1. Vermelding onderdeel organisatie June 17, 2015 1 Modeling subsurface iron removal Geochemical modeling of subsurface aeration at Schuwacht Lekkerkerk Harmen van der Laan Faculty of Civil Engineering Msc. Water Management Specilization Drinking Water

2. June 17, 20152 Content Subsurface iron removal Objective research Results Conclusions Next steps & Recommendations

3. June 17, 20153 Content Subsurface iron removal Objective research Results Conclusions Next steps & Recommendations

4. June 17, 20154 Subsurface iron removal O 2 front C/C 0 0 1 injected water O 2 front injected water Fe 2+ front C/C 0 0 1 Fe 2+ front C/C 0 0 1 0 1 Fe 2+ front injected water InjectionExtraction

5. Measured data 5June 17, 2015

6. 6 Measured data July 1998 – June 2000 March 2004 – June 2005

7. ‘Original’ Model 7June 17, 2015 V/V i

8. Expanded model 8June 17, 2015 main limitation original model No explanation for the phenomena of the increasing spread of the (iron) front over the successive cycles

9. June 17, 20159 Content Subsurface iron removal Objective research Results Conclusions Next steps & Recommendations

10. Objective The objective of this research project is to Find a theoretical foundation to explain the development of the iron front over the successive cycles Enhance the existing model to obtain a proper description of the measured iron concentrations 10June 17, 2015

11. 11 Content Subsurface iron removal Objective research Results Conclusions Next steps & Recommendations

12. June 17, 201512 Results I.Goethite / Ferrihydrite II.Ion exchange vs. Adsorption III.Transport modeling

13. June 17, 201513 Goethite vs. Ferrihydrite Ferrihydrite Hfo, FeOH 3, Fe 5 HO 8 ·4H 2 O Unstable, unstructured Amorphous / Aquaeous Spec. area ≈ 600 m 2 /g 2 sites / nm 2 pH PZC 8.1 Solubility log K = 2 – 4.5 Observed by: KIWA Research Goethite α -FeOOH Stable Crystalline Spec. area ≈ 60 m 2 /g 2 - 10 sites / nm 2 pH PZC 8.7 Solubility log K = -1 Observed by: Mettler (2002)

14. June 17, 201514 Surface complexation theory OH + / - depends on pH Number of sites Surface area Fe 2+

15. June 17, 201515 Site density

16. June 17, 201516 Surface characterization

17. June 17, 201517 Goethite vs. Ferrihydrite ? Variations in site density and surface area only result in small bandwidth Differences between Goethite and Ferrihydrite not the main limitation α -FeOOH Ferrihydrite ‘solubility’ decreases in time

18. June 17, 201518 Results I.Goethite / Ferrihydrite II.Ion exchange vs. Adsorption III.Transport modeling

19. Exchange June 17, 201519

20. Exchange June 17, 201520 Exchange and adsorption hard to distinguish Exchange capacity = lumped parameter Empirical formula does not give correct output

21. June 17, 201521 Results I.Goethite / Ferrihydrite II.Ion exchange vs. Adsorption III.Transport modeling

22. June 17, 201522 Retardation / Front spreading

23. June 17, 201523 Microdispersion Macrodispersivity Injection well

24. June 17, 201524 Dispersion

25. Stagnant zones June 17, 201525

26. Stagnant zones June 17, 201526

27. June 17, 201527 Results Subsurface iron removal Objective research Results Preliminary Conclusions Next steps & Recommendations

28. Preliminary Conclusions Objective is: Theoretical foundation and a better model I.Many ‘flavors’, but I need too pick one II.Model starts to describe the correct retardation mainly because of dispersion / stagnant zones June 17, 201528

29. June 17, 201529 Possible explanation Ferric iron I.Kinetics: decrease SI in time / combination Ferrihydrite – Goethite II.Stagnant zones III.Or: Biological activity? Complexes? Change groundwater composition?

30. June 17, 201530 Next steps & Recommendations Next steps Tracer in groundwater for dispersion? Implementation stagnant zones Influence conclusions on accumulation Finish model Recommendations Column experiments: separate transport model from geochemistry Research Ferrihydrite / Goethite

31. June 17, 201531 Questions?