Use of Well Hydrographs in Shallow Fractured Aquifers to Determine Specific Yields and Continuum Transmissivities

摘要

The aim of this work was to test and validate a new approach to quantitatively analyze well hydrographs in shallow, fractured and karstic aquifers. This approach was demonstrated to be reliable, and estimates of transmissivity (T) and specific yields (Sy) in different portions of a flow regime can be obtained by the use of this less costly, non-invasive, passive method. Under the ARO funded project, field work included collecting hydrograph data and conducting aquifer testing at selected wells at the Crane, IN, the Y- 12, TN, and the Fort Campbell, KY sites. Evaluation of the results indicates that the hydrograph analysis method produces results of aquifer parameter estimates (matrix t) of comparable reliability to those obtained using conventional aquifer testing techniques. Hydrograph analysis results differ from those of slug tests in cases where cavities are located in the well's completion zone. This results because the slug test results are biased toward the high conductivity, near well-bore conduits, whereas the hydrograph method evaluates matrix T. Using sensitivity and statistical analyses, ongoing work is directed toward assessing the various conditions under which this method is applicable and reliable, and under which site conditions it is less reliable.