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HOTSPOT is an international collaborative effort to understand the volcanic history of the Snake River Plain (SRP). The SRP overlies a thermal anomaly, the Yellowstone-Snake River hotspot, that is thought to represent a deep-seated mantle plume under North America. The primary goal of this project is to document the volcanic and stratigraphic history of the SRP, which represents the surface expression of this hotspot, and to understand how it affected the evolution of continental crust and mantle. An additional goal is to evaluate the geothermal potential of southern Idaho.Project HOTSPOT has completed three drill holes.(1) The Kimama site is located along the central volcanic axis of the SRP; our goal here was to sample a long-term record of basaltic volcanism in the wake of the SRP hotspot.(2) The Kimberly site is located near the margin of the plain; our goal here was to sample a record of high-temperature rhyolite volcanism associated with the underlying plume. This site was chosen to form a nominally continuous record of volcanism when paired with the Kimama site. (3) The Mountain Home site is located in the western plain; our goal here was to sample the Pliocene-Pleistocene transition in lake sediments at this site and to sample older basalts that underlie the sediments.We report here on our initial results for each site, and on some of the geophysical logging studies carried out as part of this project.

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The 1986 Safe Drinking Water Act Amendments include provisions for state wellhead protection (WHP) programs that address wellhead protection areas (WHPAs). In many states, WHPAs are delineated based on time‐of‐travel (TOT) criteria. This study compares 250‐day and 15‐year TOT capture zones computed in a confined to semiconfined aquifer system in an alluvial basin using semianalytical and two‐ and three‐dimensional numerical ground‐water flow models, and evaluates the relative importance of several sources of uncertainty, such as aquifer hydraulic conductivity, aquitard leakance, vertical transit time, hydraulic gradients, transient pumping effects, well interference, and three‐dimensional aquifer geometries. A numerical model should be used to delineate 15‐year TOT capture zones for wells in confined to semiconfined aquifers in alluvial basins. A semianalytical program may be acceptable for computing the 250‐day TOT capture zones; however, such codes can be applied only under a very narrow range of conditions. Hydraulic conductivity plays a critical role in controlling the sizes and shapes of capture zones computed in confined to semiconfined aquifers. Small, circular capture zones are computed in low hydraulic conductivity areas. More complex geometries should be expected where hydraulic conductivities are higher and pumping wells are in close proximity to each other. Aquifers with horizontal hydraulic conductivities that are greater than 1,000 times the vertical hydraulic conductivity of the overlying aquitard are effectively fully confined, and larger capture zones would be computed for these aquifers than for semiconfined aquifers where significant leakage is induced by pumping. In addition, relatively large drawdowns are computed in low hydraulic conductivity areas, resulting in short vertical transit times. Vertical transit times are longer where aquifer hydraulic conductivities are higher.