From June 2008 to September 2009, a field investigation for a Master’s thesis in Natural Resource Management was carried out to identify the existence of subsoil thermal anomalies that may be correlated with local faults in the Pailas Geothermal Field, located on the Pacific slope of the Quaternary Rincón de la Vieja volcanic complex in northwestern Costa Rica. A total of 240 direct subsoil temperature measurements were made at fifty-seven one-inch diameter access holes equally spaced on a one-kilometer grid and drilled to depths ranging from 47 to 167 cm in iso-hyperthermal entisol to iso-hyperthermal inceptisol type soils. This study covers the area that will be directly impacted by the operation of a 35 MWe geothermal plant at the Pailas Geothermal field, part of the north bordering Rincón de la Vieja National Park and an area extending towards the northwest of the currently developed geothermal field. Soil temperature gradient data obtained in the non-hydrothermally altered areas of the field seems to be congruent with the results of mean monthly soil temperature data in other studies from non-hydrothermally altered soils, elsewhere in Costa Rica. However, throughout the field area there are important differences in soil type, geological formations, elevation, and geothermal activity, all of which may influence the measured subsoil temperatures. This paper presents statistical analyses of these data.

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