Hydraulic Conductivity Parameterization May Depend on Investigative Methodology; Implication for Uncertainty

Hydrogeologists perform slug and pumping tests to determine aquifer coefficients of saturated subsurface materials. One key coefficient, saturated hydraulic conductivity (K) can be parameterized by these techniques, but also can be estimated through classical analysis of groundwater level recession data following the procedures developed by Rorabaugh (1960). Resultant K values are a key hydrogeologic parameter to support contaminant fate and transport models, hydrologic balance evaluations and groundwater mounding estimates.

K often is presumed to be an innate aquifer property, with its variability believed dependent solely on hydrogeologic characteristics of the aquifer such as porosity and permeability. This presentation offers field evidence that hydrogeologic factors alone do not control K values; they also depend on proper selection and careful execution of field testing methods and data analysis techniques.

Accurate hydrogeologic evaluations begin with solid controls on field-determined K values. Examples of field data will be presented, demonstrating that method selection and variances in field testing and data analysis impart profound effects upon the resultant K value. We will contrast the results of three standard techniques used to develop K values, when applied to the same sites and same data sets. We then will offer recommendations on the discussion of uncertainty in hydrogeologic evaluations dependent on accurate and defensible K parameterization.

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