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109Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
6CHAPTER
Water Quality Data Analysis and Mapping
6.1 Introduction
Quality of pumped groundwater is a major issue in terms of its usefulness and is particularly important for
the deep aquifer as there is limited data availability on the quality issues as well as possibilities of occurrences
of higher amount of total dissolved solids. The quality issue of deep aquifer becomes more important
because of the fact that over most of the country the available data show relative low concentrations of
arsenic in deeper groundwater and is considered as one of the main sources of arsenic safe water.
Available water quality data on the deep test or production wells has been collected mainly from DPHE
sources. Data on the parameters like Electrical Conductivity (EC), pH, Total Hardness (TH), Arsenic (As), Iron
(Fe), Chloride (Cl) and Manganese (Mn) are collected from various DPHE laboratories. However, results on all
the parameters are not available for all cases. In addition, the quality of the existing water quality data is a
major issue. Keeping these in minds, the following parameters have been selected for appraisal of deep
aquifer water quality. Considering WHO and Bangladesh standards, the following decision system has been
adopted for the four selected parameters:
As = <0.01 mg/L - OK as per WHO
As = > 0.01-0.05 - OK as per BDS
As = > 0.05 mg/L - NOT acceptable
Fe = 0.3 mg/L - OK as per WHO
Fe >0.3 -1.00 mg/L - OK as per BDS
Fe 1-5.00 mg/L - OK for HTWs
Fe >5.00 mg/L - NOT acceptable
Cl = 600 mg/L - OK for All over Bangladesh
Cl >600- 1000 mg/L - OK for coastal region
Cl >1000 mg/L - May NOT be acceptable
Mn = 0.1 mg/L - OK
Mn = 0.1-0.4 mg/L - may be acceptable
Mn = >0.4 mg/L - NOT acceptable
Though water quality data from the DPHE sources are used for a preliminary assessment of the quality of
deep groundwater, there remains certain factor that needs proper attention.
114 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
n No QA/QC results are available
n Not all the data available for all locations
n Depth integrated data available from DPHE R&D activities at Pourashava and Growth Centers
n Some quality trends seem unusual hydrogeologically e.g. Gohat, Kalia Pourashava, Narail
n Some quality trends conforms with local geology, e.g. Trishal Pourashava, Mymensingh
n Some parameters like pH, EC, Temperature reported in the lab results should be done onsite
6.2 Summary Statistics on Four WQ Parameters
6.2.1 Arsenic
Arsenic samples with depth information (n= 820) have been categorized is different classes as per WHO and
Bangladesh drinking water limits. Most of the samples (80%) comply with the WHO standard. 98% of the
samples comply with the Bangladesh standard and only 2% samples exceed the 0.05 mg/L limit (Figure 6.1).
Though most of the data comply with WHO standard, a relatively large number of samples fall in between the
WHO and Bangladesh limits. This number is much higher than the previously reported investigations such
the BGS & DPHE (2001). Figure 6.2 shows the location of the wells with As measurements.
Another set of data is also available from the DPHE zonal laboratories where these are recorded as deep tube
wells but without any depth. More than 6000 arsenic analysis data have been collected from the laboratories.
The analyses results show that almost all the samples comply with the Bangladesh standard as shown in
Table 6.1 and Figure 6.3. However, in terms of compliance with the WHO standard, there are variations among
the six divisions. About 20% samples exceed the WHO limit in Chittagong division whereas no sample
exceeds the 0.01 mg/L limit in Sylhet Division. About 8% samples exceed the same limit in Dhaka and Khulna
divisions whereas 3% samples exceed the same in Barisal division. This dataset also confirms that a
significant number of samples fall in between the Bangladesh and WHO limits in Chittagong division. Figure
6.4 shows the location of deep tube wells with arsenic analysis results.
Figure 6.1: Concentration ranges of arsenic (n = 820).
% o
f Sam
ple
s
<0.01 >0.10-0.05 >0.50
As concentrations (mg/L)
0
20
40
60
80
100
115Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
Figure 6.2: Location map showing various arsenic concentrations of deep tub wells included in the database
116 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
Figure 6.3: Percentage of samples exceeding the Bangladesh and WHO drinking water limits for Arsenic in different
divisions
0
5
10
15
20
% o
f Sam
ple
s
DHA (1608) CHI (1724) SYL (293) KHU (1846) BAR (588) TOT (6059)
Division
>0.05 mg/L >0.01 mg/L
Total SampleBangladesh Standard WHO
(0.05 mg/L) (0.01 mg/L)
Dhaka Division As 1598 1483 1608
Percentage 99.38 92.23 1723
Chittagang Division As 1718 1404
Percentage 99.71 81.49
Sylhet Division As 291 291 291
Percentage 100 100 1845
Khulna Division As 1827 1699
Percentage 99.02 92.09
Barisal Division As 588 576 588
Percentage 100 97.96
Table 6.1: Samples exceeding Bangladesh and WHO standards for arsenic in six divisions of Bangladesh
117Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
Figure 6.4: Location map showing arsenic concentrations of deep tub wells collected from DPHE zonal laboratories
120 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
Figure 6.8: Location map showing iron concentrations of deep tub wells collected from DPHE zonal laboratories
121Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
6.2.3 Chloride
The 3rd edition of the WHO Water Quality Guideline does not set a limiting value for chloride, as there is no
evidence of health problem associated with high chloride in groundwater. If we consider the Bangladesh drinking
water limits, most samples comply with the 600 mg/L threshold and only a very few samples exceed the 1000
mg/L, accepted limit for the coastal area as shown in Figure 6.5. DPHE zonal laboratory results also demonstrate
the same where almost all the samples comply with the 600 mg/L limit in all divisions as shown in Figure 6.6.
Figure 6.9: Concentration ranges of chloride (n = 890)
Figure 6.10: Percentage of samples exceeding various concentrations for chloride in different divisions
0
10
20
30
40
50
60
70
80
90
100
% s
amp
les
DHA(1431)
CHI(1713)
SYL (293) KHU(1490)
BAR(538)
TOT(5465)
Division
<600 mg/L >600-1000 mg/L >1000 mg/L
% s
amp
les
<600 >600-1000 >1000
Cl concentrations (mg/L)
0
20
40
60
80
100
122 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
Figure 6.11: Location map showing chloride concentrations of deep tube wells included in the database
123Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
Figure 6.12: Location map showing chloride concentrations of deep tube wells collected from DPHE zonal laboratories
124 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
6.2.4 Manganese
Manganese in drinking water is drawing more attention these days as there are some evidence of its role in
mental growth, particularly is infants. Only a small set of results are available compared to other parameters.
The current Bangladesh standard for Mn is more stringent than the WHO limit. If the Bangladesh limit is
considered almost all samples exceed the limit where majority of the samples comply with the WHO
guideline value as shown in Figure 6.13.
Figure 6.13: Concentration ranges of Mn (n = 136)
6.3 Vertical Variations in Water Quality
6.3.1 Arsenic
Although a large data set of arsenic analyses results are available from DPHE zonal laboratories, many of
those do not have any depth record. The small subset of data with depth records has been plotted against
depth as shown in Figure 6.15. The figure, shows that there are wider variations in depth range in the smaller
depth compared to grater depths. However, it is very important to note here that a good number of sample
exceed the WHO limit up to a depth of 300m. Relatively small number of samples from wells deeper than
300m show a much smaller variation in arsenic concentrations where most samples lie within the 0.01 mg/L
threshold.
0
20
40
60
80
100
% s
amp
les
~0.1 >0.1-0.4 >0.4
Mn concentrations (mg/L)
125Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
Figure 6.14: Location map showing manganese concentrations of deep tub wells included in the database
126 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
Figure 6.15: Vertical variations in arsenic concentrations in the samples with depth records (samples deeper than 100m
has been plotted; n = 820)
0
50
100
150
200
250
300
350
0.00 0.05 0.10 0.15
As concentrations (mg/L)
Scre
en D
epth
(mb
gl)
<150m >150-200m >200-250m >250-300m >300-350m
127Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
6.3.2 Iron
Dissolved iron at high concentrations is wide spread in Bangladesh groundwater and deep groundwater is
not exception to this. As show in Figure 6.16, high dissolved iron occur up to a depth of 300m and below this
depth the concentrations are relatively low.
Figure 6.16: Vertical variations in iron concentrations in the samples with depth records (only samples deeper than 100m
has been plotted (n = 927)
0
50
100
150
200
250
300
350
400
0.00 3.00 6.00 9.00 12.00 15.00
Fe concentrations (mg/L)
Scre
en D
epth
(mb
gl)
<150m >150-200m >200-250m >250-300m >300m
128 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
6.3.3 Chloride
As mentioned earlier, chloride is not considered as a health significant parameter in drinking water. However,
relatively higher concentrations can give rise to complaints from the consumer and may not be used as a
source of drinking water. Chloride concentrations in most of the exploited aquifers in Bangladesh are within
600 mg/L. However, there are sporadic occurrences of very high concentrations at various depths as shown in
Figure 6.17. From the somewhat decreasing trend with depth deeper than 250m is apparent.
Figure 6.17: Vertical variations in chloride concentrations in the samples with depth records (only samples deeper than
100m has been plotted (n = 890)
0
50
100
150
200
250
300
350
400
0 1000 2000 3000 4000 5000 6000
Cl concentrations (mg/L)
Scre
en D
epth
(mb
gl)
<150m >150-200m >200-250m >250-300m >300m
129Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
6.3.4 Manganese
Manganese is mostly low in deep groundwater as evident from the limited data plotted in Figure 6.18. In
most cases, the concentrations are within 0.1 mg/L with few high ones. However, samples deeper than 300m,
though very few in number, show characteristically low manganese concentrations.
Figure 6.18: Vertical variations in manganese concentrations in the samples with depth records (only samples deeper than
100m has been plotted; n = 136)
0
50
100
150
200
250
300
350
0.00 0.50 1.00 1.50 2.00 2.50
Mn concentrations (mg/L)
Scre
en D
epth
(mb
gl)
<150m >150-200m >200-250m >250-300m >300m
130 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
6.4 Vertical Variations in Water Quality in DPHE Growth Centre Study
Results from DPHE R&D Division's investigations of water quality at various depths at the same locations are
available. As, Fe and Cl have been measured from test tube wells installed at various depths at the same
location. Few such results from three different locations are presented here with some comments:
Figure 6.19 presents the results from four test tubewells drilled at Trishal in Mymensingh district. There is only
one aquifer up to a depth of 1000feet and which is most likely the Plio-Pleistocene Dupi Tila aquifer. Test tube
wells developed at 200, 500, 850 and 1000 feet. Arsenic is high at the shallowest (0.034 mg/L; below detection
level (bdl) at 500 and 850 feet but reappears at 1000 feet (0.006 mg/L). Fe is very low at the shallowest,
highest at 500 feet (9.80 mg/L) and decreases with depth to 0.51 at 1000 feet. Cl concentrations are very
similar at all depths.
Figure 6.19: Vertical variations in water quality at Trishal, Mymensingh
Depth (ft)
100As = 0.034Fe = 0.5Cl = 40
200
300
400 As = bdlFe = 9.80Cl = 28
500
600
700
As = bdlFe = 6.50
800 Cl = 34
Legend:
900 ClayAs = 0.006
Fine sand Fe = 2.51Cl = 28
1000 Medium sand
Depth (ft)
100
200
300
As: <0.01
Fe: 1.11
400 Cl: 533
500
600 Clay
Silty Clay
700 V F Sand
As: <0.01
F Sand Fe: 0.56
Cl: 414 As: <0.01
800 M Sand Fe: 0.64
Cl: 35
C Sand
900
1000
131Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
Figure 6.20 presents the vertical water quality data from Kalia in Narail district. Kalia Pourashava, Narail where
the following features are noted:
n Two aquifer system separated by a 250 feet silty clay layer at 450 to 700 feet
n No variation in As in the shallow and deep aquifer
n Fe little higher at the shallowest well, similar at the deep ones
n Very unusual variation in Cl at 815 and 850 feet
Figure 6.20: Vertical water quality variations at Kalia in Narail district
Depth (ft)
100
200
300
400
As: 0.04
Fe: 3.46
Cl: 41
500
Clay
600 Silty Clay
V F Sand
700 F Sand
As: 0.01
M Sand Fe: 2.57
Cl: 154
800
900
As: <0.01
Fe: 0.53
Cl: 179
1000
132 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
Figure 6.21 presents the vertical water quality profile from 500, 800 and 1000 feet at Swarupkathi in Pirojpur
district where the following facts are noticed:
n Multiple aquifer systems with a thick aquitard at 100 to 250 feet; other thinner aquitards at 350 and 650
feet
n As decreases with depth
n Cl low in all depths
n Fe decreases with depth
Figure 6.21: Vertical water quality variations at Swarupkathi in Pirojpur
133Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
6.5 Sampling of DTWs for Arsenic Measurements
As the water quality data in general, and arsenic data in particular, are consider unreliable in terms of
analytical accuracy a subset 100 deep tube wells have been sampled under this study. The samples were
collected from SW (greater districts of Kushtia, Jessore, Khulna, and Faridpur) and SE (greater districts of
Comilla and Noakhali) regions of the country. Two teams, each consisting of a graduate geologist with
adequate knowledge of groundwater sampling, were sent out for the sampling. Each team was given a list of
target deep wells based on the information contained in the deep aquifer database. In selecting the wells,
DPHE Zonal Laboratory reported arsenic concentrations were considered. All wells above the Bangladesh
limit were selected for re-sampling, numbering about 10. As a large number of wells exceeded the WHO limit,
around 40 wells with arsenic above 10 µg/L were listed for re-sampling. Remaining samples were selected
randomly from various parts of the sampled districts. Special emphasis was given to collect a few extra
samples from Satkhira-Khulna region as per DPHE's request. However, in many occasions the target wells
could not be sampled because of number of problems such as incorrect information about the locations,
non-functioning of the wells, non-existence of any pumping device and non-existence of the well. A few wells
could not be reached because of difficult accessibility.
At each site a 50 ml filtered sample (filtered with 0.45 µm membrane filter) has been collected. The well was
purged for enough time to get rid of the well bore storage and thus collect representative groundwater
sample from the aquifer. The sample was acidified on the spot using ~1% concentrated HNO3 as per
suggestion of Environmental Laboratory of BUET. Handheld GPS was used to record the geographical
coordinates of the sample location. As per request from the DPHE R&D Division, electrical conductivity (EC) of
each sample was measured on site using portable EC meters. Details of the sampled wells including depth
were collected from the caretaker/owner/user of the well.
Details of the collected samples along with the arsenic concentrations as obtained from the Environmental
Engineering Laboratory of BUET are presented in Table 6.2. Figure 6.22 shows the locations of the samples.
Ten blind duplicate samples were also sent to the same laboratory for assessing the quality of analysis. The
results are discussed in the following sections.
1M
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lia
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Sad
ar
Mag
ura
17
0.07
89
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73
23.4
5088
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iat
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3991
75
937
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hag
aban
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ar
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pu
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4.98
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119.
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7.63
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723
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9
Co
mp
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nd
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Md
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r Rah
man
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976
43
11
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hil
mad
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a M
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ram
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abra
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arai
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89
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9<
1
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mar
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aha
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89
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23.2
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16
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4
14
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8937
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<
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lla K
amal
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din
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gin
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ha
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ltal
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ala
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uln
a22
9.37
89
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64
23.4
319
2600
<
1
16
Md
.Nu
rul I
slam
M
oh
anp
ur
Man
iram
pu
rM
anir
amp
ur
Jess
ore
20
9.84
89
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61
23.0
143
1238
<
1
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Man
iram
pu
r Gir
ls
M
anir
amp
ur
Man
iram
pu
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sso
re
164.
63
89.2
3287
23
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38
1636
<
1
Deg
ree
Co
lleg
e
18
Md
. Go
lam
mo
sto
fa
Fari
dp
ur
Dia
ra
Ko
twal
iJe
sso
re
207.
32
89.1
4446
23
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88
865
16
19
Bih
arip
ara
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gah
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ld
Jh
iko
rgac
ha
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org
ach
aJe
sso
re
169.
76
89.0
9567
23
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93
908
<1
(w
ell-
3)
20
Md
. Sad
ek H
oss
ain
Pu
ron
do
pu
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ha
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org
ach
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sso
re
217.
68
89.0
9202
23
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58
976
<1
( E
x C
hai
rman
)
21
Md
.Ab
du
r Raz
zak
Sars
ha
Sars
ha
Sars
ha
Jess
ore
19
9.39
88
.945
97
23.0
5936
17
14
<1
22
Md
.Sh
ahid
ul I
slam
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ttar
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ang
H
elat
ala
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laro
aSa
tkh
ira
222.
09
89.0
252
23.9
0824
48
30
<1
Sampleno.
Ow
ner
/Car
etak
er's
nam
eV
illag
eU
nio
nU
paz
ilaD
istr
ict
Dep
th (m
) L
on
g (0
)La
t (0
)EC
(µS/
cm)
Ars
enic
(ug
/L)
Tab
le 6
.2: D
escr
ipti
on
of d
eep
tu
be
wel
l sam
ple
s co
llect
ed u
nd
er t
his
pro
ject
134 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
23
Md
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K
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roa
Satk
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1.16
89
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37
23.8
536
4200
34
24
Md
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slam
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ore
r Dan
ga
Dh
and
ia
Tala
Sa
tkh
ira
202.
44
89.1
0368
22
.826
89
5440
<
1
25
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ani m
on
do
lG
oal
pat
aN
agag
hat
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la
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5.00
89
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74
22.7
2304
15
31
94
26
Dili
p k
um
ar D
as
Bh
atsh
ala
Srip
ur
Deb
hat
aSa
tkh
ira
198.
17
88.9
603
22.6
0366
18
67
<1
27
Md
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Shei
kh
Kal
ikap
ur
kris
hn
anag
ar
Kal
igan
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tkh
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219.
51
89.1
4852
22
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08
2420
<
1
28
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du
l Kh
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h
Ind
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ard
ari
Satk
hir
a Sa
dar
Sa
tkh
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185.
92
89.0
2717
22
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34
1690
<
1
29
Ram
Pra
shad
Pa
rpar
a G
ho
na
Gh
on
aSa
tkh
ira
Sad
ar
Satk
hir
a18
9.00
88
.993
54
22.7
352
1767
33
30
Md
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ibu
r Rah
man
Pa
rpar
a G
ho
na
Gh
on
aSa
tkh
ira
Sad
ar
Satk
hir
a23
7.43
88
.960
41
22.7
4511
20
50
2
31
Md
.Ab
du
l Gaf
far (
chai
rman
)B
had
ra
Kush
khal
iSa
tkh
ira
Sad
ar
Satk
hir
a22
0.00
88
.976
65
22.7
7369
20
90
80
32
Bra
hm
araj
pu
r Sh
ard
arp
ara
B
rah
mar
ajp
ur
Bra
hm
araj
pu
rSa
tkh
ira
Sad
ar
Satk
hir
a18
9.02
89
.107
322
.681
09
859
101
M
osq
ue
33
Md
.Nis
ar A
liB
ara
Path
ra
Mo
ng
alko
tK
esh
abp
ur
Jess
ore
26
5.16
89
.286
22
.855
57
1056
5
34
Gir
idh
arn
agar
Jam
e m
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Dep
th (m
) L
on
g (0
)La
t (0
)EC
(µS/
cm)
Ars
enic
(ug
/L)
135Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
47
Bis
wan
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Dep
th (m
) L
on
g (0
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t (0
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(µS/
cm)
Ars
enic
(ug
/L)
136 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
70
Bah
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208.
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Dep
th (m
) L
on
g (0
)La
t (0
)EC
(µS/
cm)
Ars
enic
(ug
/L)
137Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
92
Shah
Ala
m
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hya
bas
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ni
202.
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Dep
th (m
) L
on
g (0
)La
t (0
)EC
(µS/
cm)
Ars
enic
(ug
/L)
138 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
139Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
Fig
ure
6.2
2: L
oca
tio
n m
ap o
f dee
p t
ub
e w
ells
sam
ple
s fo
r ars
enic
an
alys
is u
nd
er t
his
pro
ject
140 Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
The quality of analysis is very good as good agreement between the original sample and blind duplicate
sample have been reported as shown in Figure 6.23. Only for one sample, where the arsenic concentration
was very high, there was a wide variation between the original and duplicate sample. This has been analyzed
a number of time and the variations seems to stay for some unknown reasons.
Figure 6.23: Comparison of original and duplicate sample analysis results of 10 samples analyzed at the Environmental
Engineering Laboratory of BUET.
Results of the analyses of groundwater samples collected from 100 deep tube wells show that most of the
well water (85%) contains arsenic below the WHO provisional limit of 10 µg/L; 10% of the wells fall in
between the Bangladesh and WHO limit and only 5% exceeded the Bangladesh limit (Figure 6.24). These
results are consistent with previous investigations such as the BGS & DPHE (2001). A large number of samples
reported to have arsenic in the range of 10 to 50 µg/L by the DPHE Zonal Laboratories could not be
confirmed by this study. This is another confirmation about the uncertainty of analytical accuracy of arsenic at
the DPHE Zonal Laboratories.
Figure 6.24: Distribution of arsenic concentrations in 100 samples analyzed at the Environmental Engineering Laboratory of BUET collected under this project
0
50
100
150
200
250
300
1 2 3 4 5 6 7 8 9 10Sample Number
As
Co
nce
ntr
atio
ns
(ug
/L)
Original Duplicate
85
10 5
0
20
40
60
80
100
% o
f Sam
ple
s
<10 >10<50 >50
As Concentrations (ug/L)
141Final Report on Development of Deep Aquifer Database and Preliminary Deep Aquifer Map
Figure 6.25 shows the spatial distribution of arsenic in the samples collected under the study. It is evident
from the figure that arsenic concentrations in the deep aquifer are basically low all over the southern part of
Bangladesh. Samples from the Kushtia-Jessore region show relatively higher amount of arsenic which may be
due to relatively shallower depth of the wells and non-existence of clay aquitard in between the upper and
lower aquifers. Five samples which exceeded the Bangladesh limit of 0.05 mg/L are located in Satkhira (3),
Faridpur (1) and Comilla (1) region. BGS/DPHE (2001) study also reported few deep wells with high arsenic in
Stakhira. Also it was previously reported in earlier studies about the occurrence of higher concentrations of
arsenic in deeper wells of Faridpur region. The well showing high arsenic from the Comilla region is a matter
of concern. However, the very high concentrations found in a few deep wells require further investigations.
For such future investigations the depth and construction design of the wells should also be studied. The
spatial distribution of arsenic concentrations in the sampled 100 wells does not confirm the occurrence of
relatively higher concentrations of arsenic in the Noakhali Chandpur region reported by the DPHE Zonal
Laboratories. The deep wells sampled from the region showed a similar concentration pattern of arsenic as
from the other parts of the southern Bangladesh.
Figure 6.25: Spatial distribution of arsenic in the samples collected under the study