Geophysical evidence of water pollution treatment effectiveness in karst areas: a case study in Guizhou, China

Abstract Metals are a crucial resource for human society. However, the slag generated during smelting represents a serious pollution hazard for groundwater and the surrounding soils. Here, we evaluated the effectiveness of a groundwater contamination remediation project at two adjacent manganese slag storage sites in Guizhou Province, China. We applied three complementary geophysical methods—surface nuclear magnetic resonance (SNMR), electrical resistivity tomography (ERT), and self-potential (SP)—to compare groundwater conditions in January 2024, shortly after project completion, and July 2024, after a longer operation period. Using SNMR and ERT, we analyzed groundwater content and spatial distribution, while the SP method provided some dynamic information such as groundwater flow direction and gradient. Our SNMR results indicated a temporal decrease in groundwater content, consistent with an overall underground resistivity increase estimated from ERT data. This finding demonstrated that the drainage system constructed for the remediation project operated successfully, diverting most of the recharge water from the catchment area away from the slag storage sites. Consequently, the groundwater content in the study area, which was typically high in July, decreased considerably. Furthermore, SP differences indicated an alteration of groundwater flow direction caused by the drainage tunnels and ditches, with control by the regional flow field changing to a dominant influence of local microtopography. In summary, our results demonstrate that the remediation project successfully diverted groundwater and reduced the volume of groundwater flowing through the manganese slag storage sites. By minimizing water contamination, the project markedly reduced the volume of sewage necessitating treatment, along with pollution control costs.