Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D5785 – Standard Test Method Technical Guide
📐 Scope and Aquifer Assumptions
ASTM D5785/D5785M-20 establishes the analytical procedure for determining transmissivity of confined nonleaky aquifers using the underdamped well response to an instantaneous change in head (slug test). This response is characterized by an oscillatory fluctuation about the static water level with a progressive decrease in amplitude until full recovery. The standard is intended for wells tapping highly transmissive confined aquifers or deep wells with long water columns where such oscillatory behavior is observed.
⚠️ Crucial Assumptions: The analysis requires that the storage coefficient be known from independent data. The assumption of laminar flow dictates that the initial water-level displacement must be less than 0.1 to 0.2 (10% to 20%) of the length of the static water column. While the practice prescribes a fully penetrating well, it is commonly applied to partially penetrating wells if the aquifer is stratified and horizontal hydraulic conductivity is much greater than vertical hydraulic conductivity.
📊 Analytical Methodology and Data Requirements
The analytical procedure presented in this standard is derived by van der Kamp (1), which approximates the underdamped well response as an exponentially damped sinusoid. A more rigorous analysis by Kipp (2) confirms that this approximation is valid when specific conditions governing the damping characteristics are met. All observed and calculated values must conform to the significant digits and rounding guidelines of Practice D6026.
| 🟦 Parameter / Condition | 📏 Specification / Constraint | 🎯 Application / Basis |
|---|---|---|
| Aquifer Type | Confined, Nonleaky | Required for underdamped response |
| Damping Parameter | Less than 0.2 | Matching van der Kamp to Kipp solution |
| Time Analysis Window | Greater than the first peak of oscillation | Ensures analytical rigor |
| Initial Head Displacement | < 10% to 20% of static water column | Maintain laminar flow assumption |
| Well Penetration | Fully penetrating (caveats for partial) | Standard assumption for the model |
✅ Validation Check: Before applying the van der Kamp method, ensure the damping parameter values are strictly less than 0.2 and the test data is analyzed for times greater than that of the first oscillation peak. Under these specific conditions, the approximate analytical solution matches the rigorous fluid dynamics model developed by Kipp.
⚙️ Test Procedure and Compliance
This analytical practice is expressly intended to be used in conjunction with the field procedures defined in Test Method D4044/D4044M for the collection of slug test data. The standard permits the reporting of results in either SI units or inch-pound units, but these unit systems must be regarded as separate standards. Values from the two systems shall not be combined. The standard offers a set of instructions that require professional judgment and must be applied with consideration of the project’s many unique hydrogeological aspects.
| 📐 Field / Administrative Requirement | ⚡ Specification |
|---|---|
| Field Data Collection | Must strictly follow D4044/D4044M |
| Reporting Units | SI or Inch-pound (used independently, cannot be combined) |
| Significant Digits / Rounding | Must conform to Practice D6026 |
| Professional Oversight | Requires professional judgment (Section 1.7) |
❓ Frequently Asked Questions
🔍 What type of aquifer is this slug test analysis designed for?
This practice (D5785/D5785M-20) is specifically designed for analyzing the underdamped response in confined nonleaky aquifers. The oscillatory fluctuation of the water level is a prerequisite for applying this specific analytical technique.
💡 What is the core mathematical approximation of the van der Kamp method?
The van der Kamp method approximates the underdamped water level response as an exponentially damped sinusoid. Kipp’s more rigorous analysis validates this approach when the damping parameter is less than 0.2 and the analysis timeframe exceeds the first oscillation peak.
⚡ What is the maximum allowable initial head displacement for this test?
To satisfy the underlying assumption of laminar flow, the initial displacement of the water level caused by the slug must be less than 0.1 to 0.2 (10% to 20%) of the total length of the static water column in the well.
📌 What field testing method collects the data for this analytical procedure?
The field data collection must be performed strictly in accordance with Test Method D4044/D4044M. This practice acts purely as the analytical procedure applied to the data gathered from that specific field slug test procedure.