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Fetter, Ch. 5

Fetter, Ch. 5. 5.1 I ntroduction 5.2 Basic Assumptions 5.3 Radial Flow 5.4 Computing Drawdown from a Pumping Well 5.5 Determining Aquifer Parameters from t-s Data 5.6 Slug Tests 5.7 Estimating Transmissivity from Specific Cap.Data

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Fetter, Ch. 5

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  1. Fetter, Ch. 5 • 5.1 Introduction • 5.2 Basic Assumptions • 5.3 Radial Flow • 5.4 Computing Drawdown from a Pumping Well • 5.5 Determining Aquifer Parameters from t-s Data • 5.6 Slug Tests • 5.7 Estimating Transmissivity from Specific Cap.Data • 5.8 Intersecting Pumping Cones and Well Interference • 5.9 Effect of Hydrogeologic Boundaries • 5.10 Aquifer Test Design

  2. Fetter, Ch. 5 • 5.1 Introduction • 5.2 Basic Assumptions • 5.3 Radial Flow • 5.4 Computing Drawdown from a Pumping Well • 5.5 Determining Aquifer Parameters from T-D Data • 5.6 Slug Tests • 5.7 Estimating Transmissivity from Specific Cap.Data • 5.8 Intersecting Pumping Cones and Well Interference • 5.9 Effect of Hydrogeologic Boundaries • 5.10 Aquifer Test Design

  3. Introduction Pumping creates a cone of depression in the potentiometric surface

  4. Introduction Flow Flow = (r, t) After some time, t, cone will stabilize to quasi-steady-state and = (r)

  5. Introduction = (r, t) = (r, 0) [initial condition] = (, t) [boundary condition] horizontal surface, pre-pumping Aquifer of Infinite horizontal extent

  6. Basic Assumptions Aquifer bounded below by impermeable layer. Geologic formations horizontal and of infinite horizontal extent. Potentiometric surface is horizontal prior to pumping. Steady state prior to pumping. All changes in head due to pumping. Homogeneous and isotropic. Flow is radial and horizontal to well. Darcy’s Law applies Water of constant density and viscosity. Pumping and observation wells fully penetrating. Pumping well of infinitesimal diameter and 100% efficient.

  7. Radial Coordinates Cartesian coordinates Radial coordinates Solutions of the equations for radial flow to a well permit determination aquifer parameters from pumping test data

  8. Radial Flow Remember Darcy’s Law ? Q = K [(2 π rb] Q = T [(2 πr] r

  9. Radial Flow Q = T [(2 πr Q = T [ 2 π r Q/[2 π T]/r = r

  10. Radial Flow Q/[2 π T]/r = Now we integrate both sides of equation…. r

  11. Fetter, Ch. 5 • 5.1 Introduction • 5.2 Basic Assumptions • 5.3 Radial Flow • 5.4 Computing Drawdown from a Pumping Well • 5.5Determining Aquifer Parameters from T-D Data • 5.6 Slug Tests • 5.7 Estimating Transmissivity from Specific Cap.Data • 5.8 Intersecting Pumping Cones and Well Interference • 5.9 Effect of Hydrogeologic Boundaries • 5.10 Aquifer Test Design

  12. Determining Aquifer Parameters from Time-Drawdown Data Theis Equation for nonequilibrium flow to a well • πT] W(u) • u = r2S/4Tt • W(u) Well function of u

  13. Determining Aquifer Parameters from Time-Drawdown Data πT] W(u) πT] + W(u) Also, u = r2S/4Tt 1/u = 4Tt/r2S (1/u ) = t + -r2S/4T

  14. Determining Aquifer Parameters from t-s Data πT] + W() W() + constants Also, t =(1/)r2S/4T t =constants

  15. Determining Aquifer Parameters from t-s Data W(u) + constants t = constants Curve matching procedure using Theis solution

  16. Determining Aquifer Parameters from Time-Drawdown Data • u = r2S/4Tt • When gets small (≤0.01) • W() • s = (Q/4πT) W() • s = [Q/4πT] [ Well function of u

  17. Determining Aquifer Parameters from Time-Drawdown Data s = [Q/4πT] [ s = [Q/4πT] [ s = [Q/4πT] [ s = [2.3Q/4πT] [ Jacob’s Approximation of Theis Equation (for u≤0.01)

  18. Determining Aquifer Parameters from Time-Drawdown Data s = [2.3Q/4πT] [ Jacob’s Approximation of Theis Equation (for u≤0.01)

  19. Determining Aquifer Parameters from Time-Drawdown Data—Leaky Confined Aquifer Ideal Confined Aquifer Leaky Confined Aquifer Leaky Artesian Well function • πT] W(u, r/B ) Hantush-Jacob Formula

  20. Determining Aquifer Parameters from Time-Drawdown Data—Leaky Confined Aquifer B = leakage factor = (Tb’/K’)1/2

  21. Determining Aquifer Parameters from Time-Drawdown Data—Unconfined Aquifer

  22. Fetter, Ch. 5 • 5.1 Introduction • 5.2 Basic Assumptions • 5.3 Radial Flow • 5.4 Computing Drawdown from a Pumping Well • 5.5 Determining Aquifer Parameters from T-D Data • 5.6 Slug Tests • 5.7 Estimating Transmissivity from Specific Cap.Data • 5.8 Intersecting Pumping Cones and Well Interference • 5.9 Effect of Hydrogeologic Boundaries • 5.10 Aquifer Test Design

  23. Single well pumping tests • Observation wells may not be feasible. • Provides a separate analysis of aquifer • parameters even if observation wells are used. • Records from irrigation/production wells • may be available.

  24. Single well pumping tests

  25. Well Interference

  26. Hydrogeologic Boundaries

  27. Hydrogeologic Boundaries

  28. Hydrogeologic Boundaries

  29. Slug Tests

  30. Slug Tests • Advantages • Inexpensive • Quick • Water does not have to be removed from well • Can be used in low-K units • Disadvantages • Small volume of aquifer is tested • Well effects (”skin,” gravel pack, etc.)

  31. Slug Tests

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