Report

Groundwater Flow to Wells I. Overview A. Water well uses 1. Extraction 2. Injection I. Overview A. Water well uses B. Terms 1. Cone of depression 2. Drawdown 3. Unsteady Flow 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. I. Overview A. Water well uses B. Terms C. Goals D. General Assumptions General Assumptions General Assumptions (continued) I. Overview A. Water well uses B. Terms C. Goals D. General Assumptions E. Radial Flow II. Theis Method 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. II. Theis Method A. Additional Assumptions B. The Equations II. Theis Method A. Additional Assumptions B. The Equations ho -ht = Q* * wu 4πT u = r2*S 4Tt s = ho -ht THEIS CURVE 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 II. Theis Method A. Additional Assumptions B. The Equations C. Examples (with known values) D. Examples (with unknown values) THEIS CURVE DRAWDOWN DATA 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. III. Jacob Straight Line Method A. Overview B. Conditions C. The Equation D. Example T = 2.3Q 4πΔh S = 2.25T*t0 r2 III. Jacob Straight Line Method D. Example T = 2.3Q 4πΔh 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. IV. A. B. C. Distance Drawdown Method Overview Equations Example T = 2.3Q 2πΔh S = 2.25T*t r02 D is ta n c e D ra w d o w n M e th o d 16 14 12 D ra w d o w n (ft) 10 8 6 4 2 0 1 10 100 D is ta n c e (ft) 1000 IV. Distance Drawdown Method C. Example D is ta n c e D ra w d o w n M e th o d 16 14 T = 2.3Q 2πΔh 12 S = 2.25T*t r02 D ra w d o w n (ft) 10 8 6 4 2 0 1 10 100 D is ta n c e (ft) 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. 1000 V. Hzorslev Method (Slug or Bail Test) K = r2*ln(L/R) 2Lt0.37 Hzorslev Method Time since injection h h/ho 0 0.88 1.000 1 0.6 0.682 2 0.38 0.432 3 0.21 0.239 4 0.12 0.136 5 0.06 0.068 6 0.04 0.045 7 0.02 0.023 8 0.01 0.011 9 0 0.000 Hzorslev Method h/ho 1 0.1 0.01 0 1 2 3 4 5 Tim e (s) 6 7 8 9 10 V. Hzorslev Method (Slug or Bail Test) K = r2*ln(L/R) 2Lt0.37 h/ho 1 0.1 0.01 0 1 2 3 4 5 6 7 8 9 Tim e (s) 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. 10 VI. Intersecting Pumping Cones and Well Interference A. General Example A. Bounded Aquifers 1. Impermeable boundary A. Bounded Aquifers 1. Constant Head boundary VII. Recovery of Pumping Wells A. Purpose B. Example VII. Recovery of Pumping Wells Time(min) Elevation (ft) 0 520 0.2 520.2 0.4 520.3 0.8 520.6 1 521 2 522 3 523 4 524 5 525 VII. Recovery of Pumping Wells 1 ft3 = 7.48 gallons Well Recovery Time(min) Elevation (ft) 526 0 520 0.2 520.2 0.4 520.3 0.8 520.6 1 521 2 522 3 523 4 524 5 525 y = 1.0134x + 519.94 525 524 523 522 521 520 519 0 1 2 3 4 5 6