Hydrology
Dissolved Organic Carbon (DOC) (mM)
Dissolved
Carbon
0
0.4
0.8
1.2
Tr/He ~35yrs
20
Bomb C-14
40
60
Depth
(m)
Methane
80
DIC
100
DOC
120
140
160
180
0
2
4
6
8
Inorganic (DIC) and Methane (mM)
10
Carbon Isotopes
1000
• Inflow of young
carbon
Surface Water Carbon
(Atmospheric values
over last 50 years)
500
• Young carbon
drives biochemistry
Inorganic
Carbon
C0/00
0
Methanogenesis
Methane
3m
19m
0
700
30m
60m
2000
4000
Organic
Carbon
-500
CaCO3
-1000
-70
-30
-25 -20 -15 -10
13
C0/00
-5
0
Radiocarbon Age
14
• Mixture of young
and old carbon is
not the result of
pore water mixing,
but mobilization of
old organic carbon
Hydraulic Characteristics at Intensive Site
0
4.7E-05
8.2E-05
Clay
May 01
2.5E-04
3.6E-04
20
Jan 02
?
1.2E-04
1.8E-04
40
2.2E-04
60
3.9E-04
May 01
2.4E-04
80
Depth
(m)
100
7.2E-05
-10
120
0
Clay
140
160
3.9E-05
0
2E-04
4E-04
.
Hydraulic
Conductivity (m/s)
-300
-200
Relative Head
-100
0
100
-4
-3
(mm difference4 from head at 19m)
18
-2
-1
δ O (per thousand)
0
Depth-wise variation of stable water isotopic values at the filed site
Monitoring Rice
field
Pumping
River Exchange
Exchange
With River
Ponds
Model
Aquifer:
S
(
)
(
)
dha
= h f − ha K f f f + h p − ha K p f p + (hr − ha )K r fr + (hv − ha )K v fv − qI − favα v ET0
dt
Village:
Field:
Pond:
dhv
Sy
= (ha − hv )K v − (1− fav )α v ET0 + R
dt
Sy
dh f
dt
dhp
dt
(
)
= ha − h f K f − α f ET0 + R +
= (ha − hp )K p − α p ET0 + R
qI
ff
Case-A
Case-B
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
13
w/o pumping
42
22
Village ETtree from
Residence
Time (yrs)
Table 1. The estimated conductance parameter values when
the storage coefficients are fixed, the respective objective
functions (sum of square errors), and modeled residence times
for the aquifer.
Case A: Village ET out of Clay
Kf
Kp
Kr
Kv
CV
Kf
Kp
Kr
Kv
1
-0.18 1
-0.28 0.29
1
-0.30 0.01 0.09
1
0.11
0.10
0.11
5.45
Kf
Kf
Kp
Kr
Kv
Sy
S
Case B: Village ET out of Aquifer
Kf
Kp
Kr
Kv
CV
Kf
Kp
Kr
Kv
1
-0.21 1
-0.31 0.23
1
-0.11 0.05 0.00
1
0.10
0.10
0.10
0.06
1
-0.17
-0.31
-0.34
-0.26
-0.24
Case A: Village ET out of Clay
Kp
Kr
Kv
Sy
1
0.04
0.02
0.02
-0.07
1
-0.22
1
-0.29 0.92
0.81 -0.15
1
-0.19
Case B: Village ET out of Aquifer
Kf
Kp
Kr
Kv
Sy
Kf
Kp
Kr
Kv
Sy
S
1
-0.11
-0.39
-0.36
-0.36
-0.26
1
-0.06
0.10
0.11
-0.14
1
-0.07
1
-0.10 0.79
0.83 -0.16
1
-0.22
S
CV
1
0.15
0.09
0.10
0.77
0.14
0.13
S
CV
1
0.18
0.09
0.11
0.08
0.09
0.15
Transient Three-Dimensional Flow Model
River cells
Pond cells
Village areas
Irrigated rice areas
Irrigation wells
Drinking wells
Other agriculture area
Area of interest
114 row and columns 15 layers
Frequency
0.35
Estimated Groundwater Age Distribution at 30Estimated Groundwater Age Distribution
m
w/ irrigated agriculture
w/o irrigated agriculture
0.3
0.25
0.2
Median age of 66 years with irrigated agriculture
0.15
240 years without irrigated agriculture
0.1
0.05
0
40
200
360
520
680
840
1000
Groundwater Age (years)
1160
1320
1480 +
Conclusions
• 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.
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
MIT
Chris Swartz
Nicole Keon
Winston Yu
Jenny Jay
Dan Brabander
Peter Oates
Harry Hemond
U. Cincinatti
Shafik Islam
BUET
Borhan Badruzzaman
Ashraf Ali
Feroze Ahmed
Khandaker Ashfaque
Roger Beckie
Volker Niedan
Future directions
• Arsenic in other regions in Asia
Does Bangladesh indicate the future?
• 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?
P
100-m
Irrigation Wells
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P P
P
P
P
P
P
Agriculture Areas
40% boro rice
71% irrigated
P
P
P
P
Field Site
P
P
MIT/BUET/NSF Arsenic Project
Small N2 glove bag at night