1) Catchment

Hazardous event

Issues to consider and hazards associated with.

Raw risk

Risk rating

Basis for selecting the likelihood of the hazard and its consequences

Existing Control measure and its effectiveness

Residual risk

Risk rating

Li

C

S

Li

C

S

H, M or L

Cattle rearing around source water

Cryptosporidium and other infectious organisms introduced into water (M)

3

3

9

H

Li: site visits

C: cryptosporidium infection may harm human health

ECM: No

3

3

9

H

Farming activities along the river bank

Pesticide, nitrate washed into raw water (CH)

3

3

9

H

Li: site visit, historical water quality showing high nitrate

C: nitrate, pesticides in high concentration harms health and incompliance regulation

ECM: No

3

3

9

H

Human defecation into the raw water

E-coli, faecal coliforms introduced into raw water (M)

3

3

9

H

Li: site visit, human settlement present near raw water and no toilets

C: faecal microorganisms may harm the public health

ECM: No

3

3

9

H

Dumping of refuse

Solids, debris into water (P)

3

2

6

M

Li: site visit and key informant interview

C: debris into treatment plant system might clog filters, etc.

ECM: screens provided at intake side

E: yes; no floating debris within treatment

1

2

2

Lo

Algal blooms during hot season.

Changing color, turbidity, taste and odour, and heavy algae growth in treatment tanks (M)

2

3

6

M

Li: site visits key informants survey

C: record shows high turbidity in the hot season affecting the aesthetics of water

ECM: No

2

3

6

M

People bathing in the water

Contamination of raw water (CH, M)

3

3

9

H

Li: site visits, historical records

C: contamination from bathing

ECM: No

3

3

9

H

Bokoharam attack at intake side

Interrupted pumping of water, lost operators live

2

3

6

M

Li: key informant interview (some villages around the intake site has been attacked several times)

C: terrorist may harm plant operators at the raw water intake site

ECM: soldiers deployed at intake side

E: yes Several attack to villages near has been repelled with victory

1

3

3

Lo

2) Treatment

Pre-liming pump breakdown

Temporary hardness and acidity removal not achieved

3

2

6

M

Li: site visits, water quality analysis.

C: imbalance pH causes corrosion to pipes of treatment facilities

ECM: No

3

2

6

M

Natural Aeration process

Inadequate in achieving aeration benefit (CH)

3

2

6

M

Li: water quality analysis

C: DO, odour and taste not removed (aesthetics)

ECM: No

3

2

6

M

Alum pipe network clogging

Interrupted coagulation treatment (P, CH, M)

2

3

6

M

Li: operators interview (it takes 6 months before clogging occurs)

C: loss of coagulation leads to untreated water Supplied to consumers

ECM: Treatment process is halted to restore problem

E: Yes

1

2

2

Lo