Identifying sources of mixed groundwater contamination using PMF and stable isotopes: a case study of an industrial park

Groundwater contamination in industrial parks often involves overlapping inputs of nitrogen, chlorinated solvents, and dissolved salts, making source identification difficult. In this study, 45 shallow groundwater samples from a typical industrial park on the northern margin of the Hohhot Basin were investigated using hydrochemical analysis, PMF, and nitrate dual isotopes coupled with MixSIAR. The results showed pronounced salinity enrichment, high mineralization, elevated ammonium, and chlorinated hydrocarbon contamination. NH4+ exceeded the Chinese groundwater standard in 77.78% of samples, whereas vinyl chloride exceeded the WHO guideline value in all samples. Hydrochemical analysis indicated that groundwater chemistry still retained a water-rock interaction background, but had been significantly overprinted by anthropogenic inputs. PMF resolved six factors and showed that groundwater pollution was mainly controlled by high mineralization, high-ammonium wastewater input, and dissolved inorganic salt enrichment, whereas chlorinated-solvent industrial pollution had strong diagnostic significance. MixSIAR identified industrial wastewater as the largest nitrate contributor under both prior settings, followed by fertilizer-derived nitrification, whereas mountain-front soil background contributed comparatively less. These results indicate that the combined PMF-MixSIAR framework is effective for identifying mixed groundwater contamination in industrial parks.