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IMPACT OF CHEMICAL CHARACTERISTICS OF GROUNDWATER
ON DEVELOPMENT OF TUBEWELL IN KARACHI UNIVERSITY CAMPUS |
Nayyer Alam Zaigham1*,
Majid Mumtaz2 and Azhar Siddique2
1 Institute of Environmental
Studies, University of Karachi, Karachi, Pakistan
2Department of Chemistry, University
of Karachi, Karachi, Pakistan
*Email: zaigham@geol.ku.edu.pk |
| ABSTRACT |
| The task of optimizing the intellectual
potentials of our children and adolescents has required a new urgency
that we develop all our human resources to meet the worldwide challenges.
From amongst the factors in the cognitive domain that affect learning
efficiency, the intelligence is of prime importance. In this paper
we are concerned with patterns of intellectual development and have
attempted to formulate a differential model, which justifies the mentality
of a person at every stage of the age. |
| Keywords: Groundwater quality, tube well, water
supply, groundwater geology, chemical characteristics. |
| |
| INTRODUCTION |
During the last decade, Pakistan in general and Karachi in particular,
has experienced acute water crises due to rapid industrial and urban
developments and adverse impacts of climatic changes and man-made
environmental hazards. Several parts of the country have experienced
serious drought conditions since the end of the last millennium
resulting water shortage even for drinking particularly in the Sindh
and Balochistan provinces.
Karachi, the largest port and mega-industrial-city in Pakistan
having a population of over 15 million, receives its water supply
from the Indus, Hub and Malir rivers (Fig.1).
The demand is far more as compared to the supply, which is growing
at a very faster rate (KDA, 1974; KWSB, 2001). Such imbalance ultimately
causes serious crisis because of inadequate development of greater-water-supply
scheme(s) for Karachi City. Traditionally, groundwater was not a
major source of water in Karachi, but due to inadequate water supply
for the rapidly growing population, industrial and urban development,
it has now become an important source, either directly or indirectly
through shallow wells. To supplement the inadequate water supply,
people of Karachi have started using shallow groundwater in duress,
which is mainly being recharged by leakage of existing water-supply
lines and/or sewerage system (Rahman, 1995; Rahman et al., 1997).
In view to overcome the water shortage, the University of Karachi
planned a research-cum-applied project for the development of groundwater
resource within the campus. The research study, for the evaluation
of groundwater potential, was undertaken in systematic and scientific
phases of explorations from initial phase of Hydro-geological and
geophysical field investigations to the final phase of tube-well
installation. |
| Factors Controlling Quality of Groundwater |
The nature of sediments encountered at Karachi University campus
is detrital intercalated with thin beds of calcareous and clayey contamination
that favour in contributing different types of salts to the water
residing with significantly older rock units. It was also observed
that the aquifers have sufficiently high pressure and temperature
condition enhancing more reaction activities between water and the
minerals/rock units as evident from the auto-surface-flow of the groundwater
from the test borehole (Figure 2).
 |
| Quality of Groundwater |
| For the assessment of groundwater quality and yield, the borehole
was thoroughly washed with fresh water to clean off drilling-mud/bentonite
after completion of the targeted test drilling. At the site, five
water sampling tests were carried out at depths 340-360, 280-300,
200-220, 120-140 and 80-100 feet. The groundwater was pumped out by
a compressor-pump at each depth of water sampling. During this phase,
the compressor was used for producing a high pressure in the aquifer(s)
and consequently to lift water from the particular formation for assessing
its yielding capacity and water quality as well. The air pressure
gradually was increased to create jolting movement inside the hole
lifting the remains of drilling mud and rock cuttings along with the
formational water resulting in an intermittent discharge of clear
water. Pumping of groundwater was carried out for at least two hours
at each depth of water samplings. The water samples were collected
from different depth levels in the university test orehole and were
analyzed in the Department of Chemistry for the determination of dissolved
minerals/salts and other physical properties of groundwater. The results
are briefly summarized in Table-1. Primary purpose of water analyses
was to determine i) the suitability of water for the domestic, gricultural
and other requirements of the Karachi University, and ii) the selection
of tube well materials and its designing for a longer working life
in particular. |
| Colour, Odour and Taste |
| The groundwater, generally, contains no suspended matter and as
such it is usually clear, colorless and odorless. Similar is the case
with the groundwater found in the Karachi University, which is clear
and odorless and meets the basic requirement. The taste of the shallow
groundwater horizon is slightly salty due to its TDS, but it is however
unobjectionable. |
| Hardness of Water |
Salts of calcium and magnesium bicarbonates, sulfates, chlorides,
nitrates etc. cause almost all the hardness characteristics of water.
Generally, the hardness of water is demonstrated by the amount of
soap needed to produce suds. Most commonly, hardness from 50 to 150
mg/liter is not objectionable for many purposes, the amount exceeding
150 mg/liter is decidedly noticeable. However, the use of numerical
values of hardness to define hard or soft water is open to question,
because these terms themselves have only relative meaning to persons
of different areas. One who lives in Karachi, where waters (from city
water supply system) normally contain small amount of dissolved salts,
could be considered a water with 100 mg/liter hardness as very high.
In contrast, water of more than 500 mg/liter hardness in Thar Desert
and/or parts of Balochistan and Sindh provinces may be considered
by local residents as soft. In case of groundwater in the University
test borehole, it is interesting to note that the waters from shallowest
and the deepest aquifers have 150 mg/liter hardness, whereas the water
hardness is over 500 mg/liter associated with the aquifers encountered
at depths in between 100 and 300 feet (Table-1).
Considering the hydrological conditions and subsurface lithological
units, it is inferred that the shallowest aquifer within 50' depth
is mainly being recharged by the fresh-water leakages from the city
water-supply lines, and other overflows, which contain low percentage
of calcium and magnesium salts. The deepest aquifer, occurring at
about 300'-400' depth is dominantly comprised coarse sandstone, which
are devoid of calcium and magnesium salts. On the other hand, the
drilled-cutting samples show the presence of thin interbeds of limestone
within medium-coarse grained sandstones at depths between 50' and
300'. These limestone beds are the main source of dissolved calcium
and magnesium minerals in the groundwater encountered in the University
test drillhole. However, mixing the water of other horizons having
lesser hardness can reduce the hardness of the intermediate water
horizon.
 |
| Electrical Conductivity |
| Theoretically, pure water has very low electric conductance but
in case of groundwater, it is not possible to think of such ideal
conditions due to variable interactions between water and minerals
of heterogeneous compositions and variable stability. This is one
of the reasons that the amount and the nature of chemical constituents
dissolved in groundwater are thoroughly investigated before the selection
of the tube well materials and exploitation of the groundwater in
bulk. The water sample results of Karachi University test borehole
show the specific conductivity relatively on the higher side ranging
from 4.94 to 5.09 ms/cm. This level of conductivity is enough to create
active electro-chemical environment, which may cause significant corrosion
and may be harmful in the long run, if the steel or iron made screen/casing
of the tube well is used. |
| Hydrogen Ion Concentration (pH) |
| The pH values of water samples, taken from the University test borehole,
range between 7.7 and 8.3 indicating domination of the alkaline environments
of variable levels within the aquifers. These alkaline environments
possibly resulted due to the presence of variable quantities of the
calcium and magnesium bicarbonates. The pH values of groundwater ranging
from 7.7 to 8.3 are within allowable limits for water to be used for
domestic and agricultural purposes. |
| Total Dissolved Salts (TDS) |
| The concentration of the dissolved salts/minerals in groundwater
is generally considered for the over-all suitability of water for
different uses. Water that contains too much dissolved salts/minerals
is not satisfactory for certain uses. Moreover, in view of the fact,
waters with high content of dissolved solids should be taken as potentially
corrosive to well screen and to other parts of the tube well structure
regardless of other characteristics that mineral analyses of the water
may reveal. TDS concentration determined in the water samples of the
University test borehole ranges from 2700 to 2900 mg/liter, which
is relatively on the higher side for the domestic uses as compared
to the water supply based on Indus River network. Considering the
taste and the absence of harmful element concentration, the water
can also be used for domestic purposes under duress conditions due
to the acute shortage of regular fresh-water supply. Table-1 shows that the dissolve salts/minerals are within acceptable range
except the chlorides that exceed a little only. However, the water
is suitable for agricultural purposes in general. |
| Screen and Casing Material of the Tube
Well |
Selection of proper screen and casing materials was based on the
following three hydrogeological factors:
• Nature and concentration
of mineral contents of the groundwater
• Presence of bacterial
concentration in groundwater
• Strength requirements of
the screen/casing
In case of chemical analyses of groundwater samples
collected from the test borehole of Karachi University, it is revealed
that the contents found in the subsurface water can cause both corrosion
and incrustation of the screen/casing pipes. The results of water
analyses show the presence of TDS ranging between 2500 and 3000
ppm and chlorides exceeding 1000 ppm indicating possibilities of
significantly strong corrosive effect on the tube-well structures.
The high pH value ranging between 7.7 and 8.3, high carbonate hardness
ranging from 400 to 550 ppm, iron contents, and the significantly
high counts of bacteria ranging from 43 to 148 in the shallow water
aquifers, also indicate very effective incrusting tendencies. Several
types of screen/casing material are available for construction of
the tube well in specific geo-hydrological conditions, like monel
alloy, everdur alloy, stainless steel, silicon red brass, steel,
PVC, asbestos and fiberglass. Consequently, the tube well was designed
in such a way and similarly its materials of filter and casing were
selected to minimize the adverse effects of corrosion and encrustation.
The upper portion of the tube well down to depth of about 150 feet
was sealed to avoid mixing of bacteria into the groundwater from
shallow recharge. Moreover, the required strength of the screen/casing
material was considered because of the presence of dominating sandstone
and artesian/ piezometric pressure of the groundwater encountered
in the test borehole. Generally, the column load and the collapse
pressure are imposed on the screen, particularly where long screen
is used. In case of the hydrological conditions associated with
the test borehole, the earth pressure and the caving materials (loosely
cemented sandstones) were expected to squeeze the screen. In such
a situation, the selected material of the screen was of good quality
of collapse resistance. Considering quality of the groundwater,
depth of the tube well, the formational and other internal collapse
pressure conditions the screen and casing pipes made of fiberglass
were used for excellent performance and longer life of the tube
well. The fiberglass material is not only durable, tough and strong,
but it is non-corrosive and of inert quality. Moreover, it could
withstand the corrosive effects of the acid treatments, if any required
in future.
|
| Gravel Shrouding |
The annular space between outer surface of the screen/casing and
the wall of the drilled hole is generally poured with good quality
and well-graded gravel pack material. The design theory of the gravel
pack gradation was based on mechanical retention of the formation
particles. Considering the following geohydrological conditions encountered
in the test borehole, an artificially gravel-packed filter of well-graded,
water washed, free of calcareous material, clear and clean siliceous
material was used as the gravel filter pack material in the university
tube well. The fiberglass tube well assembly, comprising a bail plug,
sections of screen & blind pipes, and housing, was sunk down to
the bottom of the well. It was centered and then the selected gravel
material was poured into the annular space around the lowered assembly.
After completion of gravel packing, the development work was started
to clear the gravel treatment of fine sand and to clean up the contact-surface
between the gravel and the natural formation. The annular space above
the ground was sealed. On accomplishment of the tube well development,
the samples of the mixed water of the confined sandstone aquifers
were again collected from depth levels between 150' and 400' and chemically
analyzed. The chemical results (Table-2)
show decreasing trend of TDS, pH, hardness and concentration of calcium
and magnesium, as compared to chemical determinations of water samples
taken from specific depths in the test drillhole (Table-1).
From these results, it appears that the shallower aquifers, which
have been sealed, seem to contribute excessive TDS, pH, hardness and
concentration of other elements.
The water samples were collected from different depth levels after
two hours pumping for each sample, but the mixed water samples were
collected after 150 hours pumping for each sample. The decreasing
trend of the chemical characters of groundwater indicates that the
quality would improve with the passage of time in proportion to the
pumping of the groundwater.
|
| Climatic Impact on Yield and Quality of the Groundwater |
| In the university area, the groundwater characteristics are expected
to change in positive direction depending on good hydro-climatic conditions
and consequent future hydrodynamic dispersion. Generally, it is observed
that the primary direction and magnitude of transfer (or flux) of
mass or energy are directly proportional to the volume and direction
of groundwater-flow. Moreover, the solutes can also be moved through
groundwater by molecular diffusion. As the concentration gradient
develops, the dissolved salts would also move under the influence
of their molecular kinetic energy from areas of high concentration
to areas of low concentration. The analyzed chemical characteristics
of water samples from the test drill hole and the tube well were at
higher concentration level due to the hydrologic controlling factors
developed because of the drought conditions, prevailing in the Karachi
region from 1998 to 2001. The rainfall trend depicts significant precipitation
in years to come, which would improve the quality and the quantity
of groundwater into the tube well. Diffusion would bring new material
to the tube well site because the precipitation process will remove
the constituents from the water, reducing concentration and regenerating
the new TDS gradient. Under the influence of precipitation in and
around Karachi region, particularly in the northeast of Karachi University,
i.e. in the Gadap area, the transport of fresh water or energy by
moving groundwater towards the University area would gradually spread
and dilute the mineral concentration, the pH, specific conductivity
and other adverse characteristics of the water in the tube well.
Generally,
the carbon dioxide-bicarbonate relation is the principal control
of pH in most of the groundwater, but this relationship is not stable
when the pressure and/or temperature changes occur. Similar hydrological
conditions encountered to prevail in the university tube well. The
artesian flow indicates the change in hydrostatic pressure as well
as the change in temperature. The reduction in pressure is causing
release of carbon dioxide. Similarly, the pumping of the groundwater
will affect the hydrostatic pressure and temperature of the groundwater
in the University tube well. The results of the water samples collected
after completion of test borehole and after development of the University
tube well show the variation in pH values as a good positive sign.
The above deductions have been derived on the basis of the water
samples were taken from university test drillhole at different depth
horizons after two hours continuous pumping for each sample, whereas
the mixed water samples were taken after 150 hours non-stop pumping
of the university tube well for the determination of pH. It is expected
that the pH value will decrease more with the passage of time because
the pumping of the university well will cause further release of
carbon dioxide since the normal pressure in the aquifers will be
reduced by the amount of water drawdown. However, in case of very
high quality drinking water requirement, a reverse osmosis plant
may be installed considering the present water quality of the tube
well.
|
| CONCLUSIONS |
The results of present groundwater explorations show a good potential
of the sustainable groundwater at the Karachi University campus,
which can facilitate in solving the water shortage problem. The
better management and utilization of the available water can be
a good source to avoid water scarcity for a long time to come. It
is observed that the ‘water shortage’ sometimes is not
a problem of ‘water-scarcity’, it is a problem of inadequate
management of the available water resource. Sustainable use of water
resources requires several conditions of sustainability. One can
distinguish physical, economic, social, financial, institutional
and environmental sustainability.
|
| REFERENCES |
| Karachi Development Authority, 1974, The Karachi development plan
1974-85: Master Plan Department, KDA, PAK/68/540, p. 203-209.
Karachi
Development Authority, 1991. Karachi Development Plan 2000: Master
Plan & Environment Control Department and United Nations Centre
for Human Settlements, UNDP Project PAK/86/029, 196p.
Karachi Water & Sewerage Board (KW&SB) 2001. Basic Facts
2000-2001, 78p.
Rahman AU., 1995. Groundwater contamination in Asia's mega-cities:
Water Front, No. 1, June, Sweden, p.8-9.
Rahman, AU., Lee, HK., and Khan, MA., 1997. Domestic water Contamination
in rapidly growing megacities of Asia; Case of Karachi, Pakistan:
Environmental Monitoring & Assessment, 44:339-360. |
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