Slug tests in wells screened across the water table: some additional considerations

Area of Science:

• Hydrogeology
• Environmental Science
• Geotechnical Engineering

Background:

• Slug tests are commonly used to assess groundwater contamination sites.
• Standard slug test models do not account for mechanisms present in wells screened across the water table.
• Practical issues arise from well design, test duration, and filter pack effects.

Purpose of the Study:

• Address four practical issues in slug testing at shallow groundwater contamination sites.
• Improve the reliability of slug test data and analysis.
• Provide guidance for accurate hydraulic conductivity estimation.

Main Methods:

• Assessing well design suitability prior to field testing.
• Utilizing mass balance to differentiate test phases (filter pack drainage vs. formation response).
• Estimating the effective casing radius directly from test data.

Main Results:

• Well design significantly impacts slug test data quality (signal-to-noise ratio).
• Mass balance aids in correctly identifying test phases.
• The effective casing radius, not the nominal radius, is critical for accurate modeling.
• Conventional models can provide reasonable estimates if applied to the formation-response phase.

Conclusions:

• Careful well selection and design assessment are essential for reliable slug testing.
• Advanced data analysis techniques are needed to overcome limitations of standard models.
• Accurate estimation of the effective casing radius is paramount for valid results.