
This study presents the use of Geographic Information Systems (GIS) in
selecting suitable sites for the construction of a central wastewater treatment
plant(s)

For this purpose, several variables were analyzed using GIS technology.

This method present here, can also be used in checking the suitability of
selected sites or new areas for the purpose of constructing wastewater treatment
plants.

The study was conducted in the Accra Metropolitan Area (AMA)

AMA is a primate city in Ghana with a total land surface area of approximately
231km2

Has a total population of 3.9 million, population density 69.3 persons per hectare
and growth rate of 3.36% (GaWC, 2010)


It lacks of wastewater treatment facilities
The study was to help solve the problem of siting wastewater treatment plants

Is not likely to pose any health threat to the environment as
well as the people.

Large enough for locating central wastewater treatment
plant(s).

Accessible

No negative aesthetic effect to the city

Gain the support of the people
The study also considered the following sub objectives.

Ascertain the factors that are considered in selecting a site.

Determine what would be the best site(s) based on multi-criteria decision
making algorithm

Examine the attitude, knowledge and perceptions of residents on
wastewater treatment plants

The study was approached in two ways.

1. stakeholder interviews and criteria assessment to identify common
criteria that need to be considered in suitable site selection.

2. the application of GIS (multi-criteria decision making) in modelling
these factors in order to arrive at locations that are suitable for locating
wastewater treatment plants.
The result is a composite map, which highlights the areas that satisfy all
suitability criteria.
ArcGIS software was used
The process was divided into two steps,
A. Selection of variables and criteria with stakeholders; Key variables include
1.
slope,
2.
land cover,
3.
distance to existing major roads,
4.
distance to rivers and lagoon,
5.
distance to existing major populated communities and
6.
distance to airport facilities.
B.
the second step looked at the actual analysis using
variables and criteria to determining suitable and not
suitable locations

The final analysis of each variable was used to create
maps showing only the areas of interest.

The study applies exclusionary criteria.
Digital Elevation Model

Mild slopes would result in, higher hydraulic residence times and thus higher
pollutant removal capacity.

To minimize pumping costs and improve the overall efficiency of the wastewater
treatment plant a maximum slope value of 10% was considered based on officials
guidelines.
Slope grid of the study area
Selected areas in terms of slope less than 10%
A 2000-m buffer around existing populated areas
3000-m Buffer Around Airport in AMA
Land Cover Map of the Study Area
Selected Areas Based on Land cover.
A 90-m river, 300-m lagoon Buffer Zone.
A 300-m road buffer zone
Having examined all the different variables in the study area and maps
created for each based on criteria identified,
The final analysis was carried out using the overlay function in ArcMap
provided by the ArcGIS program.
The result is showing the areas that meet all the previously specified criteria
and are suitable for the construction of a central wastewater treatment plant
in the Accra Metropolitan Area.
Selected Areas for Central Wastewater Treatment Plant in AMA

The total land area of AMA suitable for central wastewater treatment plant
is about 20km2.

This is the parcel of land north of AMA

Most residents living around treatment plants have no knowledge about the
essence of treatment plants.

They are indifferent

Any final decision at the sub-metro level should be based on more detailed
examination on each selected sites, involving a ranking of all possible sites
using non-exclusionary criteria.

The opinion of the people in the local communities should be taken into
consideration in making the final decision to use any site for the construction
of the treatment plant.

Education of the local people is also very vital as it informs them on the essence
of the installation of the treatment plants and how they would have to handle them.
End
Of
Presentation
Thank You.