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D5850-20 – Standard Test Method Technical Guide
📐 Scope and Application
This standard practice outlines an analytical procedure for determining transmissivity, storage coefficient, and anisotropy ratio (ratio of vertical to horizontal hydraulic conductivity) in a confined aquifer. It relies on drawdown measurements from a constant-rate pumping test with a network of partially penetrating wells. The practice requires a minimum of four observation wells positioned around a partially penetrating control well.
⚙️ Procedure and Referenced Standards
The procedure is used alongside Test Method D4050 for field testing. Compliance with Practice D6026 is required for significant digits and rounding. The standard specifies inch-pound units as standard, with SI units for reference.
| 🟦 Standard | 📏 Title |
|---|---|
| D653 | Terminology Relating to Soil, Rock, and Contained Fluids |
| D3740 | Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection |
| D4050 | Test Method for Field Procedure for Withdrawal and Injection Well Tests |
| D6026 | Practice for Significant Digits and Rounding in Geotechnical Data |
📊 Key Measured Parameters
The primary parameters derived from the analytical procedure include transmissivity, storage coefficient, and anisotropy ratio. These are critical for understanding aquifer properties.
| 📐 Parameter | 🎯 Definition | ⚡ Unit |
|---|---|---|
| Transmissivity | Rate of water flow through aquifer width | ft²/day (m²/day) |
| Storage Coefficient | Volume of water released per unit area per unit head decline | Dimensionless |
| Anisotropy Ratio | Ratio of vertical to horizontal hydraulic conductivity | Dimensionless |
💡 Ensure observation wells are properly screened and completed in the aquifer to minimize errors in drawdown measurements.
⚠️ The analytical procedure assumes homogeneous and isotropic conditions in the horizontal plane, which may not reflect complex field scenarios.
❓ Frequently Asked Questions
🔍 What is the purpose of D5850-20?
It provides an analytical procedure to determine transmissivity, storage coefficient, and anisotropy ratio from a network of partially penetrating wells.
💡 How many observation wells are needed?
A minimum of four observation wells is recommended.
⚡ Is this standard used alone?
No, it is used in conjunction with Test Method D4050 for field procedures.
📌 What are the units for transmissivity?
Inch-pound units are standard, typically ft²/day, with SI units for conversion.