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Hydrostructural Geology
 

Hydrostructural Geology

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    Hydrostructural Geology Hydrostructural Geology Presentation Transcript

    • Hydrostructural Geology Thomas D. Gillespie, P.G. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Why do we have continuing education requirements for Professional Geologists?
    • Excerpted from an Amplified Record of Experience for a PG Licensing examination application submitted in 2011The [activity] revealed extensive soil and GW contamination. MWs were installedinto the Precambrian felsic gneiss overburden and sampled.MWs were installed into the ----------- Wissahickon saprolite to determine theextent of the GW plume. The -------- Wissahickon sediments accumulated in a riftbasin on top of Laurentian continental crust and consists of muscovite andtourmaline-apatite-staurolite-kyanite-garnet-bearing metamorphic mineralassemblages.
    • Hydrostructural Geology Copyright © 2011, Thomas D. Gillespie, P.G.
    • Overview of Hydrostructural GeologyElements of hydrostructural geology - hydrologically relevant structuresStructural domains and structural characterization for hydrostructuralanalysisNatural planar systemsHeterogeneity and AnisotropyDescription and measurement of planesStatistical management of structural data for hydrologic analysisHydrostructural Analysis Copyright © 2011, Thomas D. Gillespie, P.G.
    • Hydrostructural GeologyAn analytical method to: develop a second order approximation of groundwater flow in bedrock aquifers; estimate direction and magnitude of structurally controlled transport anisotropy; delineation of groundwater contamination water resource management Copyright © 2011, Thomas D. Gillespie, P.G.
    • Purpose of model developmentCombine non-random structural data with field hydrologic data to modelgroundwater flow anisotropy and the distribution of solutesApply aquifer hydraulics equations developed from aquifer stress tests tothe non-pumping conditions of the natural field hydraulic gradient to derivea numerical basis for finite difference modeling, to support predictions ofaquifer responses to extraction and the design of remedial systemsProvide a rapid, cost-effective, theoretically-supported first orderapproximation of groundwater flow and solute transport in fractured rockaquifers to guide additional phases of investigation or to provide thetechnical rationale for investigation limitsPredict behavior of aquifer under pumping conditions to support eitherextraction or injection based in-situ remedies Copyright © 2011, Thomas D. Gillespie, P.G.
    • Hydrostructural GeologyIs not: numeric modeling method particle tracking method mass transport modelCopyright © 2011, Thomas D. Gillespie, P.G.
    • Hydrostructural Modeling In contrast to numerical models of fracture flow, hydrostructural methods are: Rapid Inexpensive Testable Requires: Structural data Hydrologic dataCopyright © 2011, Thomas D. Gillespie, P.G.
    • Flow through fractured media As in porous medium aquifers, there are two physical domains in fractured rock aquifers: Solid matrix Fluid-filled pore spaceCopyright © 2011, Thomas D. Gillespie, P.G.
    • Flow through fractured mediaIn a porous medium, the pore spaces: are distributed uniformly throughout the aquifer occupy a significant percentage of the total volume bounded by grain boundaries with generally random orientationsFlow occurs only in the pore spacesCopyright © 2011, Thomas D. Gillespie, P.G.
    • Flow through fractured media In fractured media, the fluid filled pore spaces: are planar discontinuities in the otherwise solid matrix occupy only a small percentage of the total volume occur at non-random orientations Flow occurs both in the planar secondary pore spaces as well as in the primary porosity of the rock matrix.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Flow through fractured media In modeling a porous medium aquifer the solid matrix is generally ignored In a fractured rock aquifer, the matrix must many times be considered because it is porous and so contributes to the overall flow Most flow occurs in the fractures, referred to as secondary porosity. Although only a small component of flow derives from the matrix, it can be a major component of storage and, in consequence, can not always be discountedCopyright © 2011, Thomas D. Gillespie, P.G.
    • Flow through fractured media Many existing models attempt to account for the two different flows: Dual Porosity Models: Involve a routine to model flow through the porous matrix in addition to routines to model flow through the planar discontinuities. In reality, the flow from the solid porous matrix (primary porosity, is a release from storage and flow does not occur over any appreciable horizontal distance. The flow is governed by pressure differences and can be in any direction as long as it is toward a water-bearing fracture. As a result they are complicated and similar to the models for heterogeneous unconsolidated aquifers in which heterogeneity is assumed to be the result of the presence of multiple but sub-parallel layers with differing k values.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Flow through fractured media In those unconsolidated model situations, the real function of the low k aquitards is storage and release of water – the presumption in models is that flow through the low k zones between aquifers is vertical and therefore flow within them is not modeled other than to determine the flow velocity and release rate.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Flow through fractured mediaWhat is complicated in most fracture flow models is that the sub-horizontallayers common to unconsolidated aquifers become three-dimensional blocks withrelease to planes on all sides. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Flow through fractured mediaExisting models of fracture flow are based on measured anisotropy understressed conditions – they measure directional anisotropy of permeabilityunder artificial hydraulic gradients. A model is then constructed usinginduced permeability tensors under induced hydraulic gradients as theanisotropy field and fractures with random orientation and spatialdistribution – in that model, it is the behavior of the water under stresswhich is being modeled and the assignation of random fracture orientationsensures that the matrix and discontinuities are not actually modeledHydrostructural begins with the premise that natural groundwater flowin fractured rock is controlled by a combination of natural hydraulicpotential and the combined orientations of the field hydraulic gradientand planar discontinuities in the rock mass. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Structural Basis of Hydro-Structural GeologyNon-random nature of planar discontinuities;Spatial distributionPlotting and statistical treatment of structural dataDefinition of dominant plane sets and ranges of variability Systematic joints Non-systematic joints Fold-Related Shear Joints Bedding plane partingsCopyright © 2011, Thomas D. Gillespie, P.G.
    • Hydro-Structural GeologyHydro-Structural Theory Analytical model Mathematical basis and derivation of equations;Expansion of well-established mathematics to field conditions and toincorporate structural dataCopyright © 2011, Thomas D. Gillespie, P.G.
    • Utility of Modelpredictive modelanalytical toollittle hydraulic data and minimal structural datasimple format and data inputsupported by hydraulic theoryresults in readily testable predictions Copyright © 2011, Thomas D. Gillespie, P.G.
    • Utility of Modelcost-effectivefocus additional stages of investigationsupports remedial decisionsbasis for remedial designCopyright © 2011, Thomas D. Gillespie, P.G.
    • Limitationsnot a dual porosity model – does not account for matrix diffusion andrelated tailing/recession effectscan not model complex hydrogeochemical process - not fate and transporton its own but can be combined w/f&t modelsutility within a single structural style – does not translate across formationalboundaries into other rock types with unique structural stylesdoes not take into account hydraulic effects of fault planes but can becombined with fault plane solutiongraphic output limited – not an illustrative model Copyright © 2011, Thomas D. Gillespie, P.G.
    • Need for hydrostructural methods Existing fracture flow models focus on either pipe flow or parallel plate flow theory and are almost devoid of knowledge of the actual flow pathway network. That would be similar to modeling flow in a porous medium without knowing whether the medium is sand or gravel.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Groundwater Flow Modeling in Fractured Rock Currently, there is a great and widespread misunderstanding in the groundwater science and engineering community about how groundwater flows in bedrock aquifer systems, with most people making one of several fundamental errors in concept, typically based on erroneous assumptions.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: Groundwater flow is either parallel to the strike or down the dip of planar discontinuities Strike Hydraulic Gradient Water Table – slope of groundwater surface Sedimentary beddingCopyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: Groundwater flow is either parallel tothe strike or down the dip of planar discontinuitiesThe strike of any plane is, bydefinition, horizontal andgroundwater only flows downa gradient. StrikeGroundwater can not flow Hydraulicdown the dip of a plane Gradientunless it is the same dip as thehydraulic gradient. Water Table – slopeIt actually flows at some Sedimentary of groundwater“apparent dip” close to the surface beddingstrike of the planes –effectively, along strike. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: Groundwater flow is either parallel tothe strike or down the dip of planar discontinuitiesIn order for there to be ahydraulic gradient, Strikegroundwater must flow, onaverage, in that direction. Hydraulic GradientTherefore, there must be Water Table – slopecross-strike water-bearing Sedimentary of groundwaterstructures which are NOT surface beddingformed by the dip of theplane. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: Groundwater flow is controlled by a single fabric element Strike Sedimentary bedding Joint planesCopyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: Groundwater flow is controlled by a single fabric element Most investigators and regulators interpret groundwater flow according to the mantra: “Groundwater flow is generally parallel to strike.” Strike of WHAT?Copyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: Groundwater flow is controlled by a single fabric elementCopyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: Groundwater flow is controlled by a single fabric element Strike Sedimentary bedding Joint planesGroundwater flow is through an aquifer of finite thickness andthrough a network of discontinuity sets of different orientations, all ofwhich are saturated and transmit water and each of whichcontributes to flow pathways and the overall direction of flow. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: Groundwater flow is dominated by no single fabric element Most fracture flow models assume a random distribution of planar discontinuities where in fact, actual rock fractures are non-randomly distributed in space and orientation and impart some anisotropy to flow.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: Groundwater flow is dominated by no single fabric elementDual Porosity Models – assign hydraulic characteristics to both thefractures and matrix and model the system as a continuumDiscrete Fracture Network Models – use stochastic and deterministic“fractures” combined with measured hydraulic data to assign values toa finite element grid based on a Monte Carlo sampling of relevantdistributionsCopyright © 2011, Thomas D. Gillespie, P.G.
    • From Fetter, 2001. This isa non-structural method ofestimating anisotropywhich requiresmeasurement of thehydraulic conductivity intwo perpendiculardirections during anaquifer testing program
    • Assumption: Increased randomness of planar fabric elements results in more complex flow patterns Schematic of fracture network traces and groundwater elevation contours and flow arrows at a CERCLA Site at which bedrock aquifer was contaminated.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: Increased randomness of planar fabric elements results in more complex flow patterns Plan View 3 mm This example depicts a situation in which randomness of pore space orientation is maximized but flow is uniform at any scale above that of the grain size distribution.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Resolved the measured gradient into the known orientations of joints and determined that flow is not erratic as a result of joint distributions and patterns and that flow anisotropy is moderate in two directions and absent in the third around the semi-radial flow patternCopyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: The occurrence of multiple, non-random, planar discontinuity fabric elements increases the potential for dispersion (lateral spread) and transport in random or unpredictable directions Plan ViewCopyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: Groundwater flow can not be predicted usingoverall water balance analyses and domainal scale conceptual modelsCopyright © 2011, Thomas D. Gillespie, P.G.
    • Conceptualizing Flow in Fractured Media The foregoing assumptions have become de facto conclusions which have been developed and accepted by the industry, in the near- complete absence of structural geology data and without any structural analysis.Principle among those conclusions, which are pervasive amongcomputer modelers are: the incorrect premise that groundwater flow is controlled by no single fabric element the incomplete premise that groundwater flow is controlled by a single fabric elementCopyright © 2011, Thomas D. Gillespie, P.G.
    • Conceptualizing Flow in Fractured Media In most cases in actual practice, investigators tend to default to the concept of the Porous Medium Equivalent Can be valid either for some scales of observation or for studies in which the domain scale exceeds the Representative Elemental Volume by a factor large enough to approximate PME. Not universally the case and PME does not account for anisotropy which is inherent in most fractured rock aquifers.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Porous Medium EquivalentOn some scale of observation, a fractured rock aquifer can beconsidered homogeneous in terms of the sizes of the solid matrix andthe orientations of bounding fractures. 1m 1,000 mCopyright © 2011, Thomas D. Gillespie, P.G.
    • A few basics : Several fundamental concepts typical of fractured rock aquifers and critical to characterizing flow: Representative Elemental Volume Domain Field GradientCopyright © 2011, Thomas D. Gillespie, P.G.
    • A few basics : These concepts apply equally to flow in a porous medium on a micro-scale, but become necessary when considering flow in fractured media for two reasons: The blocks of rock matrix tend to be large compared with the pore spaces so local scale heterogeneities are inherent The pore spaces are not randomly oriented in fractured rock as they are in most unconsolidated formationsCopyright © 2011, Thomas D. Gillespie, P.G.
    • Representative Elemental Volume Begin in familiar territory – a porous medium. A porous medium is characterized by the presence of a pervasive solid phase or matrix. The remaining volume, or void space, is occupied by one or more fluid phases.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Representative Elemental VolumeCharacteristic of a porous medium is that both the solid phase and voidspaces are pervasive – they are distributed throughout the volume of theaquifer.If samples are collected of sufficiently large volumes of the medium atdifferent locations within the domain, each sample will contain both the solidphase and void spaces at representative scales and orientations. Bear, 1993 Copyright © 2011, Thomas D. Gillespie, P.G.
    • Representative Elemental VolumeAt the same time, if a sample at some point in the domain must providethe data to support conclusions or inferences about what happens at thatpoint and immediately adjacent volume of the medium in terms ofgroundwater flow, the size of the sample can not be too large.The volume of sample which satisfies all the conditions is known as theRepresentative Elemental Volume (REV). Bear, 1993 Copyright © 2011, Thomas D. Gillespie, P.G.
    • We can therefore define a porous medium as amultiphase material characterized by the followingfeatures: A Representative Elemental Volume which can be identified such that no matter where a template of the REV is overlaid within the entire volume of the domain it will contain both a solid phase and void space. If such an REV can not be identified for a given domain, the latter does not qualify as a porous medium domain. The size of the REV is such that the parameters which represent the distribution of the solid phase and void spaces are statistically meaningful. Bear, 1993 Copyright © 2011, Thomas D. Gillespie, P.G.
    • Representative Elemental VolumeThe size of an REV, therefore, must be larger than the scale of microscopicheterogeneities created by individual geometries of the solid phase particlesand void spaces, and much smaller than the scale of the domain of interest.It is the heterogeneity within the domain of interest which counts whendetermining the size of the REV. Bear, 1993
    • Representative Elemental Volume Considering groundwater flow on the domainal scale, the size of an REV must be larger than the scale of microscopic heterogeneities created by individual geometries of the solid phase particles and void spaces, smaller that the scale of the domain of interest but must also contain all elements which not only contain and convey groundwater, but which also affect the overall flow characteristics.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Representative Elemental Volume In terms of groundwater flow, the REV must include the solid phase and all of the boundaries along which water moves past each portion of matrix. In fractured rock, it is apparent that the REV must include the rock matrix and all fracture sets which occur pervasively throughout the formation.The elements of the REV impart heterogeneity to groundwater flow on thescale of the REV. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Representative Elemental VolumeIn the case of porous media, the boundaries occur at randomorientations but typically within a finite and regular maximumdistance.In the case of fractured rock, the orientations are generally regularbut the distances are variableCopyright © 2011, Thomas D. Gillespie, P.G.
    • REV Scale Heterogeneity also Occurs in Porous Media.Grain boundaries deflect groundwater in cross-gradient pathways so theREV must be large enough to encompass all dimensions and orientations ofgrains. This becomes more critical in non-arenaceous unconsolidateddeposits in which mineral habits are plate-like or acicular. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Representative Elemental VolumeSo, even in a porous medium in which flow is considered mostlyhomogeneous there is no such thing as flow directly down the averagehydraulic gradient on scales of the REV. Flow only becomes uniform inrelation to the overall flow field (defined by contour lines) on scales of thedomain. Copyright © 2011, Thomas D. Gillespie, P.G.
    • DomainThe previous description of flow provides a default definition for theconcept of the domain for groundwater flow.The domain is the scale of observation which is larger than the REV withinwhich average flow can be described and predicted to be essentiallyhomogeneous* within the context of the problem of interest.That is obviously a subjective designation and one which can be fluid if, forexample, the area of interest increases beyond a site boundary.* This does not imply isotropy Copyright © 2011, Thomas D. Gillespie, P.G.
    • DomainIn terms of a porous medium, the REV is small so heterogeneity of flow canbe ignored on most scales of observation.
    • Domain The same definition of the domain applies to flow through a fracture network. The Representative Elemental Volume Plan View The smallest volume of aquifer matrix which contains at least one of each of the water-bearing fabric elementsCopyright © 2011, Thomas D. Gillespie, P.G.
    • Domain In this schematic there are two REVs, but both have similar domains.Copyright © 2011, Thomas D. Gillespie, P.G.
    • This pronounced difference between REV and Domain in fractured rock aquifers can be understood by the differences between flow under the influence of the Field Hydraulic Gradient compared with the In-Plane Hydraulic Gradient The Representative Elemental Volume In fractured rock aquifers the hydraulic gradient on the scale of the domain is referred to as the Plan View Field Hydraulic GradientCopyright © 2011, Thomas D. Gillespie, P.G.
    • ExampleA site in a jointeddiabase intrusion intothe Newark-GettysburgBasin.Groundwater contourson the site revealed asemi-radial flow from ahigh toward two steams
    • Obtained 1906 USGStopo maps and mappedfeatures absent moderndevelopment.Streams described aradial pattern from topof ridge created bydiabase.
    • Watershed boundaries.A divide crosses the siteexactly in the center ofthe semi-radial flowpattern
    • Groundwater flowarrows using dividesand perennial streamsThe hydrology madesense.
    • In this case the domain is the multi-acre site, but could be defined as the area within which linearly averaged flow intercepts the measured contours normally.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Example 2Copyright © 2011, Thomas D. Gillespie, P.G.
    • Groundwater Flow in Planar Discontinuities Field vs. In-Plane Hydraulic Gradients The designation of the Field Hydraulic Gradient for bedrock flow problems is predicated on the complimentary condition that the hydraulic gradient(s) within the different components of the REV differ from the Field Gradient. Need to begin with the examination of flow through a single planar discontinuityCopyright © 2011, Thomas D. Gillespie, P.G.
    • Field vs. In-Plane Hydraulic Gradients Flow through a plane can be complicated by variables such as aperture and wall roughness, but the geometry and mechanics of flow can be understood and modeled with relative ease, regardless of the orientation of the overall flow field. Most fracture flow models focus on a mathematical description of flow through individual fractures and focus on directional anisotropies of hydraulic gradients.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Field vs. In-Plane Hydraulic Gradients Understanding and modeling flow through that same plane is a completely different problem when other, connected planes are present at different orientations.As all pore spaces below the phreatic surface are saturated, flow occursin all of them. How can the influence of each on the overall flow field beunderstood and modeled? Copyright © 2011, Thomas D. Gillespie, P.G.
    • Field vs. In-Plane Hydraulic GradientsThe first issue to resolve is the geometry of how water moves through aplanar discontinuity.Flow occurs within the void space of a planar discontinuity and the flowcomponents within the discontinuity must be resolved to understand theflow, especially in situations in which more than one plane and multipleorientations are present.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Field vs. In-Plane Hydraulic GradientsThe need to resolve the flow into components derives from the fact thegroundwater flow is a vector and the discontinuity is planar.In most cases the orientation of the plane is not parallel to the flow vectorCopyright © 2011, Thomas D. Gillespie, P.G.
    • Field vs. In-Plane Hydraulic GradientsExcept for absolutely vertical and horizontal planes, each plane can bedescribed in terms of a strike and a dip.Groundwater flow does not flow precisely parallel to either of those.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Field vs. In-Plane Hydraulic GradientsGroundwater can not flow down the dip of a plane in a situation inwhich the dip direction is the same as the hydraulic gradient but at adifferent angle.The hydraulic gradient, by definition, is the dip angle which isconstrained by the difference in hydraulic potential between pointsand, therefore, is the numeric representation of the driving force ofgroundwater flow.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Field vs. In-Plane Hydraulic Gradients e.g., in a porous medium, flow is constrained by the difference in head potential and does not flow down a pathway because it is available.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Field vs. In-Plane Hydraulic Gradients Likewise, groundwater can’t flow down the dip of a plane in a situation in which the dip direction is opposite the hydraulic gradient. How does groundwater flow within a plane and why?Copyright © 2011, Thomas D. Gillespie, P.G.
    • Resolution of the Field Hydraulic Gradient into a Sub-Vertical Plane Because hydraulic gradients are close to horizontal, groundwater generally flows along the strike of the plane but can not flow precisely Xtaln Rock parallel to strike.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Resolution of the Field Hydraulic Gradient in a Sub-Vertical PlaneThe upper surface of the water table as resolved into the plane occurs at anin-plane gradient equal to the apparent dip observed in that plane. In such a case, the magnitude of the field hydraulic gradient is greater than the magnitude of the resolved hydraulic gradient.
    • Resolution of the Field Hydraulic Gradient in a Sub-Vertical PlaneThe only exception to that general condition is where the strike of theplane is coincident with the azimuth of the flow vector in which caseflow would be precisely parallel to strike and the field gradient wouldbe equal to the in-plane gradient.
    • Viewed normal to the plane, the true dip of the field hydraulicgradient is greater than the apparent dip of the in-plane gradient. ΔX Strike of Plane ΔY ip i Dip of Plane Field Hydraulic Gradient i In-plane Hydraulic Plane A Copyright Gradient ip © 2011, Thomas Δ X1 Vertically D. exaggerated Gillespie, P.G.Therefore, groundwater flow through planes at any angle to the fieldhydraulic gradient flows under a lesser gradient than the field gradient.
    • Resolution of the Field Hydraulic Gradient in a Sub-Vertical PlaneBecause: flow is within a planar discontinuity; that discontinuity is a saturated, three-dimensional pore space; water flows approximately parallel to the strike of the plane but down a gradient which is not equal to the field hydraulic gradient;the In-Plane Hydraulic Gradient (ip) can be resolved and quantifiedboth graphically and mathematically. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Resolution of the Field Hydraulic Gradient in a Sub-Vertical Plane Plane A N Plan View intercepts the Field Hydraulic Gradient at some angle. Flow sub-parallel to the strike of the plane results in an in-plane Plane A gradient which is different than the field gradientCopyright © 2011, Thomas D. Gillespie, P.G.
    • Resolution of the Field Hydraulic Gradient in a Sub-Vertical Plane Plan View Δ Y /Δ X = i Field Hydraulic Gradient ΔX Δ X1 Δ Y/Δ X1 = ip Plane A In-plane Hydraulic Gradient ΔX ΔX Ө1 Δ X1 Δ X1 > Δ X Δ Y = Const. Δ Y /Δ X = i > Δ Y /Δ X1 = ipCopyright © 2011, Thomas D. Gillespie, P.G.
    • Resolution of the Field Hydraulic Gradient to an In-Plane GradientThe in-plane gradient (ip) for any sub-vertical plane striking Ө°from the azimuth of the field gradient (i) can be calculated. Δ X1 Ө1 ip i Δy Δ X1 ΔX Plane AΔX Δ X1 = ΔX/cos Ө1 ip = Δy/(ΔX/cos Ө1)Copyright © 2011, Thomas D. Gillespie, P.G.
    • Natural Systems of Planar DiscontinuitiesIn most settings, fractures donot occur as individualrandomly oriented planes or assub-parallel ‘sets’ with only asingle orientation. In otherwords, fractures occur inmultiple sets at statisticallypredictable, non-randomorientations. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Natural Systems of Planar DiscontinuitiesAs a result, the sum total of planar discontinuities in rock masses canbe categorized into a hierarchy based on the structures present,structural relations, respective frequencies of the structures and thescale of observation. The simple problem of resolving Strike the in-plane hydraulic gradient within a single plane must be expanded to incorporate the various planar systems within a rock mass to determine whether there is a single structural control and anisotropy, or whether the network forms aJoint planes Porous Medium Equivalent.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Natural Systems of Planar DiscontinuitiesBegan with a single plane at some angle to the field hydraulic gradient,and the resolution of flow onto that plane.We can increase the complexity of the system by adding additional setsof discontinuities. That becomes the basis of hydrostructural modeling,as well as the basis of the fundamental units of the hydrostructuralframework. Field Hydraulic Gradient But first . . . . Joint tracesCopyright © 2011, Thomas D. Gillespie, P.G.
    • The Structural Geology of Planes
    • STRIKE & DIPSTRIKE = trend (azimuth, bearing) Another definition of Strike =of a structural contour on a plane. trend of a line connecting points of equal elevation on a plane.………of a horizontal line on aplane.……….water level line on a plane.In the field this horizontal line isdefined by using bulls eye level to On a plane, structural contourshold compass as a horizontal plane will be straight lines with equaland placing edge of compass against spacing – and all are parallel tosurface to be measured. strike.Hence measuring strike of a plane isthe determination of a structural Source: Donald Wisecontour line on the plane.
    • STRIKE & DIPDIP = the angle from the horizontal to theplane as measured in a planeperpendicular to strike (or perpendicularto a structural contour) .NOTE: Dip must be measured in thevertical plan (compass must be held invertical plane).Dip is measured in direction of maximuminclination ( normal to strike)Measured in any direction other thannormal to strike, one measures anAPPARENT DIP which is somewhat lessthan true dip.NOTE: Apparent dip on any planemeasured parallel to strike is 0. (i.e. thedip on a structural contour is zero) Source: Donald Wise
    • REPRESENTATION OF A PLANE ON A MAP. Ideal is structural contours on the plane (for a true planar surface they are straight lines with equal spacing and all parallel to each other).MAPSVertical plane 1000, 2000, 3000 contours all in same place.Closer the spacing of the structural contours the steeper the dip of the plane.Vertical plane has all the contours at the same place.Commonly we only measure a tiny bit of the total plane and hence use the symbol If we are measuring a parallel set of planes (pile of dipping sediments) they all will have the same strike and dip. Source: Donald Wise
    • DETERMINING DIP FROM STRUCTURALCONTOURS - RIGHT SECTIONSA right section is a view of theplane running along a line atright angles to strike.Draw some convenient line (AB)perpendicular to strike.Draw line AB off the map,marking off points A, B &elevation points.USING SAME SCALE AS MAPgo down to proper elevations,draw plane & measure dip. Source: Donald Wise
    • BASIC METHOD : RIGHT SECTIONSA sandstone bed strikes N30W and dips 30 Either mentally orSW. Its outcrop width on a flat surface is physically fold the100m. Find its true stratigraphic thickness. paper along this line to make a right sectionIf we could look at a true cross-section drawn below the line.at right angles to the strike, we could measureoff the true thickness (to scale. Below = 1 cm Because this is a right= 100 m). section the full dip of 30’ can be used to drawDraw any random line FF’ at right angles to top and bottom of thestrike. bed in the cross-section. Measure true thickness in right section, normal to bed, using map scale. Source: Donald Wise
    • Source: Donald Wise
    • RIGHT SECTIONS AT RIGHT PLACESA Coal Bed striking N20E, 50 NW Draw a line through the shaft,crops out as shown. A mine shaft is to perpendicular to strike.be drilled 500 meters due west of theoutcrop. How deep is the coal bed in Make this line FF’ a fold line tothe shaft? draw a right section which will contain the shaft.Select come convenient scale anddraw the map. Draw the dipping coal bed and the shaft in this section. Using the scale, measure the depth of the shaft (550m). Source: Donald Wise
    • Source: Donald Wise
    • The top and bottom of asandstone crop out atelevations of 600 and 200meters, respectively, at thelocations shown on the map.The strike and dip at bothlocations is N60~E, 20 NW.Calculate the thickness ofthe sandstone. Source: Donald Wise
    • Source: Donald Wise
    • GREASY DRIP SANDSTONE AREA The Greasy Drip Sandstone is a major reservoir rock in the Petroleum Patch Quadrangle. A small exploration company owned by W.E. Findum and U.R. Lost has hired you to get some data from the outcrop above. What is the strike of the sandstone? _____ What is the dip of the sandstone? _____ to the _____? The thickness of the sandstone is _____? The depth to the top of the sandstone at Grimy Station is _____? What is the vertical thickness of the Greasy Drip SS that would be intersected in a coring made at Grimy Station? _____ Source: Donald Wise
    • GREASY DRIP SANDSTONE AREASource: Donald Wise
    • ONE POINT PROBLEMSGiven one point on a map where the strike, dip, and elevation of a planar bedare known, draw the structural contours for this bed throughout the map area.For example, in an area of very sparse exposure, you have only one outcrop ofa coal bed, point A, at an elevation of 1900 feet and strike N60W, 30 SW.Nevertheless, you need to complete a geologic map of the concealed line ofoutcrop of the bed across the area and get the predicted dill depths to the coal.These determinations will require a knowledge of the structural contoursacross the area.
    • ONE POINT PROBLEMSExtend the line of strike from A to some convenient place off the map. This line is astructural contour and all locations along it are at 1900 foot elevation.Draw a line perpendicular to the structural contour. This will be a right section.The line is at the same elevation as the structural contour (1900 feet). Using thesame scale as the map, put in the elevation lines below the 1900 foot elevation line ofDCE and mark their elevations as shown.This is a right section, so the true 30 degree dip can be plotted starting from point C(which is at 1900 feet elevation).
    • 1000 ft
    • Find the intersections of the dipping plane in the cross section with theappropriate elevations (F, G, H, I, etc.) and project them up to the surface asL, M, N, O, etc. These are now map points below which the elevations of theplane are known.Structural contours can now be drawn through each of these points parallelto the main 1900 foot contour (AB). The same spacing and trend of contourscan be continued across the entire map. Source: Donald Wise
    • How deepwould youneed to drilla well atPoint B tointersect thetop of theformationwhichoutcrops atPoint A? Contour Interval = 100 m
    • Two-Point ProblemsDetermine the Strike and Dip
    • Three Point ProblemsGiven 3 points on a planar Draw structural contours through thesurface, find the strike & dip high and low points parallel to theof that plane. strike. (AE&CG)Connect the highest and lowest Draw a fold line perpendicular to strike.of the three points on the map. Decide on elevation of this line using(A&C) same scale as map, draw elevation lines below the fold line for cross-section.Interpolate between thesepoints for a point of elevation Project the structural contours of highthe same as that of the and/or low points onto the cross-sectionintermediate elevation point. and draw the dipping plane on this right(B) section.Join these two points of equal *Measure its dip (Angle GEH).elevation as a line of strike.(BD)*Read off this strike withrespect to north Source: Donald Wise
    • Source: Donald Wise
    • Three Point Problem - Method 2Draw two lines connecting the highest elevation point with both the lowest andintermediate points: (AC; AB).Scale off divisions of equal elevations along each line.Connect points of equal elevations with structural contour lines.Construct right section as in Method 1.
    • InterpolationA common geologic problem is to be given some numerical value (elevation,for example) at two locations on a map. Intermediate values need to becalculated or INTERPOLATED as proportional distances along the linejoining the two points.THE PROBLEM: Two points A and B are located on a map as shown andhave elevations of 435 and 715 feet respectively. Find a locationproportionally spaced between them which would have a proportionalelevation of 683 feet. While you are at it, find the proportional locations for500, 600, and 700 feet elevations. B 715 A 435Draw the line connecting the two locations, A and B.Source: Donald Wise
    • InterpolationFrom the end of this line with the lower elevation (point A in this case)draw a random line (AC) at about 30 to 45 degrees from AB.Use some scale of a ruler (in tenths) with values which correspond to theelevation differences between A and B. Put the 4.35 value of the ruler onthe 435 ft elevation of point A and locate point D at the same value as theelevation point B (7.15 for the 715 foot elevation in this case). B 715 A 435 Source: Donald Wise
    • InterpolationUsing the scale of the ruler mark off on line AD all the locations corresponding to allthe elevations you seek (6.83, 500, 600, 700).Make a large triangle by connecting points D and B. By ruling parallel to line DBmake a series of similar triangles through each of the points you located in the above.A THEOREM OF PLANE GEOMETRY IS THAT DISTANCES WHICH AREPROPORTIONAL TO THE LENGTHS OF LEGS OF ONE SET OF SIMILAR TRIANGLESARE ALSO PROPORTIONAL TO THE OTHER LEGS OF THOSE TRIANGLES.Thus, the locations along line AB havespacing proportional to their elevations.
    • Outcrop PatternsIf the structural contour on some horizon has the same elevation as thetopography at that point, then that bed crops out at that location.Conversely, if an outcrop occurs at some location, the structural contourof that elevation on that unit passes through that point. Source: Donald Wise
    • Outcrop PatternsIn general, the outcrop of a dipping plane will “V” in crossing a valley,such that the “V” will point in the direction of dip. With flat dips and steep stream gradients these V’s might point in other direction. If there is no V at all, then the plane is very steep to vertical. This V principal applies to all kinds of planes: beds, dikes, faults, unconformities. Source: Donald Wise
    • A planar coal bed crops out a points A, B and C. What is the bed’s orientation _______ Draw the outcrop pattern How deep would you need to dig at point D to intersect the coal? __________Source: Donald Wise
    • Horsefeather Creek AreaStructural Contours on top of Horsefeather Sandstone. Construct a rightsection.What is the orientation of the unit? __________How deep would you drill at P _______ and Q________ to intersect theunit?Draw the outcrop pattern. Source: Donald Wise
    • Draw section FF’, the axial trace, and fully describe the structure (The numbers represent stratigraphic superposition)Source: Donald Wise
    • Describe the structure at left. What is the direction of dip of the ss? _______ What is its strike? _________Source: Donald Wise
    • The St. Valentine Sandstone crops out along ILUVU Creek Valley as shown. Sketch Section A-B.Source: Donald Wise
    • FaultsCan be either a barrier to groundwater flow, or a conduitTend to be the cause of linear topographic regional lows (valleys)Important in hydrologic evaluationsUse law of V’s to get dip directions.Erosion on upthrown side will make the outcrop of a dipping bed migratein the direction of dip.Upthrown side brings up deeper, older rocks for exposure by erosion. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Hydrogeologic Nature of Faults and Fault ZonesThe presence of faults / fault zones can have many and varied effects ongroundwater flow systems depending on the spatial relationships betweenrock types on opposing fault blocks, the orientation of the fault in relationto recharge and discharge areas, the degree to which brecciation hasresulted in a fault gouge infillingThere are some things that most faults have in common which can be usedin the development of conceptual hydrogeologic models before designingany kind of exploration program. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Hydrogeologic Nature of Faults and Fault ZonesFaults / fault zones are: Zones of fluid accumulation Integral components of Secondary Porosity Network Brecciation Zones of fluid storage Fault gouge forms a porous medium Pathways of fluid movement mineral / ore deposits seismic pumping, natural hydraulic fracturing Copyright © 2011, Thomas D. Gillespie, P.G.
    • Hydrogeologic Nature of Faults and Fault ZonesFaults tend to be long in comparison to local domains ofwater-bearing structural rock fabrics; i.e., faults tend tocross formational contacts and, therefore, create pathwaysfor water to move from one flow domain to another.Consequently, faults can provide the regional hydrogeologiccontinuity necessary for regional water budget balance. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Fault Zone Effects on Local / Regional HydrogeologyCopyright © 2011, Thomas D. Gillespie, P.G.
    • Fault Zone Effects on Local / Regional HydrogeologyCopyright © 2011, Thomas D. Gillespie, P.G.
    • Regional faults are easily eroded and tend to form linear topographiclows, with the result that groundwater in both fault blocks is at a higherhydraulic potential than is the water in the fault zone. In such cases,groundwater flow must be along the fault zone, and dissolved regulatedcompounds can not be transported to the opposite fault block. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Copyright © 2011, Thomas D. Gillespie, P.G.
    • Fault Problems Source: Donald Wise
    • What kind of fault? Which way does dike A-B dip? Why? Which side went up? Give approximate azimuth and plunge of the net slip and explain how you got it. M, S, T are all faults. Which is the oldest fault? If all the fault movements are dip slip, mark the up and down for those faults where it can be determined.Source: Donald Wise
    • Guano Creek Field AreaSource: Donald Wise
    • Guano Creek Field AreaTwo of the more intrepid members of our class, Jon and Dave, have been mapping inthe Guano Creek region, so named for the famed bird rookeries at its headwaters.(The nearly extinct “tweety bird” is rumored to roost in that area.) They are tryingto locate the source of the sulfide ores which oxidize to form a high concentration ofsulfuric acid in Guano Creek, a condition which prompted them to make a boat outof lead to withstand these corrosive waters. Using this field vehicle, they haveproduced the accompanying map but are still up the creek, still in their water craft,still without finding the ores. They need help (in many ways). Should you wish togive a concise one-line description of their condition, please feel free to do so. Inaddition please answer for them:Why is the outcrop width of the Sludge Bucket Sandstone (stippled pattern on the map) three times as wide on the SW side as on the NE side?Describe the Guano Creek fold in as full a detail as possible, including the general orientation of cleavage you might expect associated with it.In as much detail as possible describe Jon’s major fault (including approximate strike, dip direction, approximate motion sense, fault type, relative age).In as much detail as possible describe the Tweety Bird fault (same items as above). Source: Donald Wise
    • Guano Creek Field AreaSource: Donald Wise
    • Guano Creek Field Area – SolutionsWhy is the outcrop width of the Sludge Bucket Sandstone (stippledpattern on the map) three times as wide on the SW side as on the NE side? Asymmetric fold – N.E. limb is close to vertical.Describe the Guano Creek fold in as full a detail as possible, including thegeneral orientation of cleavage you might expect associated with it. Asymmetric, N.W. Plunging Anticline.In as much detail as possible describe Jon’s major fault (includingapproximate strike, dip direction, approximate motion sense, fault type,relative age). 080 ° - 90, Right Lateral Transform, younger fault.In as much detail as possible describe the Tweety Bird fault (same itemsas above). 045, Dipping S.E., Reverse, older fault.Source: Donald Wise
    • Systems of Planar DiscontinuitiesPlanar discontinuities do not occur randomly within a rock mass.Occur in response to stresses in the rock mass which can be: Tectonic Residual UnloadingCopyright © 2011, Thomas D. Gillespie, P.G.
    • Systems of Planar DiscontinuitiesOccur in sub-parallel sets which are pervasive and are oriented alongpreferential orientations
    • Systems of Planar Discontinuities Tectonic JointsGenerally occur in sub-vertical, near-orthogonal conjugate sets of tensionjointsOne set forms first and is referred to as theSystematic Joint SetThe second set is the Non-Systematic Joint Set, also known as CrossJoints. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Systems of Planar Discontinuities Tectonic JointsSource :Twiss & Moores, 2007
    • Systems of Planar Discontinuities Tectonic JointsSystematic Joint Sets are the longest of the two and can intersectnumerous non-systematic joints.Non-Systematic Joint Sets extend only from one systematic joint plane tothe adjacent plane – they can not cross a systematic joint because tensilefailure cannot be propagated across a void.Non-Systematic Joint Sets, therefore, are composed of a series of short,offset joints which connect the longer systematic joint planes. They tend tooccur at more varied orientations within a lrger range than systematicjoints. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Systems of Planar Discontinuities Fold-Related JointsAlthough also the result of tectonic stresses, fold-related joints are shearjoints and occur in distinct patterns of conjugate sets. Source :Twiss & Moores, 2007
    • Systems of Planar Discontinuities Fold-Related JointsA series of tension joints can also be superimposed on conjugate shearjoint sets. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Systems of Planar Discontinuities Fold-Related JointsCopyright © 2011, Thomas D. Gillespie, P.G.
    • Systems of Planar Discontinuities Residual Stress JointsTension joints which form intwo distinct situations: Cooling joints – tend to be sub-vertical, but can occur locally at any orientation Unloading joints – tend to be sub-horizontal Copyright © 2011, Thomas D. Gillespie, P.G.
    • Description of Joints –USEPA, Manual of Field ProceduresDescription of Bedding or of Joint or Fracture Spacing: Descriptionshould be according to the following:Spacing Joints Bedding or Foliation< 2 in. Very close Very thin2 in. to 1 ft Close Thin1 ft to 3 ft Moderately close Medium3 ft to 10 ft Wide Thick>10 ft Very wide Very thick(after Deere, 1963)
    • Description of Joints –USEPA, Manual of Field ProceduresWeathering: Terms used to describe weathering are described below:Descriptive Term Defining CharacteristicsFresh Rock is unstained. May be fractured, but discontinuities are not stained.Slightly Rock is unstained. Discontinuities show some staining on the surfaces of rocks, but discoloration does not penetrate rock mass.Moderate Discontinuity surfaces are stained. Discoloration may extend into rock along discontinuity surfaces.High Individual rock fragments are thoroughly stained and can be crushed with pressure hammer. Discontinuity surfaces are thoroughly stained and may be crumbly.Severe Rock appears to consist of gravel-sized fragments in a “soil” matrix. Individual fragments are thoroughly discolored and can be broken with fingers.
    • Formation-Specific Jointing Styles Different rock formations respond to tectonic stresses differently with the result that joint styles can vary from one stratum to the next within a sequence.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Statistical Evaluation of Planar DiscontinuitiesBecause joints tend to form along preferred orientations within a rockmass, but there is some variation, the data set of planar orientations mustbe treated statistically to determine the mean or statistically averagedorientation of each setThis is done graphically, rather than with actual statistics using lower-hemispheric projections of planar data.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Structural Data
    • If we divide a circle into ten Contouring Structural Data zones of equal width, the innermost circle will contain 1% of the area. The next circle is twice as large and will contain 4%, but 1% is in the inner circle, so the annulus will contain 3% of the area, and so on. If we stack triangles, each row will contain 1, 3, 5... triangles. A stack ten rows high will contain 100 triangles. If we divide a 60 degree sector of the circle into triangles of equal area, each sector will contain 100 triangles, each with 1% of the area of the sector.From:http://www.uwgb.edu/dutchs/structge/SL133Kalsbeek.HTM
    • Contouring Structural Data The Kalsbeek counting net is based on this principle. It consists of ten equally spaced circles. Each annulus is divided into triangles. Altogether there are 600 triangles. At each vertex, six triangles meet. The hexagon of triangles around each vertex contains 1% of the area of the net.From:http://www.uwgb.edu/dutchs/structge/SL133Kalsbeek.HTM
    • Plot the data on an equal Contouring Structural Data area net then transfer the overlay to the counting net. Of course, the two nets must be the same diameter!From:http://www.uwgb.edu/dutchs/structge/SL133Kalsbeek.HTM
    • Contouring Structural Data At each vertex, count the number of points in the surrounding six triangles and plot the number at the vertex. You may want to do this on a second overlay above the data overlay. Each triangle is common to three hexagons so every point is counted three times. (No, this does not mean the densities have to be divided by three.) Be certain to check every vertex close to the data points to be sure of not missing any. From:http://www.uwgb.edu/dutchs/structge/SL133Kalsbeek.HTM
    • Contouring Structural Data Remove the numbered overlay and contour the data.From:http://www.uwgb.edu/dutchs/structge/SL133Kalsbeek.HTM
    • Contouring Structural Data Place the contoured data over a Schmidt Net and rotate it so the highest concentration data is on the E-W diameterFrom:http://www.uwgb.edu/dutchs/structge/SL133Kalsbeek.HTM
    • Contouring Structural Data Construct a plane 90° from the central cluster of the data and read the dip angle directly off the E-W diameterFrom:http://www.uwgb.edu/dutchs/structge/SL133Kalsbeek.HTM
    • Contouring Structural Data Rotate the entire overlay back to north and read off the predominant orientation of the joint set.From:http://www.uwgb.edu/dutchs/structge/SL133Kalsbeek.HTM
    • Contouring Structural DataCopyright © 2011, Thomas D. Gillespie, P.G.
    • SCHMIDT NET
    • KALSBEEKCOUNTING NET
    • Hydrostructural GeologyCombined hydraulic and structural dataStep 1: Meld calculated in-plane flows with multiple planar sets within aformation Define the REV Define the Domain Resolve in-plane flows for all discontinuity sets Model the anisotropy Copyright © 2011, Thomas D. Gillespie, P.G.
    • Hydrostructural GeologyCombined hydraulic and structural dataStep 2: Superimpose flow modeled for each formation onto localvariability between formations and/or regional setting Identify changes in structural styles including joint styles, orientations, inter-joint spacing and frequency distribution Identify larger scale structures which cross formational boundaries – e.g., faults, dikes Reconcile domainal flow with local and regional hydrologic regimes Copyright © 2011, Thomas D. Gillespie, P.G.
    • Hydrostructural GeologyCombined hydraulic and structural dataStep 1: Meld calculated in-plane flows with multiple planar sets within aformationIn flow modeling using a Ncontour map inunconsolidated geologicsettings, the model results ina two-dimensional, orvectoral representation of Meterthe direction of sgroundwater flow with a 0 100graphical azimuth and agradient expressed as aunitless value.In this case we can reconstruct groundwater contours in the absence ofany other data. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Hydrostructural GeologyCombined hydraulic and structural dataStep 1: Meld calculated in-plane flows with multiple planar sets within aformationBecause the flow arrow is a vector (should be a vector), it is also alineament.As such it can be treated as structural data - a line with a trend andplunge: 0° 0’10” 110°and can be represented along with structural data in a threedimensional graphical model. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Hydrostructural GeologyCombined hydraulic and structural dataBecause the dip of the gradient of groundwater expressed in degrees isessentially zero, at least in terms of trend and plunge measurements, thegroundwater flow vector will plot on the primitive of a three-dimensionalplot of structural data. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Hydro-Structural Flow Modeling, Gillespie and McLane, 2009Copyright © 2011, Thomas D. Gillespie, P.G.
    • Resolution of the Field Hydraulic Gradient to an In-Plane GradientThe in-plane gradient (ip) for any sub-vertical plane striking Ө°from the azimuth of the field gradient (i) can be calculated. Δ X1 Ө1 ip i Δy Δ X1 ΔX Plane AΔX Δ X1 = ΔX/cos Ө1 ip = Δy/(ΔX/cos Ө1)Copyright © 2011, Thomas D. Gillespie, P.G.
    • Example: Formations with sedimentary bedding as well as fractures. Fractures (joints) tend to be sub-vertical Groundwater flow is through all planes. Those planes which are oriented closer to the azimuth of the hydraulic gradient will exert the greatest control on groundwater flow direction and will impart some degree of anisotropy.Joint planes Copyright © 2011, Thomas D. Gillespie, P.G.
    • Planar Joint Discontinuities Joint Δx1 Set 1 Δx2 Set 2 Δx Groundwater Contours Field Hydraulic θ1 Gradient In-Plane (Δh/Δx) Flow Gradient in Plane A = Δh / Δx1, Where: Δx1= Δx / cosθ1Groundwater flow within an individual planar discontinuity isapproximately sub-parallel to strike. The lesser the angle between thestrike of a water-bearing discontinuity and the azimuth of the fieldhydraulic gradient, the greater is the correspondence between theequipotential lines of the field hydraulic gradient and those within thediscontinuity, with maximum correspondence in a plane with a strikeequal to the azimuth of the hydraulic gradient and least correspondencewhere strike and hydraulic gradient are normal. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Planar Joint Discontinuities Joint Δx1x1 ? Δ x2 Set 2 Set 1 Δx ?x Ө1 Groundwater Contours Field Hydraulic Gradient In-Plane Flow Gradient in Plane A = Δh / Δx1 Where: Δx1= Δx / cos Ө1Copyright © 2011, Thomas D. Gillespie, P.G.
    • A particle of water at the intersection ofplanes of Joint Sets 1 and 2 (see previous Jointfigure) could flow into either Set 1discontinuity but with a greater tendency Joint Set 2to flow into the plane with the highest θ2gradient. The azimuth of Joint Set 1 is ata lesser angle (θ1) to the azimuth of the Δx2field hydraulic gradient than is that of Δx1Joint Set 2 (θ2). Comparing the in-plane Δx θ1hydraulic gradients for the planes andkeeping Δx at unity, the gradient in JointSet 1 exceeds that in Joint Set 2 by a Field Hydraulicfactor of: Gradient (Δh/Δx) ip= (Δh/Δx1 )/(Δh/Δx2) Copyright © 2011, Thomas D. Gillespie, P.G.
    • and the preferential tendency for a hypothetical particle of water to flow into Joint Set 1, expressed as a percentage, is given by: Cos θ1/Cos (180-θ2) · 100 Joint Set 1 Field Hydraulic For a hypothetical case in which θ1 = Gradient 20° and θ2 = -65° the flow ratio into planes in Joint Sets 1 and 2 is 2.2:1 for a 70% potential for flow into Joint Set 1 Joint Set 2 and a 30% potential for flow into Joint Set 2. The same result can be obtained by a graphical vector resolution (see adjacent figures) of the field hydraulic gradient and the two planes.Copyright © 2011, Thomas D. Gillespie, P.G.
    • The non-random partitioningof flow into the joint sets andthe differences in plane lengthand inter-plane spacingbetween systematic and non-systematic joint sets createsanisotropy on the scale of therepresentative elementalvolume which can extend tolarger scales in formations withheterogeneous distributions of On a local scale (~102 m) the reticulatednon-random planes. nature of joint networks typically precludes pronounced linear anisotropies but the flow partitioning into different joint sets and/or bedding planes provides for prediction of the fracture-controlled deviation of flow direction from the field hydraulic gradient and of solute deflection. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Using the 2.2:1 partitioningratio in the example, thedeflection of solutes over ahypothetical distance of 200 mwould be -4o from the fieldgradient with solute deflection of20m from a linearly interpolatedtransport line. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Non-Random planar fabric elements in consolidated rock formations arestructurally dependent, occur in sets with statistically consistentpreferential orientations and form the majority of water-bearing planes.The differences of mean plane lengths, frequencies and spacings betweenthe planar elements impart strong anisotropy to groundwater flow on thescale of the Representative Elemental Volume of the planar network, whichtend to be defined on the scale of 100 to 101 m. On the scale of most flowand solute transport investigations (101 to 102 m) the reticulated nature ofsystematic and non-systematic joint sets with or without bedding planepartings, tend to preclude development of strong aquifer anisotropy on thescale of the observations being made.The REV-imposed anisotropy is manifest on the scale of most study areas,however, in the deflection from the field hydraulic gradient of meangroundwater flow direction and solute transport. Testable predictions of theangle and distance of deflection at compliance points based on this modelcan be used to select monitoring locations for plume delineation andmonitoring. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Comparing Hydrostructural Methods… Planar Joint Discontinuities Joint Δx1 Set 1Δx2 Set 2 Δx Groundwater Contours Field Hydraulic θ1 Gradient In-Plane (Δh/Δx) Flow Gradient in Plane A = Δh / Δx1, Where: Δx1= Δx / cosθ1 To non-structurally based methods (e.g., fetter, 2001)… Copyright © 2011, Thomas D. Gillespie, P.G.
    • The measured directional anisotropy in hydraulic conductivity will vary significantly depending on the location of the pumping well and the structural relations between joint sets, bedding planes, etc. PlanarFor example, an Joint Discontinuities Joint Δx1 Set 1extraction well Δx2 Set 2along strike of Δxsystematic Joint GroundwaterSet 1 at Point A, Contourswould result in a Field Hydraulic θ1 Gradient In-Planedifferent (Δh/Δx) Flowanisotropy than a Gradient in Plane A = Δh / Δx1,well along strike Where: Δx1= Δx / cosθ1of non-systematic AJoint Set 2 at BPoint B Copyright © 2011, Thomas D. Gillespie, P.G.
    • This is because anisotropy results from preferential flow into the set ofdiscontinuities which strikes at the lowest angle to the field gradient .Changing the magnitude and direction of the field gradient changesthe entire flow regime. Models based on measured hydraulic gradientsduring aquifer stress tests are subject to induced error as a result. Planar Joint Discontinuities Joint Δx1 Set 1 Δx2 Set 2 Δx Groundwater Contours Field Hydraulic θ1 Gradient In-Plane (Δh/Δx) Flow Gradient in Plane A = Δh / Δx1, Where: Δx1= Δx / cosθ1 A BCopyright © 2011, Thomas D. Gillespie, P.G.
    • Case Study Groundwater flow in a fractured sedimentary rock formation in the Newark-Gettysburg Basin. Bedding dips at a low angle toward the northwest and there are two sub-vertical joint sets. Problem: use structural data to predict the distribution and width of a solute plume at the location of second order streamCopyright © 2011, Thomas D. Gillespie, P.G.
    • N Field Hydraulic Gradient (Green arrow: azimuth ~095°) superimposedon principal bedrock groundwater-transmitting structural fabricelements. White lines: S1 joints (045°-90) - strike is approximatelycoincident with bedding plane strike but bedding dips NW; Red lines: S2joints (105°-85NE); Buff lines: generalized groundwater elevationcontours. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Lower hemisphere projection of planar fabric elements depicting the orientation of the field hydraulic gradient (red circle) in relation to measured structural fabric elements. Bedding plane partings (blue) strike 50° from the field gradient, dip in the opposite direction and, consequently, exert little to no control on groundwater flow direction. Planar element intersections are not aligned with measured groundwater flow, plunging 80° toward 075° (joints) and 5° toward 300° (joints w/bedding). The S2 joint set is the pervasive fabric element with a strike azimuth nearest that of the field hydraulic gradientCopyright © 2011, Thomas D. Gillespie, P.G.
    • Resolution of in-plane hydraulicgradients in S1 and S2 joints (beddingplane has similar strike to S1 – dipdirection and angle are not relevant tothe model solution). Geometricresolution results in a preferentialtendency for groundwater and solutesto flow into S2 joint planes with apathway ratio (S2 : S1) of 1.53:1. Copyright © 2011, Thomas D. Gillespie, P.G.
    • Model prediction is that solute deflection will be toward the north 65m for every 100 m of transport along the field gradient, or adistance of approximately 300 m over the 450 m study area distanceto the stream discharge.Copyright © 2011, Thomas D. Gillespie, P.G.
    • Superimposed on an aerial photograph of the site, the model predicted thatsolutes should be discharging to the stream only in the shaded zone shown atleft. Regulatory review had required monitoring wells both east and westbanks along the entire length of the stream near the site. Copyright © 2011, Thomas D. Gillespie, P.G.
    • The Mathematics Behind It (Some of it)For the problem of two sub-vertical joint sets where the hydraulic gradienti is within the horizontal plane, the x and y components of ground waterflow are given by: Copyright © 2011, Thomas D. Gillespie, P.G. and Charles McLane, P.G.
    • 049 60NW 336 56NE
    • Using the Structural Data measured earlier, calculate the direction and degreeof anisotropy for the following situation: Joint Set No 1 – 049 60NW Joint Set No. 2 – 336 56 NE Field Hydraulic gradient - 0.05 180° Field Hydraulic Gradient 100 ft
    • 100 ft
    • Ө1 = 24° Ө1 Ө2 = 45° Δx – 100 ft Δh – 5 ft Ө2100 ft
    • ip1 = Δx / cos Ө1 = 100/.91 = 109.9 (Δh/ ip2)/(Δh/ ip1 ) = 1.3ip2 = Δx / cos Ө2 = 100/.91 = 141.4 Ө1 Ө2 100 ft
    • 1.3100 ft 1.09 ft
    • Hydrostructural GeologyCombined hydraulic and structural dataStep 2: Superimpose flow modeled for each formation onto localvariability between formations and/or regional setting Identify changes in structural styles including joint styles, orientations, inter-joint spacing and frequency distribution Identify larger scale structures which cross formational boundaries – e.g., faults, dikes Reconcile domainal flow with local and regional hydrologic regimes Copyright © 2011, Thomas D. Gillespie, P.G.
    • Assumption: Groundwater flow is controlled by a single fabric elementCopyright © 2011, Thomas D. Gillespie, P.G.
    • Copyright © 2011, Thomas D. Gillespie, P.G.
    • Copyright © 2011, Thomas D. Gillespie, P.G.
    • Copyright © 2011, Thomas D. Gillespie, P.G.
    • Copyright © 2011, Thomas D. Gillespie, P.G.
    • Current ResearchThe simple partitioning of groundwater into intersecting joints iscomplicated by the differential partitioning which occurs betweenupgradient-facing and downgradient-facing intersections Plan View