## 5 Conclusions  
The behaviour of uranyl ions in the shallow aquifers of the NCCP territory, if sufficient organic matter is present, can be determined from the contributions of aerobic and anaerobic microbial and geochemical processes. Microbial-mediated Eh reduction (due to aerobic microbial metabolism) is an important factor in the reduction of uranium and other heavy metals. It was shown by experiments that depending on the concentrations of nitrate and sulphate ions in solution, the kinetics of their reduction differ considerably, and uranium reduction is therefore delayed with its transformation to a solid phase.  
The forms of uranium migration, as evidenced by cascade filtration, depended on the chemical composition of the solutions, the Eh-pH environment, and the presence of microbial communities. In particular, the formation of microbial metabolites influenced the removal of uranium from the solution by forming bulky aggregates of more than 2.4 um, reducing the risk of uranium migration in colloidal and pseudocolloidal forms.  
We presented new data on changes in the amount and quality of biota during the transition from background conditions to the drainage flow of contaminated groundwater. In the water from the most polluted well, a maximum number of denitrifying and sulphate-reducing bacteria (e.g., _Sulfurimonus_) was detected. 16S rRNA gene analysis of the microbial community after whey addition demonstrated a catastrophic decrease in microbial diversity and the dominance of representatives of the genera _Rhodococcus_ and _Rhodobacter_. Physicochemical modelling of the stepwise processes affecting the distribution of transition elements between the solution and the solid phase showed that the precipitation of two types of compounds--phosphates (PO43- was supplemented with whey addition) and U(IV) oxides--promoted the removal of uranium. Oxides of U(IV) appeared when sulphate was reduced, and pyrite (black precipitate) formed. The experiments showed no formation of uranium-containing phosphates.  
It was concluded that the reduction of nitrates, sulphates, iron, and uranium could be activated successfully by adding nutritive solutions to microbial communities under conditions consistent with those of formation water in the NCCP region, suggesting the potential for the sustainable purification of contaminated aquifers by further in situ bioremediation.  
Conceptualization--A.V.S., A.E.B.; methodology--A.V.S., A.E.B., O.L.G., K.A.B., O.S.S. K.A.B.; formal Analysis--O.S.S., A.A.K., N.M.P.; data curation--A.E.B.; visualization--A.E.B., A.V.S., N.M.P.; writing--original draft preparation--A.V.S., A.E.B., O.S.S.; writing--review and editing--O.L.G., O.S.S.; supervision--O.L.G., A.E.B., A.V.S. All authors have read and agreed to the published version of the manuscript.  
The study was funded by the Russian Foundation for Basic Research, project 20-05-00602 A (fieldwork, cascade filtration, study of elemental speciation); the Russian Science Foundation, project 18-77-10029 (fieldwork, chemical analyses, sorption experiments); the State Assignment of the Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences (thermodynamic modelling).  
Not applicable.  
Data Availability Statement: Data is contained within the article or supplementary material.  
The authors declare no conflicts interests.