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CONSOIL 2005 Chlorinated compounds in groundwater : space time evolution case studies

CONSOIL 2005 Chlorinated compounds in groundwater : space time evolution case studies. Philippe MONIER. Why monitoring ?. Groundwater monitoring answers several points : Precise hydro geological network Check on assumptions choice for DRA Control hydro geological model.

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CONSOIL 2005 Chlorinated compounds in groundwater : space time evolution case studies

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  1. CONSOIL 2005 Chlorinated compounds in groundwater : space time evolution case studies Philippe MONIER

  2. Why monitoring ? Groundwater monitoring answers several points : • Precise hydro geological network • Check on assumptions choice for DRA • Control hydro geological model So, monitoring has to answer questions ask during environmental studies. It’s not a goal in itself.

  3. Chlorinated compounds in groundwater During groundwater quality monitoring, chlorinated compounds show several space time evolution in regards of hydro geologic framework, chemical and physical conditions etc. As a result, we can’t follow a simple universal method for VOC groundwater monitoring and each case needs to know what happen during transportation of VOC in the plume.

  4. What happened during flow ? • Pollutant transport in groundwater occur under effect of two phenomena main types : • Hydro geological main parameters : • advection • dispersion • Chemical parameters • diffusion • retardation • degradation

  5. Lateral dispersion Longitudinal dispersion Hydrogeological parameters advection

  6. Chemical parameters : diffusion Pollutant flow High concentration Low concentration

  7. Chemical parameters : retardation grains Free TCE Dissolve TCE

  8. Chemical parameters : degradation

  9. Case 1 : Concentration vs. time in a well

  10. Case 1 : Concentration vs. time in plume cross section Concentration evolution during 10 years

  11. Case 1 : Plume evolution during 12 years TCE plume

  12. Case 1 : Plume evolution during 12 years VC plume

  13. Case 1 : noting VOC concentrations evolve in a same way for PCE, TCE, DCE and VC Plume don’t migrate down gradient after stopping reload Evolutions observed every where in the plume enable to the same conclusion There’s no specific evolution in specific point of the plume Monitoring takes place near source to follow concentration decrease

  14. Case 2 : Concentration vs. time in a well

  15. Case 2 : Concentration vs. time in a well

  16. Case 2 : noting VOC concentrations evolve in opposite ways for PCE, TCE, DCE and VC Evolutions observed in different point of the plume show different cases According to location in the plume, we can find new products (unknown near source) Monitoring takes place far down gradient of source to follow plume evolution and degradation

  17. Case 3 : longitudinal concentration evolution in a plume

  18. Case 3 : noting In this kind of plume, according to time, we can observed different evolution as case 1 and case 2

  19. So : for VOC groundwater monitoring, what can I do ? • In some case, evolution in each point of the plume are similar, so it’s easier to follow VOC concentration evolution near source to have high values. • In an other case, if we are sure that VOC degradation occur, the better monitoring take place down gradient of the source, to follow MNA and control congeneric concentration evolution. In this case, it’s better to go away from source

  20. VOC groundwater monitoring : right approach • Geological and hydrogeological frameworks have to be perfectly known • VOC space-time evolution must be determine to know whether MNA occur or not • With these results, we can determine best points for monitoring : on site or down gradient • And we can propose a right frequency This approach guarantees an cost-effective monitoring

  21. ATTENTION • VOC concentrations in groundwater answer to a sum of complex hydrogeological and chemical characters which work together or in opposite way. • For these reasons, we can’t determine VOC concentration evolution only with two or three successive results • We need several result to determine and understand what happened in a plume

  22. Concentration increase during one year Concentration decrease during one year TRI 350 300 250 200 Cas 1 TRI Stability during one year 150 100 Cas 2 50 Cas 3 0 23/12/88 07/05/90 19/09/91 31/01/93 15/06/94 28/10/95 11/03/97 24/07/98 06/12/99 19/04/01 01/09/02 Attention : real case teaching !

  23. Thank you for your attention …..

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