Thermal model of the Piedmont Po Plain shallow aquifer (NW Italy) with the statistical temperature distribution

This study analyses the temperature distribution underneath the Piedmont Po Plain (NW Italy), where an important shallow aquifer exists due to fluvial and outwash deposits. A total of 118 thermal logs, for a total of 513 temperature measurements in spring 2008 and 585 in autumn 2008, were used to propose the conceptual thermal model of the vertical temperature distribution in the shallow aquifer of the western Po Plain. A constant temperature depth between 30 and 50 m below ground level was observed, under which aquifer temperatures were constant in the range 13 -15 degrees C during the year independent of the external climatic condition. Above the constant temperature depth, the variable temperature zone, where the temperature is strongly influenced by external seasonal variations, was observed. Moreover, the collected thermometric data were processed, and the solution to the heat diffusion equation underground allowed us to determine the average distribution of temperature at different depths over time. This study provides a more detailed conceptual model of the temperature distribution in the Piedmont Po Plain. The model can be applied to other areas with similar hydrogeological characteristics (e.g., the eastern Po Plain or large plain alluvial aquifers). The paper also furnishes a description of the physical processes of heat diffusion in the shallow aquifer, as supported by statistical analysis. The proposed methodology may be adopted as a simple statistical method for the assessment of temperature values for the low-enthalpy geothermal exploitation of groundwater resources.