Seasonal variations of subsurface humidity around a water storage pool in rural Ecuador assessed with electrical resistivity and ground-penetrating radar

Abstract:

Water management plays an important role in supplying populations with clean water for agriculture, livestock and human consumption. Hence, investigation of the quality of aquifers, watercourses and storages and their potential pollutants is important for communities all over the world. Here, we used electrical resistivity and ground-penetrating radar (GPR) combined with water chemistry analysis to evaluate the condition of a possibly contaminated open water-storage pool in Urcuqui in rural northern Ecuador. The geophysical survey results from 2017 showed that the areas with low resistivity values and high reflectance in GPR match with the dense vegetation patches on the surface. This clearly demonstrated that the channel to the pool was either blocked or broken, creating a distinct leakage pattern around the pool. After 2017 a small new channel was dug to the pool allowing the water to flow freely again. Monthly electrical resistivity measurements between October 2018 – February 2019 revealed that the subsurface water content shows fluctuations with areal precipitation. Furthermore, the electrical resistivity portrays lowered values below the pool at a location of topographical low during very rainy months. This we interpret as a signal of leakage. The water storage pool overflows when the pool is full of water. Physicochemical and biochemical analyses showed that the water flowing through the ditch is not suitable for human consumption due to its elevated content of BOD and coliforms. However, these values are below the lower limit of greywater and therefore the water is suitable for agriculture and livestock usage.