The Blundell geothermal power plant, located near Milford, Utah, is driven by the Roosevelt Hot Springs hydrothermal system. The plant consists of two units: a single-flash steam plant that has been in operation since 1984, and a binary plant commissioned in 2007. Blundell produces more groundwater from the reservoir than it reinjects, primarily due to evaporative losses from the plant’s cooling towers, resulting in a net fluid loss of about 3 billion lbs/yr. Consequently, a net pressure decline in the reservoir of approximately 40 bar over the course of Blundell’s operation is observed. We hypothesize that this pressure drop is causing drawdown of the water table, an increase in steam within the vadose zone, and subsequently forming an area of steam-heated thermal ground. Elevated soil temperatures are observed approximately 1 km north of the power plant, where the Opal Mound and Mag Lee Faults intersect. Across an area of about 1 square km, shallow soil temperatures (8 inches deep) exceed the local background levels, with the highest measurements reaching the local atmospheric boiling point (approximately 94oC). The thermal ground is associated with an extensive network of steam vents, along with dead vegetation observed in areas with the hottest soil temperatures. The extent of the thermal ground is actively increasing, and this paper attempts to delineate the thermal expansion that has occurred from 2012 to the present. The purpose of this study is to test the hypothesis that groundwater production at the Blundell power plant is the cause of the thermal ground formation and its subsequent expansion over time. Previous studies have surveyed surface temperatures (Tsurf) and CO2 fluxes (QCO2) across the area of interest. To quantify the temporal variation of these parameters, we conducted additional Tsurf and QCO2 field surveys across multiple seasons in 2022-2024. These recent data, normalized to background conditions, were compared to corresponding normalized datasets from 2012 (Tsurf) and 2017-2018 (QCO2). The comparison reveals a decade-long increase and expansion in surface soil temperatures concentrated around three hotspots within the thermal field.

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