A study on the seasonal variation of uranium in groundwater of hard rock terrain in south India

1. 2 A study on the seasonal variation of uranium in groundwater of hard rock terrain in south India Prof. S. Chidambaram Department of Earth Sciences Annamalai University

2. The element uranium (U) is distributed throughout the crust of the earth in trace quantities in all the rock types. • It is rich in acid igneous rocks like granites, syenites etc. while depleted in basic and ultra-basic rocks. • The average concentration of U in Earth crust is 2.7 ppm (Siegel and Bryan 2004). • In nature, U generally occurs in tetravalent state as insoluble species and hexavalent state as highly soluble species. • Uranium concentrations in most of the groundwatersare generally low, typically in the range of 0.1 to1 ppb, but it can reach several tens to hundreds of ppb when it reacts with U rich minerals in the aquifers. • Uranium concentration in groundwater is important in understanding the radiological impact valuation to secure the standard of life.

3. A simplified list of different uranium deposits with examples along with the share of such deposit types in the uranium inventory (after Dhalkamp, 1993 and IAEA, 1996)

4. Time bound characteristics of Uranium deposits (Modified after Simov 1979) Uranium exploration, spanning over 50 years within the 3.28 million square km area in the Indian shield has brought out the presence of uranium deposits of all major types in different geological settings. Distribution of Indian Uranium resources

5. Worldwide Uranium concentration in water

6. Geological map of India (GSI 1995) showing Uranium deposits/occurrences

7. Study area map with classification of blocks (CGWB 2007)

8. The geological succession of the study area Lithology map of the study area

9. Lineament map of the study area Water level map of the study area (amsl) Landuse map of the study area Drainage map of the study area

10. Flow chart for methodology

11. Maximum, Minimum and Average of the Chemical constituents in groundwater representing all four sampling seasons (All Values in mgl-1 except EC in μscm-1 and pH)

12. (a) (b) (c) (d) Spatial distribution of EC (µs/cm) for a)PRM, b)SWM, c)NEM and d) POM with sampling points

13. The order of dominance of cations and anions in different seasons

14. Summary of Geochemical classification by WATCLAST Program for all four seasons (Chidambaram, et al 2003)

15. Box Plot for U in groundwater samples in different seasons U (ppb) PRM- Granite > Quartzite > Fissile hornblende biotite gneiss > Charnockite > Flood Plain alluvium SWM- Granite > Flood Plain Alluvium > Quartzite > Fissile hornblende biotite gneiss > Charnockite NEM- Granite > Flood Plain alluvium > Charnockite > Quartzite > Fissile hornblende biotite gneiss POM- Granite > Charnockite > Fissile hornblende biotite gneiss > Flood plain alluvium > Quartzite

16. Schematic of U concentration distribution along a groundwater flow path. (Revised from Ivanovich et al. 1991).

17. Spatial distribution of U (ppb) and lineaments for all seasons a) PRM, b) SWM, c) NEM and d) POM

18. Maximum, Minimum and average values of 222Rn (Bq/l) for four seasons of different lithologies Granite> Quartzite> Fissile hornblende biotite gneiss> Charnockite> Flood Plain Alluvium

19. (a) (b) Spatial distribution of 222Rn (Bq/l) for groundwater samples of all seasons a. PRM; b. SWM; c. NEM, d. POM (d) (c)

20. Plot between U Vs 222Rn in groundwater

21. The mechanism for identification of major process for all samples (Gibbs 1970) Chadha’s geochemical process evolution plot Piper plot exhibiting the chemical facies of groundwater samples for different seasons

22. Weathering Plot of U vs pH in groundwater samples of all seasons Plot of U vs EC in groundwater samples of all seasons Groundwater with more resident time Open system Plot of U vs HCO-3 in groundwater samples of all seasons Plot of pCO2 Vs U in groundwater samples of all seasons

23. Plot between ORP and U in groundwater for all seasons Correlation coefficients of U with other parameters

24. Box plot for temperature irrespective of seasons Plot of U vs Temperature in groundwater samples of all seasons

25. Stacked plot for average concentration of Heavy metals in different seasons Correlation analysis of U with Heavy metals

26. Evaporation dominant Precipitation dominant Plot for δ18O versus δD of groundwater samples compared with GMWL and LMWL Plot for d-excess versus δ18O permil data of groundwater samples

27. Plot for δ18O versus U for groundwater samples Plot for d excess versus U for groundwater samples U (ppm) d excess

28. Factor analysis of PRM samples (Varimax rotated) Factor analysis of SWM samples (Varimax rotated)

29. Factor analysis of NEM samples Factor analysis of POM samples

30. Spatial distribution of dominant regions of four factors irrespective of all seasons

31. (A) (B) Comparison of dominant factor with a. Lineaments, b. Water level, c. Lithology and d. Land use maps (D) (C)

32. Species is specific forms of an element, differing in oxidation state and exhibiting characteristic chemical reactivity and stability. • the speciation of ions in groundwater is very important to understand its hydrogeochemical evolution. • Speciation of Uranium is very important as it determines the availability and toxicity in water. • Each species will vary in its tendency to hydrolyse, sorb or combine with other species depending on its size and charge considerations. The order of dominance of U species in groundwater with maximum values are as follows PRM - UO2 (CO3)22- >UO2 (CO3)34->UO2 (HPO4)22->UO2CO03 SWM - UO2 (HPO4)22-> UO2 (CO3)22- >UO2 (CO3)34- >UO2CO03 NEM - UO2 (CO3)22- >UO2 (HPO4)22-> UO2 (CO3)34- >UO2CO03 POM - UO2 (CO3)22- >UO2 (CO3)34->UO2 (HPO4)22->UO2CO03

33. Plot of pH vs U species(ppm) irrespective of seasons

34. (b) (a) (c) (d) Spatial distribution of U species (ppm) for a) PRM, b) SWM, c) NEM and d) POM

35. Eh-pH plot for U species in groundwater in all seasons

36. (b) (a) (c) (d) Correlation coefficients of U species (ppm) and other parameters for a) PRM, b)SWM, c)NEM and d) POM

37. (a) (b) (c) (d) Variation of Saturation index of U minerals with total U for a) PRM, b) SWM, c) NEM and d) POM

38. CONCLUSIONS • U is highly correlated with 222Rn indicates the U may be the source for 222Rn in groundwater during PRM, SWM, NEM but it is noted that there is no significant correlation in POM. • The negative relation of pH with Mg indicates the dominance of ion exchange processes. • There are mainly two conditions prevailing in this region viz., enrichment of δ18O with low U content and depleted δ18O with high U content. • The higher concentration of U is observed in depleted δ18O samples. This is observed due to the direct relation to recharge from precipitation or due to weathering induced factor. • Using factor analysis four major processes has been identified 1. Anthropogenic and ion exchange processes, 2. Weathering processes, 3.Radionuclides dissolution processes and 4. Fluoride dissolution processes. • The spatial distribution of these processes for all seasons has been plotted to identify the hidden sources which shows that lineament, water level, land use and lithology are the major driving forces for change in chemical composition of groundwater. • The dominant species of Uranium in the study area during PRM and POM is UO2 (CO3)22- and in SWM and NEM is UO2 (HPO4)22-.