ARSENIC IN DEEP GROUNDWATER: INSAR AND HYDROMECHANICAL MODELING IN THE MEKONG DELTA LAURA E. ERBAN

Transcription

1 ARSENIC IN DEEP GROUNDWATER: INSAR AND HYDROMECHANICAL MODELING IN THE MEKONG DELTA LAURA E. ERBAN

2 ARSENIC IN ASIA

3 COMMON ARSENIC SOURCE

4 STUDY AREA MEKONG DELTA

5 MEKONG DELTA CAMBODIA VIETNAM Data source: DWRM arsenic survey

6 THE MEKONG DELTA Dry season ENVISAT imagery courtesy of spaceinimages.esa.int Wet season MODIS imagery courtesy of NASA images

7 VILLAGE-SCALE Mekong river Photos: L. Erban

8 VILLAGE-SCALE Photo: L. Erban

9 VILLAGE-SCALE Mekong river Arsenic data source: RDI Cambodia

10 ARSENIC MOBILIZATION well land surface water table microbe iron oxide As carbon

11 ARSENIC MOBILIZATION well land surface water table microbe As microbially-mediated reductive dissolution

12 ARSENIC MOBILIZATION well land surface water table microbe As microbially-mediated reductive dissolution

13 ARSENIC MOBILIZATION well land surface water table microbe As microbially-mediated reductive dissolution

14 ARSENIC MOBILIZATION well land surface water table microbe microbially-mediated reductive dissolution

15 ARSENIC MOBILIZATION IN THE LANDSCAPE Mekong river Arsenic data source: RDI Cambodia

16 SHALLOW ARSENIC CONTAMINATION wetland arsenic plume confining clay aquifer

17 REGIONAL-SCALE ARSENIC Erban et al., 2013, PNAS

18 REGIONAL-SCALE ARSENIC Focus area Erban et al., 2013, PNAS

19 ARSENIC ACROSS BASINS Erban et al., 2013, PNAS

20 THE FOCUS AREA Shallow zone Deep zone : Holocene-Pleistocene, million years ago : Pliocene-Miocene > 2.6 million years Erban et al., 2013, PNAS

21 THE FOCUS AREA Shallow zone Deep zone Erban et al., 2013, PNAS

22 THE FOCUS AREA Deep zone pumping Deep zone arsenic Erban et al., 2013, PNAS

23 WATER FOR PUMPING WELLS water level well screen

24 WATER FOR PUMPING WELLS water level overburden

25 WATER FOR PUMPING WELLS land subsidence water level clay compaction overburden

26 COMPACTION-INDUCED ARSENIC CONTAMINATION Erban et al., 2013, PNAS

27 SUPPORT FOR A DEEP SOURCE HYDROMECHANICAL MODELING Erban et al., 2013, PNAS

28 MONITORING THE SYSTEM RESPONSE TO PUMPING well nest Hydraulic head (m) Data source: DWRPIS

29 HYDROMECHANICAL MODELING: PUMPING SCHEDULE Erban et al., 2013, PNAS

30 SIMULATING THE SYSTEM RESPONSE TO PUMPING Erban et al., 2013, PNAS

31 SIMULATED SUBSIDENCE Subsidence rate (cm/yr) Erban et al., 2013, PNAS

32 CONFIRMING SIMULATED SUBSIDENCE Subsidence rates Observed Simulated? Erban et al., 2013, PNAS

33 CONFIRMING SIMULATED SUBSIDENCE Observed Approach:? Interferometric Synthetic Aperture Radar InSAR

34 MEASURING SUBSIDENCE USING INSAR Pass 1 Pass 2 ϕ 1 ϕ 2 λ Δϕ Δz = Δϕλ 4π

35 INSAR IN THE DELTA flood radar wave young rice mature rice

36 MAJOR SOURCES OF INSAR ERRORS Topographic Orbital Atmospheric

37 MINIMIZING INSAR ERRORS THROUGH STACKING interferograms data n ALOS PALSAR: time interval for all interferograms: 1 year

38 SELECTING HIGH QUALITY INSAR ESTIMATES levee paddy InSAR amplitude Ho Chi Minh City Mekong river

39 INSAR-BASED SUBSIDENCE ESTIMATES

40 INTERCOMPARISON OF SUBSIDENCE RATES InSAR InSAR, upscaled Simulated cm/yr Erban et al., 2013, PNAS

41 OTHER AREAS OF COMPACTION-INDUCED ARSENIC? Erban et al., 2013, PNAS

42 FINDINGS 3) InSAR as a reconnassaince tool 4) InSAR success in challenging region 1) Pervasive, deep arsenic in wells in the Mekong Delta 2) New mechanism of arsenic contamination

43 IMPLICATIONS FOR WATER RESOURCES MANAGEMENT Understand deep arsenic Site wells strategically Treat or blend contaminated groundwater Limit intensive extraction

44 Thank you! And thanks to: CUAHSI Steve Gorelick Scott Fendorf Howard Zebker DWRM, Vietnam DWRPIS, Vietnam Contact info: UPS Foundation and School of Earth Sciences, Stanford National Science Foundation (EAR ) Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.