Hydrology

Dissolved Organic Carbon (DOC) (mM)

DOC

0 0.4 0.8 1.2

Methane

0 2 4 6 8 1 0

Inorganic (DIC) and Methane (mM)

DIC

Dissolved Carbon

20

40

60

80

100

120

140

160

180

Depth(m)

Bomb C-14

Tr/He ~35yrs

InorganicCarbon

OrganicCarbon

30m19m3mMethanogenesis

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

40002000

Radiocarbon A

ge

Carbon Isotopes

• Inflow of young carbon

• Young carbon drives biochemistry

• Mixture of young and old carbon is not the result of pore water mixing, but mobilization of old organic carbon

13C0/00

Hydraulic Characteristics at Intensive Site

0

May 01

-10

Jan 02

Relative Head (mm difference4 from head at 19m)

-100-200 1000-300

May 01

0δ18O(per thousand)

-1-2-3-40 2E-04 4E-04

4.7E-05

3.6E-042.5E-04

8.2E-05

2.2E-04

1.8E-04

1.2E-04

2.4E-04

3.9E-04

7.2E-05

3.9E-05

Clay

?

Clay

0

20

80

60

40

100

160

140

120

.Hydraulic Conductivity (m/s)

Depth(m)

Depth-wise variation of stable water isotopic values at the filed site

Monitoring Rice field

Pumping

River Exchange

ExchangeWith River

Ponds

Model

Aquifer:

Sdha

dt= hf − ha( )K f f f + hp − ha( )K p fp + hr − ha( )Kr fr + hv − ha( )Kv fv − qI − favαvET0

Village: Sydhv

dt= ha − hv( )Kv − 1− fav( )αvET0 + R

Field: Sy

dhf

dt= ha − hf( )K f −α f ET0 + R +

qI

f f

Pond: ( ) RETKhhdt

dhpppa

p +−−= 0α

Case-A Case-B

Village ETtree from clay aquifer

Kf (1/d) [conductance for field] 8.9x10-4 8.9x10-4

Kv (1/d) [conductance for village] 6.3x10-6 9.1x10-4

Kp (1/d) [conductance for pond] 9.3x10-3 8.3x10-3

Kr (1/d) [conductance for river] 7.7x10-2 8.7x10-2

Objective Function w/ pumping 5.9x10-1 5.7x10-1

w/ pumping 19 13ResidenceTime (yrs) w/o pumping 42 22

Table 1. The estimated conductance parameter values whenthe storage coefficients are fixed, the respective objectivefunctions (sum of square errors), and modeled residence timesfor the aquifer.

Case A: Village ET out of ClayKf Kp Kr Kv Sy S CV

Kf 1 0.15Kp -0.17 1 0.09Kr -0.31 0.04 1 0.10Kv -0.34 0.02 -0.22 1 0.77Sy -0.26 0.02 -0.29 0.92 1 0.14S -0.24 -0.07 0.81 -0.15 -0.19 1 0.13

Case B: Village ET out of AquiferKf Kp Kr Kv Sy S CV

Kf 1 0.18Kp -0.11 1 0.09Kr -0.39 -0.06 1 0.11Kv -0.36 0.10 -0.07 1 0.08Sy -0.36 0.11 -0.10 0.79 1 0.09S -0.26 -0.14 0.83 -0.16 -0.22 1 0.15

Case A: Village ET out of ClayKf Kp Kr Kv CV

Kf 1 0.11Kp -0.18 1 0.10Kr -0.28 0.29 1 0.11Kv -0.30 0.01 0.09 1 5.45

Case B: Village ET out of AquiferKf Kp Kr Kv CV

Kf 1 0.10Kp -0.21 1 0.10Kr -0.31 0.23 1 0.10Kv -0.11 0.05 0.00 1 0.06

Transient Three-Dimensional Flow Model

Pond cells

River cells

Irrigation wells

Irrigated rice areas

Drinking wells Other agriculture area

Village areas

114 row and columns 15 layers

Area of interest

Frequency

Median age of 66 years with irrigated agriculture

240 years without irrigated agriculture

Estimated Groundwater Age Distribution

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

40 200 360 520 680 840 1000 1160 1320 1480

Groundwater Age (years)

w/ irrigated agriculturew/o irrigated agriculture

+

Estimated Groundwater Age Distribution at 30-m

• Arsenic concentrations are subject to change and irrigation pumping is sufficient to have significantly changed flow paths, drawing young water and chemicals into the aquifer.

• Geochemical parameters at our site are consistent with a scenario of concomitant arsenic release and organic carbon oxidation.

• Deeper wells have the potential to alleviate the problem, but could also become contaminated.

Conclusions

Tremendous disparity with US groundwater contamination problems• In the developed world people don’t drink seriously contaminated groundwater when contamination is known.

• Relative to US, efforts to understand the physical and chemical processes are not funded.

Need a serious scientific/engineering program

People

Chris SwartzNicole KeonWinston Yu

BUETBorhan BadruzzamanAshraf AliFeroze AhmedKhandaker AshfaqueJenny Jay

Dan BrabanderPeter OatesHarry Hemond

MIT

U. CincinattiShafik Islam

Roger BeckieVolker Niedan

Future directions

• Arsenic in agriculture and food chain

• Combined surface-water groundwater management pathogens vs. arsenic

Can these be done without a detailed hydro-bio-geo-chemical model?

• Arsenic in other regions in AsiaDoes Bangladesh indicate the future?

Field Site

100-m

Agriculture Areas40% boro rice71% irrigated

Irrigation Wells

P P

P

PP

PP

PP

PP

P

P

P P

P

PP

P

P

P

P

PP

P

P P P

P

P

P

MIT/BUET/NSF Arsenic ProjectSmall N2 glove bag at night