Slug Test Calculator
The Slug Test Calculator is a reliable online tool for hydrogeologists, environmental consultants, engineers, and students to estimate aquifer hydraulic conductivity (K) from slug test data. This Slug Test Calculator supports the Bouwer and Rice (1976) method for unconfined aquifers and the Hvorslev (1951) method for confined aquifers, both based on peer-reviewed, established analytical solutions.
Slug tests provide a quick, cost-effective way to characterize near-well hydraulic properties.
Calculator Inputs
About the Slug Test Calculator
The Slug Test Calculator implements two classic semi-analytical methods: the Bouwer and Rice (1976) solution for partially or fully penetrating wells in unconfined aquifers, and the Hvorslev (1951) solution for confined aquifers. Both are widely cited in hydrogeology textbooks and used globally for estimating hydraulic conductivity from overdamped slug tests.
A slug test involves instantaneously adding or removing a volume of water ("slug") to/from a well and monitoring the recovery of the water level over time. The rate of recovery reflects the aquifer's ability to transmit water.
Scientific Basis and Formulas
For both methods, data are plotted as normalized head (H/H₀) vs. time on a semi-log plot. The basic time lag T₀ is the time where H/H₀ = 0.37.
Bouwer & Rice (Unconfined):
$$ K = \frac{r_c^2 \ln(R_e / r_w)}{2 L T_0} $$
where $$ \ln(R_e / r_w) = \left[ \ln\left(\frac{H_0}{r_w}\right) + A + B \right] $$ for partial penetration, approximated via:
If (L / r_w ≥ 8): $$ \ln(R_e / r_w) = \frac{A \ln(L / r_w) + C}{1 + (A + B) \ln(L / r_w)/C} $$ (approximation)
Standard values: A=1.472, B=0.237, C=2.364 (common log-based adjustment in code).
Hvorslev (Confined):
$$ K = \frac{r_c^2 \ln(2L / r_w)}{2 L T_0} $$ (for L / r_w ≥ 8)
These are derived from quasi-steady-state flow assumptions and validated in numerous studies.
Importance of Slug Tests
Slug tests are essential for site characterization in groundwater investigations, contamination assessments, well design, and water supply projects. They are faster and cheaper than full pumping tests, requiring minimal equipment and no water disposal. In agriculture, they help evaluate irrigation well performance and aquifer sustainability.
Accurate K values inform recharge estimates, contaminant transport modeling, and dewatering plans.
When and Why You Should Use This Tool
Use the Slug Test Calculator for:
- Rapid analysis of field slug test data
- Estimating K in monitoring wells or piezometers
- Comparing results from multiple tests
- Educational purposes in hydrogeology courses
- Preliminary assessments before detailed modeling
Ideal for overdamped responses; oscillatory data may require advanced methods.
User Guidelines
- Plot normalized head vs. time (semi-log) and fit straight line to late-time data.
- Determine T₀ accurately (time to H/H₀=0.37).
- Use rs > rc if gravel pack present (Bouwer & Rice).
- Ensure screen fully submerged for best results.
- Avoid early-time data affected by wellbore storage or skin.
- Conduct multiple tests (rising/falling head) for consistency.
Purpose of the Slug Test Calculator
This tool makes scientifically sound slug test analysis accessible, promoting best practices in groundwater evaluation. It supports sustainable resource management by providing quick, reliable K estimates.
Typical parameter ranges:
| Parameter | Typical Range | Notes |
|---|---|---|
| Casing Radius (rc) | 0.025–0.15 m | Inside radius |
| Screen Radius (rs) | 0.05–0.3 m | Includes gravel pack |
| Screen Length (L) | 1–10 m | Submerged portion |
| Hydraulic Conductivity (K) | 10⁻⁷ – 10⁻³ m/s | Depends on material |
| T₀ | 10–10000 s | Longer in low-K |
In conclusion, the Slug Test Calculator enables evidence-based aquifer characterization crucial for environmental protection and water management. For more on slug tests, see the Slug Test Calculator page on Wikipedia or resources at Agri Care Hub.
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