A study was performed to evaluate the current permafrost and groundwater conditions in the reclaimed floodplain of the Lena, one of the largest rivers in the permafrost zone. Data from ongoing hydrogeological monitoring were compared with earlier observations conducted during the reclamation process. The results demonstrate that the placement of dredged fill led to the development of suprapermafrost thaw zones (taliks). The anthropogenic taliks vary in thickness from 10 to 15 m in areas of buried bars to 20 m or more in the former locations of oxbow lakes. There is similarity in seasonal groundwater fluctuation patterns and response to river stage variations across the study area suggesting that a continuous aquifer connected to surface water. The connection with the river is most evident during the spring flood period. Two mechanisms of ground saturation are identified during this time. One is lateral seepage flow from the Lena River into the fill mass. The zone of its influence is limited to 150–170 m from the stream. The second is hydraulic pressure transmission from the river through the subchannel flow connected with the anthropogenic suprapermafrost aquifer. Its influence extends across the entire fill area. Continuous water movement at the base of the fill prevents permafrost aggradation from below. The study results should be taken into account when developing and implementing design and construction standards for engineering structures in the reclaimed floodplains of the permafrost zone.

In this study, we reviewed and summarized the data on permafrost and groundwater areas of Central Yakutia to understand the formation and distribution of subpermafrost mineral waters of sodium bicarbonate and chloride-bicarbonate types, and to evaluate their potential use for medical purposes. Analysis of the data indicated that these low-mineralized groundwaters are basic analogues to the Maykop and Karachi mineral waters, with no particular bioactive components. These mineral water types contain 400 to 1200 mg/dm3 bicarbonates, 100 to 600 mg/dm3 chlorides, 50 to 250 mg/dm3 (Karachi) and <50 mg/dm3 (Maykop) sulfates, 400 to 800 mg/dm3 sodium, and <10 mg/dm3 calcium and magnesium. The formation of sodium bicarbonate and chloride-bicarbonate type water in Central Yakutia is influenced by permafrost which promotes concentration of major chemical components under the cold temperatures and slow groundwater circulation. The study of minor and trace constituents indicates that the subpermafrost waters in the study region contain fluorine and lithium in excess of the drinking water standards but are potentially appropriate for balneotherapy. Further research on the bio-physiological effects of subpermafrost waters with elevated fluorine and lithium concentrations contribute to the development of the spa and health resort industry in Yakutia. Moreover, the study will expand the balneological spectrum of disease prevention and treatment for the benefit of residents of Yakutia and the adjacent regions.