Groundwater Flow to Wells

1. Groundwater Flow to Wells

2. I. Overview A. Water well uses 1. Extraction 2. Injection

3. I. Overview A. Water well uses B. Terms 1. Cone of depression 2. Drawdown 3. Unsteady Flow

4. I. Overview A. Water well uses B. Terms C. Goals 1. Compute dh/dt given knowledge of the properties of the aquifer 2. Determine the properties of the aquifer based on the rate of dh/dt.

5. I. Overview A. Water well uses B. Terms C. Goals D. General Assumptions

6. General Assumptions

7. General Assumptions (continued)

8. I. Overview A. Water well uses B. Terms C. Goals D. General Assumptions E. Radial Flow

9. II. Theis Method

10. II. Theis Method A. Additional Assumptions The aquifer is confined on the top and bottom There is no source of recharge to the aquifer The aquifer is compressible, and water is released instantaneously from the aquifer as the hydraulic head is lowered. The well is pumped at a constant rate.

11. II. Theis Method A. Additional Assumptions B. The Equations

12. II. Theis Method A. Additional Assumptions B. The Equations s = ho -ht ho -ht = Q* * wu 4πT u = r2*S 4Tt

14. THEIS CURVE

15. II. Theis Method C. Examples (with known values) A well is located in an aquifer with a hydraulic conductivity of 15 m/d, storativity is 0.005, aquifer thickness is 20 m, and the pumping of the water well is occurring at a rate of 2725 m3/d. What is the drawdown at a distance of 7 m from the well after 1 day of pumping? ho -ht = Q* * wu 4πT u = r2*S 4Tt

16. II. Theis Method A. Additional Assumptions B. The Equations C. Examples (with known values) D. Examples (with unknown values)

18. THEIS CURVE

19. DRAWDOWN DATA

22. Problem: A well in a confined aquifer was pumped at a rate of 42,400 ft3/d for 500 minutes. The aquifer is 48 ft. thick. Time drawdown data from an observation well located 824 ft away yields the following data (see previous slide of drawdown data). Find T, K, and S.

23. III. Jacob Straight Line Method A. Overview B. Conditions C. The Equation D. Example T= 2.3Q 4πΔh S= 2.25T*t0 r2

25. T= 2.3Q 4πΔh III. Jacob Straight Line Method D. Example S= 2.25T*t0 r2 Problem: A well in a confined aquifer was pumped at a rate of 42,400 ft3/d for 500 minutes. The aquifer is 48 ft. thick. Time drawdown data from an observation well located 824 ft away yields the following data (see previous slide of drawdown data). Find T, K, and S.

26. IV. Distance Drawdown Method A. Overview B. Equations C. Example T= 2.3Q 2πΔh S= 2.25T*t r02

28. IV. Distance Drawdown Method C. Example T= 2.3Q 2πΔh S= 2.25T*t r02 A well is pumping 77,000 ft3/d, and has observational wells located 10, 40, 150, 300, and 400 ft away from the pumping well. After 0.14 days of pumping, the Following drawdowns were observed in the observation wells (see graph). Determine T (ft2/d) and S of the aquifer.

29. Hzorslev Method (Slug or Bail Test) K= r2*ln(L/R) 2Lt0.37

30. Hzorslev Method

31. Hzorslev Method

32. K= r2*ln(L/R) 2Lt0.37 • Hzorslev Method (Slug or Bail Test) A slug test is performed by lowering a metal cylinder into a piezometer that is screened in coarse sand. The inside of the bore hole has a radius of 0.500 ft, and the inside radius of the piezometer is 0.083 ft. The screened section of the well is 10 ft. The well recovery data is shown via tables and the respective graph. Determine the Hydraulic Conductivity of the aquifer.

33. VI. Intersecting Pumping Cones and Well Interference • General Example

34. Bounded Aquifers 1. Impermeable boundary

35. Bounded Aquifers 1. Constant Head boundary

36. VII. Recovery of Pumping Wells • Purpose • Example

37. VII. Recovery of Pumping Wells

38. 1 ft3 = 7.48 gallons VII. Recovery of Pumping Wells