The remediation of polluted sites with mixtures of hydrophobic organic contaminants (HOCs) is a challenge attracting the interest of researchers. In situ chemical oxidation (ISCO) has been successfully applied for this scope. However, ISCO takes place in the aqueous phase. The low solubility of HOCs in water limits the ISCO application, increasing the time needed to remove the contamination from heavily contaminated soils with HOCs. The simultaneous application of surfactants and oxidants (S-ISCO) has recently gained attention to overcome this disadvantage. The surfactant enhances the HOCs solubilization in the aqueous phase and improves the oxidation rate of HOCs.S-ISCO and ISCO technologies are proposed and validated in this work for treating chlorinated organic pollutants, COCs, present in the Sardas and Bailin landfills subsoil at Sabiñánigo (Huesca, Spain). The enormous environmental problem created by the lindane production in Sabiñánigo is explained in the introduction. The production process of lindane generated tons of solid and liquid wastes worldwide. Although lindane, as a pesticide, was extensively produced in the world during most of the 20th century, it came to be considered a highly toxic and dangerous compound and its production was eventually banned. The inadequate management of the production wastes from lindane has become a huge environmental problem. The presence of COCs in the subsoil of Saniñanigo landfills is due to the liquid wastes from lindane production dumped in unlined landfills decades ago...