Problems with contaminated sites exist in most European countries and important for Republic of Moldova. The inventory of old pesticide storages in Moldova, executed in 2009 – 2010 years, showed a large quantity of POPs contaminated sites. The risk assessment of contaminated sites provided their ranking and high risks. Despite the realized projects the area of POPs management, still a lot needs to be done for the remediation. In situ soil treatment is a good approach because leaves the soil structure intact, reduces the potential migration of contaminants through soil and water systems, for example in situ bioremediation, phytoremediation, or natural attenuation. In this case, the soil structure is not dramatically transformed and there are no limitations for its future use, as these techniques aim to reduce the total quantity of contaminants in the site. The case study for one POPs contaminated site is presented in this presentation. The toxic substances were studied for the different zones of the selected site for the delineation of different contaminated zones and risk assessment procedure. The interval of the total concentration of POPs substances in soil is changed from 0.31 to 214.9 mg/kg dry soil. The composition of the indigenous population of microorganisms involved in nitrogen transformation and survived in the hard conditions of a long-term toxic stress of contaminated soil was determined for the elaboration of the remediation approach. An analysis of microbial population revealed that the total number of these microorganisms in the polluted soil (5.31x106CFU/1g dry soil) was by 5.3 times lower than in the reference soil. It has been observed that, under the long-term influence of the toxicants, the restructuring of the soil microbial cenosis took place in the direction of the decrease of the microbial diversity, but with the appearance of more resistant species. The number of bacteria involved in nitrogen transformation processes (bacteria that assimilate mineral nitrogen, oligonitrophilic and ammonifying bacteria) was reduced in polluted soil in 3-8 times in compare with the reference soil. The number of micromycetes and Azotobacter spp. was small, the representatives of the group of actinomycetes were not observed. The preliminary laboratory experiment by the bioremediation showed that the contamination spectrum and concentration as far as the soil microbiological diversity should to be determined for the appropriate remediation project design.