Journal Published Online: 20 November 2023
Volume 47, Issue 3

Specific Storage or Elastic Modulus of Solid Matrix in Aquifers and Aquitards—Results from Slug Tests: A Review and a Clarification



Hydrogeology defines specific storage, Ss, to quantify the ability of a saturated layer to release or take water when the hydraulic head is changed, resulting in a change in the solid matrix volume. ASTM D4104/D4104M-20, Standard Practice for (Analytical Procedures) Determining Transmissivity of Nonleaky Confined Aquifers by Overdamped Well Response to Instantaneous Change in Head (Slug Tests), has a method to assess the Ss value. The article explains how continuum mechanics relate Ss to the constrained (one-dimensional vertical) elastic modulus, E′, of the solid matrix. As a result, Ss has a limited range of values for soil and rock, but this limitation has not received enough attention. Continuum mechanics have already proven that slug tests cannot give Ss, contrary to the opinion of a few slug test users. Short tables clarify and summarize the strangeness of the slug test theory with Ss. The Ss values are in the 10−4–10−7 m−1 range according to continuum mechanics, but the slug test theory yields a 100–10−20 range. The comparison shows that the slug test theory with Ss gives only 5 % of realistic Ss values. The tests in soil and rock often yield Ss values that are those of materials either stiffer that steel or softer than peat. An example clarifies this finding. A monitoring well (MW) was tested with three sets of sensors having different calibration errors: the three test datasets yielded a wide Ss range for the sand tested by the MW. Recommendations are made to avoid misinterpreting test data and improve current standards. The slug test theory with Ss is based on errors in math and physics, and its supporters have so far delayed the use of physically correct methods in ASTM standards. The article does not question the ability of pumping tests and geophysical methods to extract the value of Ss or E′.

Author Information

Chapuis, Robert P.
Department of Civil, Geological and Mining Engineering, Polytechnique Montréal, Montréal, Quebec, Canada
Pages: 32
Price: $25.00
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Stock #: GTJ20230383
ISSN: 0149-6115
DOI: 10.1520/GTJ20230383