Delimiting Pig Slurry Affected Subsurface Areas by Combining Geophysical and Geochemical Techniques

In Spain, livestock farming is a significant activity area that generates substantial revenues and essential jobs. However, the actual impact that this intensive activity might have on the environment is not entirely understood. Moreover, coastal aquifers are subjected to a significant environmental pressure due to nearby growing population, intensive agriculture, and livestock farming. In this work, three representative pig slurry ponds, under semiarid conditions, were studied using different techniques to evaluate the subsurface conditions in terms of pH, electrical conductivity, salts, and nitrate content. The electrical resistivity tomography (ERT) technique was employed in this study, which provides electrical resistivity values from the subsurface materials and fluids. These electrical resistivity values were compared to data obtained from geochemical analyses to derive their relationships and establish the pig slurry-affected subsurface area. Thus, ERT-based lower electrical resistivity values were associated with higher salts concentrations and nitrate content. ERT values indicated a near-surface affected by slurry infiltration that coincided with the increase of geochemical values obtained from sample analyses. Additionally, Spearman's correlation was used to evaluate the correlation between electrical resistivity data and the physical-chemical properties of soil. The most important pollutant accumulation mainly occurs in the two-meter depth. Therefore, the risk of slurry ponds affecting deep aquifers is limited in the studied area. Finally, this study proves a complete, affordable, and scalable methodology application to livestock residue storage facilities.