URBAN GROUNDWATER POLLUTION MONITORING:

CASE OF WATER SUPPLY AQUIFER OF ABIDJANJOURDA J.P1, KOUAME K.J2, SALEY M.B.1, KOUADIO H.B.1, ADJA M.G.2, DEH S.K 2 et KAKOU K.F 2

1 Laboratoire des Sciences et techniques de l’Eau et de l’Environnement (LSTEE) et Centre Universitaire de Recherche et d’Application en Télédétection (CURAT), U.F.R-STRM, Université de Cocody, 22 BP. 801 Abidjan 22, Côte d’Ivoire.2Laboratoire des Sciences et Techniques de l’Eau et de l’Environnement, U.F.R. STRM, Université de Cocody, 22 BP. 582 Abidjan 22, Côte d’Ivoire, O7371759 EMAIL: jourda_patrice@yahoo.fr

OBJECTIVE & METHODOLOGY

• In response to the serious sudden attacks on the water supply aquifer of Abidjan, laboratory STEE in the framework of UNESCO/UNEP jointly Project carried out 2 actions:

• a survey to identify the threats to the aquifer of Abidjan.

• The water quality monitoring and assessment of pollution in the aquifer and its source recharge areas.

CONCLUSIONS • The water supply aquifer of abidjan is threatened

Qualitatively, insufficient sanitation implies bad practices which pollute the water supply aquifer (Boreholes of southern Abidjan were abandoned because of nitrate pollution. Quantitatively (lower precipitation and sealing aquifer outcrop areas) has reduced recharge, aand has made water more scarce because of the growth of water demand and its overexploitation. If nothing is done to protect urban aquifer from now until 2015, the Abidjan population will be at risk with respect to is water availability and quality.

• Abidjan is located at the South of and is economic capital of the Ivory Coast (Côte.d'ivoire )

• Area: 57.735 ha• Population : about 4 million• Geology : coastal basin sediments Cretaceous to

Quaternary age. •• Groundwater resources : three aquifers of unequal

importance:•• Only the Continental Terminal aquifer called commonly "

Aquifer of Abidjan " is exploited for the water supply.RESULTS

1 MAJORS THREATS• Non-existence of the institutional framework• Non-respect of the public property utility• Embryonic network of sewage implies bad

practices • Lack of organised domestic waste disposal• Expansion of urbanization

Holes into which sludges from septic tanks are drained.

The hollows and the storm basins are used as septic tanks and as outfalls of wastewater and solid waste.

Reduced infiltration from surfaces sealed to groundwater recharge as a result of regionally extended urbanisation.

Sewage emerges in the valleys and is evacuated from the lagoon with when there is rainfall. Some sewage pits and ponds are

veritable septic tanks under open sky conditions representing a serious threat to the water supply aquifers

• Lack of respect for public property utility arising from uncontrolled construction causes contamination of groundwater and the associated wells fields.

• All borehole’s protection zones are invaded by the habitats and become intra-urban and are destined to be abandoned.

Pie Chart

Rate of individual on-site sanitation in the various municipalities of Abidjan

2 ASSESSMENT OF POLLUTION STATUS • TWO AXES OF POLLUTION DETECTED: SOUTH TO NORTH and TOWARDS EAST ( NEW AXE)

BOREHOLES CLOSED

BOREHOLE

STOPPED

Curves of variation of conductivity indicates 3 groups:

Third group corresponds to pollution level 2 & 3 (polluted water, axe South-North.

Second group corresponds to pollution level 1 (New axis of pollution toward East).

First group characterizes unpolluted water & second group characterizing water not polluted.

NITRATESSince October 1995, values continue to exceed potability standards in certain boreholes. This pollution progresses towards north in direction of the " clean " zone where the recharge is coming from.

Since July 1997 another direction of progressive pollution (ZO 6) is fpr the deep aquifer according to second the radial East-West one made its apparition;

At the bacteriological level, the monitoring shows healthy water (negative Culture) for all sites except western zone 6 (ZO 6) which contained, in June 2004, a high rate (909 u/100ml) of Escheriechia coli .The high percentage of nitrates and the presence of Escherichia coli in water of site ZO 6 prove that pollution have anthropogenic and recent origin, related probably to the infiltration of domestic wastewater amplified by the strong rains of May and of June 2004.

Western zone 6 borehole polluted by on-site sanitation which has ats it source nearby habitations

Variation of NO3 in some deep boreholes of the water supplyaquifer of Abidjan from 1994 to 2004.

RECOMMENDATIONSCreate an institutional framework for integrated water resources management to establish lawful measurements in the various agencies and domains linked to water: Establish an authority of waterDevelopment a real sanitation policy and create sewage and wastewater treatment stations for Re-use potential.Create a network of reliable piezometers to monitor the water tableCreate synergy among scientific community, NGOs, the various water users and the local and regional and state authorities who are responsible for water management and the aquifer and to also collect and disseminate information; Develop a strategy of management of waste disposal with the adjustment of suitable sites as needed according to the observed conditions of a healthy environment.

Boreholes closed

POLLUTION PROGRESSION

DISCLAIMER: Poster draft prepared by IWRM.org on behalf of the author(s). Any inconsistencies between author(s) input materials and the poster is unintentional.

Ivory Coast

COUNTRY AND CASE STUDY SETTING

DEWA