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Effect of diffuse recharge and wastewater on groundwater contamination in Douala, Cameroon
- Source :
- Environmental Earth Sciences. 76
- Publication Year :
- 2017
- Publisher :
- Springer Science and Business Media LLC, 2017.
-
Abstract
- High water demand for domestic use in Douala with over 3 million inhabitants is met mainly by shallow groundwater. Field measurements and water sampling in January 2015 were carried out to examine the major controls on the groundwater composition and spatial view of ions in the water, timing of recharge and link between the recharge process and quality of the water. Fifty-two water samples were analysed for major ions and stable hydrogen and oxygen isotopes. Low pH values (3.61–6.92) in the groundwater indicated an acidic aquifer; thus, prone to acidification. The dominant water type was Na–Cl. Nitrate, which exceeded the WHO guide value of 50 mg/l in 22% of the groundwater, poses a health problem. Mass ratios of Cl−/Br− in the water ranged from 54 to 3249 and scattered mostly along the mixing lines between dilute waters, septic-tank effluent and domestic sewage. A majority of the samples, especially the high NO3 − shallow wells, clustered around the septic-tank effluent-end-member indicating high contamination by seepage from pit latrines; hence, vulnerable to pollution. Stable isotopes in the groundwater indicated its meteoric origin and rapid infiltration after rainfall. The δ18O values showed narrow ranges and overlaps in rivers, springs, open wells and boreholes. These observations depict hydraulic connectivity, good water mixing and a homogeneous aquifer system mainly receiving local direct uniform areal recharge from rainfall. The rapid and diffused recharge favours the leaching of effluent from the pit toilets into the aquifer; hence, the high NO3 − and Cl− in shallow wells. Silicate weathering, ion exchange and leaching of waste from pit toilets are the dominant controls on the groundwater chemistry. Drilling of deep boreholes is highly recommended for good-quality water supply. However, due the hydraulic connection to the shallow aquifer, geochemical modelling of future effects of such an exploitation of the deeper aquifer should support groundwater management and be ahead of the field actions.
- Subjects :
- Groundwater flow
Water table
0208 environmental biotechnology
Soil Science
Aquifer
02 engineering and technology
010501 environmental sciences
01 natural sciences
Groundwater pollution
Depression-focused recharge
Environmental Chemistry
Groundwater discharge
0105 earth and related environmental sciences
Earth-Surface Processes
Water Science and Technology
Hydrology
Global and Planetary Change
geography
geography.geographical_feature_category
Environmental engineering
Geology
Groundwater recharge
Pollution
020801 environmental engineering
Groundwater
Subjects
Details
- ISSN :
- 18666299 and 18666280
- Volume :
- 76
- Database :
- OpenAIRE
- Journal :
- Environmental Earth Sciences
- Accession number :
- edsair.doi...........f71cb997053a04c6225cf9fa4f24cff0