141.%20Groundwater

141.%20Groundwater - Groundwater Lecture 14 Groundwater Law...

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Unformatted text preview: Groundwater Lecture 14 Groundwater Law Lecture 14: Groundwater Page 1 of 34 Lecture 14: Groundwater Aquifers — Aquicludes Aquifer A body of rock that is sufficiently body permeable to conduct groundwater and to yield economically significant quantities of water to wells Aquitard A confining bed that retards but does confining not prevent the flow of water to or from an adjacent aquifer; a leaky confining bed. It does not readily yield water to wells or springs, but may serve as a storage unit for groundwater. Lecture 14: Groundwater Page 2 of 34 Lecture 14: Groundwater Aquiclude A body of rock that will absorb water body slowly but will not transmit it fast enough to supply a well or spring (impermeable bed — K>0) Environments of Formation of Aquifer Units Primary Environments An environment of An formation that results in a naturally porous media in which the pores are interconnected to allow the free flow of groundwater. Clastic Sedimentary Clastic Environments Aeolian Aeolian Fluvial/Alluvial Fluvial/Alluvial Deltaic Deltaic Coastal Coastal Shallow/Near Shore Shallow/Near Marine Open Marine Open Glacial Glacial Volcanic Volcanic Lecture 14: Groundwater Page 3 of 34 Lecture 14: Groundwater Aeolian Setting Uniform Uniform Contains Cross-beds Contains Well Sorted/Poorly Well Graded Fine Grain Size Fine Commonly Quartz Commonly Particles Contacts Not Defined Contacts Alluvial/Talus Setting Alluvial/Talus Highly Non-Uniform Highly NonOften Step Often Sorted/Graded Boulders to Clay Sizes Boulders Particles Derived from Particles Nearby Stacked High Energy Stacked Streams Unconformable Unconformable Contact Lecture 14: Groundwater Page 4 of 34 Lecture 14: Groundwater Braided Stream Irregular Irregular Inter-fingered Beds Inter Dominantly Gravel Dominantly + Sand Bounded Laterally Bounded Measurable Measurable Gradient Linear Feature Linear Meandering Stream Vertical Variability Vertical Generally Fining Generally Upward Bounded Laterally Bounded Measurable Measurable Gradient Linear Feature Linear Misfit Systems Misfit Lecture 14: Groundwater Page 5 of 34 Lecture 14: Groundwater Deltaic Setting Vertical Variability Vertical Coarsening Upward Coarsening Medium—Fine Medium grain size Bounded by ClayBounded Rich Beds “Triangular” Feature Coastal Environment Vertical & Lateral Vertical Variability Linear Feature Linear Narrow Narrow Depositional Zones Bedrock Not Bedrock Predictable Lecture 14: Groundwater Page 6 of 34 Lecture 14: Groundwater Carbonate Setting Complex Complex Environment Irregular Irregular Distribution Highly Variable Highly Properties Bedrock Not Bedrock Predictable Shallow/Near Shore Marine Complex setting Complex Highly localized Highly Clays to gravel Clays Organic deposits Organic Irregular contacts Irregular Contacts not Contacts defined Lecture 14: Groundwater Page 7 of 34 Lecture 14: Groundwater Open Marine Regional extent Regional Very fine-grained Very Clay or Carbonate Clay Uniform Uniform Thick bedded Thick Often Massive Often Glacial Setting Complex, Variable System ^ Boulders to Clay Lateral Continuity ^ Stacked Aquifer Units Lecture 14: Groundwater Page 8 of 34 Lecture 14: Groundwater Volcanic Setting Vertical NonVertical Uniformity Horizontally NonHorizontally Uniform Controlled by Flow Controlled History Measurable Measurable Gradient Unknown Unknown Boundaries Primary Discontinuities Lateral discontinuities associated Lateral with short-term changes in the deposition conditions during deposition of the primary rock unit Lecture 14: Groundwater Page 9 of 34 Lecture 14: Groundwater Bedding Plains Parallel Flow Paths Parallel Anisotropic System Anisotropic High/Low Permeability High/Low Secondary Features Discontinuities Discontinuities that develop after deposition or formation of the primary rock unit that are capable of transmitting groundwater. Lecture 14: Groundwater Fractures Fractures Joints Joints Faults Faults Karst, Solution and Karst, Caves Page 10 of 34 Lecture 14: Groundwater Faults & Fractures Karst/Solution/Caves Enlarged Fractures Stratigraphic Control ^ Structural Control Chemical Influences ^ Climatic Controls Lecture 14: Groundwater Page 11 of 34 Lecture 14: Groundwater Stratigraphic Control Dissolution along Bed with Hydrodynamic Enlargement Structural Control Structural Cross Bedding Plains “Vertical” Flow Path Allows Cross Transfer Lecture 14: Groundwater Page 12 of 34 Lecture 14: Groundwater Secondary Discontinuities Characteristics Continuity Modification/Alteration Modification/Alteration Lecture 14: Groundwater Page 13 of 34 Lecture 14: Groundwater Fractured Aquifers Variable Flow Paths Variable Variable Flow Variable Velocity Transport Transport Particulate Matter Aquifer Geometry Perched Above Regional Water Above Table Unconfined Direct Recharge From Direct Above No Excess Pressure No Head Confined No Direct Recharge No Excess Pressure Head Excess Lecture 14: Groundwater Page 14 of 34 Lecture 14: Groundwater Aquifer Properties Physical (Hydrodynamic) properties Physical of an aquifer unit viewed on the local scale that cause localized variation in the characteristics of an aquifer. Aquifer Properties Head Head – Elevation/Pressure Head Hydraulic Gradient Hydraulic Radius of Influence Radius Specific Capacity Specific Hydraulic Conductivity Hydraulic – Permeability – Intrinsic Permeability – Transmissivity Storativity Storativity – Specific Yield/Storage Porosity Porosity Lecture 14: Groundwater Page 15 of 34 Lecture 14: Groundwater Head (h) h = z + P/γw h = Total Head Total z = Elevation Above Datum Elevation P = Pressure Head Pressure γw = Unit Weight of Water Hydraulic Gradient HG = Δh/Δx HG = Hydraulic Gradient HG Δh = Change in Head Δx = Change in Distance Lecture 14: Groundwater Page 16 of 34 Lecture 14: Groundwater Radius of Influence (R) Cone of Depression R = Distance from the Pumping Well Distance to the Outer Edge of the Cone of Depression Specific Capacity Ratio of discharge (Q) to drawdown Ratio (s) at a pumping well at a specified time (t) since pumping began. Lecture 14: Groundwater Page 17 of 34 Lecture 14: Groundwater Hydraulic Conductivity (K) K = the rate at which groundwater the flows through a unit area of a material under a unit hydraulic gradient. Darcy’s Law v = - K(Δh/Δx) v = Apparent Groundwater Velocity Apparent K = Hydraulic Conductivity Hydraulic Δh/Δx = Hydraulic Gradient Intrinsic Permeability (k) k = correction for the hydraulic correction conductivity (K) of a material when the fluid is NOT water. k = Kμ/ρg k = Intrinsic Permeability K = Hydraulic Conductivity Hydraulic μ = Fluid Absolute Viscosity ρ = Fluid Density g = Gravitational Acceleration Gravitational Lecture 14: Groundwater Page 18 of 34 Lecture 14: Groundwater Estimate Hydraulic Conductivity Geological Description Geological Grain-Size Distribution Grain Soil Index Properties Soil Laboratory Sample Testing Laboratory Geological Description (cm/sec) Peat .................... 10-2 – 10-4 Clay Unweathered .......... <10-8 High Plastic ............ <10-7 Low Plastic ..... 10-6 – 10-8 Silt High Plastic .... 10-5 – 10-7 Low Plastic ..... 10-4 – 10-7 Sand – Well Sorted Fine................. 10-3 – 10-5 Medium........... 10-2 – 10-4 Coarse ............ 10-1 – 10-3 Sand – Poorly Sorted Fine................. 10-2 – 10-4 Medium........... 10-1 – 10-3 Coarse ............ 10-1 – 10-3 Silty-Sand ....... 10-4 – 10-6 Clayey-Sand... 10-5 – 10-7 Gravel Well Sorted.........10-3 -- 1 Poorly Sorted...... 10-2 – 1 Silty-Gravel..... 10-3 – 10-6 Clayey-Gravel. 10-4 – 10-7 Lecture 14: Groundwater Page 19 of 34 Lecture 14: Groundwater Soil Descriptions Effective Grain-Size D10 = grain-size from a sieve analysis where 10% of the sample is smaller than this size. K = C(D10)2 K = Hydraulic Conductivity (cm/sec) C = Coefficient (varies from 40 – 150 depending on size and gradation of sample) D10 = Effective Grain Size (cm) Valid for 0.1 – 3.0 mm size Representative Values for C 40 – 80: Very fine, Poorly Sorted (well graded) 80 – 120: Medium, Well Sorted (poorly graded) or Clean, Poorly Sorted (well graded) 120 – 150: Very Course, Very Well Sorted (poorly graded), Gravel, Clean Lecture 14: Groundwater Page 20 of 34 Lecture 14: Groundwater Grain Size Distribution (U.S. Army Corps of Engineers) Soil Index Properties K = cυmυγw K = Hydraulic Conductivity Hydraulic cυ = Coefficient of Consolidation mυ = Coefficient of Volume Compressibility γw = Unit Weight of Water (Terzaghi One-dimensional theory) (Terzaghi Lecture 14: Groundwater Page 21 of 34 Lecture 14: Groundwater Soil Index Properties K = cυ[aυ/(1 + eo)]γw K = Hydraulic Conductivity Hydraulic cυ = Coefficient of Consolidation aυ = Coefficient of Compressibility eo = Initial Void Ratio γw = Unit Weight of Water (Terzaghi One-dimensional theory) (Terzaghi Laboratory Tests Laboratory Constant Head Test Constant Falling Head Test Falling Constraints on Test Results Sample Disturbance Sample Test Procedure Test Hydraulic Gradient Hydraulic Leaks Leaks Fluid Properties Fluid Limited Sample Size Limited Lecture 14: Groundwater Page 22 of 34 Lecture 14: Groundwater Transmissivity & Permeability Transmissivity Discharge that occurs through a unit Discharge width along an aquifer thickness b under a hydraulic head of 1. Permeability Discharge that occurs through a unit Discharge aquifer cross-section under a hydraulic head of 1. Permeability = Transmissivity/Thickness Transmissivity Permeability Lecture 14: Groundwater Page 23 of 34 Lecture 14: Groundwater Storativity (S) S (Coefficient of Storage) = dimensionless (Coefficient coefficient that represents the volume of water an aquifer/aquitard releases from storage per unit surface area per unit decrease in piezometric (pressure) head. Sy = Specific Yield Ss = Specific Storage b = Aquifer Thickness (Saturated Thickness) (Saturated Aquifer S = Sy + Ssb Specific Yield (Sy) Sy = the volume of water that a unit volume of aquifer or aquitard releases from storage by gravity drainage. Sy > 0 in Unconfined Aquifer Sy = 0 in a Confined Aquifer Lecture 14: Groundwater Page 24 of 34 Lecture 14: Groundwater Estimate Specific Yield (Sy) Peat .................. 0.30 – 0.50 Very Fine Sand . 0.30 – 0.40 Fine Sand ......... 0.10 – 0.30 Medium Sand.... 0.15 – 0.30 Coarse Sand..... 0.20 – 0.35 Sand & Gravel .. 0.15 – 0.30 Gravely Sand .... 0.20 – 0.35 Fine Gravel ....... 0.20 – 0.35 Medium Gravel . 0.15 – 0.25 Coarse Gravel... 0.10 – 0.25 Silt..................... 0.01 – 0.30 Clay................... 0.01 – 0.20 Siltstone ............ 0.01 – 0.35 Limestone ......... 0.01 – 0.25 Specific Storage (Ss) Specific Ss = the volume of water that a unit volume of aquifer or aquitard releases from storage by the expansion of water and compression of the aquifer rock Ss = γw[(Θ/Ew)+(1/Es)] Θ = Effective Porosity Ew = Modulus of Elasticity - Water Es = Modulus of Elasticity - Aquifer Lecture 14: Groundwater Page 25 of 34 Lecture 14: Groundwater Estimate Specific Storage (Ss) Clay…………………………………………..10-4 Clay Sand and Gravel………………..…….10-5 Sand Fractured Rock…………………..…….10-6 Fractured Transmissivity/Storativity Impact on Drawdown Cone Lecture 14: Groundwater Page 26 of 34 Lecture 14: Groundwater Porosity (n) n = ratio of the Volume of the Voids (Vv) to the Total Volume (VT), expressed in percent. n = (Vv)/(VT) Non-Linear Relationship 0≤n≤1 Void Ratio (e) e = (Engineering Term) ratio of the Volume of the Voids (VV) to the Volume of the Solids (VS). e = (VV)/(Vs) (V Linear Relationship 0≤e≤∞ Lecture 14: Groundwater Page 27 of 34 Lecture 14: Groundwater Values of Porosity (%) Clay……………………………………45 - 50 Clay Silt……………………………………..35 - 50 Silt Sand…………………………………..25 - 40 Sand Gravel…………………………………25 - 40 Gravel Sand/Gravel Mix…………………10 - 35 Sand/Gravel Glacial Till…………………………..10 - 25 Glacial Sandstone………………………….<5 - 30 Sandstone Shale…………………………………..0 - 10 Shale Vesicular Basalt………………….10 - 50 Vesicular Crystalline Rock (Unfractured)…..<1 (Unfractured) Crystalline Types of Porosity Lecture 14: Groundwater Page 28 of 34 Lecture 14: Groundwater Types of Porosity Secondary Porosity Cooling Fractures Solution Enlargement Faults & Fractures Lecture 14: Groundwater Page 29 of 34 Lecture 14: Groundwater Porosity (n) vs. Void Ratio (e) vs. n = (Vv/VT) e = (Vv/Vs) n = e/(1 + e) Vv = Volume of Voids Vs = Volume of Solids VT = Total Volume = Vv + Vs Effective Porosity (ne) ne = includes only that portion of the Volume of Voids (Vv) that are interconnected and can allow the movement of water through the aquifer. Coarse-grained = Small Coarse Fine-grained = Very Large Fine n - ne Similar to Specific Yield Lecture 14: Groundwater Page 30 of 34 Lecture 14: Groundwater Groundwater Flow Flow at a Well Lecture 14: Groundwater Page 31 of 34 Lecture 14: Groundwater Drawdown Creates a Gradient Flow Across a Boundary K2>K1 Lecture 14: Groundwater Page 32 of 34 Lecture 14: Groundwater Well Interference Saltwater Intrusion Lecture 14: Groundwater Page 33 of 34 Lecture 14: Groundwater Break Lecture 14: Groundwater Page 34 of 34 Lecture 14: Groundwater ...
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