Session 4: Protecting groundwater source(s)
Risks to Groundwater sources
QUIZ 3: Risks to Groundwater sources
Q: What are some of the risks to groundwater resources?
A:




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

Reduction of groundwater availability / Depletion of aquifer yield due to excessive drawdown,
sustainability, interference from other bores
Water quality impacts - contamination in the catchment and near the bore -eg salt water intrusion,
latrines, other pollutants
Protection of the bore itself -eg animals, agricultural runoff, dirty equipment, including vandalism
Contamination from upgradient contaminants, salt water intrusion
Set up costs, time lags, proper investigation and design
Costs of pumping, maintenance of pumps and fuel supply
Interruption to power or fuel supply (related to well infrastructure and delivery–session GW???)
Groundwater Drilling and Development _Session GWD4
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Reduction in groundwater availability
QUIZ 4: Reduction aquifer yield from a well
Q: Based on the previous discussion of geology and aquifer types and on well construction and
pumping effects, what factors will affect the amount of water that can be extracted from a well?
A: Type of aquifer, rate at which water flows back into a well, depth of the well and the length of
exposed area of screens/ well,
Q1: What will happen if the well is pumped at too high a rate:
A: There will be excessive drawdown and the well may dry out – risk then to the pump
Q2: What happens when the pump stops?
A: The water level is expected to recover to the pre-pumping level from flow of groundwater from
the aquifer into the well
Q3: What can be inferred if the water level does not recover to the pre-pumping level?
A: The inflow from the aquifer is not sufficient to replace the water pumped out and the pumping
rate is too high.
Q4: Does this apply to all wells?
A: Yes - if there is not sufficient groundwater inflow to the well to replace the volume that has
been removed it will apply to any type of well (ie hand dug wells as well as drilled bores with
carefully designed screens)
Q5: What might the long term effect of this be?
A: There will be a long term drawdown of the groundwater level in the aquifer and reduction in the
groundwater resource available until recharge occurs
Relevance to Emergency
The amount of drawdown detected in any type of well or the reduced flow in a spring, is related to the
balance between the amount of water removed from an aquifer and the amount that recharges.
Even if the volume can be extracted for extended periods (days, weeks or months), unless there is
adequate seasonal recharge into the aquifer, the water level and therefore the volume of groundwater
stored in the aquifer will be reduced and until it is ultimately unsustainable.
The short term effect is that if the rate of groundwater removal is too great on a particular day, the
yield of the well on that day may eventually decline and the well not be able to supply the volume
required.
To maintain supply of groundwater careful monitoring of groundwater levels in wells and in specifically
designed monitoring bores is needed to keep track of the changes due to pumping drawdown and
recovery due to recharge .
Groundwater Drilling and Development _Session GWD4
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Water Quality Effects
One of the advantages of using groundwater over surface water as a water source is that being
subsurface, groundwater is potentially protected from pollution and in some cases pollutants are
filtered in the soil or degrade between their entry into an aquifer and recovery in a well. However,
not all groundwater is of suitable quality for potable use.
The water quality in an aquifer can be influenced by naturally occurring chemical constituents in the
aquifer and also due to contamination by introduced chemicals. The availability of a groundwater
resource can be compromised by the groundwater chemistry even if there is a substantial available
volume.
Substantial guidance on the acceptable concentration of constituents is provided by the World
Health Organization (WHO) (Reference). Many countries also have adopted their own water quality
guidelines for drinking water and a range of other water uses.
Naturally occurring constituents
Salinity: The basic criterion of suitability of water for drinking is the salinity indicated by the Total
dissolved Solids (TDS). In the field, the groundwater salinity is often determined by the Electrical
conductivity (EC). The TDS is not directly equivalent to the EC and a ratio of around 0.6 -0.7 times
the EC is often applies
Naturally occurring groundwater can be less than 100mg/L (milligrams per litre) to more than 50,000
mg/L (Hem, 1985) According to WHO, the palatability of drinking water is considered to be good at
less than 600mg/L TDS, becoming much less palatable at above around 1000mgL/. Groundwater
salinity varies within an aquifer and between aquifers as discussed in section GWD_1.2.
Turbidity is less a problem in Groundwater than surface waters especially where wells have been
constructed and lined, although open wells (particularly hand dug wells) can yield very turbid water,
and in some places visible organisms.
Other constituents provide unpleasant odours or taste and while not likely to result in health
impacts in the short or long term. Dissolved Iron at high enough concentrations can cause an
unpleasant taste, and colour although there is no particular concentration considered to be toxic.
Iron also has the potential to cause fouling of wells screens as Ferrous Iron oxidises to Ferric and
deposits a slimy coating of iron bacteria. The Iron dissolved in groundwater can also lead to
corrosion of well materials. This can affect the integrity of the bore and long term reliability of
supply.
Dissolved Carbonate and bicarbonate that occurs naturally in groundwater is a measure of
groundwater hardness. Aquifer water containing elevated concentrations can lead to precipitation
and encrustation of pipes, although it is not likely to occur immediately and so is not expected to be
serious issue in the first phase of an emergency.
Natural toxic contaminants:
Groundwater Drilling and Development _Session GWD4
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Even in low salinity drinking quality water, there can be naturally occurring constituents that can
have negative impact on water quality as a potable source. As these constituents are naturally
occurring , they are likely to be relatively extensive in the aquifer. Some well known constituents are
Arsenic and Fluoride have been associated with health concerns.
High Fluoride concentrations, (>10mg/L) occur in aquifers associated with granitic rocks and deposits
derived from them that contain minerals such as Fluorspar and Fluorapatite, and have been found in
groundwaters in parts of India, China, Central Africa and south America. The WHO guideline for
drinking water is 1.5mg/L. A detailed study of Fluoride in Groundwater is underway by IGRAC (see
www.igrac.net/publications/153
Arsenic in groundwater drinking sources has also been responsible for serious health problems.
Arsenic is widespread in many igneous and metamorphic rocks as well as sediments and
sedimentary rocks. Groundwater is vulnerable to Arsenic contamination because it can be mobilised
by weathering and microbial action and is dissolved in groundwater it interacts with the minerals
that comprise the aquifer . While this is a common problem, a particularly severe and extensive case
of Arsenic contamination is in Bangladesh.
http://www.wedc-knowledge.org/wedcopac/opacreq.dll/fullnf?Search_link=AAAA:1878:60934793
http://www.wedc-knowledge.org/wedcopac/opacreq.dll/fullnf?Search_link=AAAA:8324:86458480
http://www.wedc-knowledge.org/wedcopac/opacreq.dll/fullnf?Search_link=AAAA:4502:30659360
see www.igrac.net/publications/302 for an overview of Arsenic in groundwater and additional
references
It must be noted that the majority of the problems with Arsenic are the result of long term
consumption of groundwater.
Contamination of Groundwater
Potable groundwater sources can be made unusable because of the health effects of artificially
introduced contaminants. Mechanisms that affect the quality of groundwater resources can be from
within the aquifer (eg a polluted aquifer) or seepage of contaminants from the surface or nearsurface and through the unsaturated zone into the aquifer. Once in the groundwater the
contaminants migrate, generally in the direction of the groundwater flow (remember sectionXXX).
A large range of contaminants enter aquifers as a result of anthropogenic activities.
Some of these are sources at individual sites these are referred to as point sources and are often
chemicals involved in industrial processes(eg organic pollutants such as various hydrocarbons,
metals and pesticides) introduced from spills of chemicals, leakage from landfills, leaking pipes or
underground storages).
A common type of groundwater degradation with rapid impact on health results from
microbiological contaminants (biological, bacteria and viruses ). These are often point source
especially when they are associated with latrines, although they can also occur from proximity of
wells to animal wastes. This may also be a source of nitrate. Ingestion of nitrate in drinking water
Groundwater Drilling and Development _Session GWD4
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can be the cause of the fatal illness Methhaemoglobinemia in infants . The WHO guideline
concentration for Nitrate is 10mg/L (NO3 as N).
Broader scale contamination, often referred to as diffuse sources of contamination result from a
regional scale activities. This includes nitrates and phosphates that are applied as fertilisers.
Mechanisms for entry of contaminants through soils and aquifers for a localised (point source) as per
fig below
The contaminant impact varies with soil conditions and the nature of the contaminant. In the short
term contaminant migration may not be rapid in some materials – particularly clays where the
groundwater flow rate is low, but in sands and in fractured rocks with strongly interconnected
fractures, there can very rapid migration through the soil / unsaturated zone into the aquifer and
contaminant impacts may be observed over short time frames particularly in shallow water table
areas. The distance that the contamination extend and the time it takes to travel there varies with
teh aquiifr properties and hydraulic gradient and also the nature of the contaminant.
Some contaminants degrade in the ground over time in the aquifer, eg some of the organic
contaminants.
Microbiological components have a short half life in groundwater and so lateral extent is likely to be
limited. A significant and the most easily identified is the bacterium Escherichia coli (E.coli) which is
one of the many constituents in the intestines of humans and warm-blooded animals. It is therefore
found in faeces. Within human and animal faeces, E. coli is present at a concentration of
approximately 109 per gram. In groundwater, the contaminant load can be very high.
Groundwater Drilling and Development _Session GWD4
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The length of time that E. coli survives in the environment , depends on factors such as sunlight,
temperature, other bacteria or microflora, and in what type of water sources such as surface water,
groundwater or in a piped system (Reference: Canadian Ministry of Health Website). Studies
suggest that E. coli survives for about 4-12 weeks in water containing a moderate microflora at a
temperature of 15-18°C (Kudryavtseva, 1972; Filip et al., 1987; Edberg et al., 2000).
E. coli rarely grows outside the human or animal gut (Geldreich, 1996) so it will not grow in the
water. So when it is found in water, it is a good indication of recent contamination from faeces. It is
therefore a common parameter measured in the field as an indicator of contamination.
Note: Some authorities suggest that latrines can be located 30m from wells because of the relatively
short life of bacteria and viruses, particularly where the water table is greater than 2m deep.
However before making a decision careful consideration must be given to the direction of
groundwater flow, the hydraulic gradient and the soil and aquifer type (the rate of groundwater flow
depends on these factors). In addition, in sandy soil, water can rapidly seep down to the water
table, thereby reducing the time at which microbes may enter the groundwater.
EXERCISE 8: LOCATING LATRINES AND WELLS
EXERCISE 8:- WHERE TO PUT WELLS and LATRINES– POTENTIAL SITE PLAN
What things need to be taken into account
When on a site, what would you do to protect the wells
Groups to consider a sanitary survey of possible impacts that looks at:
location and distance of sources of pollution from wells,
drainage – would wells be inundated in floods,
are wells protected from leakage of contaminants into the well,
how is water collected and
how would the groundwater in a well be protected for contamination during water
collection
The figure below shows the potential issues associated with not having adequate sanitation and
poor location of wells.
Groundwater Drilling and Development _Session GWD4
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Protection of the Well - Poor well construction / Deterioration of the headworks
Wells surrounds can be damaged by animals, there can be flooding around the well in
wet periods, dirty equipment entering the well and vandalism;
The seal of a bore must be maintained so that contamination does not migrate from
the surface into the well or be transferred into the well from contamination sources at
the surface by collection methods such as dirty buckets.
Contaminated water occurring on the ground surface in the vicinity of a well can seep
downwards into the well and contaminate the water in the well.
Groundwater Drilling and Development _Session GWD4
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:Poorly maintained well head at pumping well, Osire Refugee
Camp, Namibia
Filthy surrounds to shallow well and likely contamination introduced to a well by
rope. Note the broken hand pump has compromised the security of the well head. To access the well buckets are use. Gassire, Eastern
Chad
Sanitary well conditions at the well head but a
contamination source (pig pens) is immediately behind the fence (Nias, Indonesia, 2006).
Relevance to Emergency
Groundwater Drilling and Development _Session GWD4
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Siting of wells in relation to sources of contamination – not to be in the immediate flow path
Awareness of potential sources of contamination that may result in degradation of the groundwater
– a sanitary survey essential
Contamination in groundwater that might migrate to surface waters that may be water sources
A comprehensive guide to manage water quality including wells and springs is presented in Safe
water guide for the Australian aid program 2005, Australian Government Ausaid.
http://www.ausaid.gov.au/publications/pdf/safe_water_guide.pdf
Maintenance of aquifers and well infrastructure
Existing wells can be an immediate source of groundwater in an emergency, and can be an effective
way of upgrading existing groundwater sources without having to install new bores. There are a
number of issues relating to the use of existing wells, including wells installed as part of the
emergency response.
Note the need for ownership of the groundwater sources to be determined before commencing any
works at existing wells or springs.
Overuse of wells
A key issue is the availability of groundwater, because in an emergency, there can be an enormous
additional demand for water placed on the existing wells from increased population of displaced
people or refugees.
This can lead to reduced yield in a short period of time, resulting in excessive drawdown and strain
on the water resource as well as stress on the well and pumping infrastructure. In pumped wells,
evaluation of the well yield by monitoring daily pumping rates and drawdown is required and may
involve alteration to the pumping regime to meet demand.
For open wells from which water is taken by individuals in a community, overcrowding around the
wells can lead to excessive drawdown of the water level and reduction in supply. In this case access
issues may need to be controlled and alternative sources explored.
Repairing and disinfecting wells
Groundwater quality in wells can deteriorate for a number of reasons.
Hand dug wells;
In hand dug wells, this may be due to influx of contaminated water from flooding, Tsunami or
hurricanes, material from mudslides or litter from a range of sources.,
For example in Sri Lanka as a result of the Indian Ocean Tsunami, damage to existing wells resulted
from introduction of saline water, from introduction of litter into the well and from structural
damage such a soil collapse that allowed surface water to migrate into damaged wells..
In war torn locations existing wells have been consciously polluted by warring parties, including the
disposal of dead bodies.
Groundwater Drilling and Development _Session GWD4
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Litter in well, Banda Aceh, Indonesia
Cleaning wells can involve removal of waste and sludge from the well and disinfecting the well. This
involves cleaning the well lining with disinfectant (typically a chlorine solution), dewatering the well
and protecting the well from on-going sources. Refurbishment well platforms and surrounds is a key
benefit
http://www.oxfam.org.uk/resources/learning/humanitarian/downloads/TBN6_well_cleaning.pdf
Rubbish removed from the base of an open well during well
rehabilitation, Gassire, Chad
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Original well surrounds, above, rehabilitated apron
with drainage point.
Protected well site, including fenced off area to restrict
entry (Kailahun District, Sierra Leone). Village water committees monitor entry and there are rules regarding entry such as
removal of footwar to reduce potential contamination sources.
Deep drilled bores:
In the same way that shallow and hand dug wells can be contaminated, microbiological
contamination can occur in deep drilled bores. Disinfection can be undertaken by applying chlorine
solution and pumping groundwater. In this situation, it is important to make sure that surface
contamination is unable to enter the well.
Deep drilled bores installed with casing and well screen can suffer from longevity; most commonly,
corrosion of materials can occur , particularly if the screens are made of steel.
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In some deep drilled wells, reactions of dissolved constituents can occur that can result in reduced
efficiency or even fouling of the bore. Well screens have large surface areas and the chemical change
from anaerobic conditions in an aquifer to an aerobic environment in the well, allows reactions of
constituents such as sulphate, hydrogen sulphide and ferrous ions, and carbonates. This can result
in build up of bacterial growth that reduces the screen openings and reduces flow into the well. In
some situations Hydrogen sulphide can be generated producing odours and also lead to reaction
that may precipitate sulphide minerals. Dissolved Carbonates in groundwater can also lead to
precipitation of minerals that may reduce the efficiency of a well.
Techniques to examine these effects include inserting a borehole camera into the well to obtain a
view the condition of a well.
In the event that the well is damaged, for the first phase of an emergency it is unlikely to be justified
to take time to do well maintenance, and a simple approach may be to continue to use a well if
possible and to monitor drawdown and water quality. With time, a new well may be required to
replace existing wells, or as a water system is established, take the well offline and rehabilitate.
Treatment of wells in which screens are clogged or there is encrustation or fouling needs careful
assessment and specialist inputs and may not be a focus for first phase emergencies. However the
following may be attempted if considered suitable in the time frame. Types of rehabilitation after
Davis and Lambert include:
Blocked screen:
Redevelop the well by pumping
Chemical encrustation
specialist people)
Treat with acid solution (NB this is a safety issue and requires
Biofouling (iron bacteria)
Treat with strong chlorine solution
In the event of pollutants such as organic chemicals etc, the costs of identifying the extent of the
contamination, determining the remediation approaches and the clean-up system makes this an
unlikely activity in an emergency.
Groundwater Drilling and Development _Session GWD4
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Protection of Spring heads
Springs occur when groundwater within an aquifer naturally flows out at the ground surface. Water
extracted from springs has the same chemical constituents of the groundwater extracted from wells
intersecting the same aquifer. However being exposed and readily accessible, there are risks to
these spring derived groundwater sources. These are:
•
Quality is not controlled
•
Protection of the source eg from animals,
•
The seasonality of source
•
Depletion of flow to spring from overuse
•
Degradation of the spring surrounds – dirt, erosion of the feature
•
Conflict with local population that may already be using the spring source
The flow rate and seasonality of a spring source may govern the extent to which springs are
protected, particularly for large scale water use. Many of these risks associated with springs can be
managed by adequate design and maintenance of the spring collection method. Construction and
maintenance of a covered catchment collection chamber as well as fencing off direct access to a
spring by animals provides a high level of protection of the water source.
It is advisable to train local community and users of the management of the spring to ensure
ongoing quality and quantity of spring water. Tapped discharge pipes or dedicated collection
buckets prevent contamination during collection, and occasional cleaning of the springbox may be
necessary.
Dedicated buckets and collection cell, Nias,Indonesia
Key reference:
http://www.oxfam.org.uk/resources/downloads/emerg_manuals/draft_oxfam_tech_brief_springpr
otect.pdf as well as the references therein.
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Monitoring
QUIZ 5: Monitoring quiz
Q1: Why monitor
A:To keep an understanding of the on-going availability from a well / bore both yield volume and
quality.
Q2: What factors need to be considered in the design of a monitoring program
A: important thing about monitoring is to have a clear idea of the purpose of the monitoring, what
parameters need to be measured and at what frequency.
Q3: What type of information could be collected in relation to a groundwater source.
A: Typically range of parameters:
Water level;
Well yield (or amount of water taken per day by a community),
Various water quality parameters – typically e.coli and EC in first phase type situations, other
Data collection: – generally by hand, perhaps initially by NGOs and later by community. the
equipment required needs to be maintained. Minimum equipment needs for monitoring are an
electronic dipmeter and water quality meter(s). For microbiological testing, a Del Agua kit is a
standard tool although there are a number of other
Water level measurement
A dipmeter is used to measure the depth of water in wells. Electronic dipmeters have a an
electronic probe that is attached to a survey tape that triggers an alarm the probe contacts the
water. More detail on a dipmeters and other monitoring equipment are obtain from suppliers eg
Environmental Systems and Services (ES&S)
http://www.esands.com/Geosystems/Products/pgwm01.html
At a minimum, a weight attached to a length of cord can be used and the depth of water detected by
the sound of the weight hitting the water surface. In shallow wells, even a graduated stick can be
used.
Groundwater Drilling and Development _Session GWD4
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Dipmeter from ES&S (commercial website)
Hand monitoring of groundwater level with
electronic dipmeter
In some situations, data recording devices (data loggers) are installed so that a continuous record of
the parameter, particularly water level in bores can be measured. However these are perhaps not
the highest priority for a first phase emergency.
Groundwater Drilling and Development _Session GWD4
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installed data logger in a monitoring well during a
pumping test
Water Testing equipment
A DelAgua kit is an a example of a portable unit for microbiological testing of water (including
groundwater). Key components are the media and incubator to allow growth of bacteria that can be
counted. In addition, a turbidity measurement tube and pool tester for measuring chlorine and pH
are generally included.
Del Agua field testing kit (from
DelAgua website)
There are a range of other field water testing equipment for measuring parameters such as Electrical conductivity
( an indicator of water salinity, Temperature, Dissolved oxygen, Eh and pH as well as some specifically for
Arsenic and some heavy metals. Commercial suppliers (eg Wagtech) can provide details of instruments that
available and applicable to the situation and should be investigated before deployment.
Groundwater Drilling and Development _Session GWD4
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Data recording:
Can be done by hand onto field note books, or electronic data devices or transfer of data
(downloading) from loggers into electronic files
It is important in monitoring to clarify the data recorded and who is responsible for the data
collection, recording, evaluation and interpretation of data. It is no point simply monitoring a
parameter without analysing the data.
Example of the use of monitoring data for a pumping well:
Information monitored is flow rate, groundwater level during pumping and recovery level after
pumping stopped.
Groups to discuss what the graph may be indicating
The graph shows that over time the well is drawing down (6m in 5months) and there is a risk to
pump infrastructure as water level was dropping towards the pump , Drawdown was stopped when
the pumping rate was lowered – implications for community was lower availability.
Without examining the monitoring data the pump could have been damaged and potentially the
well over used and resource depleted
WASH Cluster – Water in Emergencies
Pumping rates:
GWD
2.3, 3 L/sec
Static Water level,
8m.
Pumping Water level
200mm diam
bore,
150mm casing
Screen: 12m long
Depths: 35, 40m
Groundwater Drilling and Development _Session GWD4
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Depth to water
0
2
4
6
8
10
12
14
16
18
20
22
24
20
18
16
pump set at 21.9
Groundwater Drilling and Development _Session GWD4
14
12
10
8
6 F1 (SWL)
4
F1 (PWL)
2
0 no of hours pumped
Number of hours pumped
8M
29 a r
-0
19 -Ma 4
r
10 -Ap - 04
r
31 -Ma -0 4
y
21 -Ma - 04
y
25 -Ju n - 04
16 -Ju l -04
31 -Au 04
g
3- -Au -0 4
S g
17 e p -0 4
27 -Se 04
p
8- -Se -0 4
O p
19 ct- -0 4
0
29 -Oc 4
t
9- -Oc -0 4
N t
19 ov -0 4
19 -No 04
v
29 -Ja n -0 4
9- -Ja n-05
F
19 eb -05
2- -Fe 0 5
M b
12 a r - 05
-0
23 -Ma 5
r
2- -Ma - 05
Ap rr-0 05
5
WASH Cluster – Water in Emergencies
GWD
Water level monitoring
Forage 1 Water Level trends
Date
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References for facilitators
Paper on groundwater, latrines and health
http://www.lboro.ac.uk/well/resources/well-studies/full-reports-pdf/task0163.pdf
Papers on cleaning and disinfecting wells, including seawater inundated wells in Tsunami affected
areas http://wedc.lboro.ac.uk/knowledge/notes_emergencies.html
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