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  3. 3. Field Manual – Geo-hydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 1 GENERAL The Field Manual on Geo-Hydrology comprises the procedures to be carried out to ensure proper execution of design of the groundwater water level monitoring network, operation and maintenance of observation well and piezometers. The operational procedures are tuned to the task descriptions prepared for each Hydrological Information System (HIS) function. The task description for each HIS- function is presented in Volume 1 of the Field Manual. It is essential, that the procedures, described in the Manual, are closely followed to create uniformity in the field operations, which is the first step to arrive at comparable hydrological data of high quality. It is stressed that water level network must not be seen in isolation; in the HIS integration of networks and of activities is a must. • Volume 4 of the Field Manual deals with the steps to be taken for network design and optimisation as well as for its operation and maintenance. It covers the following aspects. • Part I deals with the steps to be taken for network design and optimisation. Furthermore, site selection procedures are included, tuned to the suitability of a site for specific measurement procedures. • Part II details with piezometer construction procedure with details of the different elements and the significance of different elements in the piezometer construction • Part III comprises the preparatory activities and procedures for carrying out aquifer tests. The procedures to be adopted for analysis of pumping test data is briefly discussed • Part IV comprises the testing and installation of DWLR’s. Procedures to be followed for procurements and installation are outlined in Volume 4 of the reference manual. • Part V deals with the need for carrying out Reduced Level Surveys and the procedures in carrying out the survey are outlined. • Part VI deals with the standardised procedures to be adopted for manual collection of water level data from open wells and piezometers. • Part VII deals with the standardised procedures to be adopted for retrieval of data from DWLR and integration with the software. • Part VIII, deals with procedures to be adopted for regular inspection and maintenance of piezometers and DWLR’s. The procedures as listed out in this manual are in concurrence with the ISO standards as far as available for the various techniques and applicable to the conditions in Peninsular India.
  4. 4. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 2 1 ESTIMATION OF AQUIFER PARAMETERS Generally two methods may be distinguished to estimate aquifer parameters. One method is to take samples of the geological formations composing the aquifer and test these in the laboratory. The other method is to carry out an in-situ test by pump testing the aquifer through a pumping well. The laboratory test may yield information on the hydraulic conductivity (K) and the porosity. The test includes determining the granular composition of unconsolidated sediments or permeameter tests on consolidated rocks. The tests may give an indication of the parameters of the rocks composing the aquifer, but they will not provide accurate estimates of the parameters. The most reliable and commonly used method for estimating aquifer parameters is based on generating an artificial, temporary flow pattern, by means of pumping and measuring water levels during a certain period. These methods are referred to as: • Pumping test, if the water is pumped from a well and the drawdown is measured in the well and in piezometers at a known distance from the well • Well test, if the water is pumped and the water level is measured in the well only. The aquifer parameters which can be obtained during the pumping tests include transmissivity (T), storage coefficient (S) and leakage factor (L). From the analysis of well test data only transmissivity (T) can be obtained. In this chapter an overview of steps in the estimation of aquifer parameters using a pumping test is presented. Pumping tests are different from a pump test, which basically is for understanding the discharge from a pump. Pumping tests require a greater degree of preparatory work. Since it works out to be expensive, preliminary data of the well development, airlift and slug test should be used to determine the pumping test design. Pumping tests should be carried out in two phases. The first phase under the pumping test would be to carry out a step drawdown test. This is recommended to estimate the greatest flow rate that may be sustained by the pumping well. As part of the step drawdown test the pumping well should be pumped at a very low discharge and at a constant rate for 100 minutes. The water level decline should be monitored in the pumping well. Thereafter the discharge should be doubled and maintained constant for the next 100 minutes and the water level measurement continued. Similar steps should be repeated upto 4 times. The well should be allowed to fully recover and water levels monitored. The step drawdown test should be followed by a constant discharge test, where the pumping well is pumped at a discharge which is kept uniform all through the test (for several hours or days), depending on the extent of the aquifer. Measurements should be made at the pumping well and each of the observation wells. The distance of the observation well to the pumping well, the depth to water level and the time of observation have to be systematically recorded. When the pumping test is concluded, the observed data should be run through a series of calculations to determine the aquifer characteristics. For calculation of aquifer parameters, the manual calculation has been traditionally performed, with a best-fit match to a hand-drawn plot. Today, software is available to compute T and S for an aquifer. The user inputs the pumping rate, the drawdowns at each observation well and the time since pumping started.
  5. 5. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 3 Normally pumping tests are carried out in representative pumping wells and piezometers, soon after completion of construction. All the agencies have been advised to carry out the pumping tests in piezometers, which are representative of wider areas, and which are not very close to roads with heavy traffic or railway lines. Furthermore, the pumping well or piezometer should be in a location, where the pumped water can be safely discharged. 2 GENERAL PUMPING TEST PROCEDURES 2.1 PRELIMINARY STUDIES A fundamental understanding of the hydrogeology of the area is required before preparing for the pumping test. The following tasks have to be carried out: • Transfer the monitoring structure location to a topographic base map along with all the locations of the observation wells and distances. • Prepare a note on the hydro-geologic description of the test site containing a hydro-geologic cross section of area, including the pumping well and observation wells. • Prepare the lithological log of the pumping well or piezometer being tested and of the observation wells. • Prepare a note on the dominant types of permeability (fractures, joints, faults, etc.) and their spatial characteristics (spacing and orientation) and on the potential boundary conditions (streams, dykes, etc). • Prepare a contour map of water level elevations including the pumping well, observation well and other wells in the neighbourhood. Determine the approximate hydraulic gradient and direction(s) of ground-water flow. The hydrogeological inventory provides information on the thickness and lateral extent of the aquifers and confining beds and possible hydraulic contact with any recharge boundary (river, irrigation channel). This information is essential for the interpretation of the test data. Next to the hydrogeological conditions, the following factors may effect the performance of an aquifer test: • Railways or roads where heavy traffic might produce fluctuation of hydraulic heads. • Presence of discharging wells in the vicinity of testing site. Information on these issues must be available in time. 2.2 PREPARATION FOR A PUMPING TEST Conducting a pumping test requires preparation to arrange a mobile pumping test unit with the necessary ranges of pumps, generators, discharge measurement equipment and accessories for disposing the pumped water. All observation wells/piezometers need to be pump tested, yet the piezometers generally cannot stand to a long duration of pumping. The selection of piezometers for a pumping test should be based on the drilling details and on the well development results and should be based on the final discharge after pumping.
  6. 6. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 4 2.2.1 FIELD EQUIPMENTS The following items are required to perform a pumping test: • Detailed lithological description of pumping well and observation wells • Brunton compass, • Toposheet, • Measuring Tape (50 m) for measuring distances, • Electric water level indicator, • Steel tape ( 5 m), • Weighted tapes (for measuring depth of piezometer), • Digital Water Level Recorder, • Submersible pump, • Generator, • Winch assembly for lowering pump, • Pipe assembly, • Control Valves (including spares), • Tool kit for pipe lowering, • Electrical insulation tape, • HDPE 1” pipe for measuring water levels, • Measuring Drum, • Orifice assembly, • Manometer, • LDPE pipes for conveying pumped water, • Flow meter, • Stopwatch, • Ordinary graph paper, • Semi-log, log-log, graph paper, • Calculator, • Data recording forms, • Pencils, Water proof ink pen, • pH meter, • Conductivity meter, • Thermometer, • Torch, Flashlights and candles/lanterns. 2.2.2 SITE PREPARATION • Review all available data and become familiar with information on the piezometer to be tested. • Check and ensure the proper operation of all field equipment. • Ensure that the DWLR are working properly. Test the DWLR at a field site. • Check the approach road for the Pump Test Unit to approach. • Check the site for disposing the pumped water. • Interact with local population to stop any pumping in the neighbouring wells during the tests. • Ensure that the piezometer is properly developed.
  7. 7. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 5 2.3 PRE-TEST MONITORING Prior to the pumping test, background monitoring should be carried out in the pumping well and the designated observation wells. No pumping should be carried out in all these wells 48 hours prior to the pumping test. The purpose of the preliminary monitoring is to determine how water levels are fluctuating over time under pre-pumping conditions. It has to be determined if the aquifer is experiencing an increase or decrease in head with time due to recharge or pumping in the nearby area, or caused by diurnal effects of evapo-transpiration. The pre-pumping water level trend must be used to correct drawdowns measured during the pumping test. The corrected values should reflect only the effects of the pumping well. Rainfall at the test site should also be monitored prior to pumping test. Any precipitation greater than 2 mm should be recorded. The test should not be performed during or shortly after a precipitation/recharge event, which could result in a rapid change of water level or flow. 2.4 SELECTION OF OBSERVATION WELLS 2.4.1 THE NUMBER OF OBSERVATION WELLS Observation wells need to be identified for monitoring the influence of pumping around the pumping well. Since the hydraulic constants of an aquifer system are not homogenous in all directions, observation wells should be selected around the pumping well in all directions. Usually, at least two or three observation wells are recommended. 2.4.2 DISTANCE FROM THE PUMPING WELL The distance from the pumping well depends on aquifer type, transmissivity, duration of test, discharge rate and length of the well screen. While selecting the observation well it has to be ensured that the selected well is not too close, while it has to be reasonably near to reflect the effects of pumping. The distance can range from 10-300 meters. The upper range (> 100 m) is recommended for thick aquifers or stratified aquifers. In the fractured consolidated aquifers, the number of observation wells will depend on the orientation of the fracture and on the transmissivity of rock on the opposite sides of the fracture (Kruseman and de Ridder, 1999). Since both these factors are usually not known more observation wells are required in variable distances from the pumping well. The distance between the pumping well and the observation well should be accurately measured. 2.4.3 DEPTH OF THE OBSERVATION WELLS The depth of the observation well is also important. However, unless the observation wells are specially designed for the aquifer testing, the choice of observation wells with suitable depth is very limited. In a homogeneous aquifer, the piezometers should be placed at the depth that coincides with that of half the length of the well screen. For heterogeneous aquifers it is recommended that a cluster of piezometers be placed at various depths. 2.5 REQUIRED PUMPING EQUIPMENT The submersible pump should be used to pump test the observation well / piezometer. For proper testing, have a reliable power source (generator) is required so that testing will not be interrupted. The power must be sufficient to drive the pump at a rated speed so that full capacity can be developed. A
  8. 8. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 6 second generator should be available if the pumping is to last beyond 24 hours. The pump and accessories must be reliable, capable of drawing water at a constant rate through the duration of the test. If a pump fails, the data may be insufficient to obtain reliable estimates of aquifer properties. The rate of discharge of the pump and the depth of lowering of the pump should be decided based on the well depth, aquifer position and diameter. Set the pump deep enough to attain the maximum pumping rate and drawdown. When testing a piezometer with a screen, set the suction of the pump above the top of the screen to prevent lowering of the water level below the screen. When testing a piezometer without a screen, try not to dewater the production part of the aquifer. 2.6 DURATION OF PUMPING The test should be conducted for at least 24 hours or until stabilized drawdown has occurred, whichever is longer. A stabilized drawdown is defined as an unchanging water level within the pumping well, or within an observation well located within 5 metres of the pumping well, for a minimum of five hours, accompanied by a constant pumping rate. In some cases, stabilized drawdown (steady state conditions) occurs within a few hours after the start of pumping. In other cases steady state conditions will never occur. It is not absolutely necessary to continue pumping until a steady state is reached, because methods are available to analyse unsteady state data. Under average conditions in confined aquifers, a steady state condition is reached within 24 hours. In an unconfined aquifer a period of about 3 days is required. 2.7 MEASUREMENT OF DISCHARGE The pumping discharge should be monitored using more than one method. The discharge measurement should be accurate to within 5 percent. The delivery line should have fine and coarse valves for controlling the pumping rate. The flow rate (m3 per day) and cumulative flow (total m3 pumped) must be recorded a minimum of once per hour. All flow-rate adjustments must be documented with a measurement of flow before and after adjustment, and the time at which the adjustments were made. This information should be included in the required hydro-geologic report. The different discharge measurements to be used are outlined in Chapter 3 of this volume. 2.8 MEASUREMENT FREQUENCY OF WATER LEVELS Water level measurements are the most important part of the pumping test. A sufficient number of measuring tapes should be available at the pump test site. The electric tapes/DWLR’s should be compared and calibrated. The tapes should be numbered and the number of the tape used in the different observation wells should be recorded in the water level measurement sheet. All depth-to- water measurements should be made from the surveyed reference points. At the beginning of the test, the discharge rate should be set as quickly and accurately as possible. The water levels in the pumping well and observation wells should be recorded with a set schedule. Data should be entered on the Pump/Recovery Test Data Sheet. Water levels from at least two observation wells and the pumping well should be measured during the test. A suggested schedule of measurements at all wells is as follows (Table 2.1):
  9. 9. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 7 Time after pumping started Time Intervals 0 to 5 minutes 30 seconds 5 to 15 minutes 1 minute 15 to 30 minutes 2 minute 30 to 60 minutes 5 minute 60 to 120 minutes 15 minute 120 to 360 minutes 30 minute After 360 minutes 1 hour Table 2.1: Measurement Schedule for water level during pumping test If a DWLR is used, it should be programmed to start at a small measurement interval and ramp upward logarithmically. During the pumping test, measurements should be taken on all observation points. Water level measurements should be made to the nearest mm, especially at the beginning of the test. Fluctuations in nearby surface water bodies should also be monitored. A log of weather conditions should be maintained during the test. After the end of a pumping test, recovery measurements should be measured in the pumping well and observation wells. In theory, the water levels will recover at the same rate as they fall. Recovery data can be used to derive an additional estimate of aquifer transmissivity, which may be better than the first estimate. In some cases, there are uncontrolled variations in the pumping rate during the pumping test, which affect the drawdown. However, such variations do not affect the recovery rate. Recovery period water level measurements should commence one minute prior to shut down of the pumping well and continue for at least 12 hours. To obtain accurate data during the recovery period, backflow should be limited using a non return valve. During recovery, manual measurements should be recorded at close time intervals, just as after pumping started and every 15 minutes after the first hour and every hour after 6 hours. 2.9 WATER CHEMISTRY Water quality measurements should be carried out for pH, EC and temperature every hour. In areas prone to water quality issues (coastal areas, industrial areas subjected to pollution, canal command with water logging problems, riverbeds, etc.) continuous water quality monitoring is recommended. Changes in water quality should be recorded and samples collected for detailed analysis. Two sets of samples have to be collected at different stages of pumping for detailed analysis in the lab. The procedures for the sample collection are outlined in Volume 6 on Water Quality Sampling. 2.10 RECORDING OF DATA During a pumping test, the following data must be recorded accurately on the aquifer test data form. The data collected should be recorded in a pre-designed format. A sample format is enclosed in Annexure - I.The data include • Site ID of the pumping well/piezometer as given in the database, • Location of the pumping well/piezometer, • Location of the observation well and distance from the pumping well, • Test Start Date: the date when the pumping started, • Pumping rate including any changes during the test, • Static water levels at pumping well and observation wells and a description of the measuring point used,
  10. 10. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 8 • Depth of test pump setting, and • All pumping and recovery water level measurements reported in tabular form. 2.11 PLOTTING OF DRAWDOWN DURING THE TEST The plots of drawdown against time should be carried out as the test proceeds. On plotting the pumping test data against the time axis on graph paper with linear scales one gets a picture of the trend of water level during pumping. This plot will give an idea of the magnitude of water level fluctuation, delayed yield phenomena if any, the duration to which pumping can be continued and the type of cyclicity in the data if any. Distance drawdown plots should also be made and quantity of water dewatered in the cone of depression should be calculated and compared with the corresponding amount of water pumped. Recovery data should also be recorded and plots should be prepared of residual drawdown against elapsed time. 3 DISCHARGE MEASUREMENT METHODS 3.1 FLOW METER The most accurate discharge measurements are obtained by a calibrated flow meter. A commercial water meter of appropriate capacity can be used. The meter should be connected to the discharge pipe preferably at the bottom of a U-bend. If no appropriate flow meters are available, alternative methods must be used. 3.2 MEASURED DRUM METHOD By this method the flow rate from the piezometer/ pump is measured by measuring the time required to fill a container of known volume. In this method, use more than one volume of container. Use the small containers for early measurements and large containers for later measurements. Use a stopwatch, for an accurate measurement of time. 3.3 CIRCULAR-ORIFICE METHOD Figure 3.1: Circular orifice setup for measuring discharge 0.75 m
  11. 11. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 9 A circular-orifice meter is a device for measuring discharge rates. This device gives good results and is compact and easily installed. The meter consists of a sharp-edged circular orifice at the end of a horizontal discharge pipe. The orifice is from one-half to three-fourths the diameter of the pipe. The inside of the pipe must be smooth and free from obstructions for a length of 2 metre from the orifice. The discharge pipe has a small hole on one side with a rubber-tube connection. The pipe should be of such design, that the pressure (head) in the discharge pipe can be measured at a distance of 0.75 m from the orifice. The height of the hose and scale should be based on the diameter of the pipe. The discharge pipe must be horizontal, and the stream must fall free from the orifice. The orifice must be vertical and centered in the discharge pipe. The combination of pipe and orifice diameters for a given test should be such that the head measured will be at least three times the diameter of the orifice. Flow values in m3 /day for a number of pipes and opening diameter are presented in Table 3.1. Pipe diameter (inches)/Orifice diameter (inches)h (m) 4”/2.5” 4”/3” 6”/3” 6”/4” 6”/5” 8”/4” 8”/5” 8”/6” 0.14 323 537 0.16 345 574 0.18 366 609 484 0.20 385 642 510 970 1880 919 1500 2370 0.22 404 674 535 1020 1970 964 1580 2490 0.24 422 703 559 1060 2060 1010 1650 2600 0.26 440 732 582 1110 2140 1050 1710 2710 0.28 456 760 604 1150 2220 1090 1780 2810 0.30 472 787 625 1190 2300 1130 1840 2910 0.35 510 850 675 1280 2480 1220 1990 3140 0.40 545 908 722 1370 2650 1300 2130 3360 0.45 578 963 765 1460 2820 1380 2250 3560 0.50 610 1020 807 1530 2970 1450 2380 3750 0.55 639 1060 846 1610 3110 1520 2490 3940 0.60 668 1110 884 1680 3250 1590 2600 4110 0.65 695 1160 920 1750 3380 1660 2710 4280 0.70 721 1200 955 1810 3510 1720 2810 4440 0.75 747 1240 988 1880 3630 1780 2910 4600 0.80 771 1280 1020 1940 3750 1840 3010 4750 0.85 795 1320 1050 2000 3870 1900 3100 4890 0.90 818 1360 1080 2060 3980 1950 3190 5040 0.95 840 1400 1110 2110 4090 2000 3280 5170 1.00 862 1440 1140 2170 4200 2060 3360 5310 1.10 904 1510 1200 2270 4400 2160 3530 5570 1.20 944 1570 1250 2380 4600 2250 3680 5820 1.30 983 1640 1300 2470 4790 2340 3830 6050 1.40 1020 1700 1350 2570 4970 2430 3980 6280 1.50 1060 1760 1400 2660 5140 2520 4120 6500 Table 3.1: Circular-orifice flow in m3 /d for different pipe diameters and orifice diameters (in inches) as a function of head of water in the tube above the centre of the orifice (m) 3.4 DISPOSAL OF PUMPED WATER There must also be a means for conveying water away from the test site. This is especially important for shallow unconfined aquifers that could be recharged by discharge from the pumping well. Such recharge would interfere with the interpretation of the test results and must therefore be avoided at all costs. Make sure, that the discharge water is released downstream of the test site, in order to prevent interference of the discharged water with the pumping test.
  12. 12. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 10 4 ANALYSIS OF PUMPING TEST DATA 4.1 General considerations After the pumping test has been completed the following procedures should be followed: • All field data should be converted to a single set of time, length and volume units. • If necessary, the observed water levels should be corrected for external influences. • Information on fully or partial penetration of the well must be obtained. • Aquifer type must be identified, since this is crucial for the choice of the theoretical model for data analyses. If the wrong model is chosen, the calculated parameters for the real aquifer will not be correct. 4.2 IDENTIFICATION OF THE AQUIFER SYSTEM (TYPE AND BOUNDARY CONDITIONS) Plots of drawdown versus time since pumping started on log-log and semi-log scale can be used to identify the aquifer system. Figures 4.1 and Figure 4.2 show some theoretical curves for time- drawdown relationships of respectively unconsolidated aquifers and consolidated fractured aquifers. The theoretical curves will be affected by the well’s partial penetration, recharge from rivers and irrigation and impermeable boundaries. The curves may augment the available hydro-geological information for selection of an appropriate analysis method. Note: A and A’: confined aquifer; B and B’: unconfined aquifer; C and C’: leaky aquifer Figure 4.1 Log-log and semi-log plots of the theoretical time-drawdown relationships of unconsolidated aquifers; (source: Kruseman and de Ridder, 1990).
  13. 13. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 11 Note: A and A’: confined fractured aquifer, double porosity type; B and B’: single plane vertical fracture; C and C’: permeable dike in an otherwise poorly permeable aquifer Figure 4.2 Log-log and semi-log plots of the theoretical time-drawdown relationships of consolidated, fractured aquifers; (source: Kruseman and de Ridder, 1990) 4.3 METHODS FOR PUMPING TEST ANALYSES All methods for analysis of test data are based on the solution of well equations using plots of observed drawdowns in piezometers. There are many methods, which apply to different conditions regarding the aquifer type, flow state, discharge rate and well penetration. The methods apply either to the pumping phase or the recovery phase. The recovery-test measurements (residual drawdown) are more reliable than pumping test data. Recovery occurs at a constant rate, while a constant discharge during pumping is often difficult to achieve. Each of these methods is based on special assumptions. A comprehensive overview of the main methods used for analysis and evaluation of pumping data is given by Kruseman and de Ridder (1990). The main methods for confined aquifers are: • Thiem method, • Theis method, and • Jacob method The main methods for unconfined aquifers are: • Neuman’s method, and • Thiem – Dupuit method. Most of the above methods deal with the well-flow equations developed for homogeneous aquifers. For the fractured consolidated aquifers new theoretical models were developed. The models are very complex. The most universally applicable method is the Bourdet-Gringarten’s curve-fitting method,
  14. 14. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 12 which is based on the Theis well-function. The description of the procedure and the type curves are given in Kruseman and de Ridder (1990). Since the manual method involves plotting the data points on the graph sheet for estimating the best match line or for generating the curve for comparing with the match curve, it has to be ensured that there are no plotting errors. A misplot of a datapoint could have drastic consequences for the fitted line/generation of curve and the subsequent calculations. 4.4 EXAMPLES OF PROCEDURES FOR (MANUAL) INTERPRETATION OF TEST DATA 4.4.1 ANALYSIS OF STEP DRAWDOWN DATA For the analysis of step drawdown test data, plot on semi-logarithmic paper the drawdown on the vertical axis, which is linear and time on the horizontal axis, which is logarithmic. Extrapolate the curve to the anticipated duration of the constant duration test and determine the probable drawdown. The maximum drawdown should correspond to 1 meter above the pump setting. For determining the discharge to be maintained during the constant duration test, select on the semi-log plot the pumping rate, which can permit the maximum allowable drawdown. The step drawn down test data should not be the basis for computing the aquifer parameters. Only the data obtained during the constant discharge test can provide an accurate estimate of the hydraulic constants. However, the step drawdown test may give some useful results in the situation that no observation wells are available. 4.4.2 THIEM’S METHOD Thiem’s method is applicable to drawdown data of confined aquifers under steady state flow conditions. Data of at least three observation wells are needed to get reliable results. This will be difficult in many sites. The following procedure can be used. • Plot on a semi-logarithmic paper the drawdowns of each observation well against the corresponding value r (distance from the pumping well) on logarithmic scale. • Draw the best fitting line through the plotted points to describe the distance drawdown curve. • Determine the slope of the curve (difference per log cycle). • Use the equation for computing T: s2 Q3.2 T ∆π = (4.1) where: T = transmissivity [m2 /d] Q = discharge [m3 /d] ∆ = drawdown [m] 4.4.3 THEIS’S METHOD The Theis’s method is used for analysis of the pumping test data of confined aquifers under unsteady state flow conditions. The following procedure can be used: • Plot on a double logarithmic paper drawdown for different observation wells of the pumping phase in the vertical axis and time/radius2 (t/r2 ) on the other axis.
  15. 15. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 13 • Match the field curve with the type curve. • Keep the vertical and horizontal axes of both the plots parallel. • Locate the portion of best match between the data plot and type curve. • Select an arbitrary point match point on the overlapping portion of the two sheets of graph and determine for the co-ordinates W(u), 1/u, s and t/r2 . • Using the pumping test discharge rate and the co-ordinates W(u), s and t, compute the transmissivity using the equation: )u(W s4 Q T π = (4.2) where: T = transmissivity [m2 /d] Q = constant well discharge [m3 /d] s = drawdown in a piezometer measured at distance r from the well W(u) = well function: . !4.4 u !3.3 u !2.2 u u)u(lu5772.0)u(W 432 −+−+−−= substituting the values of T, t/r2 and 1/u and use the equation to calculate the storativity S: ( ) u1 r/tT4 S 2 = (4.3) where: S = storativity [-] t = time since pumping started [d] r = distance of piezometer from well [m] 1/u = 4T(t/r2 )/S, parameter in the well function. 4.4.4 JACOB’S METHOD The Jacob’s method is popular largely because of the simplicity of application and interpretation. It supplements the type curve method. This method can be applied to pumping test data of short duration. The pumping well data itself as well as the observation wells data can be used. The following procedure can be used: • Plot the drawdown against time on a semi-logarithmic paper. The time t should be plotted on the log scale. • Draw a straight line "best fit" across the data points, leave the initial drawdown data which falls on a gentle curve. • Extend the straight line till it intersects the time axis where s=0 and record the value of to. • Determine the difference in drawdown s in one log cycle of the time. • Substitute the values for the pumping rate Q and the difference in drawdown s for a log cycle of time to compute, the Transmissivity T. • Determine the T by considering the equation:
  16. 16. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 14 s4 Q3.2 T ∆π = (4.4) where: T = transmissivity [m2 /d] Q = constant well discharge [m3 /d] ∆s = difference in the drawdown in one log cycle of time [m] • Assess the storage coefficient by extrapolating the straight line until it intersects the zero drawdown axes and read the time to. • Insert the value of T, time to from the plot and distance r into equation to compute storage: 2 0 r t T25.2S = (4.5) where: S = storativity [-] t0 = time since pumping started [d] r = distance of piezometer from well [m] 4.4.5 THEIS’S RECOVERY METHOD The recovery data can be analysed for computing the aquifer parameters. Data from the pumping well and observation wells can be used. The following procedure can be used: • Plot residual drawdown against t’/t* on a semi-log paper (t is the time since pumping started, t’ is the time since pumping stopped). The time t’/t* should be plotted on the log scale. • Draw a straight line "best fit" through the data points. Read the difference in residual drawdown for a log cycle difference in t’/t*. Substitute the values for the pumping rate Q and the difference in drawdown s for one log cycle of t’/t* to compute the transmissivity: s4 Q3.2 T ∆π = (4.6) where: T = transmissivity [m2 /d] Q = pumping rate during t-t’ [m3 /d] ∆s = difference in the drawdown for one log cycle of t’/t 4.5 ANALYSIS OF PUMPING TEST DATA USING SOFTWARE The dedicated software does not have a provision for analysis of pumping tests. The agencies should procure the software for pumping test analysis separately. No mention is made of any commercial package brand names. A number of public domain and commercial software packages is available for the analysis of pumping test data. The different programs generally provide a similar approach with respect to data entry, however major variations are seen in the type of analysis and reporting.
  17. 17. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 15 The commercial software supports the analysis of pumping tests, slug tests and step tests, using both traditional manual techniques and numerical optimisation. They offer the utility to import data from just about any source using a sophisticated data import wizard. They also permit creation of a database giving details of time, drawdown, pumping rates, distance and dimension of the wells. The software provides numerous analyses supporting confined, leaky-confined, unconfined and fractured aquifers, some of which support recovery, partial penetration, delayed yield or variable pumping. They perform traditional curve matching techniques, matching data to families of type curves. They generate custom type curve suites comparable to those found in the literature. They customize the user-interface to the type of analysis selected by presenting only pertinent parameters. Based on the data entered the programs offer options for carrying out interpretations using curve fitting (Theis, Hantush etc.) and straight-line analysis (Jacob) using pumping and recovery data. In the curve fitting and straight-line method, the program provides a user interface for fitting the curve and for choosing the intercept while drawing the straight line. The programme on analysis computes the transmissivity, storage co-efficient and leakage coefficient and estimation error. The software provides options for printing the data, generation of graphs and interpretation results. The software also provide tab views, property sheets, context menus, print preview, context sensitive help and much more. It supports totally custom headers, footers and legends with embedded text, lines, symbols, analysis parameters, frames, bitmaps and/or metafiles. The software enables simultaneous analysis of any number of monitoring wells with user-selectable parameter optimisations against a single monitoring well or across all monitoring wells. They allow instantaneous unit conversions that do not affect the analysis results specifically designed to help the peer review process. The software provides a simulation feature to design pumping tests providing contour maps of drawdown at given times and/or predicted drawdown versus time graphs at any number of monitoring wells. The software extends many of the pumping test solutions into a modeling environment capable of generating contour maps and/or colour floods of predicted drawdown or hydraulic head. 5 References • Kruseman, G.P. and N.A. de Ridder (1990) Analysis and Evaluation of Pumping Test Data. Second edition, ILRI publication 47, Wageningen, The Netherlands.
  18. 18. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 16 Annexure I: Aquifer Test Data Sheet Agency Name: ……………………………………….. State: …………………………..…………….…… Site ID: ……………………………………………….. Village: …………………………………………… District: ……………………………………………….. Location: ……………………………………..…… Date of Test: .….…………………………………….. Type of Test: ……………………………………… Depth of Well: ….…………………………………….. Pump Type: ……………………………….……… Pump Installation Depth: …………………………….. Discharge Pipe Dia: ……………………………… Pumping from date ………………., ……., ……… hrs. to date ………………., ……., ……… hrs. Measuring Point Details: ……………………………………………………………………………… Details of the aquifer being tested…………………………………………………………………… Screen below ground level from ……………………. to ……………………… (m) Screen dia (mm): ………………………………………… Details of Observation wells Observantion well No Distance from pumping well Depth of Observation well Static Water Level Discharge Measurement method: ………………………………………………………………. Water level Measurement Method:………………………………………………………………. No of Water Quality samples collected………………………………………………………….. Name of Officer In-charge:………………………………………………………………………… Team Members……………………………………………………………………………………. (Attach a sketch of aquifer test location)
  19. 19. Field Manual – Geohydrology (GW) Volume 4 – Part III Geo-hydrology March 2003 Page 17 Data Sheet Pumping well Observation well-1 Observation well-2Date and time Elapsed Time Depth to water (m) Draw Down (m) Depth to water (m) Draw Down (m) Depth to water (m) Draw Down (m) Discharge Remarks