Surface and ground water pollution status in Addis

Ababa, Ethiopia

Tamiru AlemayehuADDIS ABABA UNIVERSITY, Ethiopia

Solomon Waltenigus & Yirga TadesseADDIS ABABA WATER SUPPLY & SEWARAGE AUTHORITY, Ethiopia

INTRODUCTION

Addis Ababa is the capital of Ethiopia Since its foundation, the city has grown

from sparse and scattered settlements to an expansive and highly populated city.

Addis Ababa lies in the center of the country on the western escarpment of the main Ethiopian rift.

The altitude of the city varies from 2100 m a.s.l. to 2700 m a.s.l.

The city covers an area of about 530 km2 with a population of more than 3,000,000 inhabitants.

The environment of the city is threatened by severe pollution due to anthropogenic activities for more than a century.

GEOLOGY The region is constituted by volcanic

rocks ranging from acidic to basic in composition (27 to 3.2 Ma).

The typical volcanic centers of the region are the Entoto Ridge (3200 m a.s.l), Mt. Wochacha (3385 m a.s.l), Mt. Yerer (3100 m a.s.l), Mt. Furi (2839 m a.s.l).

DRAINAGE Big and Little Akaki rivers, with their different

tributaries, drain the city from north to south.

Big Akaki (900 km2) and Little Akaki basin has a catchment area of about 540 km2.

The rocks are highly fractured and permit fast circulation of the pollutants over large distances and to a great depth.

Taking into consideration the underlying fractured rocks and the widespread uncontrolled waste disposals, groundwater in Addis may be generally considered as highly vulnerable to any type of pollution.

IT IS UNLIKELY TO CLEAN POLLUTED AQUIFERS. Hence groundwater must be protected above

all where, rising up in the form of springs, are the only source of water supply for the community.

The streams serve as natural sewerage lines for domestic and industrial wastes, hence making them known for their offensive odor.

Eutrophication process in the streams is a result of water pollution

WASTE DISPOSAL In the city are septic tanks, open dumps and

surface impoundments. The majorities of private septic tanks are

characterized by open bottoms or peculiar channels, which facilitate the seepage in depth or the direct connection with the nearby streams.

Large and small-scale factories are clustered within the city having unregulated waste disposal systems.

The major solid waste disposal site of the city is located within the city premise that pollute the urban environment.

It is open system, no impermeable layer with continuous low temperature burning.

The most known large-scale human activities producing dangerous refuses are:

garages, car washing centers, petrol stations, chemical factories, paint factories, tanneries, slaughterhouses, market centers, breweries, textile factories, hospitals tyre factories, thread and garment factories, oil mills, flour mills, metal works, tobacco factories, pharmaceutical factories, Cemeteries

The most widespread diseases in the city are:

flu, typhus, acute bronchitis, bronco pneumonia

Water supply: There are three dams that supply the city

with treated water. At least there are about 271 boreholes

distributed in the city with a maximum yield of a single well of 87l/s. Highly productive aquifers are located in the southern part of the city.

Numerous cold and thermal springs

Volume

Three dams= 173,000 m3/day

Wells & springs=10,000 m3/day

Akaki wells= 30,000 m3/day

Supply cover=70% of the population

Surface water pollution problem: Turbidity and algaeIncrease in the use of AlSO4 for coagulation due to

increase in turbidity leave Al in public waterUse of CuSO4 for Algae eradication leaves Cu in

public water

There is a basin plan study but requires financial support

GROUNDWATER POLLUTION PROBLEM

Case study:- Focused on streams, rivers, springs and boreholes

Heavy metals, total coliform and nitrate

Streams (ppb)Heavy metals 01 02 03 04 05 06 07

pH 7.59 7.68 7.90 8.00 8.03 7.31 7.51

Mn 34.1 1756 6531 1219 1190 2044 2538

Cr <0.1 14.12 <0.1 <0.1 2.28 <0.1 13.31

Ni 44.45 4.8 <0.1 <0.1 5.05 8.9 <0.1

As <0.1 2.3 <0.1 0.6 0.42 2.2 2.88

Pb <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

Zn <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

Springs (ppb)Heavy metals

08 09 10 11 12 13 MCL

pH 6.90 6.50 6.32 6.40 5.93 7.60

Mn 0.3 21.47 128 5.1 24 0.39 100

Cr 1.88 1.18 0 5.85 1.21 0.94 50

Ni <0.1 <0.1 <0.1 0.49 0.92 0.53 100

As 1.0 <0.1 <0.1 0.22 0.2 0.2 50

Pb <0.1 <0.1 <0.1 8.33 4.31 15.5 50

Zn <0.1 <0.1 <0.1 9.35 8.06 0.87 5000

BOREHOLE (ppb) Heavy Metals 14 15 16 17 18 19 20

pH 7.62 7.44 6.98 7.53 6.42 8.03 7.68

Mn 0.86 0.64 5.25 3.48 1.97 16.9 1.75

Cr 0.69 0.86 3.29 0.22 0.72 0.24 1.8

Ni 0.57 0.31 0.33 0.69 0.63 <0.1 0.51

As 0.37 0.3 0.3 0.32 0.2 0.63 0.5

Pb 25.1 8.98 10 25.3 15.7 9.75 4.66

Zn 23.3 85.8 3.9 34.2 33.5 10.3 20.5

Total coliform count Sample code. Streams 01 560/ml 02 Too Many to Count (TMC) 03 660/ml

04 Too Many to Count (TMC) 05 1010/ml

06 Too Many to Count (TMC) Springs 07 290/ml

08 350/ml 09 Nil

Total coliform count Borehole 10 10/ml

11 160/ml12 24/ml13 16/ml14 340/ml15 24/ml16 8/ml

Storm drain 17 3000000/ml

18 350000/ml19 6000000/ml20 20000/ml21 100000/ml

Streams 8.9-531 mg/L

Springs 55-728 mg/L

Boreholes 0-35 mg/l

Nitrate

N

4

CONCLUSION Heavy metal pollution Total coliform and pathogen pollution The major part of the city including some part of the

Akaki well field, has bare rock outcrop–high risk for pollution

The Akaki well field is crossed by railway and high way-potential danger

The unconfined aquifer in the city center and along the rivers is vulnerable.

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