Environmental tracers to evaluate groundwater residence times and water quality risk in shallow unconfined aquifers in sub Saharan Africa

In sub-Saharan Africa, shallow aquifer systems are relied on as the main safe and secure water resource available to rural communities. Information on the sustainability and vulnerability of groundwater abstraction is becoming increasingly important as groundwater development increases. As part of the UpGro Consortium Project- Hidden Crisis, 150 hand pumped boreholes (HPBs), ranging between 15 and 101 m depth were investigated to examine the resilience of aquifer systems in the Ethiopian Highlands, and the crystalline basement rocks of Uganda and Malawi. Environmental tracers (chlorofluorocarbons (CFCs), SF6, chloride and the stable isotopes of water), water quality indicators (nitrate and E. coli), and groundwater-level time series data were used to estimate groundwater residence time and recharge at a regional scale (100–10,000 km2) and investigate the risks to water quality and water supply over different timeframes, and geological and climatic environments. Average estimated recharge rates using three different techniques (CFCs, chloride mass balance, water table fluctuation method) were between 30 and 330, 27–110 and 30–170 mm y−1, for sites in Ethiopia, Uganda and Malawi, respectively. These estimates of recharge suggests abstraction from dispersed low-yielding HPBs is sustainable. Comparison of stable isotopes in rainfall and groundwater indicates that there is little evaporation prior to recharge, and recharge events are biased to months with greater rainfall and more intense rainfall events There was a weak correlation between nitrate and CFCs within all three countries, and no correlation between E. coli and CFCs within Ethiopia or Malawi. The presence of E. coli at a large proportion of the sites (Ethiopia = 38%, Uganda = 65% and Malawi = 47%) suggests rapid transit of contaminated surface water into the borehole and its presence in groundwater that has CFC-12 concentrations less than 75 pg kg−1 indicates mixing of very young water with water >40 years old. The rapid transit pathways are most likely associated with damaged HPB headworks and poor construction. In several monitored HPBs, daily drawdown due to pumping, drew the groundwater levels close to the base of the HPB, indicating that these HPBs were located in parts of the aquifer with low permeability, or were poorly designed, offering limited capacity for increased demand. Improved HPB siting and construction, coupled with groundwater level monitoring are required to capitalise on the more resilient groundwater within the shallow aquifers and safeguard adequate and good quality water supply for rural communities

Functionality and resilience of hand-pumped boreholes in sub-Saharan Africa

In sub-Saharan Africa as many as 184 million people rely on hand-pumps. Thus, hand-pumps are, and will remain, a crucial water source in a changing climate, although as many as one in three are non-functional at any time. Drawing on the results of three studies we demonstrate that hand-pumps are resilient and safe, and we examine the physical factors that determine hand-pump functionality. In the first study we analysed the performance of 5196 water points (hand-pumps, motorized boreholes, springs, open-sources) and the success of a proactive maintenance programme during the 2015-16 drought in Ethiopia. Water sources were visited every week for 12 weeks to gather data on access and functionality. The second study, again in Ethiopia, involved monitoring 51 groundwater points (hand-pumps, springs, hand-dug wells) over an 18-month period in 2016. Water sources were equipped with water level loggers and were tested monthly for thermo-tolerant coliforms. All sources were put under considerable strain during the drought. Most demand was placed on motorised boreholes in lowland areas. However, increases in functionality of motorised boreholes, as a result of the maintenance programme, lagged behind those of hand-pumps. Functionality was low for both sources at the on-set of the drought (65% and 75% respectively). Motorised boreholes had longer downtimes due to a lack of appropriate and/or accessible maintenance skills. Water level monitoring showed that hand-pumped boreholes recovered most quickly from daily abstractions. All sources were contaminated with thermo-tolerant coliforms during the rains marking drought cessation but hand-pumped boreholes were least affected. Our results show that hand-pumped boreholes are resilient and less prone to contamination than springs and hand-dug wells. However, like the other sources we studied, hand-pumps had low levels of functionality at the onset of the drought. To better understand the factors affecting functionality we systematically dismantled 150 hand-pumped boreholes in Ethiopia, Uganda and Malawi in 2017. We conducted detailed inspections of hand-pump components and borehole design. Water levels were measured and a pumping test was conducted to measure aquifer yield (transmissivity). In each country specific contextual factors influence functionality. In Ethiopia deep water levels (>60 m) strongly influence functionality. Many hand-pumps operate beyond lift limits (45 m). Aquifer yield is an order of magnitude larger for fully functional hand-pumps than partially functional hand-pumps in Ethiopia. In Uganda many hand-pumps are installed in aquifers with transmissivities close to the minimum required to sustain a hand-pump (c.1 m2/d). The use of galvanized steel components, along with corrosive groundwater, results in high rates of corrosion in Uganda. In all three countries hydrogeology, borehole design and pump condition interact to determine functionality outcomes. Our results reinforce the importance of appropriate borehole siting and design, on-going operation and maintenance and use of appropriate and good quality materials. When supported by responsive and proactive maintenance hand-pumped boreholes, which are less prone to contamination than other shallow groundwater sources, are a resilient water source in a changing climate and are capable of providing water continuously during drought

Handpump borehole functionality in rural Africa: using environmental tracers to evaluate groundwater residence times, water quality risk and supply in Shallow Unconfined Aquifers

Poor performance of water supply has been a persistent problem in rural Africa. The UPGro Hidden Crisis project (2015 – 2020) has brought together an interdisciplinary research team to investigate and identify different factors affecting the functionality status of boreholes equipped with hand pumps (HPs). A three-tiered survey approach to define and measure functionality was applied to 600 hand pumped boreholes across Ethiopia, Uganda and Malawi. The results, in agreement with national surveys, show that c.80% of hand pumped boreholes produce some water. However, <50% can deliver HP design yield reliably for more than 11 months of the year and far fewer provide water that meet WHO guidelines on chemical parameters and total thermo-tolerant coliforms (TTC). To determine the major contributing factors to functionality outcomes, detailed hydrogeological and engineering investigations, combined with social, institutional and economic factors, were conducted on a subset of 150 HPBs. Within this second survey a full range of HPB functionality outcomes (e.g. aquifer properties, borehole construction and the condition of HP components) were generated. In all three countries water level, aquifer yield, borehole construction and materials, and pump cylinder placement interact to produce conditions that are sub-optimal for HPs to meet design capacity (pumping head and yield). In many instances, the apparent groundwater age from the shallow HPs was at odds with the measured positive counts of e-coli, suggesting a mixture of different age waters and/or contamination issues related to well construction and completion. Improving our knowledge and understanding of handpump borehole functionality in rural Africa will provide the necessary hydrogeological and social frameworks (e.g. functionality monitoring and asset mapping and assessment) that are necessary in evaluating groundwater as a safe and secure water supply to meet the local demands and regional development pressures with the larger external changing climatic conditions