design: After 16 months of the construction of the capping layers over the studied old unlined landfill (Sao Carlos, Brazil), solid waste samples were collected in 4 different sites and 2 different depths, totaling 8 samples (D11, D12, D21, and D22 were collected within the capped area, and F11, F12, F21, and F22 were collected outside the capped area). The depths considered for sampling at each site were 30cm deep (just after the landfill soil cover, where waste starts to appear) and 1m deep (depth considered to be still affected by the capping). DNA extraction from the collected solid waste samples was performed using the FastDNA SPIN Kit for Soil DNA Extraction (MP Biomedicals), using 0.5-g subsamples. It was also necessary to perform DNA purification, using the Geneclean  Turbo Kit (MP Biomedicals). After DNA extraction, the 16S rRNA genes of distinct regions (V3-V4 466 bp) were amplified using the domain bacteria (341F CCTAYGGGRBGCASCAG; 806R GGACTACNNGGGTATCTAAT) with the barcode. Sequencing libraries were generated usingTruSeq DNA PCR-Free Sample Preparation Kit (Illumina, USA) following manufacturer's recommendations and index codes were added. The library quality was assessed on the Qubit@ 2.0 Fluorometer (Thermo Scientific) and Agilent Bioanalyzer 2100 system. At last, the library was sequenced on an IlluminaHiSeq2500 platform and 250 bp paired-end reads were generated. The 16S rRNA sequencing and bioinformatics were performed by GenOne Biotechnologies, situated in Rio de Janeiro, Brazil.