ENVIRONMENTAL IMPLICATIONS OF SEWAGE DISPOSAL METHODS IN ENUGU METROPOLIS SOUTH-EASTERN NIGERIA.

ABSTRACT

A questionnaire and observational study were randomly conducted on 204 houses to acquire information  on  different  sewage  disposal  methods  used  in  Enugu  metropolis,  and  to investigate  the impact  of the sewage  disposal  methods  on  available  water  supplies.  The results obtained show that 51% of the resident’s wells are located at a distance less than 9m from the toilets. Samples from 21 different locations in the area were analyzed and studied in order to assess the quality of the groundwater.  The result of the physico-chemical analysis shows  presence  of  some  sewage  sensitive  parameters  such  as  Chlorides  (CL–),  Total

Dissolved Solids (TDS), Electrical Conductivity  (EC), and Nitrates (No3–), although not in significant   quantity.   The   bacteriological   analysis   of   the   samples   reveals   that   the

aquifer/groundwater has very high concentrations of coliform bacteria varying between 130 and 2400MPN/100ml  of water.  Further  bacteriological  investigation  of the  groundwater quality shows significant concentrations of Escherichia coli which is an indication of faecal contamination  of  the  groundwater.  Simple  hydrogeological  studies  of  the  area  such  as ascertaining depth to groundwater table and direction of groundwater flow prior to siting of wells and toilets would minimize groundwater contamination. Relevant agencies should make continuous effort to control, regulate and educate the populace on indiscriminate disposal of sewage within the study area.

CHAPTER ONE

INTRODUCTION

1.1 Background of Study

Sewage can be defined as liquid waste containing some solids produced by humans and typically consisting of washing water, faeces, urine, laundry waste and other materials which go down drains and toilets from households and industry. Sewage is a type of domestic wastewater and it is a major or potential source of pollution especially in urban areas (Myer and Sylvester,

1997). Thus, inappropriate disposal of sewage constitutes a major challenge in urban areas. Indiscriminate defecation, either in pit latrines, water closets (soak- away  pit)   or  vacant  plots  and  open  drains  can   often   lead  to   several environmental problems. Groundwater contaminations are major occurrences in urban areas and these normally result to epidemic of water borne diseases such as cholera, typhoid fever, gastro-intestinal disorder and so on. These diseases have led to the death of millions of people globally.

In Enugu metropolis, sewage waste constitutes a major contaminant of groundwater. The groundwater in the area is increasingly getting contaminated essentially due to negligence of the aquifer. Toilets facilities in the area are not designed to approved and recommended specifications in terms of width, depth and other parameters. In the metropolis, studies are not carried out to ascertain the  nature  of  the  soil  (topography,  porosity  and  permeability),  direction  of

groundwater flow and depth to water table before citing toilets facilities. Hand dug  wells  are  designed  and  located  without  proper  site  investigation  to determine nearness to source of pollution (pit latrines and soak-away pits). The level of illiteracy among the inhabitants contributes to problems of portable water provision.     Most consumers do not know the consequences of using contaminated water. There is a serious misconception, that groundwater; so long as it is clear is safe for use.

1.2 Aims and Objectives

1.  To acquire information on different sewage disposal methods used in the study area.

2.        To investigate the impact of the sewage disposal methods on available water supplies.

1.3 Location and Accessibility

The study area lies between latitudes 60 23′ N and 60 29′ N and longitudes 70 29′ E and 70 32′ E. (Fig 1). The area is easily accessible through the Onitsha-Enugu express road. From the Garki road end of Enugu metropolis, the study area ascends to the Uwani-Ogbete road and runs towards Asata area. The study area is within the developed Enugu Urban and consists of streets that are connected by a good network of tarred roads.

6029’N

70 29’ E

FROM ONITSHA

70 32’E

6029’N N

NEW HEAVEN

ENUGU

COAL CAMP

INDEPENDENCE LAYOUT

OGBETE

UWANI

ASATA

FGC ENUGU

6023’N

GARIKI

6023’N

70 29’E

0                                            2km

7032’E

Fig 1: Accessibility Map of Enugu Metropolis.

1.4     Physiography, Climate and Vegetation

The Enugu Shale outcrops occur in the plains east of the North-South trending escarpment (Ezeigbo and Ezeanyim, 1993). Most of the Enugu metropolis is underlain by the Enugu Shale. Having been subject to weathering and  erosion  for  long  periods,  the  characteristics  landscape  of  this  area  is extensive level plains interrupted by steep valleys and low hills. These features form a major landscape of the metropolis.

The topography in Enugu metropolis ranges from 15 to 75 m (Uma and Ezeigbo,1999). The general relief comprises gently undulating plain with low hills and steep valleys (Fig. 2). The topography within the city is much gentle when compared to the Western part which shows high relief with undulating hills. Much of the population of the area is located within the city.

The climate is humid tropical and characterized by day time temperature of 27 -320c  and night time temperature of 17-280c. The area has two distinct seasons namely, wet (April-October) and dry (November-March) seasons. The annual rainfall ranges from about 1500-1830mm. (Okagbue and Ifedigbo, 1995) The natural vegetation which is tropical rainforest is reduced to Guinea Savanna type as a result of human activities except along river/stream channels

where remnants of original vegetation can still be observed (see fig. 3).

70 29’ E                                     70 30’ E                                     70 31’ E                                  70 32’ E

60 29’ N

60 29’ N

N

W             E

S

27’ N

25’ N

60 23’ N

650 600  BARRACKS       CRH   700MKT OGBETE   ENUGU   550  850600 750 700 650

70 29’ E

70 32’ E

0                                          2Km

Fig. 2: Topographic Map of Enugu Metropolis.

70 27’ E                                                                                 70 36’E

6032’N                                                                                                         6032’N

N

KEY

Road

Vegetation

6023’N

7027’E                                                                                70 36’E

6023’N

Fig 3:   Satellite Image of Enugu Metropolis Showing Network of Roads. (Source : Google Map, 2009)

1.5     Literature Review

The  different  methods  of  sewage  disposal  have  generated  a  lot  of controversy  and  discussions  among  engineering  geologists,  environmental

experts and other researchers. Dapo (1990) stated that people in developing countries do not have adequate sanitation system. He pointed out that most of their soak-away pits are not properly designed and sometimes are located close to  sources  of  water  supply,  which  eventually  become  contaminated.  Cook (1998) mentioned that urbanization contributes to the problem of groundwater contamination.

Todd (1980) has observed that leakage of sewage into the ground is always a common   occurrence   especially   from   old   sewers   and   thus,   can   affect groundwater quality. Onwuka, et al (2004) have observed that lateritic aquifer of Enugu, Southeastern Nigeria, which is an important source of water supply to the inhabitants, is contaminated through sewage from soak-away/ absorption tanks. Uma (2003) suggested that the hydrogeologic environment of shallow water table and high permeability of the host laterite have rendered the perched aquifer vulnerable to pollution especially from domestic sewage buried in septic tanks and soak-away pits.

Sharma, et al (1987) on their work in the area distribution of infiltration parameters and some soil physical properties in lateritic catchment concluded that  lateritic  soils  have  very  high  infiltration  rates.  Okogbue  and  Ezeigbo, (1990)   mentioned that the provision of potable water has remained an unsolved problem in developing nations.

North  Carolina  University  (1997)  noted  that  the  presence  of  certain bacteria can provide clues about the origin of contamination.   According to them,  E-coli  and  enterococci  inhabit  the  intestinal  tract  of  worm-blooded animals   and   their   presence   in   water   is   a   direct   indication   of   faecal contamination. Ofoma et al (2005) stipulate that high population of coliform bacteria  indicate  poor  sanitary  condition,  arising  from  poor  handling  of domestic waste (sewage).

Wilhelm and Maluk (1998) on their work on National water quality Assessment programme (NAWQA) pointed out that high levels of faecal indicator bacteria  such  as faecal coliforms,  and  Escherichia coli (E-coli) in groundwater are used as indicators of sanitary water quality and are present in high numbers in sewage material. These coliforms and E-coli have been shown to be associated with water borne diseases such as typhoid / paratyphoid fevers and gastro intestinal disorders. Uma and Oteze, (1999), Uma, (2003) Howard (1985) and Foster et al (1998) noted that chlorides and nitrates are well known sewage sensitive indicators.

1.6 Regional Geology

Reyment (1965) described the stratigraphy of the different depositional basins in the country including the Anambra Basin of the study area and delineated

several lithostratigraphic units.The earliest documented marine transgression in the Anambra Basin occurred during the mid-Albian.

Albian deposits outcrop in several locations within the basin and also within the Benue Trough (Kogbe,1989). which has been described as a failed arm of a rift system associated with the break up of the Gondwanaland (Nwajide and Reijers

1996). The Trough which streches NE-SW is a complex pull-apart basin formed by transcurrent movement (Benkhelil et al, 1989). The stratigraphic successions of sedimentary deposits within the trough are represented by three main marine depositional  cycles,  the  Albian-Cenomanian,  Turonian-Santonian  and Campano-Maastrichtian (see Table 1) Reyment (1965); Ofoegbu, (1985); Tijani et al, (1996); Ojoh, (1992). Figure 4 shows the geologic map of southeastern Nigeria.

The  Albian  sediments constitute the  Asu River Group and consist of poorly bedded sandy shales including the Abakaliki Shales (Reyment, 1665; Nwachukwu, 1972). The Cenomanian was a regressive period, during which the sediments of the Odukpani Formation were deposited unconformably on the Precambrian Basement rocks (Reyment, 1965).

Table 1: Summarized Stratigraphy of the Benue Trough and Anambra Basin

(after Reyment, 1965 and Ojoh, 1992)

TIME                                        STRATIGRAPHY

MA

TERTIARY-RECENT

65

MAAASTRICHTIAN

IMO, AMEKI, OGWASHI- ASABA ETC.

NSUKKA AJALI

MAMU

74

83.0

86.6

CAMPANAIN SANTONIAN

NKPORO GROUP:

OWELLI SANDSTONE/ NKPORO SHALE/ENUGU SHALE

FOLDING

CONIACIAN                                                      AGBANI SSN

AWGU SHALE GROUP

88.5

90.4

TURONIAN

U  NKALAGU FORMATION/ AWGU SHALE

M                                              AGU OJO/AMASERI/AGALA SANDSTONES

L                     NARA SHALES

EZE- AKU SHALE GROUP

CENOMANIAN

U                         EZILLO

M

ODUKPANI

97

100

L

U ALBIAN

M

PRE ALBIAN

–

ALBIAN

IBRI AND AGILA SANDSTONES NGBO

EKEGBELIGWE

UN-NAMED UNITS

ASU RIVER GROUP

PRECAMBRIAN                          BASEMENT COMPLEX

Fig 4: Geological Map of Southeastern Nigeria.

This was succeeded by the Turonian which featured extensive marine transgression. Turonian deposits belong to the Ezeaku Group (1200m thick). The transgression continued during the Coniacian with the deposition of Awgu Group  (900m  thick).  The  Asu  River  Group  and  Awgu  Group  have  been described extensively by Reyment, (1965) Murat, (1972) and Kogbe, (1989).

The Santonian was a regressive period during which crustal movement accompanied  by  magmatism  resulted  in  the  folding  and  uplifting  of  the Abakiliki area to form the Abakaliki Anticlinorium as well as Anambra Basin and Afikpo Syncline. Murat, (1972) and Hoque, (1981) have found numerous mafic to intermediate rocks, cal-alkaline lavas, and pyroclastic tufts, including lead zinc mineralization in deformed sediments of the Abakaliki Anticlinorium.

The  Campano-Maastrichtian  began  with  a  short  marine  transgression followed by a regression and this gave rise to the Nkporo Group (100m thick). The  Nkporo  Shale  and  its  lateral  equivalents  the  Enugu  Shale  and  Owelli Sandstone constitute the basal beds of the Campanian. Outcrops of the Nkporo Formation are scarce but borehole cores show that Enugu Shale is light to dark grey and contains bands of clay ironstone. The topmost part of the Enugu Shale is weathered to a dirty brown lateritic regolith which is porous and varies in thickness up to a maximum of 20m, depending on the topography of the area. The  terminal  Cretaceous  marine  cycle  deposited  the  basal part  of  the  coal sequence known as the Mamu Formation. The Mamu Formation is overlain by

the  Ajali  Formation  which  was  previously  known  as  the  False  Bedded Sandstone and consists of thick friable, poorly sorted sandstone typically white in colour but sometime iron-stained. The Nsukka Formation lies conformably on the Ajali Sandstone. The formation was first described as the “Upper Coal Measure.” and is similar to the Mamu Formation.

Detailed  descriptions  on  the  Ajali  and  Nsukka  Formations  are  found  in  the  works  of

Nwachukwu (1972) and Kogbe (1989).

1.7      Hydrogeology of the Area

Enugu metropolis is underlain by the Enugu Shale. Thus, its geological location is such in which depth to water table is controlled by the seasons of the year. The Enugu Shale essentially constitutes an aquiclude. The Shales are fractured and weathered to a lateritic regolith which is highly porous and permeable that suggests localized  saturated  conditions.  The  permeable  laterite  rests  on  the impermeable   shalely  bedrock   and   thus  a   perched   aquifer  is  developed constituting the only known aquifer directly beneath the metropolis.

The perched aquifer of the Enugu Shale is thin and most times becomes reduced in thickness especially during dry season. The aquifer is regionally discontinuous and sometimes intersects the surface bedrock to form springs as shown in the model below (Fig. 5).

Fig. 5: A Model of Perched Aquifer, Showing Water Table varying with

Surface Topography.

The Enugu Shale perched aquifer unit which supports local flow pattern are reasonably thick and extensive and have potentials to store large volumes of water especially if secondary porosity / permeability (planar, fracture or fissure type) are present (Awalla,1998).

The aquifer is recharged by rainwater. Filtration is estimated to be about

31.1%  of  atmospheric  precipitation,  representing  9.76%    107m3/yr  (Nfor,

2006). Precipitation in the study area is highest during the month of September and is about 280mm (Fig 6). At the peak of the rainy season when the water table is high and the discharge volume increases, springs do frequently occur.

mm

300-

250-

200-

150-

100-

50-

0

Jan   Feb   Mar  Apr   May  Jun Jul    Aug   Sept Oct    Nov    Dec

Months of the year

Fig. 6: Bar Chart Showing Annual Rainfall in the Study Area. (Source: Metrological Station Enugu, 1988)

The study area is well drained by different rivers. The rivers which rise from near the base of the escarpment and flow eastward into the Cross River Basin consist of Ekulu, Iva, Njaba, Asata, Mmiri Ani and Ogbete rivers (Fig. 7). Some  of  the  rivers  appear  fracture-  controlled  in  their  flow  path  thereby resulting into dendritic drainage pattern (Egboka, 1985).

7029’E

7030’E                                    7031’E                                 7032’E

6029’N

6029’N

N

W           E

S

KEY

Roads

HOSPIT AL EKULU      RIVERBARRACK S    ASATA RIVERCRH    MKT OGBETEMKT ENUGU   AG BA NIRD                      MMIRI ANI      RIVERSCH

Ogbete River

Rivers

Njaba River

6023’N

7029’E

7032’E

6023’N

0                                    2Km

Fig. 7: Drainage Pattern of Enugu Metropolis

1.8     Sewage Disposal Methods in Enugu Metropolis

The  problem  of  urbanization  in Enugu  metropolis has  resulted  to  a number of environmental problems such as sewage generation, its collection, treatment and disposal. The collection and disposal of sewage effluents by the inhabitants are executed using various methods as discussed below:

Pit Latrine

The principle in pit latrine is that it is designed for the onsite disposal (but not treatment) of human excreta with little or no water usage. Pit latrine consists of squatting plate (Fig. 8), or riser type which is placed over an earthen pit. The duration of pit latrine varies, depending on the number of users (they can last for several years). Outhouses types are generally used in Enugu metropolis with a roof for shelter provided.The diameter of pit latrine is usually between 1-1.5m. Its depth is usually more than 3m. Pit latrine is not suitable in crowded area and in areas where groundwater level is high. Pit latrines are crude toilets. Most pit latrines in the metropolis are located without considering the population of the area involved and the groundwater level.

Fig. 8: A Typical Pit Toilet

Water Closets (W. Cs) and Soak-away Pit

Water closets are the most accepted sanitary system of sewage disposal. They constitute a toilet system that disposes human waste by using water to flush it through a drain pipe into a soak-away pit / septic tank.

A proper septic tank usually has two chambers that are separated by a dividing wall with openings located at the midway. Wastewater enters the first chamber, allowing solids to settle and scum to float. The settled solids are anaerobically  digested  while  the  scum  component  flows  into  the  second chamber for further settlement. The excess liquid drains into a seepage field which is often constructed with a stone filled trench. When constructing a septic

tank, the porosity of the soil, size of the drainage field, depth of the toilet, depth to water table, location and distance between wells and septic tanks should always be considered.

Fig. 9: A typical water closet with soak-away pit

Open Defecation

This is a system of sewage disposal method practiced during the ancient times. People without toilets normally resort to open defecation method. Faeces are indiscriminately defecated either in vacant plots, open drains or streams. It is generally believed that the attenuation systems are capable of eliminating the pathogens that may eventually contaminate groundwater.

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