Geology for Global Development

Water and Sanitation

Guest Blog: Managed aquifer recharge in coastal Bangladesh

Donald John MacAllister has a BSc in Geophysics from the University of Edinburgh and an MSc in Water Management from Cranfield University. He has spent three years working as a hydrologist and water engineer, both in the UK and in the international development sector. He is currently pursuing a PhD at Imperial College London researching the use of a naturally occurring geoelectric phenomenon  to monitor saline intrusion into freshwater aquifers. Donald has done extensive practical work on groundwater on the Indian sub-continent, and here he discusses how we can improve water security in coastal Bangladesh. This blog post draws on a recent presentation by Dr. Kazi Matin Ahmed from the University of Dhaka in Bangladesh. Dr. Ahmed shared some of his recent work with staff and students in the Civil Engineering Department at Imperial College London.

Managed Aquifer Recharge (MAR) is increasingly used around the world for improvement of water storage. MAR consists of adding water, possibly recycled water, to an aquifer under controlled conditions for withdrawal at a later stage. Recent research suggests it may also be a useful tool for improving water access in coastal Bangladesh.

Water supplies in coastal areas of Bangladesh often suffer from salinity problems caused by coastal flooding and seawater intrusion. The problem is compounded by the highly seasonal nature of rainfall which predominantly falls in three to four months during the monsoon from June to November. Throughout the rest of the year these areas suffer from a lack of potable water.

Traditionally, pond water has been the main water source for coastal communities in Bangladesh. These ponds store rainwater that has fallen during the monsoon. However they are highly vulnerable to contamination, both from runoff and from salinity problems due to storm surges and sea level rise. The ponds undergo high rates of evaporation during the dry season. Shallow aquifers tend to be brackish due to seawater intrusion and little groundwater development takes place. There are very few handpumps in the area. As a result tankers are commonly used to bring freshwater into the area during the dry season.

The work carried out by Dr. Ahmed and his team looked to address this problem by applying Managed Aquifer Recharge. The recharged water was intended to create a freshwater buffer in shallow aquifers. The team hoped to provide the freshwater buffer by artificially recharging the aquifers during the rainy season using water from the ponds, and in some places from rooftop rainwater harvesting. The freshwater could then be abstracted during the dry season to provide a more reliable and protected water source for domestic use. Twenty sites were then selected based on the water available from ponds, the relative roof area available for rainwater harvesting and the characteristics of the aquifer. The main hydrogeological requirements were a thin clay layer (less than 15m) and a relatively thick aquifer (about 20m). Socio-economic factors were also considered. These included the capacity of local NGO’s to run and manage the system, the interest and support of the local public health engineering department (PHED) and crucially the willingness of the community to participate in each stage of the process – community support and participation is critical to the success of any activity in development, and should always be considered throughout the project cycle.

Conceptual model of the managed aquifer recharge system created in Bangladesh. Adapted from an image in the Acacia Water Report

Once the community were on board and the sites were selected the project commenced withthe drilling of one large diameter well and two monitoring wells. The large diameter wells were filled with gravel and used to recharge  the aquifer. The flow through the infiltration well is metered to measure the total recharge provided to the aquifer. When rooftop rainwater harvesting was used as the primary source for recharge, the system was effectively gravity driven. In the case of pond water supply the water was pumped from the pond into a sand filter. The sand filter reduced turbidity which is a big problem in these types of water sources. The pond water was then driven by gravity flow through the infiltration well. There are plans to use subsurface sand filters to reduce the pumping costs – potentially making the whole systems gravity driven and hence more financially viable in the long term.

The monitoring wells were primarily used to monitor electrical conductivity of the system to determine the change in salinity in the aquifer. The team set up an SMS based monitoring system allowing the monitoring teams to send the data via mobile phone to the team based at Dhaka University. It was found that the system reduced electrical conductivity at all sites. The maximum reduction in electrical conductivity was found to be about 85%, where the conductivity was reduced from 5930 uS/cm to 838 uS/cm, considering the former is classified as brackish water and the latter as freshwater this is a hugely encouraging result.

The system as it looks on the surface. Left – the recharge well and monitoring wells surrounding the handpump used by the community for abstraction. Middle – the recharge well. Right – Construction of the system. Source Acacia Water Report.

Dr. Ahmed emphasised the need for ensuring all the stakeholders were on board from the outset, and ensuring that the community operators are properly trained, as the team observed differences in successes levels between the communities who were more involved and those that were less involved.  It also found that where rooftop rainwater harvesting was the only source of recharge the quantity of water supplied to the aquifer was not enough to sufficiently reduce the conductivity. In addition the recharge rate needs to be consistent otherwise the conductivity in the aquifer can recover, more infiltration means more freshwater storage and decreased salinity providing a more resilient community water supply.

Clearly this is early days for Dr. Ahmed and his team, but the initial results suggest that the technique could help improve water security in coastal Bangladesh. Further monitoring and assessments are required before this can be rolled out to further areas of Bangladesh, however this project is hugely exciting because it illustrates very clearly the benefit geoscientists, and in this case hydrogeologists, can bring to the water and sanitation sector. It is an excellent example of the types of innovative technologies that are becoming routine in more developed countries being used to solve water supply problems in the development sector. It is also a great example of geoscience research being used to solve real world development problems.

 

For more information on the project please see this report by Acacia Water, a Dutch consultant involved in the project.

For more information on managed aquifer recharge please see DFID’s report  and this CSIRO information sheet.

 

Event: Water security at the Overseas Development Institute

Despite the clear advantages to investing in water and sanitation, water security remains an elusive goal for many communities around the world. We discussed the importance of a clean and reliable water supply last year in the GfGD Blog ‘water series‘.

The Overseas Development Institute are hosting a public event to discuss ‘water security: global concerns and local realities‘. This event marks the launch of a research drive into water security.

Speakers will include Lydia Zigomo (head of East Africa for Wateraid), Fekahmed Negash (Director of Boundary and Transboundary Rivers Affairs Directorate in Ethiopia) and Roger Calow (head of the water policy programme at the ODI), with discussion from Robert MacIver (DFiD).

The event will be held in the ODI on Blackfriars Road, London, 17.15 – 18.45 on the 6th February 2013. You can register to attend free of charge, and see the talk as well as look through a photo exhibition over refreshments. If you can’t make it in person then you can join in online with live streaming.

Follow #watersecurity on Twitter for live coverage.

Pumping clean water from a borehole in Ethiopia

In the News – November 2012

GfGD’s Director, Joel Gill, shares some of the things that have caught his eye in the news recently:

Natural Disaters: The past couple of weeks have seen a significant number of natural disasters, from earthquakes in Guatemala and Myanmar (Burma) to hurricanes in the Atlantic – impacting developing nations such as Haiti, and a landslide dam break in Indonesia. The earthquake in Guatemala triggered numerous landslides, and initial reports suggest that a significant proportion of those that died did so as a result of landslide activity.

Conflict Diamonds: In the past couple of days serious allegations have been made by the campaign group ‘Partnership Africa Canada’ (PAC) about the income from Zimbabwe’s Marange diamond fields. PAC alleges that more than £1.25bn has been plundered from this resource rich area of Zimbabwe, although the allegations have been denied by Zimbabwean mining officials. In 2011 the Kimberley Process controversially lifted the export ban on diamonds from this region amid serious concern about human rights abuses, violence and corruption. This disturbing report highlights the need for continued investigation and monitoring of these highly controversial diamond fields.

UK Aid: The UK Government last week announced that they would be ending all financial aid to India by 2015. Whilst India has one of the world’s fastest growing economies, it is also home to around 1/3 of the world’s poorest people. There is debate in the development community about the UK’s long-term decision, with particular concern from organisations such as Oxfam that cutting aid will impact upon these poorest communities. Many of these communities have no access to clean water and safe sanitation facilities. It is worth noting that the UK will still be providing technical expertise to the Indian government, and it is hoped that this will involve support in the important area of water and sanitation.

Water Series (3): Arsenic Contamination in Drinking Water

Following our post about fluoride contamination last week, our water series is now focused on the equally serious problem of arsenic contamination.

Some arsenic is present in all groundwater sources (see table 1). Of course this is only a problem if the arsenic has the chance to leak into groundwater as it filters through the rock. Arsenic leaching is more likely to occur in groundwater that is hot, oxygen-depleted, alkaline or extremely acidic.

Table 1: table of different geological rock types and their associated arsenic content (from UNICEF arsenic report, 2008)

Rock or sediment type Average arsenic content (parts per million) Range of arsenic content (parts per million)
Sandstone 4.1 0.6 – 120
Limestone 2.6 0.4 – 20
Granite 1.3 0.2 – 15
Basalt 2.3 0.2 – 113
Alluvial sand 2.9 1.0 – 6.2
Alluvial silt 6.5 2.7 – 15
Loess 5.4 – 18

A 2008 UNICEF report found that over 137 million people in more than 70 countries are probably affected by elevated arsenic levels in their drinking water (above 10 parts per billion is considered a risk to health). Arsenic can be transferred into the body through drinking contaminated water, or eating food that was irrigated using contaminated water.

There is no available treatment for the suite of health problems, collectively known as arsenicosis, caused by the build up of arsenic in the body over several years. Arsenic exposure can cause cancer, as well as vomiting, blindness and paralysis. High arsenic levels are a major problem in SE Asia. In Cambodia concentrations of up to 250 parts per billion have resulted in cases of arsenicosis so severe that amputations are required.

Small child using a well in Bangladesh. Photo taken by Donald John Macallister whilst working on a water project.

Arsenic poisoning can often remain undetected for a long time, as the symptoms do not occur until after a long, slow period of toxin build-up in the body. It is often health workers that have the first opportunity to identify the problem, but many are not trained to recognize the effects of early arsenicosis – lesions on the skin.

Once a high-risk area is identified, water samples can be taken over a wide area to map contaminated wells. The samples can be analysed in the field or sent back to a permanent laboratory. Field testing is cheaper and the results can be conveyed back to the relevant communities immediately, but laboratory testing may be necessary if more precise results are needed.

The most effective way to reduce exposure to arsenic is to identify contaminated wells and explain to the affected communities why they should avoid them. Communicating the severity of arsenic poisoning can be difficult, as arsenic in water can’t be seen or tasted, and there are no immediate consequences of drinking arsenic-contaminated water.

In cases where a local, uncontaminated well cannot be identified, the only option may be to remove arsenic from drinking water by passing it through an ultrafiltration membrane. Polyelectrolytes (long-chained molecules that acts like salt and dissociate in water) form complex molecules with arsenic that are too large to pass through the membrane. These large molecules form more efficiently at higher pH (8.5), as arsenic becomes more negatively charged (-2) and so is more attracted to the positive polyelectrolyte. Conveniently, groundwater often has a slightly elevated natural pH. The filter should have grains with a high surface area and high absorptive capacity. Goethite amended sand works well, with added iron oxide.

Filtering out arsenic can cause the concentration of other elements to drop as well, some of which, such as chromium, may be beneficial. It is always more desirable to source water from an alternative well than to filter water from an existing well.

 

UNICEF have produced an excellent and extensive report documenting their knowledge and experience of working with arsenic contaminated wells. To learn more, you can read it for free online.