This article considers the problem of improving safety for reconstruction and restoration of historical buildings of 1898-1902s located in Telejnaya St., Saint-Petersburg. The multiple investigation of bearing constructions mentioned above buildings as well as their foundations was made. The geotechnical analysis of foundation soils of the buildings was carried out. The underground water contamination level was assessed, contaminant sources were found. Taking in consideration palustrain deposits widespread occurrence and the term of sewer leakage, microbiological examination of foundation soils of the buildings, groundwater and constructional materials (bricks, mortar, wood, out of service  waterproofing layer and other) were made. Abundance and species of micromycetes, aerobic and anaerobic bacteria were established. Change in microorganisms number with depth of foundation soils of the buildings depending from redox conditions was found. Reducing conditions with ORP (Oxidation-Reduction Potential)