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D4106-20 – Standard Test Method Technical Guide
This article outlines the essential aspects of ASTM D4106-20, which provides an analytical procedure for determining the transmissivity and storage coefficient of nonleaky confined aquifers. The Theis nonequilibrium method is employed to analyze water-level responses during constant discharge or injection tests. This practice complements the field procedures described in Test Method D4050.
📐 Scope and Key Assumptions
This practice covers the analysis of data from radial flow to or from a well in a nonleaky confined aquifer. The primary outputs are transmissivity (T) and storage coefficient (S). The method assumes an aquifer that is homogeneous, isotropic, and infinite in extent, with constant thickness and fully penetrating wells. Limitations arise when field conditions deviate from these assumptions, requiring professional judgment.
| 🟦 Standard | 📏 Description |
|---|---|
| D653 | Terminology Relating to Soil, Rock, and Contained Fluids |
| D3740 | Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock |
| D4043 | Guide for Selection of Aquifer Test Method for Determining Hydraulic Properties by Well Techniques |
| D4050 | Test Method for Field Procedure for Withdrawal and Injection Well Testing for Determining Hydraulic Properties of Aquifer Systems |
| D6026 | Practice for Using Significant Digits in Geotechnical Data |
⚙️ Test Procedure and Data Requirements
The field test must be conducted according to Test Method D4050. Data on water-level response (drawdown) are collected at a pumping or injection well and observation wells. All measurements must conform to the significant digit guidelines in Practice D6026. The data should be recorded with appropriate precision, and calculated values should be reported with consistent significant figures based on field conditions and project objectives.
⚠️ Important: The analytical procedure is only valid for nonleaky confined aquifers. For leaky or unconfined conditions, alternative methods should be used. Professional experience is essential for proper application.
📊 Key Measured Properties and Calculations
The Theis nonequilibrium method involves matching drawdown data to type curves or using analytical solutions to estimate transmissivity and storage coefficient. The method is based on the well-known Theis equation, which expresses drawdown as a function of distance from the well, time, and aquifer properties. The accuracy of results depends on the quality of field data and adherence to method assumptions.
| 📐 Property | ⚡ Symbol | 📏 Units |
|---|---|---|
| Transmissivity | T | L²/T (e.g., ft²/day) |
| Storage Coefficient | S | Dimensionless |
| Discharge Rate | Q | L³/T (e.g., gpm) |
| Drawdown | s | L (e.g., ft) |
💡 Tip: For best results, ensure that the test duration is sufficient to capture the Theis curve shape. Long-term tests may be required for low permeability aquifers.
❓ Frequently Asked Questions
🔍 What is the primary purpose of D4106-20?
The standard provides an analytical procedure for determining transmissivity and storage coefficient of nonleaky confined aquifers using the Theis nonequilibrium method.
💡 How is this practice used with field tests?
It is used in conjunction with Test Method D4050, which describes the field procedure for withdrawal or injection well testing.
⚡ What are the main limitations of this method?
The limitations are related to deviations from simplifying assumptions, such as non-homogeneous aquifers or partially penetrating wells. Professional judgment is required.
📌 Which standards are referenced in this practice?
Referenced standards include D653, D3740, D4043, D4050, and D6026, which cover terminology, laboratory requirements, test method selection, field procedures, and significant digits.