Abstract: We measured the hydrochemical composition of leachate in phosphogypsum stock dumps and the surrounding groundwater in Mapingchang Town, Fuquan City, Guizhou Province, analyzed the pollution source of groundwater by principal component analysis, and then inferred the geochemical process of karst groundwater under the influence of leachate leakage by PHREEQC inverse modeling. Results showed that the leachate was strongly acidic. EC of the leachate was as high as 8750 μS·cm^-1. The main pollutants were TP, SO₄^2- and F^-. The leachate characteristics were mainly related to the wet phosphoric acid process. Facaidong groundwater (G1) was affected by the leakage from phosphogypsum stock dump, TP, SO₄^2- and F^- in which were much higher than the prescribed limit of GB 3838-2002 and GB/T 3838-93. Longjing groundwater (G10) was probably influenced by the surrounding factories (phosphate fertilizer factories and abandoned ordinary superphosphate factories). Both sites showed increasing SO₄^2- and decreasing HCO₃^-, and the hydrochemical type became SO₄-Ca. The rest of the sampling sites were HCO₃-Ca type, mainly from the natural geological waterrock reaction. The results from PHREEQC simulation showed that leachate speeded up the waterrock reaction and karst development. After PO₄^3- and Fe entered groundwater system, the hydroxyapatite, Fe(OH)₃, and vivianite would be formed under certain reaction conditions.

Key words: structure parameter, kilometer-scale evapotranspiration., similarity theory, microwave, near infrared