## 1 Introduction  
Uranium ore mining and processing facility activities can lead to the uncontrolled migration of heavy metals, radioactive elements, and other toxic compounds, followed by groundwater pollution and entry into water sources and surface water bodies. Groundwater contamination by natural actinides--uranium and thorium--is a particular problem due to their long half-life and high toxicity [1].  
A significant contribution to groundwater pollution is made by facilities with large volumes of solid wastes, tailings, and sludge repositories, which form potential environmentally hazardous sites on the surface. Due to infiltration from atmospheric precipitation, heavy metals, acid anions (sulphates and nitrates), and radioactive elements enter the groundwater of shallow aquifers through the walls and bottom of storage facilities for a long time [2; 3]. In the described cases, high uranium migration and groundwater contamination are controlled by the main components of the filtrate, which provide a high redox potential (nitrate and sulphate), uranyl ion complexation, and colloidal and pseudocolloidal transfer with particles of clays and metal oxides (iron, manganese, and chromium). Additionally, underground microbiota play a significant role in uranium immobilization via the processes of enzymatic reduction [4; 5], sorption on biofilms [6; 7; 8], and biomineralization [9; 10; 11; 12; 13]. It should be noted that the main components of liquid wastes entering underground ecosystems are additional electron donors or acceptors that affect the development of microbiological processes (denitrification, sulphate reduction, iron reduction, etc.) and can indirectly affect uranium mobility significantly in underground aquifers [14; 15; 16].  
While many treatment methods have been developed and effectively used for soil and surface water pollution, such methods are difficult to apply for deep aquifers, and they tend to have limited effectiveness in preventing pollution spread under \"slurry wall\" conditions [17]. Slurry wall configurations restrict the movement of contaminated water without pollution neutralization. The use of microbial methods for the purification of aquifers can lead to significant complex effects--the complete removal of nitrogen compounds, the immobilization of sulphur in compounds with heavy metals, and the creation of optimal reducing conditions for uranium immobilization. This approach is currently being used successfully to clean contaminated sites [18; 19; 20; 21; 22].  
We studied groundwater taken from depths of 5-10 m near the sludge pond of the Novosibirsk Chemical Concentrates Plant (NCCP), one of the world's leading producers of nuclear fuel for atomic power plants and research reactors in Russia and foreign countries, as well as of lithium and its salts. Since the beginning of plant operation in 1950-1951, over 100,000 tons of low-activity solid wastes have accumulated in sludge ponds at the facility. Over the 65-year facility history, the areas of the sludge repositories have exhibited permanent groundwater pollution by sulphate and nitrate anions, uranium, and a number of heavy metals. The uranium concentration in the liquid phase of the slurries varies depending on season and ranges from 2-4 mg/L. Long-term observations indicate that contaminated water has filtered into the first aquifer. This contaminated water mixes with natural water, which leads to a multiple dilution effect. The contents of pollutants in water outside the NCCP industrial site do not exceed the existing standards' MACs (maximum allowable concentration).  
The main purpose of this work is to study biogeochemical processes in technogenic and natural underground NCCP systems contaminated by nitrate, sulphate, and uranium to develop an integrated approach for remediation using microbiological and microbiologically mediated mechanisms for pollutant immobilization.