Hydrochemical and bacteriological features of the groundwater: southern border of the Rharb basin (Morocco) / Caractérisation hydrochimique et bactériologique des eaux souterraines:

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Hydrochemical and bacteriological features ofthe groundwater: southern border of the Rharbbasin (Morocco) / Caractérisation hydrochimiqueet bactériologique des eaux souterraines: bordureméridionale du bassin du Rharb (Maroc)Brahim Ben Kabbour & Lahcen Zouhria Department of Earth Sciences, Faculty of Sciences and Technology, University CadiAyyad, BP 597, Beni Mellal, Morocco.b Ecole Polytechnique de Lille, c/o Prof. J. Mania, UMR CNRS 8107, LML, Avenue PaulLangevin, F-59655 Villeneuve d'Ascq Cedex, France.Published online: 15 Dec 2009.

To cite this article: Brahim Ben Kabbour & Lahcen Zouhri (2005) Hydrochemical and bacteriological features of thegroundwater: southern border of the Rharb basin (Morocco) / Caractérisation hydrochimique et bactériologique des eauxsouterraines: bordure méridionale du bassin du Rharb (Maroc), Hydrological Sciences Journal, 50:6, -1149, DOI: 10.1623/hysj.2005.50.6.1137

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Hydrological Sciences–Journal–des Sciences Hydrologiques, 50(6) December 2005

Open for discussion until 1 June 2006 Copyright 2005 IAHS Press

1137

Hydrochemical and bacteriological features of the

groundwater: southern border of the Rharb basin

(Morocco)

BRAHIM BEN KABBOUR1 & LAHCEN ZOUHRI

2

1 Department of Earth Sciences, Faculty of Sciences and Technology, University Cadi Ayyad, BP 597, Beni Mellal, Morocco

2 Ecole Polytechnique de Lille, c/o Prof. J. Mania, UMR CNRS 8107, LML, Avenue Paul Langevin, F-59655 Villeneuve d’Ascq Cedex, France [email protected]

Abstract The western reservoirs represent the principal groundwater system in Morocco. Demographic, industrial and agricultural developments during the last decade have markedly altered groundwater quality. The Mamora coastal aquifer system is among the Atlantic systems which are most heavily threatened by pollution. Agricultural and industrial activities, and rapid urban growth contribute to the pollution of the groundwater. Contamination transport is facilitated by a high permeability of the aquifer formations. In order to assess the actual groundwater quality of the Mamora aquifer and to understand the influence of the factors generating the pollution, an extensive multidisciplinary research programme is in progress, with hydrochemistry and microbiology playing essential roles. The present paper concerns the spatial distribution of physico-chemical parameters in the groundwater, subjected to domestic, industrial and agricultural pollution. Fifty-seven samples were analysed for several parameters (Ca

2+, Mg

2+, Na

+, K

+, Cl

-, SO4

2-, HCO3

-,

NO3-, pH, electrical conductivity and temperature). The microbiological analysis of

143 samples reveals the presence of four kinds of indicator bacteria in the ground-water resources: faecal Streptococci, faecal coliform, Escherichia coli and Clostridium. The physico-chemical results and bacteriological monitoring show that the nitrate and bacteria concentrations exceed the maximum admissible levels, notably around pumping stations in the sectors of Sidi Taibi, Sidi Ahmed Taleb and Aïn Sbaâ. Contamination is generated by uncontrolled anthropogenic activities and accentuated by the high intrinsic vulnerability of the aquifer system. Several parameters appeared to exceed admissibility standards. Measures are recommended to prevent groundwater pollution in the region.

Key words assessment; bacteria; contamination; groundwater; monitoring; Morocco; nitrates

Caractérisation hydrochimique et bactériologique des eaux souterraines: bordure méridionale du bassin du Rharb (Maroc) Résumé Les aquifères occidentaux représentent le principal système hydrogéologique du Maroc. Le développement démographique, industriel et agricole de la dernière décennie a fortement dégradé la qualité des eaux souterraines. Le système aquifère côtier de la Mamora est le plus fortement menacé par la pollution parmi les systèmes Atlantiques. Les activités agricoles et industrielles, ainsi que le développement urbain rapide, contribuent à cette pollution des eaux souterraines. La contamination est facilitée par une forte perméabilité des formations aquifères. Afin d’apprécier la qualité réelle des eaux souterraines de l’aquifère de la Mamora et de comprendre l'influence des facteurs générateurs de pollution, un ambitieux programme de recherche pluridisciplinaire fondé sur des approches hydrochimiques et microbiologiques a été mis en place. Cet article s’intéresse à la répartition spatiale des paramètres physico-chimiques dans les eaux souterraines victimes de pollutions domestiques, industrielles et agricoles. 57 échantillons ont été analysés en termes de plusieurs paramètres (Ca

2+, Mg

2+, Na

+, K

+, Cl

-, SO4

2-, HCO3

-, NO3

-, pH, conductivité

électrique et température). L'analyse microbiologique de 143 échantillons indique la présence dans les ressources en eaux souterraines de quatre genres de bactéries indicatrices : streptocoques fécaux, coliformes fécales, Escherichia coli et Clostridium. Plusieurs paramètres ont dépassé les normes d’admissibilité. Cet article envisage des mesures à prendre pour lutter contre la pollution des eaux souterraines de la région.

Mots clefs diagnostic; bactéries; contamination; eau souterraine; surveillance; Maroc; nitrates

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Brahim Ben Kabbour & Lahcen Zouhri

Copyright 2005 IAHS Press

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INTRODUCTION

The coastal aquifer system of the Mamora basin is located between the Rifean

cordillera in the north of Morocco (Fig. 1), the Hercynian Meseta in the south and the

Atlantic Ocean in the west. The study area is about 390 km2, half of which is covered

by forests composed of native (cork oak) and introduced (eucalyptus, pine and acacia)

species.

The Mamora basin is characterized by a Mediterranean climate. The temperature

varies between 13°C in winter and 27°C in summer (Zouhri & Colbeaux, 2003). The

groundwater recharge is principally estimated to be 25% of the average annual rainfall

of about 560 mm year-1

(Zouhri, 2000; Zouhri & Colbeaux, 2003). The exception to

this was in 1996, when 1163 mm was recorded in Rabat and 1132 mm in Kenitra.

The socio-economic development in the area is generally dependent on ground-

water abstraction, which has increased since 1940 (Zouhri, 2002b). Agriculture is the

principal economic activity in the region providing 53% of industrial jobs, in particular

in the food production sector. The Kenitra region has 1 million inhabitants; 56% of

them in rural areas.

The hydrographic network in northwestern Morocco, for instance, in the Sebou

River basin of 40 000 km2, is well developed. Various industries (paper mills, sugar

plants, tanneries, food industries) have developed in this region. However, the sector is

not equipped with facilities for the treatment of either industrial or domestic waste-

waters. Anthropogenic activities generate a variety of domestic, industrial, urban and

agricultural pollution. Many contaminated water supply wells have been investigated

(Annoua & Himmi, 1992; Mouaddine, 1997; Zouhri, 2003). The detection of pollution

in the recharge zones has raised serious concerns with regard to the quality of the

drinking water. The movement of the population from rural areas to the vicinity of the

Fig. 1 Structural domains of Morocco and location of the study area.

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Hydrochemical and bacteriological features of the Mamora basin groundwater


1139

capital city Rabat and to the Kenitra area, has contributed to shanty town expansion

and the development of unhealthy habitats: settlements which discharge liquid and

solid wastes directly into permeable bodies or into abandoned quarries.

In this paper, the hydrochemical quality of the Mamora groundwater resources is

examined. Bacterial contamination in this aquifer system was studied by the analysis

of 143 samples collected in the active abstraction wells, which are uniformly dis-

tributed across the study area. The data obtained were then analysed by statistical

approach, in order to determine the origin of the contamination and its spatial

evolution.

GEOLOGY

The analysis and interpretation of hydrogeological borehole logs (Zouhri, 2002a,b;

Zouhri et al., 2004) show that the aquifer is formed by Plio-Quaternary deposits

(sandstone, unconsolidated sand, limestone and conglomerate). Its structure (mono-

layered, generally unconfined) was regarded for a long time as homogeneous with

some local undulations (Thauvin, 1966; Combe, 1975; DGH, 1995). The permeable

bodies rest on the Mio-Pliocene blue marl substrate. The area is overlain by highly

permeable sandy layers.

The geometry of the aquifer is characterized by raised and subsided blocks (Zouhri

et al., 2001) which are controlled by two NE–SW and NW–SE fault sets. This

structure influences the aquifer partition and the groundwater flow (Zouhri, 2002b).

HYDROCHEMISTRY AND BACTERIOLOGY ASPECTS

The coastal aquifer system of the Mamora basin is unconfined. The groundwater flows

toward the north (Rharb basin) and west (the Atlantic Ocean) (Fig. 2). The aquifer base

is underlain by Mio-Pliocene blue marls. The saturated and vadose zones are generally

composed of calcarenitic deposits. Their transmissivity values are about 1.5 × 10-1

m2 s

-1

and the storage coefficients are 3.6 × 102. The study area is covered by sandy forma-

tions which have an infiltration coefficient fixed at 25% (DRPE, 1989; Zouhri, 2000).

Groundwater recharge is exclusively from rainfall, at 132.5 mm year-1

. The abstraction

rate is about 38 mm year-1

. Seventy-five percent of abstracted water is intended to

supply the urban industrial sectors (Kenitra: 42%, Sale: 53%, Bouqnadel: 3.8% and

Mehdia: 1.2%), and the remaining 25% is used for agricultural activities (DRPE,

1989).

Physico-chemical parameters

The groundwater chemistry of the Mamora aquifer system has been studied in terms of

the major ionic constituents: Ca2+

, Mg2+

, Na+, K

+, Cl

-, SO4

2-, HCO3

-, NO3

- and the

physical parameters (pH, electrical conductivity, EC and temperature, T). The physico-

chemical parameters have been measured at 57 boreholes tapping the aquifer (Ben

Kabbour, 2002). The analysis methods used are summarized in Table 1.

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Fig. 2 Piezometric map of the study area (in summer 1999 and 2000) [1. Pumping station, 2. Observing wells, 3. Dividing limit, 4. Drainage axis, 5. Piezometric level in summer (2000), 6. Piezometric level in summer (1999), 7. Groundwater flow, 8. Cities].

Table 1 Physico-chemical methods used for groundwater analysis.

Element Method of analysis

Na+, K

+ Spectro-photometry

Cl- AFNOR NFT 90-014 Norm

HCO3- AFNOR NFT 90-036 Norm

SO42-

AFNOR NFT 90-040 Norm

NO3- ISO 7890-3 Norm

Ca2+

, Mg2+

Atomic absorption

pH Jenco electronic, LTD Models 6209

Electric conductivity (EC) Field conductometer

The ionic balance is computed by the following ratio (Banton & Bangoy, 1999):

Error (E) = 100×+−

� ��

anionscations

anionscations (1)

(cations and anions in mEq L-1

)

Errors vary between 0.006 and 0.05. If the error is less than 5%, the analysis is

acceptable (Banton & Bangoy, 1999).

Analysis and interpretation of the saturated zone reveal a thickening of the Plio-

Quaternary deposits towards the Atlantic Ocean and towards the Rharb basin (Fig. 3).

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Fig. 3 (a) Location of drillings realized in the study area; (b) thickness map of the saturated zone of the Plio-Quaternary aquifer of the Mamora basin.

For Streptococci, total coliforms, faecal coliforms and Clostridium, bacteriological

analysis was performed on samples collected from 143 wells. The samples were taken

in sterile glass bottles and then stored at 4°C. They were transported to the laboratory

and analysed after a short preservation time. The analysis stages consisted of:

(a) Membrane filtration: allowing concentration of the bacteria to be determined; and

(b) Evaluation of bacteria counts: the membrane and filtrate deposited on an agar

surface with a specific medium for each type of bacteria (e.g. Chapman medium

for the total coliforms, Slanetz medium for the Streptococci). The appropriate

medium was identified in collaboration with microbiologists. Statistical results

summarizing the chemical analyses are provided in Table 2.

The spatial distribution of the electrical conductivity, EC, is presented in Fig. 4(a).

This parameter reveals the sector which is characterized by a strong mineralization of

water. Three types of mineralization can be identified in the Mamora groundwater in

accordance with the classification of Rodier (1992):

Table 2 Statistical parameters of the major elements content (mg L-1

) analysed from 57 wells pumping in the Mamora coastal aquifer (summer 2000).

T(°C)

Salinity (mg L

-1)

EC pH Na+(+) K

+ Mg

2+ Ca

2+ Cl

- SO4

2- HCO3

-

Mean 20.91 613.97 1006.5 7.17 106.00 14.00 248.70 120.73 27.70 248.95

Median 21.00 556.93 913.0 7.2 80.00 11.89 248.5 101.15 15.85 250.5

Mode 20.00 358.07 587.0 7.3 36.00 2.79 250.00 33.79 5.00 260.00

SD 1.14 293.41 481.0 1.14 80.00 12.17 22.19 87.34 23.67 23.28

Minima 17.5 317.81 521.0 6.68 31.00 1.01 195.00 33.79 4.00 165.00

Maxima 25.00 1604.91 2631.0 7.3 391.00 57.98 346.00 423.00 80.00 360.00

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Fig. 4 Spatial distribution of the physico-chemical parameters in the Mamora ground-water: (a) electrical conductivity and (b) chloride concentration.

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333 < EC < 666 µS cm-1

: marked mineralization

666 < EC < 1000 µS cm-1

: significant mineralization

EC > 1000 µS cm-1

: high mineralization

The analysis results (Fig. 4(a)) show a strong mineralization of the water, notably near

Rabat, Kenitra and Sidi Bouqnadel, where the electrical conductivity is about 1000,

800 and 900 µS cm-1

, respectively. Chloride concentrations (Fig. 4(b)) are marked by

the same spatial configuration with: 120 mg L-1

in the Rabat city sector and 80 mg L-1

in the Sidi Bouqnadel and Kenitra sectors.

Several climatological, geological and hydrogeological factors can affect the

groundwater geochemistry. The description of the hydrochemical facies is presented

by a Piper diagram (Fig. 5). Examination of Fig. 5 indicates the dominance of two

hydrochemical facies: alkaline water (Ca+Mg-CO3+HCO3) and saline water (Na+K-

Cl). The first facies is due to the presence of the sand dunes in the area. The source of

the second facies could be saline intrusion from the western part of the Mamora.

The mineralization of water of the Mamora aquifer may be caused by marine

intrusion, which is promoted by groundwater abstractions for supplying the region

with drinking water (Zouhri, 2003). However the salinity is not a critical problem for

the groundwater in comparison with other aquifers belonging to the Atlantic margin or

Mediterranean coasts of Morocco (Lhadi, 1996; Fakir, 2001; El Mandour et al., 1996).

Fig. 5 Hydrochemical facies obtained by the Piper diagram. Water types—Normal earth alkaline water: (a) with prevailing bicarbonate; (b) with prevailing bicarbonate and sulphate or chloride; (c) with prevailing sulphate or chloride. Earth alkaline water with increased proportions of alkalis: (d) with prevailing bicarbonate; (e) with prevailing sulphate and chloride. Alkaline water: (f) with prevailing bicarbonate; (g) with prevailing sulphate-chloride.

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Fig. 6 Durov diagram based on the hydrochemical data of the Mamora groundwater.

By plotting the major ions as percentages of milli-equivalents, a Durov diagram

(1948) provided more information on the hydrochemical facies (Fig. 6) by helping to

identify the water types. The values of cations and anions are plotted in the appropriate

triangle and projected into the square of the main field. The advantage of this diagram

is that it can display some possible geochemical processes that could affect the quality

evolution of water. The Durov diagram for the major cations and anions is plotted

using Aquachem software.

The fields and lines on the diagram show the classifications of Lloyd & Heathcoat

(1985). The spatial distribution of ions is located in field 1 (Fig. 6), between 4 and 5.

In the western part of the Mamora, the lithological heterogeneity in the aquifer is

marked by the Plio-Quaternary deposits (limestones, sandstones, sands and clays)

covering the blue Mio-Pliocene basement (marls). The predominance of HCO3- and

Ca2+

, as shown in the Piper diagram, indicates recharging waters in limestone,

sandstone and sands aquifers. The mapping of the hydrogeological formations (Zouhri,

2000) indicates that salt-rich waters are found notably in the northeastern part of the

Mamora, where Ca2+

dominates. The presence of SO42-

frequently indicates a recharge

in a mixed water or a simple dissolution.

Nitrate pollution

The monitoring of nitrate pollution in many wells reveals that the standard acceptable

limit of 50 mg L-1

has been exceeded. High nitrate levels occur in two principal zones:

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Fig. 7 (a) Spatial distribution of groundwater nitrates (in mg L-1

, August 2000); and (b) location of wells.

The first zone is around Sidi Ahmed Taleb and Aïn Sbaâ pumping stations (Fig. 7)

where nitrate concentrations can exceed 300 mg L-1

. Several factors can explain the

increasing concentrations:

(a) the infiltration of water contaminated by agricultural activities: the aquifer is

perched and it is directly exposed to agricultural pollution; and

(b) the spreading of industrial solid and liquid wastes.

The second zone of anomalously high nitrate occurs around Sidi Taibi (Fig. 7),

located to the south of Kenitra town. Nitrate concentrations are less than 100 mg L-1

and decrease towards Rabat. Pollution in this zone may be caused by the leakage of

wastewater from septic tanks, traditionally built for sewage disposal in the shanty

towns expanding rapidly in this area, or by infiltration of irrigation water. The lowest

levels of nitrate content (<50 mg L-1

) are found in wells located in the Mamora forest.

Bacteriology

Four types of bacteria have been studied in 143 samples taken for the Mamora

groundwater analysis: faecal Streptococci, faecal coliform, Escherichia coli and

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Table 3 Descriptive statistical analysis of groundwater bacteria (in cfu per 100 mL, summer 2000).

Bacteria species Faecal coliforms Escherichia coli Faecal Streptococci Clostridium

Average 42 6 9 3

Median 9 0 0 0

Mode 4 0 0 0

SD 135 25 32 5

Minima 0 0 0 0

Maxima 1100 240 240 20

Total samples 143 143 143 143

Fig. 8 (a) Faecal coliform, (b) Escherichia coli and (c) faecal Streptococci distribution in the Mamora groundwater.

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Clostridium. Their statistical parameters are summarized in Table 3 and in order to

understand their distribution, three maps have been generated (Fig. 8(a), (b) and (c)).

(a) The faecal coliform type (Fig 8(a)) was found to exceed 1000 cfu mL-1

in Sidi

Taibi and Sidi Ahmed Taleb regions. However, in the Ain Sbaâ sector, the

concentration of this kind of bacteria does not exceed 240 cfu mL-1

.

(b) A maximum of Escherichia coli concentration (Fig. 8(b)) of about 240 cfu mL-1

was observed in Sidi Taibi and Ain Sbaâ zones. However, for Sidi Ahmed Taleb,

this concentration does not exceed 90 cfu mL-1

.

(c) High concentrations (240 cfu mL-1

) of faecal Streptococci (Fig. 8(c)) were

identified in the Sidi Taibi and Ain Sbaâ zones. In the Sidi Ahmed Taleb area, the

concentration recorded was about 93 cfu mL-1

.

(d) The concentrations of the Clostridium species, reached 20 cfu mL-1

in a well

situated in the vicinity of Ain Sbaâ station.

The bacteriological analysis results for Streptococci and coliforms indicate that

faecal pollution has originated from animal wastes and human excrement. The

existence of one of the four types of bacteria does not necessarily imply the existence

of the other. Indeed, the coliforms are more sensitive than the Streptococci and can

disappear in a short period of time as they fail to survive outside the human or animal

bodies. Consequently, their existence indicates an unquestionable pollution by animal

or human excrements, but their absence does not indicate that groundwater is healthy

from a microbiological point of view.

The high infiltration coefficients of the surface soils, and the strong vertical

permeability of the unsaturated section, facilitate the transfer of bacteria towards the

aquifer. In addition, this may be due to the bio-films constituted on the walls of the

karstic network (Dussart et al., 2003; Dussart-Baptista et al., 2003; Whiteley et al.,

2001). These bacterial films or bio-films have a very specific behaviour and can be

released into the groundwater under random space-time conditions. Consequently, in

order to avoid bacterial and nitrate contamination, it is necessary to stop several

activities and practices in the area, such as: (i) the construction of permeable traditional

septic tanks (in shanty towns); (ii) the spreading of animal excrement in badly selected

sites; (iii) the use of organic fertilisers; (iv) the removal of liquid wastes towards the

topographic basement (e.g. abandoned quarries); and (v) domestic and industrial

landfill on badly selected sites.

DISCUSSION AND CONCLUSION

The hydrochemical and bacteriological analyses show that nitrate and bacteria concen-

trations do not meet water quality standards in several wells, especially in the Sidi

Ahmed Taleb, Sidi Taibi and Ain Sbaâ zones. This contamination reflects the impacts

of human activities on the groundwater quality and the strong intrinsic vulnerability of

the aquifer. The area most affected by nitrate contamination corresponds to the zones

which are characterized by a vadose zone of thickness below 5 m. The area with a

vadose zone thicker than 10 m shows a concentration of less than 50 mg L-1

of nitrates

(Fig. 9(b)). Nitrate pollution has been detected in those areas which are dominated by

intensive agriculture, settlements and industrial activity (Fig. 9(a)). Consequently, the

wells located in the vicinity of contamination sources should be routinely analysed.

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Fig. 9 (a) Map of the coastal Mamora land use, deduced from topographic maps, aerial photography and field missions [1. Forest, 2. Extensive agriculture, 3. Habitation and industries, 4. Intensive agriculture, 5. Military base, 6. Nuclear reactor, 7. Municipal landfill, 8. Pumping station, 9. Cities, 10. Highway, 11. Road, 12. Railway]; and (b) depth (D) to water table (m).

The protection of pumping stations and hydrogeological consulting must be imple-

mented. In order to set up protectionist measures, the following recommendations are

made:

– settlement downstream of the aquifer, parallel to the coast, should be encouraged;

– unsanitary conditions from settlements, industry and intensive agriculture should

be prevented, in particular in zones with high pollution susceptibility;

– the forest should be protected and extended. This latter activity will protect surface

soils and further protect the aquifer from pollution.

Acknowledgements The authors are grateful to anonymous reviewers, the Editor,

Dr D. Vachard (CNRS, University of Lille I, France) and Dr J.-P. Colbeaux

(University of Lille I, France).

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Received 27 August 2004; accepted 18 July 2005

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Documents

Hydrochemical and bacteriological features of the groundwater: southern border of the Rharb basin (Morocco) / Caractérisation hydrochimique et bactériologique des eaux souterraines: