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D6028 – Standard Test Method Technical Guide
This standard practice, designated D6028/D6028M-20, provides an analytical procedure for determining the transmissivity and storage coefficient of confined aquifers. It accounts for the change in storage of water in overlying or underlying confining beds, extending the Hantush-Jacob method. The analysis applies to water-level or head data from observation wells or piezometers during constant-rate pumping or injection tests.
📐 Key Assumptions and Parameters
The Modified Hantush method is valid for hydrogeologic settings that match its assumptions, including confined aquifers with leaky confining beds where storage changes are significant. All combinations of impermeable beds and source beds on the distal side of the confining layers are considered. The following table summarizes the types of confining beds and their characteristics as per the standard.
| 🟦 Confining Bed Type | 📏 Description | 🎯 Hydraulic Characteristic |
|---|---|---|
| Impermeable Bed | Negligible water movement; no storage contribution. | No vertical leakage |
| Source Bed | Maintains uniform head; provides or receives water. | Constant head boundary |
| Leaky Confining Bed | Permits vertical leakage and stores water. | Storage and leakage effects |
The method determines transmissivity (T) and storage coefficient (S) using data from constant-rate tests. This practice is used in conjunction with Test Method D4050 for data collection.
⚙️ Test Procedure and Data Collection
Water is pumped from a control well at a constant rate, and water-level or head data are collected from one or more observation wells or piezometers. The same procedure can be applied to injection tests with appropriate sign changes. All observed and calculated values must conform to the significant digit and rounding guidelines of Practice D6026.
Technical Note: This method is specifically designed for confined aquifers with leaky confining beds. Ensure that the field conditions include storage effects in the confining layers for accurate application of the Modified Hantush method.
📊 Analysis and Results
The analysis yields hydraulic properties such as transmissivity and storage coefficient. The procedures for significant digits are representative of the industry standard, but may be adjusted based on project objectives. Professional judgment is essential, as the standard is not a substitute for education or experience. The table below lists the primary parameters determined from the analysis.
| 🟦 Parameter | 📏 Symbol | 🎯 Unit (SI) | ⚡ Unit (Inch-pound) |
|---|---|---|---|
| Transmissivity | T | m²/s | ft²/day |
| Storage Coefficient | S | dimensionless | dimensionless |
Important Limitation: This practice does not address all safety concerns. Users must establish appropriate safety, health, and environmental practices. The standard is intended to be used with professional judgment and is not a replacement for the standard of care.
❓ Frequently Asked Questions
🔍 What is the Modified Hantush Method?
It is an analytical procedure for determining transmissivity and storage coefficient of confined aquifers, considering storage changes in overlying or underlying confining beds during constant-rate pumping or injection tests.
💡 How does it differ from the Hantush-Jacob method?
The Modified Hantush method explicitly accounts for the gain or loss of water in storage in the confining beds, whereas the Hantush-Jacob method does not. This allows for more accurate analysis in leaky aquifer systems.
⚡ What are the key limitations?
The valid use is limited to hydrogeologic settings that correspond to the assumptions of the method, including the presence of leaky confining beds with storage effects. It requires data from constant-rate tests and must be applied with professional judgment.
📌 Which referenced standards are associated?
This practice references Test Method D4050 for data collection procedures and Practice D6026 for significant digits and rounding guidelines.