[1] Spatial variations in hydraulic conductivity (K) provide critical controls on solute transport in the subsurface. Recently, new direct-push tools were developed for highresolution characterization of K variations in unconsolidated settings. These tools were applied to obtain 58 profiles (vertical resolution of 1.5 cm) from the heavily studied macrodispersion experiment (MADE) site. We compare the data from these 58 profiles with those from the 67 flowmeter profiles that have served as the primary basis for characterizing the heterogeneous aquifer at the site. Overall, the patterns of variation displayed by the two data sets are quite similar, in terms of both large-scale structure and autocorrelation characteristics. The direct-push K values are, on average, roughly a factor of 5 lower than the flowmeter values. This discrepancy appears to be attributable, at least in part, to opposite biases between the two methods, with the current versions of the direct-push tools underestimating K in the highly permeable upper portions of the aquifer and the flowmeter overestimating K in the less permeable lower portions. The vertically averaged K values from a series of direct-push profiles in the vicinity of two pumping tests at the site are consistent with the K estimates from those tests, providing evidence that the direct-push estimates are of a reasonable magnitude. The results of this field demonstration show that direct-push profiling has the potential to characterize highly heterogeneous aquifers with a speed and resolution that has not previously been possible.

[1] A new probe has been developed for high-resolution characterization of hydraulic conductivity (K) in shallow unconsolidated formations. The probe was recently applied at the Macrodispersion Experiment (MADE) site in Mississippi where K was rapidly characterized at a resolution as fine as 0.015 m, which has not previously been possible. Eleven profiles were obtained with K varying up to 7 orders of magnitude in individual profiles. Currently, high-resolution (0.015-m) profiling has an upper K limit of 10 m/d; lower-resolution (%0.4-m) mode is used in more permeable zones pending modifications. The probe presents a new means to help address unresolved issues of solute transport in heterogeneous systems.

Recognition and quantitative characterization of subsurface stratigraphic units in coarse unconsolidated fl uvial deposits are diffi cult because large grain size and the large scale of sedimentary structures make direct interpretation from core diffi cult or impossible. In this paper, we use porosity data from well logs and grain-size distribution (GSD) data from core to investigate four pebble-and cobble-dominated units that have been identifi ed in porosity logs in deposits at a research well fi eld (Boise Hydrogeophysical Research Site). Lacking direct observation at an appropriate scale, questions about distribution of parameters and textural composition in these units are analyzed with statistical tests. The four pebble-and cobble-dominated "porosity stratigraphic" units may be grouped into two types: (1) Units 1 and 3 have low porosity (mean ~0.17-0.18) and low porosity variance; and (2) Units 2 and 4 have higher porosity (mean ~ 0.23-0.24) and higher porosity variance. Based on GSD data, core samples are subdivided into fi ve lithotypes. The fi ve lithotypes occur in different proportions and have different vertical transition probability characteristics in the two types of units: (1) Units 1 and 3 have only frameworkgravel-dominated lithotypes and have random vertical transition probability between these two lithotypes; and (2) Units 2 and 4 consist of both framework-gravel-dominated and sand-or matrix-dominated lithotypesand have structured vertical transition probability. The two framework-gravel-dominated lithotypes occur in all four stratigraphic units but have distinctly lower porosity in Units 1 and 3 (i.e., tighter packing) than in Units 2 and 4 (looser packing). Considering the repeated stratigraphic occurrence of (and the statistical signifi cance of differences between) the two types of units, both the individual unit distinctions and the two unit groupings appear to be valid. It is reasonable to interpret that the observed packing differences associated with Units 1 and 3 compared with Units 2 and 4 are related to different sedimentary processes that produce different bedforms or grain fabrics, perhaps under different bedload transport rates.