Recommended Normalized Head Range for Slug Test Analysis

by Glenn M. Duffield, President, HydroSOLVE, Inc.

What Are Recommended
Normalized Head Ranges?

Data from an overdamped slug test in a well with a fully submerged screen may exhibit a concave upward appearance on a plot of log normalized head vs. time (Figure 1). The curvature can make analysis by straight-line methods such as Bouwer and Rice (1976) somewhat ambiguous.

Slug test data with concave upward curvature
Figure 1. Data showing concave upward curvature collected during falling-head slug test with fully submerged well screen (data from Batu 1998).

Butler (1998) suggests matching straight-line slug test solutions to data within recommended normalized head ranges to overcome ambiguity associated with data curvature and thereby enhance reliability of data analysis.

Note that a different phenomenon, the so-called double-straight line effect, is sometimes observed in slug test data from wells screened across the water table.

Applying Recommended Normalized Head Ranges

Recommended Normalized Head Range
for Straight Line Match
Hvorslev (1951) 0.15 to 0.25
Bouwer-Rice (1976) 0.20 to 0.30

With recommended normalized head ranges to guide us, we can readily match a straight-line solution like Bouwer and Rice (1976) to concave data (Figure 2).

Analysis of slug test data with concave upward curvature using Bouwer and Rice (1976) method
Figure 2. Analysis of falling-head slug test using Bouwer and Rice (1976) solution and recommended normalized head range.

Slug test analysis software can superimpose recommended normalized head ranges on data plots to enhance visual curve matching.