groundwater exploitation and arsenic occurrence in the
TRANSCRIPT
ARSENIC IN DEEP GROUNDWATER: INSAR AND HYDROMECHANICAL MODELING IN THE MEKONG DELTA
LAURA E. ERBAN
10.25.2013
ARSENIC IN ASIA
COMMON ARSENIC SOURCE
MEKONG DELTA
STUDY AREA
CAMBODIA
VIETNAM
Data source: DWRM arsenic survey
MEKONG DELTA
THE MEKONG DELTA
ENVISAT imagery courtesy of spaceinimages.esa.int
MODIS imagery courtesy of NASA images
Dry season Wet season
Mekong river
VILLAGE-SCALE
Photos: L. Erban
VILLAGE-SCALE
Photo: L. Erban
VILLAGE-SCALE
Mekong river
Arsenic data source: RDI Cambodia
water table
As
land surface
ARSENIC MOBILIZATION
well
iron oxide
carbon
microbe
water table
As
land surface
ARSENIC MOBILIZATION
well
microbe
microbially-mediated reductive dissolution
water table
As
land surface
ARSENIC MOBILIZATION
well
microbe
microbially-mediated reductive dissolution
water table
land surface
ARSENIC MOBILIZATION
well
microbe
microbially-mediated reductive dissolution
As
water table
land surface
ARSENIC MOBILIZATION
well
microbe
microbially-mediated reductive dissolution
ARSENIC MOBILIZATION IN THE LANDSCAPE
Mekong river
Arsenic data source: RDI Cambodia
SHALLOW ARSENIC CONTAMINATION
wetland
arsenic plume
aquifer confining clay
REGIONAL-SCALE ARSENIC
Erban et al., 2013, PNAS
REGIONAL-SCALE ARSENIC
Focus area
Erban et al., 2013, PNAS
ARSENIC ACROSS BASINS
Erban et al., 2013, PNAS
THE FOCUS AREA
Shallow zone
Deep zone
: Holocene-Pleistocene, 0-2.6 million years ago
: Pliocene-Miocene > 2.6 million years
Erban et al., 2013, PNAS
THE FOCUS AREA
Shallow zone
Deep zone
Erban et al., 2013, PNAS
THE FOCUS AREA
Deep zone arsenic
Erban et al., 2013, PNAS
Deep zone pumping
WATER FOR PUMPING WELLS
well screen
water level
WATER FOR PUMPING WELLS
overburden
water level
WATER FOR PUMPING WELLS
clay compaction
land subsidence
overburden
water level
COMPACTION-INDUCED ARSENIC CONTAMINATION
Erban et al., 2013, PNAS
SUPPORT FOR A DEEP SOURCE HYDROMECHANICAL MODELING
Erban et al., 2013, PNAS
well nest
MONITORING THE SYSTEM RESPONSE TO PUMPING
Hydraulic head (m)
Data source: DWRPIS
HYDROMECHANICAL MODELING: PUMPING SCHEDULE
Erban et al., 2013, PNAS
SIMULATING THE SYSTEM RESPONSE TO PUMPING
Erban et al., 2013, PNAS
SIMULATED SUBSIDENCE
Subsidence rate (cm/yr)
Erban et al., 2013, PNAS
CONFIRMING SIMULATED SUBSIDENCE
Simulated Observed
?
Subsidence rates
Erban et al., 2013, PNAS
CONFIRMING SIMULATED SUBSIDENCE
Observed
?
Approach: Interferometric Synthetic Aperture Radar InSAR
Pass 1 Pass 2
Δz
ϕ1 ϕ2
λ
Δϕ
MEASURING SUBSIDENCE USING INSAR
= Δϕλ 4π
young rice mature rice flood
radar wave
INSAR IN THE DELTA
MAJOR SOURCES OF INSAR ERRORS
Topographic Orbital Atmospheric
MINIMIZING INSAR ERRORS THROUGH STACKING
1 2 3
n
4
interferograms data
ALOS PALSAR: 2006-2010
time interval for all interferograms: 1 year
SELECTING HIGH QUALITY INSAR ESTIMATES
Mekong river
Ho Chi Minh City
levee paddy
InSAR amplitude
INSAR-BASED SUBSIDENCE ESTIMATES
INTERCOMPARISON OF SUBSIDENCE RATES
InSAR InSAR, upscaled Simulated
cm/yr
Erban et al., 2013, PNAS
OTHER AREAS OF COMPACTION-INDUCED ARSENIC?
Erban et al., 2013, PNAS
FINDINGS
2) New mechanism of arsenic contamination
3) InSAR as a reconnassaince tool
4) InSAR success in challenging region
1) Pervasive, deep arsenic in wells in the Mekong Delta
IMPLICATIONS FOR WATER RESOURCES MANAGEMENT
• Understand deep arsenic • Site wells strategically • Treat or blend contaminated groundwater • Limit intensive extraction
And thanks to: CUAHSI Steve Gorelick Scott Fendorf Howard Zebker DWRM, Vietnam DWRPIS, Vietnam UPS Foundation and School of Earth Sciences, Stanford National Science Foundation (EAR‐1313518 ) 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.
Thank you!
Contact info: [email protected]