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D4105 – Standard Test Method Technical Guide
📐 Overview of the Modified Theis Nonequilibrium Method
This practice covers an analytical procedure for determining transmissivity and storage coefficient of a nonleaky confined aquifer under conditions of radial flow to a fully penetrating well of constant flux. It serves as a shortcut procedure to apply the Theis nonequilibrium method, which is described in Practice D4106. This practice is intended for use in conjunction with the field procedure specified in Test Method D4050.
All observed and calculated values must conform to the guidelines for significant digits and rounding established in Practice D6026. The values stated in either SI units or inch-pound units are to be regarded separately as standard. Combining values from the two systems may result in non-conformance with this practice.
⚙️ Analytical Procedure and Limitations
The limitations of this practice are primarily related to the correspondence between the field situation and the simplifying assumptions of radial flow to a fully penetrating well in a homogeneous, isotropic, nonleaky confined aquifer. Notably, the application is valid only for values of u less than 0.01, where u is defined in Eq 2 of the standard (see 8.6). The practice relies on constant flux from the well.
This practice offers a set of instructions for performing specific operations but cannot replace education or experience. It should be used in conjunction with professional judgment. The standard is not intended to represent or replace the standard of care for professional services.
| 🔍 Parameter | 📏 Value | 📐 Condition |
|---|---|---|
| u (defined in Eq 2) | Less than 0.01 | Validity of the method |
| Transmissivity (T) | Determined from analysis | Constant for nonleaky confined aquifer |
| Storage Coefficient (S) | Determined from analysis | Radial flow to fully penetrating well |
📊 Key Measured Properties and Data Interpretation
This practice yields the transmissivity and storage coefficient of the aquifer from time-drawdown data collected during constant-rate pumping tests. The Theis nonequilibrium method assumes a homogeneous, isotropic, nonleaky confined aquifer of infinite extent. Referenced standards include Practice D3740 for minimum requirements for testing agencies and Terminology D653 for definitions of terms.
| 🟦 Standard | 📏 Title | 🎯 Relevance |
|---|---|---|
| D653 | Terminology Relating to Soil, Rock, and Contained Fluids | Provides definitions for terms used |
| D3740 | Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection | Specifies qualifications for testing agencies |
| D4050 | Test Method for (Field Procedure) for Determining Transmissivity and Storage Coefficient | Describes the field procedure for data collection |
📌 Tip: The application of this practice is valid only for u less than 0.01. Ensure your data meets this condition for accurate interpretation of aquifer properties.
⚠️ Warning: Do not combine SI units and inch-pound units. Each system must be used independently to avoid non-conformance with the standard. Reporting results in units other than SI is acceptable.
❓ Frequently Asked Questions
🔍 What is the condition for u in this method?
The method is valid only for u less than 0.01, as defined in Eq 2 of the standard. This ensures the approximations of the shortcut procedure hold.
The method is valid only for u less than 0.01, as defined in Eq 2 of the standard. This ensures the approximations of the shortcut procedure hold.
💡 Can I use this practice for leaky aquifers?
No, this practice is specifically for nonleaky confined aquifers under radial flow. For leaky conditions, refer to other appropriate standards.
No, this practice is specifically for nonleaky confined aquifers under radial flow. For leaky conditions, refer to other appropriate standards.
⚡ What units are allowed for reporting?
Either SI units or inch-pound units can be used, but they must be used independently. Combining values from both systems is not permitted.
Either SI units or inch-pound units can be used, but they must be used independently. Combining values from both systems is not permitted.
📌 Does this practice replace professional judgment?
No, this practice offers a set of instructions but should be used with professional judgment. It is not a substitute for education or experience.
No, this practice offers a set of instructions but should be used with professional judgment. It is not a substitute for education or experience.