A new procedure is presented for the analysis of slug tests performed in partially penetrating wells in formations of high hydraulic conductivity. This approach is a simple, spreadsheet-based implementation of existing models that can be used for analysis of tests from confined or unconfined aquifers. Field examples of tests exhibiting oscillatory and nonoscillatory behavior are used to illustrate the procedure and to compare results with estimates obtained using alternative approaches. The procedure is considerably simpler than recently proposed methods for this hydrogeologic setting. Although the simplifications required by the approach can introduce error into hydraulic-conductivity estimates, this additional error becomes negligible when appropriate measures are taken in the field. These measures are summarized in a set of practical field guidelines for slug tests in highly permeable aquifers.

In most field investigations, information about hydraulic conductivity (K) is obtained through pumping or slug tests. A considerable body of data has been amassed that indicates that the K estimate from a pumping test is, on average, considerably larger than the estimate obtained from a series of slug tests in the same formation. Although these data could be interpreted as indicating a natural underlying scale dependence in K, an alternate explanation is that the slug‐test K is artificially low as a result of incomplete well development and, to a much lesser extent, failure to account for vertical anisotropy. Incomplete well development will often result in only the most permeable zones being cleared of drilling debris, with much of the screened interval remaining undeveloped. More cursory development can leave a low‐K skin along the entire screened interval. Failure to recognize such conditions can result in a K estimate from a slug test that is much lower than the average K of the formation in the vicinity of the well. By contrast, neither a skin nor vertical anisotropy will have a significant impact on K estimates from pumping tests when semi‐log analyses and/or observation wells are used. However, a reasonable estimate of aquifer thickness is required to convert the transmissivity calculated from a pumping test into an average K for the aquifer. Prior to invoking a natural scale dependence to explain the results of different types of hydraulic tests, head data should be closely examined and serious consideration given to alternate explanations.

Fine‐scale hydrostratigraphic features often play a critical role in controlling ground water flow and contaminant transport. Unfortunately, many conventional drilling‐ and geophysics‐based approaches are rarely capable of describing these features at the level of detail needed for contaminant predictions and remediation designs. Previous work has shown that direct‐push electrical conductivity (EC) logging can provide information about site hydrostratigraphy at a scale of relevance for contaminant transport investigations in many unconsolidated settings. In this study, we evaluate the resolution and quality of that information at a well‐studied research site that is underlain by highly stratified alluvial sediments. Geologic and hydrologic data, conventional geophysical logs, and particle‐size analyses are used to demonstrate the capability of direct‐push EC logging for the delineation of fine‐scale hydrostratigraphic features in saturated unconsolidated formations. When variations in pore‐fluid chemistry are small, the electrical conductivity of saturated media is primarily a function of clay content, and hydrostratigraphic features can be described at a level of detail (<2.5 cm in thickness) that has not previously been possible in the absence of continuous cores. Series of direct‐push EC logs can be used to map the lateral continuity of layers with non‐negligible clay content and to develop important new insights into flow and transport at a site. However, in sand and gravel intervals with negligible clay, EC logging provides little information about hydrostratigraphic features. As with all electrical logging methods, some site‐specific information about the relative importance of fluid and sediment contributions to electrical conductivity is needed. Ongoing research is directed at developing direct‐push methods that allow EC logging, water sampling, and hydraulic testing to be done concurrently.