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Bangladesh Arsenic Case Study


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Source: Ahmed (2002)

Persons(per unit)

Unit Cost($)

Option Cost per arsenicosiscase avoided

Deep Tubewell $500 - 790 250 $2 - 3 $30 - 50

Dug Well $560 - 620 125 $4.5 - 5 $65 - 70

Pond Sand Filter $400 - 600 250 $2 - 4 $35 - 65

Rain Water $100 - 200 5 $20 - 40 $350 - 630

Household Treatment $5 - 50 5 $3 - 20 $55 - 330

Piped Supply $30,000 2000 $17 $280

Cost perPerson ($)

Cost comparison


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Extent of Contamination

and Health Effects


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Predicted National Rates of Arsenicosis and Cancer

125,000 people ( 0.1%)

3,000 people/yr

1,860,000 people (1%)Arsenicosis

Skin Cancer

Internal Cancers

West Bengal Dataour model fit

Taiwan Dataour fit

Taiwan DataNRC model f it

150m Wells Remedy

690,000 people (0.57%)

37,000 people (0.04%)

800 people/yr

Present Conditions

The 150m well remedy: Replaces 30% of the nations wells That is 800,000 wells at a cost of $500/well Total cost of $395,000,000

$340 per reduction in arsenicosis prevalence


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0 352515 3020105

0

2.5

1.5

0.5

3

2

1

Age of Well (years)

Groundwater Arsenic Concentrationvs. Age of Well

Each point represents an average of ~200 wells.Wells were sampled in 1997-1999.

Concen

tra

tion

(ln

-pp

b)


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Big Basic Questions:Why are dissolved arsenic levels so high?

Where does it come from? -- Little solid phase arsenic Why isnt it flushed away? -- Flow + Little retardation

Why are arsenic concentrations so variable on small scales?

Important Questions for Decision Making:Will arsenic concentrations change?Can deep aquifers provide a long-term solution?

Key Scientific Questions:What is the solid state of arsenic?How do shifts in water chemistry affect arsenic mobility?

????


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MIT/BUET

Field Site


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Padma River

Dhaleswari River

Field Site5 km


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Biogeochemistry

Arsenic Profile


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CoreSurfaceClay

Sand

Clay

Sand

15 Piezometers0

20

40

60

80

100

120

140

160

Depth(m)

0 2 4 6 8 10

Solid phase Arsenicug/g or ppm

0 400 800

Dissolved As (ppb)

Arsenic Profile

Solid FeSolid As


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Clay

0 200 400 600 800(moles/g dry wt.)

Clay

0 20 40 60 800

20

40

60

80

100

120

140

160

(nmoles/g dry wt.)

Depth(m)

Mostly Fe II(Except for magnetite)

Carbonates, AVS,amorphous oxides

Weakly adsorbedStrongly adsorbed

Crystalline Fe oxides,amorphous As

sulfidesSilicates, As2O3

Crystalline Sulfidespyrite

Arsenic Extraction Targets


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0

0.01 0.1 1 10 100 1000

Phosphate SilicateArsenic

80

160

(M)

Competing Anions

Depth

(m)

log saturation index (SI)


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1. quartz (SiO2) 2. Ca-phosphate

3. rutile (TiO2) 4. REE-phosphate

SEM Bangladesh aquiferDepth: 91Fraction: non-magnetic heavy

1

2

3

4

20 m

0

20

40

60

80

100

120

140

160

180

-2 0 2 4 6 8

g ( )

Ca5(PO4)3OH(Hydroxyapatite)

Fe3(PO4)2 (Vivianite)

CaCO3(Calcite)

FeCO3(Siderite)

Depth

(m)

Sulfur Chemistry


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D

epth(m)

0

20

40

60

80

100

120

140

160

180

0.1 1 10 100 1000 10000

SO4

H2S

As

H2S detection li mit

0.01 0.1 1 10 100

Solid phase Sulfur(umoles/g)

Total sulfur

AVS

Dissolved Sulfur (uM) and As (nM)

y

Dissolved Carbon


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0 2 4 6 8 10

20

40

60

80

100

120

401

601

180

0 0.4. 0.8. 1.2. 1.6. 2

Methane

DOC

DIC

Dissolved Organic Carbon (DOC) (mM)

Inorganic (DIC) and Methane (mM)

Depth

(m )

Arsenic Ammonium and Calcium


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0

20

40

60

80

100

120

140

160

180

0 1 2 3 4 5 6 7 8

Depth(m)

0 0.5 1 1.5 2.52 3

Dissolved As ( M)NH4

+ ( M x 10 )

Arsenic,Ammonium and Calcium

Dissolved Ca (mM)

Comparison of MIT field site to BGS national data set


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Comparison of MIT field site to BGS national data set

NH4 +( M x 10) As ( M)

2 4 61 3 5 70

210Calcium (mM )

A s

NH4

+

Ca

uns gan a c umA m m on ium

averag e a c u m

1.00 1.5 2.5

(mM )

1 10 100

Sulfat e ( M)

Ac id Volat ile Sulf ideTotal Solid Sulfu r ( mol/g)

AVS

Total solid phase S

0.1 1 10

average u ateuns gan u ate

2000 50 100 150 250

( M)Dissolved ( M)

80 2 4 6

20

40

60

80

100

120

140

160

1000

uns gan rsen c

Dissolved A s

Solid phaseA s

7525 50Solid (nmol /g dry wt .)

Depth (m )

average rsen c

0.80 0.2 0.4 0.6 1.0

( M)


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Arsenic in Withdrawn Water


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Arsenic in Withdrawn Waterafter Injection of Low-Arsenic Groundwater Water

0 100 200 300 400

hours

0

50

100

150

200

250

300

ppb

Original Value = 700 ppb

0 400 800

Dissolved As (ppb)

0

20

40

60

80

100

120

140

160

Depth(m)

Arsenic in Withdrawn Water after Injection of Nitrate


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0 400 800

Dissolved As (ppb)

0

20

40

60

80

100

120

140

160

Depth (m)

Injected Volume Removed

0

100

200

300

400

500

600

700

800

0 50 100 150 200 250 300 350 400 450

hours

ppb

Injectate: Nitrate Added to

High-Arsenic Groundwater


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Arsenic in Withdrawn Water after Injection of Molasses


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0

10

20

30

40

50

60

0 100 200 300 400 500

ppb

hours

Injectate: Molasses Added to

Low-Arsenic Groundwater

Original Value = 120 ppb

0 400 800

Dissolved As (ppb)

0

20

40

60

80

100

120

140

160

Depth (m)


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Carbon Isotopes


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InorganicCarbon

Organic

Carbon

30m

19m3mMethanogenesis

CaCO3

(Atmospheric valuesover last 50 years)

60m

14C0/00

-1000

-500

0

500

1000

-30 -25 -20 -15 -10 -5 0-70

Methane

Surface Water Carbon

0700

4000

2000

Radioc

arbonAge

Inflow of youngcarbon

Young carbon

drives biochemistry

Mixture of young

and old carbon isnot the result ofpore water mixing,but mobilization of

old organic carbon

13C0/00

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