bacterial growth.
How to remediate iron bacteria?
either oxidizers or acids are commonly used, Shock chlorination, consisting of adding amounts of chlorine greater than 1000 mg/L, followed by well agitation, breaks up the masses. Acid treatment may include hydrochloric acid, sulfuric acid or hydroacetic acid.
Wellhead Protection Program
The The 1986 amendments to the Safe Drinking Water Act require states to have a (WHPP) approved by the EPA.
Source Water Assessment Programs
SWAP - in 1996 amendments to the Safe Drinking Water Act required states to develop and implement SWAP to analyze existing and potential threats to the quality of the public drinking water.
Three major steps are outlined to create a source water assessment:
1. Delineate the source water assessment area
2. Inventory for the potential sources of contamination
3. Determine the susceptibility of the water supply to contamination.
Well Development
After construction removal of drill cuttings and drilling fluids that may accumulate in the well and mud cake that developed on well screens. Removal is necessary to increase the well production during development and improve the success of disinfection. Methods of well development may be either mechanical or chemical and include over pumping, backwashing, surging/agitation, air lift, jetting, or acid wash.
Drilling Water and Disinfection
Drilling water must come from an approved potable water supply having a free chlorine residual of at least 10 ppm.
Simplest and most effective way to disinfect water supply system
A chlorine solution between 50-200 mg/L. More chlorine is needed at higher pH water and less at lower pH because chlorine is corrosive at low pH.
Most common sources of chlorine used to disinfect wells
Sodium hypochlorite - common household bleach (5.25 to 6.0%)
Calcium hypochlorite - swimming pool chlorine (10 to 12%)
What standard must chemicals used for treating drinking water meet?
ANSI/NSF/CAN Standard 60 and does not have additives such as algicide. This also applies to corrosion and scale inhibitors; coagulants and flocculants; disinfection and oxidation chemicals; pH adjustment, softening, precipitation, and sequestering chemicals; well drilling aids; and specialty chemicals used in drinking water treatment.
ANSI
American National Standards Institute
NSF
National Sanitation Foundation, Inc.
Seals
Seal the annulus to protect against poor groundwater quality and surface contaminants to a minimum of 50 feet from the surface.
Well Destruction Safety Standards
No national standards, states have their own requirements. Important to prevent contaminants form entering groundwater through the confining layers
Two most typical methods for destroying a well
drilling out the casing and backfilling with an approved sealant or pressure grouting in place. Everything is removed and usually pumped neat cement (grout, no debris) is used to backfill. Backfill can be neat cement grout, 10-sack sand cement grout or a bentonite slurry.
Why are aquifer test performed?
To determine the hydraulic properties and boundary conditions of aquifers.
Drawdown in a pump test
first very rapid, but as pumping continues the rate of drawdown decreases.
bailer or Bail-down test
The well is bailed at a constant rate recording both the rate of wter removal and the drawdown. Used to determine hydraulic conductivity, transmissivity, and specific capcaity.
Pump-in Test
Water is added to the well to maintain a constant water level. This test is usually done in shallow boreholes with access to a water supply. Used to determine horizontal hydruaulic conductivity.
Step-Drawdown Test
A test in which the well is pumped at a series of increasingly higher pumping rates with measurements of drawdown at each change. USed to obtain hydraulic conductivity, transmissivity, storage coefficient and shows reduction of specific capcaity with incrased yields. Allows the computation of turbulent and laminar drawdown needed to determine the optimum pumping rate and pump depth. Used as a well-performacne test.
Constant-Rate Pumping Test
A well is pumped at a constant rate for a given period of time (usually 24 or 72 hours) and drawdown is measured periodically utilizing one oro more observation well for recording data. Usually recovery is also recorded. Used to determine the specific capcaity of the well, transmissivity and storage of the aquifer.
Theis Method
The mathematical model most often used for analysis of aquifer tests. This model is an exact analytical solution for hte radial flow of groundwater in a confined aquifer to a well.
Theis Method Assumptions
- Transmissivity of the aquifer tapped by the pumping well is constant
- The water withdrawn from the aquifer is derived entirely from storage and is discharged instantaneously with the decline in head.
- The discharging well penetrates the entire thickness of the aquifer and its diameter is small in comparison with the pumping rate, so that storage in the well is negligible.
- Materials are homogenous and isotropic.
SWAP
Source Water Assessments Programs
WHPP
Wellhead Protection Program
Theis Drawdown Equation
T = 15.3 Q W(u) / s
Q = pumping rate (gal/min)
s = drawdown (feet)
t = time (minutes)
r = distance from pumping well to observation well (feet)
W(u) = well function of u ( an infinite series)
Formula for u
= 360 r^2S / Tt
How is drawdown plotted for more than one observation well
on log-log paper versus t/r^2
Time-drawdown method
Also known as Jacob straight-line method, a simplified approach to the solution of the Theis equation.
-Drawdown from one pumping well is noted in an observation well, and drawdown values are plotted on semi-log paper as a function of time since pumping started.
-A straight line is drawn through the data points and extended backward to the zero-drawdown axis.
-The straight line is fit through the points farthest from the pumping well because these points are more accurate.
-Aquifer parameters are then calculated using the slop of the straight line and the intercept of the line with the time axis when drawdown is zero.
Data during the first ____ minutes of a pump test are relatively invalid.
10 minutes
Time-drawdown (Jacob-straight line) method equations for Transmissivity and storativity.
T = 35Q / ds
S = T to / 640 r^2
Units of measurement for Theis and Jacob straight-line method
ft^2/day
Distance-drawdown method
-A variation of the Jacob method if the drawdowns in three or more observation wells are measured simultaneously.
-In this situation the drawdown varies with the distance from the pumping well in accordance with the Theis equation
-Drawdown are plotted on the arithmetic scale as the time-drawdown method and distance is plotted on the log scale (x-axis).
-The data will form a straight line first through the points closest to the pumping well.
T Calculation for Time-drawdown
ft^2/day = 35Q / ds
gpd/ft = 264Q / ds
T Calculation for Distance-drawdown
ft^2 / day = 70Q / ds
gpd/ft = 528Q / ds
Conversion from 1 gpd/ft to ft^2/day
= 0.134 ft^2/day
Conversion from 1 ft/day to gpd/ft^2
= 7.48 gpd/ft^2
How to estimate well efficiency from the distance-drawdown graph
Assumption - full thickness of the confined aquifer is screened.
- Plot the points and fit a straight line through them. Extend the line back toward the pumping well.
- Plot the radius of the pumped well.
- The intersection of the straight line with the radius of the pumped well is the theoretical drawdown for a well that is 100% efficient.
- Compare the theoretical value of drawdown from the plot with the actual drawdown measured in the well, which is more than the theoretical drawdown.
- Find the ratio between the theoretical and actual drawdown. This is the well efficiency.
What is the maximum well efficiency in ideal conditions
80% while a value of 60% is more realistic.
Where are national guidelines for drilling and installing groundwater monitoring wells and groundwater sampling described?
In EPA document “Handbook of Suggested Practices for the Design and Installation of Ground-Water Monitoring Wells”
What is the National Ground Water Association well construction standard?
ANSI/NGWA A-01-14, however each state and local jurisdictions adopt individually.
Ideal monitor wells and placement
a minimum of 3 downgradient and 1 upgradient
Standard monitor well construction
Small diameter, usually 2 or 4 inch, to be able to accommodate the transducers and to be able to effectively sample.
What is ideal monitor well construction material?
Non-reactive well screens and casings (stainless steel, PVC, or Teflon) depend on the contaminants present.
Monitor well sterilization
All materials must be sterilized prior to placement in well.
Monitor well drilling technique?
Must be drilled using a method that precludes the introduction of foreign materials into the formation fluids - this usually means no drilling fluids.
Monitor well seal placement?
Seals must be placed to preclude potential for contaminating other units - this usually means sealing the entire annular space.
Where are national guidelines for groundwater sampling described?
In the EPA “Handbook of Suggested Practices for the Design and Installation of Ground-Water Monitoring Wells” and “Ground-Water Sampling Guidelines for Superfund and RCRA Project Managers”
Groundwater sampling method depends on what factors?
-type of device used
-sampler intake position (either within the screen or above the screen)
-purging method used
-condition of the groundwater
Why is purging important and what device should be used?
To insure that the water tested is representative of the in-place water. The same device sued for purging should also be used for sampling and should not change the physical or chemical properties of the groundwater or increase turbidity.
Purging devices should be constructed of Teflon, stainless steel, or glass. Ideally, positive-displacement pumps or low-flow submersible pumps are recommended to prevent overpumping the well.
Purging method: purge 3 to 5 well casing volume minimum
Requires removal of a minimum of 3 well bore volumes to remove the stagnant water in the blank casing in conjunction with testing for water quality stabilization. Sampling would occur after either a minimum of 3 volumes or testing indicates stabilization.
Limitations: Pure 3 to 5 well casing volume
Initially based simple on volumes of water but testing technology allows verification of stabilization for the least pumping volumes. Can’t be used in low-flow wells, turbid water, or fractured rock.
Purging to stabilization (well volume approach)
Requires removal of the stagnant water in the blank casing in conjunction with continuous monitoring of pre-established groundwater indicator parameters until the variation is acceptable.
Limitations: Purging to stabilization (well volume approach)
Criteria for indicator parameter stabilization must be established prior to testing.
1. Time interval of measurements
2. minimal purge time
3. purge rate
4. parameter selection
Low-flow Purging (Minimal Drawdown Methods)
Requires water be pumped from the screened interval until continuous monitoring of pre-established groundwater indicator parameters shows an acceptable variation. This method presumes isolation of the water in the screened interval from the stagnant water in the blank casing.
Limitations: Low-flow Purging (Minimal Drawdown Methods)
Well screen must be less than 10 feet. Careful measurement of pumping rate and water levels required. Well drawdown must be minimized.
Standard equipment for purging and sampling monitoring wells
pumps: suction, peristaltic, positive displacement, submersible
bailers
in-situ devices
Preferred equipment depends on a number of well conditions such as well diameter, depth to water, water volume in the well, accessibility of the well site and the type of contaminants being monitored.
One of the biggest problems when sampling groundwater
VOCs since differing amounts of turbulence will result in different levels of VOC release from the water.
Grab Samplers (Bailers)
Collects water through a bailer type device. Bailers have a check valve at the base of the device. This valve is blocked by a check ball that allows water in using the pressure differential between the inside of the bailer and the outside, then the check ball seats as the bailer is withdrawn retaining water sample. Double check valves are generally required for sampling in water monitoring wells.
Conventional bailer, Dual-check valve bailer, Syringe pump (Grab Sampler - Bailer)
Advantages and Disadvantages
Inexpensive, easy to use and easy to clean. No outside power source is required
Can detrimentally impact the well possibly causing issues with sample quality. Time consuming and labor intensive. Transfer to sample jars can cause aeration which impacts VOC levels. Requires complete removal of stagnant water in blank casing.
Bat Sampler, Hydropunch, Geoprobe (Grab Sampler - Bailer)
Advantages and Disadvantages
Well development not required as sample is retrieved from depth the device is pushed to.
Requires heavy equipment to push the samplers into the ground.
Positive-displacement Pumps (Submersible)
There are a variety of this type of pump that might be appropriate for use in monitoring wells. The principle behind this type of pump is the fluid is moved by trapping a fixed amount of it then forcing the trapped fluid into the discharge pipe. They are constant flow pumps where the flow is the same for any given speed regardless of pressure. This is the preferred method of water removal for sampling water monitoring wells. Low flows are optimal for water sample collection because the agitation of the water can cause higher than normal turbidity and allow the release of VOCs.
Bladder Pump (Positive-displacement Pump)
Advantages and Disadvantages
Nearly continuous flows can result from a properly operating pump. Practical to a depth of about 100 feet. Optimal for VOC sample collection.
Difficult to decontaminate so dedication to one well is recommended. Requires a power supply and a compressed gas/air supply.
Helical Rotor (Positive-displacement Pump)
Advantages and Disadvantages
Can be used for both sallow and deep wells. Good for purging prior to sampling.
Requires a power supply. May cause agitation of sample making it not as appropriate for VOC sampling Difficult to decontaminate.
Stabilization Criteria for Water Quality Indicators (In order of stabilization)
pH - +/- 0.1
Temperature - N/A
Specific Conductance - +/- 3%
Oxidation-Reduction (Redox) Potential - +/- 10 millivolts
Dissolved Oxygen - +/- 0.3 milligrams per liter
Turbidity - +/- 10% (if turbidity > 10NTUs)
Adsorption
The attraction and adhesion of ions or molecules in solution onto the surface of a solid.
Advection
The process by which solutes are transported by flowing groundwater
Diffusion
The process of movement of solutes from areas of higher concentrations to areas of lower concentrations.
Dispersion
The spreading and mixing of a solute in groundwater because water containing the solute is traveling at a different velocity than the groundwater. The result is a dilution of the solute at the advancing edge of the flow.
Effluent
Liquid waste discharged to the environment from a treatment or manufacturing facility. It could be untreated, partially treated or completely treated.
Equivalent weight
The formular atomic weight of a dissolved ionic species divided by the electrical charge.
Hardness
A property of water in which evaporation produces a scale and in combination with soap produces an insoluble residue. Hardness is caused principally by the presence of calcium and magnesium ions although other ions may also be present like iron or manganese.
Hardpan
A hard, impervious near-surface soil layer, usually in clayey soils, formed by cementation from the precipitation of insoluble materials such as silica, iron oxide, calcium carbonate, and organic matter.
