groundwater exploitation and arsenic occurrence in the

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: lerban@stanford.edu