Aquifer Test Modeling

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Constant-Rate Pumping Tests

Proper planning includes the design of the test , acquisition and preparation of field equipment , measurement and control of flow rates , measurement locations and schedules with pre- and post-test collection periods for water levels , disposal of pumped water and test duration. Consider taking the following items into the field with you on your next pumping test assignment:. The foregoing equipment list is provided as a general guide for a typical pumping test and should not be considered exhaustive. Modify or supplement the list to meet the requirements of your specific test and field conditions.

Please send us your suggestions for additions to the list! A controlled pumping stress is imposed on an aquifer system during a pumping test. Therefore, carefully measuring , controlling and recording the flow rate throughout the test is essential for a successful outcome. Although a constant pumping rate is most often the goal, the rate may vary during a pumping test. Software such as AQTESOLV can account for variable pumping rates ; however, results will depend on how closely the recorded flow rates correspond to actual rate changes.

Pumping Test Analysis :. AQTESOLV Tour

Measuring the flow rate during a pumping test can be accomplished in a number of ways including the following:. Flow rates should be recorded with sufficient frequency to demonstrate a constant rate or to monitor planned rate changes. In the event of temporary test interruption e. Bear in mind that the discharge rate often decreases with time as the water level in the control well drops. Kruseman and de Ridder recommend checking and, if necessary, adjusting the flow rate at least once every hour; however, one should consider more frequent measurements until it becomes evident how often rate adjustments are required Stallman Estimating discharge from a pumped well by use of a circular orifice weir USGS Controlling the flow rate is also important for a successful pumping test.

State and local regulations may offer additional guidance regarding an acceptable tolerance for rate variation during a pumping test. During a pumping test, water levels in wells may be measured by means of manual techniques or through the use of sensors with data loggers.

Manual water-level measurement techniques include chalked steel tape , electric water-level sounders and air line methods. The USGS has published procedural documents for measuring water levels with graduated steel tapes and electric tapes:. Steel tapes are not recommended for taking water-level measurements in the pumped well owing to rapid water-level drawdown and the possibility of cascading water in the well.

When taking manual measurements in the pumped well, be sure to secure the measuring device when sounding the well to prevent accidental entanglement with the pump.

AquiferTest 2015.1 Webinar

Pressure transducers combined with data loggers provide rapid and accurate measurements of water levels in wells. Even when working with reliable transducers and data loggers, it's good practice to obtain periodic manual measurements at each observation well to 1 confirm transducer readings and 2 provide backup readings in the event of accidental data loss. A logarithmic schedule is appropriate for recording water levels a during a constant-rate pumping test.

For variable-rate tests e. You can find recommended schedules for manual water-level measurements in Driscoll and Kruseman and de Ridder Pressure transducers are available in vented and nonvented models e. Vented transducers measure pressure relative to the ambient barometric pressure. Nonvented transducers measure absolute pressure including the pressure of the air column above the sensor. A barometric sensor is required to correct readings from nonvented transducers for changes in barometric air pressure.

For any pumping test, an on-site barometric sensor is recommended in the event that water levels require correction for barometric efficiency. Most modern data loggers have an option for logarithmic sampling; however, you may convert measurements from a linear to a logarithmic schedule with software such as AQTESOLV. Pre- and post-test water-level measurements are essential for the identification of trends e. A linear schedule is recommended for monitoring water levels before and after the test. Pre-test water-level measurements should begin at least several days before pumping begins Figure 5.

In the case of a pumping test that extracts water from an aquifer, care should be exercised in the disposal of the pumped water. First and foremost, be certain that you dispose of the water in accordance with any applicable laws and regulations. Bear in mind the following considerations as you weigh options for the disposal of discharge water:. The decision to terminate a pumping test is best made on the basis of hydrogeologic conditions at the test site and the objectives of the test.

Longer tests may be necessary to estimate specific yield in an unconfined aquifer or to observe boundary effects.

Benchmark Comparison

Plotting and inspecting pumping test data as they are collected in the field can help you to decide when it's appropriate to end a pumping test. Other factors may influence the planned duration of a pumping test including budgetary constraints and regulatory requirements. Often, applicable regulations may establish a minimum duration required for a test, but longer tests may be necessary to achieve other test objectives. Estimation of the vertical hydraulic conductivity, K z , of a nonleaky or leaky confined aquifer requires pumping and observation wells that are partially penetrating.

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Hantush a showed that the effect of partial penetration becomes negligible at radial distances given by the following equation:. Use the following calculator to compute the radial distance from the control well at which partial penetration may be ignored. Find additional guidelines and procedures in the collection of guidance documents. Find additional pumping test literature in the list of aquifer testing references. Pumping Tests by Glenn M.

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Figure 1. Typical well configuration for pumping test in nonleaky confined aquifer. Figure 2. Estimation of aquifer properties by matching Theis type-curve solution to time-drawdown data collected in an observation well during a constant-rate pumping test in a nonleaky confined aquifer data from Walton Three aquifer testing methods are in common use by groundwater hydrologists to estimate hydraulic properties of aquifer systems. In all of the methods, a control well imposes a hydraulic stress on an aquifer system.

Modelling flow converging to a pumped borehole

The methods differ according to the type of hydraulic stress:. Since the s, aquifer system properties have been estimated from aquifer tests by fitting mathematical models type curves to response data water-level changes or pumping rates using a procedure known as curve matching. Traditionally, curve matching has been performed using various graphical procedures; more recently, automated curve-matching methods involving nonlinear least-squares techniques have come to the fore.

Modern evaluation of aquifer test data has augmented graphical and automatic curve-matching techniques with derivative analysis for more thorough and robust data interpretation. A pumping test stresses an aquifer by pumping a test well at a controlled rate while water levels are measured in one or more surrounding wells. A constant-rate test is the most commonly performed pumping test; however, variable-rate pumping tests such as step-drawdown tests for assessing well performance or designing a constant-rate test are sometimes carried out as well.

Pumping tests are conducted to estimate the hydraulic properties of aquifer systems as well as identify aquifer boundaries. Among groundwater hydrologists, the most familiar curve matching procedure for estimating aquifer properties from pumping tests is due to Theis The Theis method allows one to estimate the transmissivity and storativity of a nonleaky confined aquifer having infinite extent by means of matching the Theis type curve to water-level changes drawdowns measured in wells during a constant-rate pumping test Figure 3.

Publication of the work by Theis marked a major stride forward in groundwater science because of the mathematical rigor applied to the evaluation of transient nonequilibrium pumping test data. In the decades since Theis' seminal work, a great number of progressively more sophisticated models have appeared in the literature that further facilitate the interpretation of pumping tests for different well configurations and aquifer geometries.

For example, Hantush and Jacob published the first transient solution for the interpretation of pumping tests in leaky confined aquifers Figure 4. A slug test is initiated by causing the water level in the control well to suddenly rise or fall and subsequently recording the recovery of the water level to its pre-test level. In addition to estimating hydraulic properties, slug tests are sometimes performed to provide an indicator of well performance.

These relatively inexpensive tests, which involve little or no water added to or removed from a well, can be advantageous at groundwater contamination sites. Beginning in the late s, rigorous mathematical models became available for the analysis of slug tests including the KGS Model by Hyder et al. In practice, constant-head tests are performed less frequently than either pumping tests or slug tests. In a constant-head test, the head or drawdown in a control well is maintained at a constant level and the declining discharge rate from the control well is recorded with time; in addition, water level changes may be measured in surrounding wells.

Multi-Well Analysis for Groundwater Control Design

One particular application for a constant-head test is a flowing artesian well in which groundwater under confined or artesian pressure flows at the land surface Figure 7. In the literature, one finds constant-head tests were performed on flowing artesian wells in the Grand Junction area, Colorado, USA, to estimate the transmissivity and storativity of a confined aquifer Lohman The first analytical solution in the groundwater literature for the interpretation of a constant-head test in a nonleaky confined aquifer is due to Jacob and Lohman Using this solution, one matches type curves to transient discharge data measured at the control well to estimate transmissivity and storativity Figure 8.

Looking for literature relating to aquifer tests? Check out the annotated aquifer testing reference list to find publications and articles pertaining to pumping tests, slug tests, constant-head tests and more. Please visit the glossary for a list of aquifer testing terms and their definitions. Aquifer Tests by Glenn M. Methods Of Aquifer Testing. Figure 1. Aquifer testing methods used to estimate hydraulic properties of aquifers and aquitards.

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