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Status on Groundwater recharges and availability in the Mining areas of North Goa.


Abstract and Figures

The opencast iron ore mining in North Goa has induced significant changes in water quality and quantity besides topographical, morphological, and landuse changes. In the present study, a detailed account of the status of groundwater availability, its recharge, aquifer types, etc. has been presented. The study has been carried out on 10 sub-watersheds that are in the region where large-scale iron ore mining has been in operation. The stage of groundwater development in each of the sub-watershed can be used for groundwater development planning activities including artificial recharge, rainwater harvesting, and restricting the quantum of withdrawals from groundwater reservoir.
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Status of groundwater availability and
recharge in the mining watersheds of
North Goa*
B S Choudri and A G Chachadi
The opencast iron ore mining in North Goa has induced significant changes
in water quality and quantity besides topographical, morphological, and land-
use changes. In the present study, a detailed account of the status of
groundwater availability, its recharge, aquifer types, etc. has been presented. The
study has been carried out on 10 sub-watersheds that are in the region where
large-scale iron ore mining has been in operation. The stage of groundwater
development in each of the sub-watershed can be used for groundwater deve-
lopment planning activities including artificial recharge, rainwater harvesting,
and restricting the quantum of withdrawals from groundwater reservoir.
Water stress conditions arise whenever the quantity of groundwater extracted
within a given watershed exceeds the total recharge. Depending on the magni-
tude of this difference between total extractions and recharges, the watershed
can be classified into four categories (modified from CGWB 1984): non-critical
(white; <50% of the utilizable groundwater is developed), sub-critical (grey;
50%–75% of the utilizable groundwater is developed), critical (black; 75%–100%
of the utilizable groundwater is developed), and most critical (red; >100% of the
utilizable groundwater is developed). Generally, no groundwater development
activity is allowed in the watersheds in critical and most critical category areas
where groundwater extraction exceeds 75% of the mean annual recharge. When
groundwater extraction is less than 50% of the mean annual recharge, the area is
* This paper is an output of a project funded by the DFID (Department for International
Development), UK, for the benefit of developing countries. The views expressed are not
necessarily those of the DFID.
624 B S Choudri and A G Chachadi
categorized as non-critical and no restrictions on groundwater extractions are
imposed in such watersheds. In watersheds where the total groundwater extrac-
tion balances mean annual recharge, a cautious approach is adopted in the
groundwater development. Therefore, assessment of the water stress status of a
watershed is an important parameter in the decision-making process in
groundwater development.
It is usually much wiser to strike a balance between groundwater availabil-
ity and extraction at a high level (shallow groundwater conditions) of
groundwater heads compared to low levels (deep groundwater conditions)
(Teresa and Lobo-Ferreira 2002). First of all, high levels provide flexibility for
temporal overdraft and, therefore, supply safety. Second, the cost of pumping is
lower, as the water levels are at shallower depths from the ground. Thirdly, the
adverse impacts on groundwater regime, such as seawater intrusion, pollutant
mixing, etc., are not inflicted. In dry regions, bigger rainstorm events with con-
siderable replenishment of groundwater reservoirs may take place rarely and at
long time intervals. Sustainable use of groundwater means that within this long-
term time period, a balance between recharged and extracted volumes must be
reached. In the years without adequate replenishment, groundwater can be ex-
tracted if it can be assumed that till the next recharge, enough water remains in
the reservoir to satisfy the basic needs. In other words, in the context of
groundwater management, sustainability implies a limitation of the extraction
rate to a value below the long-term natural replenishment rate. There are, how-
ever, additional aspects to sustainability such as the following (Kinzelbach and
Kunstmann 1999).
Maintaining shallow groundwater levels to meet vegetation water de-
mands in the area
Guaranteeing of minimum flow rates in downstream drainage basins
Preventing of seawater intrusion or salt-water upconing
Preventing of long-lasting pollution, land-subsidence, and soil salinization.
Under natural undisturbed conditions, the groundwater regime is in dy-
namic balance with recharges equalling discharges. However, any
anthropogenic activity would change this natural balance. Mining is one such
activity wherein invariably the groundwater regime is disturbed. The
groundwater quantity and quality in such areas may get affected at different
intensities, depending on the magnitude of the activity and intensity of interfer-
ence in the groundwater regime. Groundwater withdrawals for domestic use
and moderate agricultural activity may not offset the groundwater balance sig-
nificantly as recharges balance such withdrawals under normal rainfall
conditions. However, if large-scale activities, like dewatering of the mine pit, are
introduced in the watershed, as in Goa, then it is but natural that the
groundwater balance in the watershed may get offset. There may be deficit or
Status of groundwater availability and recharge 625
surplus groundwater balance depending on the changed recharge regimes and
water-use practices in the area.
Existing groundwater estimation methodology and associated
Generally, groundwater recharge in an unconfined aquifer is estimated by water
table fluctuation method using the expression
R = A × ∆s × SY........................................................................................................................................................................ (1)
R = recharge to groundwater (L3)
A = area of the watershed (L2)
s = groundwater level change or fluctuation (L)
SY = specific yield (fraction) of the unconfined aquifer
In this method, three parameters, viz. the watershed area, groundwater
level fluctuation, and specific yield of the aquifer, are required to be known.
Among the above three required parameters of the groundwater balance equa-
tion, watershed area and groundwater level fluctuation can be measured with
good precision. However, the accuracy and determination of the aquifer-specific
yield are generally inadequate because they are influenced by several factors in-
cluding economic aspects of expensive field experiments.
The above-mentioned equation is straightforward and simple but can give
erroneous results due to inadvertent use of unreliable values of aquifer-specific
yield. In general, it is a common practice to use either text book values of spe-
cific yield derived from relational tables or average values from few distributed
parameters. Under these circumstances, the computed groundwater volumes
can be misleading, which ultimately influence the groundwater development
planning. It is, therefore, wise to use these recharge values as only approxima-
tions for any planning purpose. The best way, therefore, is to adopt some direct
method of estimating the rainfall recharge to the ground, as the entire
groundwater is mainly derived from this source.
Objective of the present study
The North Goa region has been witnessing a rapid growth in the mining-related
activities in the recent past. Local communities of the mining district are of the
view that groundwater reserves in the vicinity of the mining areas have been
declining. Therefore, there is a need to assess the current status of groundwater
regime in order to find the reasons of reported decline in groundwater reserves
in these areas. The study results would ultimately be instrumental in taking ap-
propriate corrective measures to overcome groundwater overdrafts, if any, in
the mining watersheds.
626 B S Choudri and A G Chachadi
Study area location
The study area located between Sirigao in north-west and Surla-Velguem in
south-east has been chosen keeping in mind the high intensity and aerial extent
of the mining activity. The total area covered in the study is about 194 km2
(square kilometres). The entire area is divided into 10 sub-watersheds (B-1 to
B-6 and S-1 to S-4), varying from 4 to 45 km2 (Figure 1). The area falls mainly in
the talukas of Bicholim and Sattari. All the major mining companies have their
working leases in this belt. The well-known villages in the mining belt include
Sirigao, Lamgao, Mulgao, Mayem, Piligao, Bicholim, Sanquelim, Cudnem,
Honda, Pissurlem, Sonshi, Surla, and Velguem.
Evaluation of rainfall type and variation in the study area
Attempt has been made to study the variation in the rainfall pattern over the
study area because a major part of the study area is spread in the east–west di-
rection and it is seen that the rainfall varies considerably from west (coast) to
east (inland). In order to understand the relationship between the rainfall, topo-
graphical elevation, and the distance from the coast, the long-term average
annual rainfall for four rain gauge stations, viz. Panaji, Mapuca, Bicholim, and
Valpoi, has been plotted along with their ground elevations (Figure 2). From the
Figure 1e 1
e 1e 1
e 1 Location map of sub-watersheds in the North Goa mining area
Status of groundwater availability and recharge 627
plot, it is clear that the rainfall increases linearly from coast (Panaji) to inland
(Valpoi). The positive correlation between topographical elevations of the place
and the rainfall also indicates the predominance of orographic type of precipita-
tion in the study area.
The non-monsoon rainfall (during October to May) contribution varies
from 2.7% to 3.9% of the annual rainfall over Goa. The distribution of normal
annual monsoon rainfall for the entire state of Goa has been plotted as an
isohyetal map and shown in Figure 3. As seen from the figure, rainfall increases
from coast towards the eastern side consisting of Western Ghats, indicating
orographic type of precipitation. The rainfall contours (isohyets) remain nearly
parallel to the coast.
Types of aquifers in Goa
Based on the exploratory drilling data by the CGWB (Central Ground Water
Board), State Groundwater Agency, and groundwater-related studies by various
academic and private organizations, Chachadi (2002) has classified the main
aquifers of Goa into following five types.
Figure 2e 2
e 2e 2
e 2 Relation between rainfall and ground elevation along Panaji–Mapusa–Bicholim–Valpoi profile
628 B S Choudri and A G Chachadi
1Aquifers underlying lateritic plateaus without ore body Lateritic plateaus are the
most common topographical features confined to the midlands and coastal
plains of Goa. They are generally made of flat-topped elevated landmasses
about 40–80 m (metres) above sea level. Generally, they are covered with
hard, sometimes massive, laterite on the flat portion and bouldary detrital
laterites on the slopes. These detrital laterites are the transported masses and
are embedded in lateritic soils. These slopes are covered with evergreen veg-
etation made up of variety of fruit-bearing plants. Most of the rural and
urban settlements are found along the slopes of these plateaus. A typical non-
ore-bearing plateau is shown in Figure 4. The laterites vary in thickness from
less than 5 m to more than 30 m and are underlain by a thick sequence of
lithomarge (lateritic) clay. The boundary between the lithomarge clay and the
underlying fractured and weathered basement rock, often made of phyllites
and metasediments, forms an important water-bearing zone in the form of a
confined aquifer. The groundwater in this fractured deep aquifer in the
coastal plateaus is often found below sea level. The laterites located on the
plateaus do not generally form aquifers because they cannot hold water
mainly due to their topographical settings. The intervening lithomarge clay is
Figure 3e 3
e 3e 3
e 3 Normal monsoon rainfall (mm) distr ibution over Goa
Status of groundwater availability and recharge 629
not totally impermeable; it can store and vertically transmit water through it,
which enhances the storage in the lower confined aquifer. The confined aqui-
fer also receives its recharge from lateral directions through the low-lying
alluvial plain areas around the plateaus. The most interesting feature of the
plateaus in Goa is the presence of natural springs around the slopes. These
are the lifelines of the rural water needs. When rainwater enters the laterites,
which are porous and fractured, it moves along the contact zone between low
permeable lithomarge clay and bottom of the overlying laterites to emerge as
a spring along the slope where the laterite–clay contact are exposed. Many
open wells, streams, and even bore wells located in the low-lying flat areas
around the plateaus are fed by these springs.
2Aquifers under lateritic plateaus having iron ore body Majority of the mineral
deposits of Goa region are located below the hilly plateau areas ranging in el-
evation from few metres to over 100 m above the msl (mean sea level) in the
midland areas. These plateaus are composed of lateritic cover followed by a
thick layer of various types of clays. Intervening these clays are the iron ore
bodies, mainly in the form of powdery ores and lumps. The plateaus act as
rainfall recharge areas for local groundwater regime. The rain percolates
through the fractured laterites and sometimes underlying clays. The resulting
water table is much above the surrounding plain area and quite often inter-
sects the ground surface at the hill slopes resulting in springs. A typical
cross-section of the plateau area, having iron ore deposits and the associated
hydrological components, is shown in Figure 5.
In order to mine the iron ore, the mining activity is done by cutting the
top lateritic cover on the plateaus and removing the clay overburden. This
Figure 4e 4
e 4e 4
e 4 Hydrogeological cross-section of the lateritic plateau in Goa
630 B S Choudri and A G Chachadi
process at first eliminates the area from where the rain water recharge was
taking place and consequently the water table in the surrounding low-lying
areas is affected due to the reduction of recharge area in the neighbourhood.
The mining activity also induces groundwater flow into the mine pit from
both unconfined lateritic layer and confined iron ore aquifers during mining.
This water has to be pumped out to provide dry conditions at the bottom of
the mine for ore extraction. The mining areas also have deep confined aqui-
fers in the fractured basement rocks, which are not being exploited.
3Aquifers under the plain area covered with laterites Laterites are widespread
rock types occupying large aerial extent in Goa. In the plains of the midland
and the coastal areas, the laterites form potential unconfined aquifers due to
the presence of porous and fractured laterites. These laterites can sustain
groundwater for long durations. They are recharged annually through rain-
fall. The groundwater levels are less than 10 m below ground having good
water quality. A large number of open wells are found in these laterites and
meet large water requirements of the people. Yields from these wells are
sometimes quite high. These laterites, like the plateau, are also underlain by a
thick sequence of lithomarge clay, which extends up to the basement rock.
The basement rocks are quite often weathered and fractured and hence form
confined aquifers. Dependable and sustainable well yields can be achieved
by drilling bore wells in these fractured basement aquifers.
4Aquifers under alluvial plains Particularly in the coastal zone, large tracts of
land are covered with river, coastal, and intermountain valley deposits. These
are alluvial sediments composed of varying amounts of sand, clay, and silt.
The thickness of these alluvial sediments varies largely depending on the to-
pography of the basement rock. Groundwater occurs under unconfined
Figure 5e 5
e 5e 5
e 5 Hydrogeological cross-section across a plateau in the mining area
Status of groundwater availability and recharge 631
condition in the alluvium. The alluvium is highly permeable having primary
porosity and gets recharged very quickly. It is also highly drainable in nature.
These alluvial sediments grade into weathered laterites, which, in turn, rest
on basement rocks, that are often fractured. These shallow unconfined allu-
vial aquifers are very sensitive to pollution and cannot hold water in large
quantities for longer periods due to their typical hydrogeological characteris-
tics. These aquifers are, therefore, not sustainable sources of fresh
groundwater. The deeper aquifers in the basement rock are confined to semi-
confined in nature and are generally tapped by bore wells. The shallow
unconfined alluvial aquifers are commonly reached through open wells of
varying dimensions. The groundwater levels are generally less than 10 m be-
low ground level. Most of the coastal alluvial aquifers are contaminated by
indiscriminate disposal of septic tank and cesspool wastes besides sewage
from hotels and municipalities (Chachadi, Lobo Ferreira, and Oliveira 2001).
Near the coast, these aquifers at places are subjected to seawater intrusion
due to overpumping for various activities.
5Aquifers in crystalline rocks In the highlands of Sahyadris and areas occupied
by granitic rocks in South Goa, the groundwater is found in the fractured and
weathered mantle of these rocks. Unconfined to confined conditions are en-
countered. Deep-seated fractures give rise to confined water bodies that are
recharged by rainwater. The water quality is generally good. The yield from
these aquifers is low to moderate.
Groundwater recharge and discharge
In Goa, the main source of groundwater recharge is south-west monsoon that
spans over a period of nearly four months between June and September. The
rainfall varies from about 2500 mm (millimetres) along the coast to about 4500
mm towards the Western Ghats. The magnitude of recharge to groundwater
also varies from place to place, depending on the nature of the surface soil and
rock characteristics. Chachadi, Choudri, Naronha, et al. (2004) have quantified
the rainfall recharge to groundwater using daily sequential water balance
method (BALSEQ) for various land uses in the mining belt of Goa. The
groundwater levels in the wells generally reach the shallowest levels during the
month of July/August under normal rainy season. The groundwater in the state
is mainly used for drinking and industrial purposes, followed by agriculture use
to some extent. The groundwater development vis-à-vis balance in the state
varies from place to place. In the coastal belt at most of the locations, there is a
state of overdevelopment of groundwater. This is partly due to natural drainage
of groundwater to the sea besides human consumption, which is highest along
the coast due to very high population density and industrial withdrawals. At
few locations in the mining belts, there is an overdeveloped condition mainly
due to dewatering from the mine pits and mine reject dumping.
632 B S Choudri and A G Chachadi
Groundwater flow-net analysis in the mining watersheds in
North Goa
A groundwater flow-net is a sketched representation of the flow paths taken by
water molecules through the subsurface. The ‘grid’ of a flow-net comprises
flow-lines (idealized paths followed by water molecules in moving from posi-
tion of high hydraulic head to those of lower head represented by smooth
curves at right angles to equipotential lines) and equipotential lines (lines along
which the hydraulic head is equal). Flow-net is a very powerful analytical tool
for studying the groundwater behaviour. Flow-nets may be constructed by a
number of procedures including trial-error sketching, physical modelling, elec-
trical analog method, and computer-assisted mathematical modelling.
In the present study, manual as well as computer-assisted (SURFER) flow-
net sketching has been adopted. The input to the SURFER program includes X
and Y co-ordinates of observation wells with respect to a fixed point of origin
and water level data above msl in metres (Z co-ordinate). The catchment bound-
ary is plotted using X and Y coordinate data manually sampled from the base
map along the watershed boundary. The flow-net contour maps for pre- and
post-monsoon periods have been constructed for all the 10 watersheds. Kriging
technique is used for plotting of various contours as it was found that it is the
best-fit method for plotting of smooth contours (Vijay Kumar and Remadevi
2003). Owing to space constraint, only one flow-net is shown in Figure 6. An ob-
servation well network consisting of 116 open wells was established and the
groundwater levels were monitored on monthly bases. The location of the
groundwater monitoring network stations is shown in Figure 7.
Figure 6e 6
e 6e 6
e 6 Groundwater flow-net for the mining watershed S-1
Status of groundwater availability and recharge 633
Figure 7e 7
e 7e 7
e 7 Location of groundwater monitoring well network in the mining belt
Long-term groundwater level changes through well hydrograph
Monthly groundwater level data for 49 observation wells was collected for four
consecutive years from April 1997 to March 2001 (Chachadi 2002). In order to
ascertain the long-term behaviour of the groundwater levels, the groundwater
level data has been used to construct the well hydrographs for all the 49 moni-
toring stations. Monthly normal rainfall is also plotted on each of the
hydrographs for the purpose of correlation and interpretation. A time-trend
analysis was carried out on each of the hydrographs. Based on their
groundwater level trends, all the 49 well hydrographs have been classified into
the following three categories.
Hydrograph trend
Number of stations showing the trend % of the total
Increasing 38 77.6
Decreasing 06 12.2
No Change 05 10.2
Well hydrographs from the study area indicate that the water levels in the
unconfined aquifers respond prominently to rainfall recharge. There is a delay
time of about one month between rainfall peak and the shallowest groundwater
634 B S Choudri and A G Chachadi
level. In most of the cases, the groundwater levels are restored to the base level
(pre-monsoon level) long after the cessation of monsoon rainfall. The steep gra-
dient of the rising limb of the hydrographs indicates a quick recharge to
groundwater and the gentle slope of the falling limb of hydrograph shows
slower drainage of the aquifer, which is considered to be ideal for sustainable
groundwater supplies. The quick rising limbs of the hydrographs indicate a per-
meable rock/soil matrix in the top unsaturated zone. It is interesting to note that
although both saturated and unsaturated rock matrices are made up of same
lateritic rock having channel-like pores, the drainage of groundwater from the
saturated zone becomes sluggish which could be due to gentle groundwater
level gradients. On the other hand, vertical flow of water from rainfall recharge
is not influenced by groundwater flow gradient problems. Majority of the
hydrographs show an identical shape, indicating presence of similar
hydrogeological rock matrix throughout the area.
The phenomenon of decreasing groundwater level (Figure 8) is confined to
the mining areas located in the upper reaches of the watershed, as the recharge
to groundwater is limited at these locations. Majority of the well hydrographs
(77.6%) from the study area show a rising trends of varying magnitudes in the
groundwater levels. This is a very interesting fact in the mining belt where large
quantity of groundwater is being pumped out annually to win the ore from be-
low the water table. This fact could also be an indicator that the large volume of
groundwater that is pumped out from the mine pits is derived mainly from the
ore body aquifers and not from the shallow lateritic aquifers. An increasing
Figure 8e 8
e 8e 8
e 8 Well hydrograph and rainfall for well no. 45 (falling water levels)
Status of groundwater availability and recharge 635
trend in the hydrograph is an indication of surplus groundwater being retained
in the shallow unconfined lateritic aquifer year after year. It happens when an-
nual recharges exceed annual discharges. Assuming natural recharges and
discharges to remain unchanged, it is only either the human-induced recharges
or the reduced groundwater discharges that can cause such increasing trends in
groundwater levels. The possible reasons for the rising groundwater levels in
the present study area are listed below.
During mining excavations, powdery iron ore bodies, which form confined
deeper aquifers in the area, release large quantity of groundwater. This water
along with the accumulated rainwater during four months of rain is pumped
out from the pits to create the dry working conditions at the pit bottoms. The
pit water is let into the settling pond from where it is let out to natural drains,
agricultural fields, and streams. Some water is put in the beneficiation plants
for washing the ore. Water is also used for dust suppression on the roads dur-
ing summer months. All these uses provide for additional non-monsoon
recharge to unconfined aquifers via return flow from agricultural lands,
seepages from streambeds, settling ponds, etc.
The ore to waste ratio is about 1:2.5–3 in case of Goa. Annually, about more
than 30–35 million tonnes of mining rejects are being generated. These rejects
are mostly composed of clays, silts, and low-grade powdery iron ores. Stud-
ies have shown that these reject materials have fairly good hydraulic
conductivity. They are dumped mostly on the hill slopes and nearby places.
As of today, these reject dumps occupy large areas in the mining watersheds.
During four months of rains, the rejects absorb and retain sizable amount of
water in them and transmit it to underlying lateritic layer over a period of
time even after the rains. This provides continued recharge to aquifers and
hence maintains groundwater levels and steadily raises the water table levels.
There are large number of abandoned/non-operational mine pits of huge di-
mensions. These pits act as both collection ponds of surface (rainfall) run-off
and groundwater inflow during monsoon when water table levels are high.
These water-filled pits act as recharge sources to the confined aquifers in the
study area during most part of the year. This could also add to the rising wa-
ter table levels in the area.
Although small, but important fact is that day by day, there is lesser depend-
ence of people on groundwater to meet their domestic needs as tap water
from surface source is made available.
In order to minimize the silting of the streambeds, mining companies have
constructed several silt traps, which are the temporary brick walls across the
streams carrying mine water discharges. These silt traps retain water and al-
low for longer contact time with ground. This process enhances the recharge
to groundwater. Similar desilting ponds near the active mine pits also
provide for additional groundwater recharge.
636 B S Choudri and A G Chachadi
Any mining activity has to be preceded by drilling of a large number (in hun-
dreds) of exploratory boreholes at different depths. There are thousands of
such exploratory boreholes in the mining area in Goa. These bore holes cut
across different litho-units and act as conduits connecting aquifers to the
ground surface through which recharge from rainfall takes place even in ar-
eas on impervious surface layers.
About 10% wells show no change in trend in the groundwater levels. It
seems that although they are located in close proximity of active mines, the
groundwater levels are maintained due to balancing of recharge and discharge
components of groundwater regime. The pumped pit water and waste water
from beneficiation plants recharge the groundwater regime and this recharge
equals all the discharges and hence a balance is reached in the groundwater
Current status of groundwater balance and use in the mining area
The water demand, availability, and use in the 10 mining watersheds have been
worked out under the following heads.
1 Estimation of basin-wise water requirement (demand) in the North Goa min-
ing area based on sectoral demands including the following.
Domestic water requirements (Table 1)
Irrigation water requirements (Table 2)
Industrial water requirements (Table 3)
Live stock water requirements (Table 4)
Requirements for wet beneficiation and ore washing (Table 5)
Groundwater drafts from active mine pits (Table 6)
2 Estimation of basin-wise groundwater recharge based on daily sequential
water balancing (BALSEQ) model.
3 Estimation of basin-wise groundwater draft in the mining area of North
Goa and groundwater balance.
Status of groundwater availability and recharge 637
able 1le 1
le 1le 1
le 1 Basin-wise domestic water requirements
Population distribution Annual water requirement Total water requirement
Taluka Total WS area in WS in the WS 1991*
Urban @0.073 Rural @0.073
per year
(Ha) (km2)
Urban Rural Ham Km3Ham km3Ham km3
B-1 Bicholim 391 3.91 1348 331 1053 2.42 2.42 ×10-5 2.12 2.12 ×10-5 4.54 4.54 × 10-5
B-2 Bicholim 861 8.61 3048 729 2320 5.32 5.32 ×10-5 4.67 4.67 ×10-5 9.99 9.99 × 10-5
B-3 Bicholim 1920 19.20 6797 1625 5173 11.86 11.86 ×10-5 10.40 10.40 × 10-5 22.26 22.26 × 10-5
B-4 Bicholim 1172 11.72 4149 992 3157 7.24 7.24 ×10-5 6.35 6.35 × 10-5 13.59 13.59 × 10-5
B-5 Bicholim 400 4.00 1416 338 1078 2.47 2.47 ×10-5 2.16 2.16 × 10-5 4.63 4.63 × 10-5
B-6 Bicholim 3778 37.78 13374 3196 10178 23.33 23.33 × 10-5 20.45 20.45 × 10-5 43.78 43.78 × 10-5
S-1 Sattari+
Bicholim 2674 26.74 6070 1141 4929 8.33 8.33 × 10-5 7.30 7.30 × 10-5 15.63 15.63 × 10-5
S-2 Sattari 4518 45.18 15994 3823 12171 27.91 27.91 × 10-5 24.47 24.47 × 10-5 52.38 52.38 × 10-5
S-3 Bicholim 3034 30.34 10740 2567 8173 18.74 18.74 × 10-5 16.43 16.43 × 10-5 35.17 35.17 × 10-5
S-4 Bicholim 661 6.61 2340 559 1781 4.08 4.08 × 10-5 3.58 3.58 × 10-5 7.66 7.66 × 10-5
*As per IS: 1172; 1993, urban water requirement of 200 lpcd (litre per capita per day) and rural requirement of 175 lpcd is adopted. The population
density is 354 and 100 per km2, respectively, for Bicholim and Sattari. The urban and rural population, respectively, is 23.9% and 76.1% for Bicholim
and 13.7% and 86.3% for Sattari
Note Note
Note Note
Note WS refers to watershed; some watersheds do not strictly confine to the
boundaries; Ham – hectare metre; km3 – cubic kilometres
638 B S Choudri and A G Chachadi
able 2le 2
le 2le 2
le 2 Irrigation water requirement (mainly for paddy cultivation)
Average annual Total water
Area under agriculture water requirement requirement per year
WS no. Taluka name Ha km2for Paddy* (m) Ham km3
B-1 Bicholim 107.31 1.0731 0.55 59.02 59.02 × 10-5
B-2 Bicholim 510.94 5.1094 0.55 281.02 281.02 × 10-5
B-3 Bicholim 1081.97 10.8197 0.55 595.08 595.08 × 10-5
B-4 Bicholim 782.10 7.8210 0.55 430.16 430.16 × 10-5
B-5 Bicholim 231.90 2.3190 0.55 127.55 127.55 × 10-5
B-6 Bicholim 1997.44 19.9744 0.55 1098.59 1098.59 × 10-5
S-1 Sattari + 1386.81 13.8681 0.55 762.75 762.75 × 10-5
S-2 Sattari 1833.08 18.3308 0.55 1008.19 1008.19 × 10-5
S-3 Bicholim 978.09 9.7809 0.55 537.95 537.95 × 10-5
S-4 Bicholim 256.08 2.5608 0.55 140.84 140.84 × 10-5
*CGWB (1997)
Ha – hectares; Ham – hectare metres; m – metre
able 3le 3
le 3le 3
le 3 Industrial water requirements
Annual water requirement
WS no. Taluka name Industrial estate water requirement Ham km3
B-1 Bicholim -
B-2 Bicholim -
B-3 Bicholim -
B-4 Bicholim -
B-5 Bicholim -
B-6 Bicholim Bicholim Ind. Est. 250 m3/day 9 9 × 10-5
S-1 Sattari + Bicholim -
S-2 Sattari Honda and Pisssurlem Ind. Estate 69 69 × 10-5
1900 m3/day
S-3 Bicholim -
S-4 Bicholim -
Notes Ha – hectares; Ham – hectare metre; m3 – cubic metre; km3 – cubic kilometre
The proposed five industrial estates in the study area at Bordem, Dhumacam, Latambarcem, Ladphe,
and Sal together would require 108 Ham of water. This demand is not considered in the present
ce Goa Industrial Development Corporation, Government of Goa
Status of groundwater availability and recharge 639
able 4le 4
le 4le 4
le 4 Livestock water requirements
Annual water require-
ment @ 30 lpcd is
Area Livestock* population 0.0011 Ham
WS no. Taluka name Ha km2as per 1991 census Ham km3
B-1 Bicholim 391 3.91 313 0.3443 0.3443 × 10-5
B-2 Bicholim 861 8.61 689 0.7579 0.7579 × 10-5
B-3 Bicholim 1920 19.20 1536 1.6896 1.6896 × 10-5
B-4 Bicholim 1172 11.72 938 1.0318 1.0318 × 10-5
B-5 Bicholim 400 4.00 320 0.3520 0.3520 × 10-5
B-6 Bicholim 3778 37.78 3022 3.3242 3.3242 × 10-5
S-1 Sattari+Bicholim 2674 26.74 1591 1.7501 1.7501 × 10-5
S-2 Sattari 4518 45.18 3614 3.9754 3.9754 × 10-5
S-3 Bicholim 3034 30.34 2427 2.6697 2.6697 × 10-5
S-4 Bicholim 661 6.61 529 0.5819 0.5819 × 10-5
Note According to 1991 census, the cattle population is 80 and 39 per km2, respectively, in Bicholim
and Sattari
; Ha – hectares, Ham – hectare metres; km2 – square kilometres;
km3 – cubic kilometres; lpcd (litres per capita per day)
640 B S Choudri and A G Chachadi
able 5le 5
le 5le 5
le 5 Water requirements for wet beneficiation and ore washing
Annual ore Annual water requirement @
concentrate 0.00014 Ham/ton of ore
Ws Taluka Name of beneficiation produced concentrate
no. name plant tonnes Ham km3
B-1 Bicholim - - - -
B-2 Bicholim - - - -
B-3 Bicholim - - - -
B-4 Bicholim - - - -
B-5 Bicholim Dempos–Piligao 900 000 126 126 × 10-5
B-6 Bicholim Dempos–Bicholim 350 000 49 49 × 10-5
S-1 Sattari +
Bicholim - - - -
S-2 Sattari Sesa Goa–Cudnem 1 000 000 140 140 × 10-5
S-3 Bicholim D.B.Bandodkar–Cotambi
Dempos–Surla 320 000 130 130 × 10-5
S-4 Bicholim Mangali–Navelim
Sesa Goa–Amona 250 000 147 147 × 10-5
Note The quantity of water used for beneficiation varies from 1.3 to 1.5 m3/tonne of ore concen-
trate, averaging to about 1.4 m3/tonne of ore concentrate (Ministry of Mines, Government of India,
IBM [Indian Bureau of Mines], and BRGM-France Report 1999: 32). About 50% of this water comes
from groundwater via mine pits and 50% of the remaining water is pumped from tidal Mondovi
River as seawater is highly flocculating.
Actually 12–15 m3/tonne of ore concentrate is the water requirement for wet beneficiation of which
80% is derived from recirculation via tailing ponds. About 20% (that is, 2.7 m3/tonne) is added afresh
and 50% of this, that is 1.35 m3/tonne is derived from groundwater (Ministry of Mines, Government
of India, IBM [Indian Bureau of Mines], and BRGM-France 1999: 33). Therefore, in the present
computation, groundwater use @ 0.00014 Ham/tonne of ore concentrate is adopted. Ha – hectares;
Ham – hectare metre; km3 – cubic kilometres
ce TERI (1997), AEQM (Area-wide Environmental Quality Management) plan for the mining
belt of Goa
Status of groundwater availability and recharge 641
Rainfall recharge estimation for the study area
Methodology of recharge estimation for the study area
Using daily sequential water balance model BALSEQ, Chachadi, Choudri,
Naronha, et al. (2004) estimated the rainfall recharge values for different land-
use classes in the mining belt of North Goa. The unit values of aquifer recharge
(recharge as a fraction of rainfall) derived for each land use have been adopted
for the computation of aquifer recharge in the present study area. Therefore, by
using the estimated area under each land-use class (Table 7) and the unit rainfall
recharge values, groundwater recharge has been computed for each of the wa-
tersheds and is given in Table 8. Table 9 presents the groundwater drafts
computed using the adopted norms for the mining area in Goa. The status of the
groundwater development is also shown in the same table. The total
groundwater recharge minus all the withdrawals provides the balance in the aq-
uifer storage. As seen from the table of the 10 mining watersheds, two are
classified as red (>100% groundwater draft), one as black (75%–100%
groundwater draft), five as grey (50% to 75% groundwater draft), and two as
white (<50% groundwater draft). This indicates that seven watersheds are in the
safe storage and three are critical (B-1, B-2, and B-5). This status is only applicable
to shallow lateritic unconfined aquifer in the area under investigation. The deep
confined and semi-confined aquifers do not form part of this groundwater
balance computation.
able 6 le 6
le 6 le 6
le 6 Groundwater drafts through active mine pits
Total groundwater draft per year
Ore Production @ 0.0002 Ham/tonne of ore
WS no.
Taluka name
(tonnes per year) Ham km3
B-1 Bicholim 1 010 000 202 202 × 10-5
B-2 Bicholim 1 160 000 232 232 × 10-5
B-3 Bicholim
B-4 Bicholim
B-5 Bicholim
B-6 Bicholim
S-1 Sattari + Bicholim
S-2 Sattari 3 960 000 792 792 × 10-5
S-3 Bicholim 1 350 000 270 270 × 10-5
S-4 Bicholim
Total 4196 4196 × 10-5
Ham – hectare metres; km3 – cubic kilometres
ce TERI (1997)
able 7le 7
le 7le 7
le 7 Area computation under each category of land use based on latest IRS satellite image data
Watershed number and area in hectares
Land-use class*
B–1 B–2 B–3 B–4 B–5 B–6 S–1 S–2 S–3 S–4
Agricultural land 107.31 510.94 1081.97 782.10 231.39 1997.44 1386.81 1833.08 978.09 256.08
Forest land – – 512.54 354.66 – –
Built-up/Industrial/ – 67.26 53.07 255.14 2.46 14.08 –
hard surfaces, etc.
Pastures/grass land/ 959.87 – 238.90 624.82 –
open shrubs
Barren/degraded/ 51.80 224.93 209.86 150.21 92.45 411.98 684.24 1583.19 745.98 186.38
fallow/waste land, etc.
Mine pits 51.80 67.93 133.53 57.77 39.76 180.03 257.63 156.18
Barren dumps 89.41 75.77 – – – – – 369.35
Vegetated dumps 56.66 51.03 34.85 – – – – – – –
Wetlands 33.63 159.77 – 47.11 185.39 – 62.52
Water bodies 6.63 157.23 187.05 75.88 48.60 48.60 128.18 58.76
including mine pits
having water
Total area (hectares) 390.61 861.46 1920.24 1172.40 399.72 3777.91 2674.41 4517.51 3034.60 661.16
*Land-use classification and area are derived from the latest IRS satellite data of the study area.
able 8le 8
le 8le 8
le 8 Computation of groundwater recharge for each of the land–use class using watershed area and BALSEQ derived recharge rates for
different land-use classes
BALSEQ Watershed number and groundwater recharge in Ham
Land–use class recharge (m) B–1 B–2 B–3 B–4 B–5 B–6 S–1 S–2 S–3 S–4
Agricultural land 0.54 57.95 275.91 584.26 422.33 124.95 1078.62 748.88 989.86 528.17 138.28
Forest land 1.97 ––––– 1009.70 698.68 –
Builtup/industrial/ 0.69 46.41 36.62 – 176.05 1.70 9.72 –
hard surfaces, etc.
Pastures/grassland/ 2.08 ––––1996.53 496.91 1299.63 –
open shrubs
Barren/fallow/ 1.19 61.64 267.67 249.73 178.75 110.02 490.26 814.25 1884.00 887.72 221.79
Mine pits 1.19 61.64 80.84 158.90 – 68.75 47.31 214.24 306.58 185.85
Barren dumps 0.73 65.27 55.31 – 269.63 –
Vegetated dumps 1.46 82.72 74.50 50.88 – – – – –
Wetlands 0 0 0 0 0 0 0 0 0 0 0
Water bodies 0 0 0 0 0 0 0 0 0 0 0
including mine pits
having water
Total groundwater
Ham 329.22 698.92 1145.49 637.70 234.97 3810.21 2621.84 4293.41 3291.73 545.92
km3×10–5 329.22 698.92 1145.49 637.70 234.97 3810.21 2621.84 4293.41 3291.73 545.92
Ham – hectare metres; km3 – cubic kilometres
644 B S Choudri and A G Chachadi
Estimation of basin-wise groundwater draft in the mining area of North
Norms adopted in the present study
Based on the field knowledge and information, following norms have been
adopted for estimation of groundwater drafts.
1Domestic water requirement 80% of the total water demand (20% is assumed
to come from sources other than groundwater)
2Irrigation drafts 60% of the total irrigation water requirements (balance 40%
of the water requirement is assumed to be met from sources other than
3Industrial drafts 50% of the total water requirements (balance 50% is drawn
from other sources)
4Livestock drafts 50% of the requirements (remaining 50% is used from
sources other than groundwater)
5Wet beneficiation of ores 10% of the water added afresh (the details are seen in
the Table 5)
6Real Evapotranspiration losses from groundwater Real evapotranspiration
derived from BALSEQ model for paddy fields, forestlands, and vegetated
7Base flow to rivers, streams, and spring flow drafts 20% of the groundwater
recharge for all land covers
8Groundwater drafts through active mine pits Actual estimated values
Status of groundwater availability and recharge 645
able 9le 9
le 9le 9
le 9 Annual groundwater balance of different watersheds in North Goa
Norms adopted for
Groundwater ground water Groundwater drafts (Ham) in different watersheds
use category withdrawal B-1 B-2 B-3 B-4 B-5 B-6 S-1 S-2 S-3 S-4
Domestic water 80% of total 3.63 7.99 17.81 10.87 3.70 35.02 12.50 41.90 28.14 6.13
drafts demands (Table 1)
Irrigation water drafts 60% of total 35.41 168.61 357.05 258.10 76.59 659.15 457.65 604.91 322.77 84.50
requirement (Table 2)
Industrial water drafts 50% of total ––––– 4.534.50 –
requirement (Table 3)
Livestock water drafts 50% of total 0.172 0.379 0.845 0.516 0.176 1.662 0.875 1.988 1.335 0.291
requirement (Table 4)
Water drafts for wet
beneficiation of ores 10% of water added ––––126.00 49.00 – 140.00 130.00 147.00
afresh (Table 5)
Real Evapotranspira– Paddy field area 12.34 21.2 24.70 41.94 1.69 32.53 40.93 43.12 38.16 46.07
tion losses from × 0.382 m
Dense forest cover ––––––369.54 255.71 –
area × 0.721 m
Vegetated mine 35.64 32.10 21.92 ––––––
δυµπ × 0.629 m area
Groundwater contri– 20% of aquifer 65.84 139.78 229.10 127.54 46.99 762.04 524.37 858.68 658.35 109.18
bution to base flow recharge derived from
and spring from BALSEQ model
(Table 8)
Groundwater drafts Actual computed @ 202.00 232.00 –––––792270.00 –
through active mine of 2 m3 / ton of ore
Continued. . .
646 B S Choudri and A G Chachadi
Pits working below Mined out (Table 6) –––––
water table
Total groundwater
draft in the watershed
(Ham) 355.03 602.06 651.43 438.97 255.09 1543.90 1405.87 2772.81 1448.76 393.17
Total groundwater
recharge from
BALSEQ model
(Ham) 329.22 698.92 1145.49 637.70 234.97 3810.21 2621.84 4293.41 3291.73 545.92
Groundwater balance
(Ham) –25.81 96.81 494.06 198.75 –20.19 2266.31 1215.97 1520.60 1842.97 152.75
% Groundwater
utilization in the
watershed as on date 107.84 86.14 56.87 68.84 108.56 40.52 53.62 65.00 44.00 72.02
Categorization of the
watershed as per
CGWB (1984) Red Black Grey Grey Red White Grey Grey White Grey
Note Modified groundwater basin classification criteria
(1) White (non–cr itical): <50%; (2) g rey (sub–critical): 50%–75%; (3) black (critical): 75%–100%; (4) red
(most critical): >100% of recharged
groundwater is being used presently.
Norms adopted for
Groundwater groundwater Groundwater drafts (Ham) in different watersheds
use category withdrawal B-1 B-2 B-3 B-4 B-5 B-6 S-1 S-2 S-3 S-4
Table 9 Continued. . .
Status of groundwater availability and recharge 647
Problems identified through the study
The following problems in the mining area under study have been identified.
The suspended particulate matter in the mine discharge water used for
paddy cultivation could be a major threat to sustainability of fertility of these
agricultural lands. Besides, the direct surface run-off from the adjoining mine
dumps into the agricultural lands could add to the problem of siltation.
In some of the watersheds, the mine pit dewatering has caused depletion in
the groundwater levels in the adjoining villages, causing water stress condi-
tions. Therefore, there is a need to rejuvenate these depleted groundwater
reservoirs by some means of augmentation.
As a short-term solution, mining companies are supplying water through
their tankers to the problematic villages within their mine jurisdiction. How-
ever, the quality of this water needs to be monitored for maintaining the
required standards.
Some suggested solutions
The most effective way of handling the above-mentioned problems is through a
multi-stakeholder participation approach. The most probable and effective
nodal agency, which can co-ordinate these works, is the Mineral Foundation of
Goa. In the comprehensive groundwater balance report, the problematic water-
sheds have been identified under red and black categories. Using the MPR
(mine pit rehabilitation) methodology (TERI 2004), suitable and easily available
mine pits should be identified in cooperation with the local mining companies
for storage of rainwater to recharge the depleted aquifers. There is a need to
check the tanker water quality periodically for any contamination by random
sampling of the tanker waters.
The problematic watersheds categorized as water stressed include B1:
Sirigao; B2: Mulgao; B5: Piligao; S2: Pissurlem upper catchment. Immediate at-
tention should be paid to these areas for solving the water-related problems.
The authors gratefully acknowledge the DFID (TERI-WRC/2002WR43) authori-
ties for the providing necessary financial and infrastructure help to complete
this work. The authors are thankful to Sri R S Subramanian, Senior General
Manager, V M Salgaoncar and Bro. Pvt. Ltd, for providing daily rainfall data of
their station at Surla, North Goa. The first author expresses his gratitude to
Dr J P C Lobo-Ferreira, Head of Groundwater Research Division, LNEC, Lisbon,
Portugal, for providing training and transferring the model BALSEQ after
necessary modifications.
648 B S Choudri and A G Chachadi
Chachadi A G. 2002
Impact Assessment and Remediation of Open-cast Mine Dewatering on Rural
Drinking Water Supplies in Goa
[R&D project report sponsored by the Rajiv Gandhi National Drinking Water
Mission, Ministry of Rural Development, Department of drinking water supplies,
Government of India]
Goa: Department of Earth Science, Goa University. 132 pp.
Chachadi A G, Lobo Ferreira J P, and Oliveira M M. 2001
GIS and Mathematical Modelling for the Assessment of Groundwater
Vulnerability to Pollution: Application to an Indian Case Study Area in Goa
[Second year report of DG Research Programme INCO-DC. Interim Report of the
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64 pp.
Chachadi A G, Choudri B S, Naronha L, Lobo-Ferreira J P. 2004
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Ground Water Estimation Methodology
[Report of the ground water estimation committee]
New Delhi: Ministry of Irrigation, Government of India. 49 pp.
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Master Plan for Development of Groundwater in Goa State
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Bangalore: Government of India. 33 pp.
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Full-text available
The aim of this paper is to present several concepts and European, American, African and Asian case studies regarding the assessment of groundwater vulnerability to pollution. We highlight the results of a European Commission sponsored groundwater project developed in Portugal. The groundwater vulnerability method used was the DRASTIC, developed by ALLER et al. (1987) for the US Environment Protection Agency. The Portuguese case study was published by Lobo-Ferreira et al. (1995). In Section 2 of the paper, we review the criteria of vulnerability ranking used in the 70's and 80's for the elaboration of a few existing European Economic Community (EEC) vulnerability maps. What we consider to be some of their limitations are pointed out. In Section 3, we propose a definition of the term vulnerability in the context of groundwater pollution. In Section 4, we suggest a system of evaluation and ranking of groundwater pollution vulnerability as defined in Section 3, to be adopted by EU Member-States in the elaboration of their new vulnerability maps. The Portuguese DRASTIC groundwater vulnerability map is presented in Section 5 and an application of this methodology to two Chinese case-study areas is presented in Section 6.
Central Ground Water Board)
CGWB (Central Ground Water Board). 1984