As a bulk potable water supplier, Rand Water is responsible for the protection of water quality in the rivers. The major problem is to know which industries’ effluent will drain to a specific waste water treatment works (WWTW). To be able to trace these high effluent values at specific WWTW’s to potential industries, there must be a relationship between them.

These connections have been made in ArcView by linking the Industries Database to the Effluent Database, the Drainage Database and the Laboratory Results Database. Potable water resource protection can now be performed optimally.

To effectively manage and protect the catchments’ source water, monitoring and proactive decision making are important tasks. Monitoring not only includes the sampling of water at specific sample points and waste water treatment works (WWTW), but also the understanding of the origin of high values of certain variables.

Rand Water supplies water to 13 local authorities which supply water to about 9 million people and thus is the main bulk water supplier in the Gauteng area as well as in South Africa.

Figure 1 shows the location of Rand Water’s area of interest in South Africa. The area of interest for Rand Water is the area for which it is responsible, namely the supply and catchment areas located in four provinces. This area is shown in more detail in Figure 2. This map indicates the catchment of the Vaal Dam, the major resource of Rand Water, as well as the Barrage catchment. The latter is the focus of this study in terms of the WWTW located there.

The Barrage is the only catchment area which overlaps with part of the supply area so there is the responsibility of both catchment matters and the distribution of water. The Vaal Barrage is an impoundment of the Vaal River between the Vaal Dam and the Barrage wall. This is a major recreation area in Gauteng. The northern supply area drains north, away from the resource and does not fall within Rand Water’s responsibility.

Figure 2: Rand Water Area of Interest in more detail.

In total, the effluent of approximately 13600 industries would potentially drain into the Vaal Barrage. This number includes more than half of all of the estimated 22700 industries in the whole Witwatersrand area, as well as another 1500 industries in the Vaal Triangle and rural areas (Swart, 1999a, b). Therefore, the Vaal Barrage catchment faces a greater potential threat than the Vaal Dam catchment where there are only approximately 1100 industries. Figure 3 indicates the concentration of industries within the area.

Figure 3: Number of industries in catchments (Swart, 1999a, b).

Although this area is not a source of water for potable water purposes for Rand Water at the moment, it is a major recreation area with an important aquatic ecosystem. There is also a responsibility to the down stream users of Parys, Klerksdorp-Orkney, Bloemhof Dam, Vaalharts Scheme and further down stream.

The major problem is to know which industries’ effluent will drain to a specific WWTW and sample points in rivers. The Sanitation Section needs to know the origin of specific effluent. Some of the major known problem industries are laundries and dairies. The question now is: Where are these laundries and dairies situated ?

The general problems experienced at WWTW could be divided into three types as shown in the graphs in Figure 4. The graphs show the results of the data in the Effluent Database, which contains the variables expected for each type of industry (see Methods, Existing Databases).

Figure 4: Known problem variables at WWTW.

The major variables that are problematic are BOD, COD, metals, FOG (fat, oils and grease), SOG (soaps, oils and grease) (lower right graph, Figure 4) and detergents (phosphates).

The potential variables in the effluent of laundries and detergent industries (soap and cleaning products) are shown in the top graph of Figure 4.

Three types of industries have been classified as dairy industries, namely:

• manufacturing of ice cream,
• manufacturing of milk powder, condensed milk and other such products and
• processing of fresh milk.

Their potential effluent is shown in the lower left graph in Figure 4.

The major challenge is to be able to trace the high values of these variables at specific WWTW back to the potential source industries.

To trace the high values of certain variables at specific WWTW and sample points to the potential source industries.

GIS, especially ArcView, is the only method and tool which can be used to solve this kind of problem. To be able to trace the high values of certain variables at specific WWTW to potential source industries, there must be a connection or link between the WWTW, the sample points up and down stream of the WWTW and the source industries.

The existing data sets in shape format with their location shown in Figure 5 are as follows:

• Catchments of WWTW (polygons)
• Sample Points in rivers to monitor the catchments (points)
• Sample Points at different locations in the WWTW’s to monitor the treated sewage quality (points)
• Streets of MapStudio Street Map Data Set (lines)
• Suburbs of MapStudio Street Map Data Set (polygons)
• Rivers (lines)
• River catchments (quaternary and catchment management areas) (polygons)
• WWTW (points)
• Topographical Map scaned images as backdrops.

Figure 5: Location of WWTW and suburbs of Witwatersrand and Vaaltriangle in study area.

The following existing databases were either in Access or developed in Excel and then converted to DBF:

• WWTW to which the effluent from each suburb will potentially drain.

• Sample points in river (catchment sample points):

• upstream [CATH_UP1] and [CATCH_UP2] and
• down stream [CATCH_DOWN] from the WWTW.

• Sample points in the WWTW (sewage sample points):

• at the beginning or inflow of the works [WWTW_IN]. For future use, at the moment no point "No_point".
• in the works [WWTW_MID] and
• at the maturation ponds outflow [WWTW_OUT].

Industries have been located in industrial areas or suburbs by linking their individual data in the Industries Database (with the address details, standard industrial codes (SIC) and descriptions) to the Suburbs Coverage. The relationship between the Suburbs coverage and the sample points and WWTW coverages has been created through the linkage of the Industries Database to the Effluent Database and Drainage Database. The Effluent Database contains the variables (chemical elements and biological indicators) which could potentially be found in the effluent of certain types of industries. The Drainage Database forms the link back to the Sample Point Coverage. The laboratory data (LabWare) of the different water quality variables measured at the sample points and WWTW’s has been linked to the Sample Point and WWTW Coverages. All links have been created in both directions. This relationship between data sets is shown in Figure 6. The layout of the ArcView window with all these linked data sets is shown in Figure 7.

Many different searches can be done on these linked data sets in the ArcView project. It is best to first do a global search in the whole area and then break the search down to specific areas.

Single searches can be done by clicking on the feature on the map or in a database. Clicking on a specific WWTW on the map will show the suburbs of origin of the effluent at that WWTW. The industries records potentially draining to that WWTW will also be highlighted in the Industries Database.

Figure 8 shows an example of the Sebokeng works chosen to show all the areas which drain to it.

Clicking on a suburb on the map or choosing it by using the Query Builder on the suburb theme or on the Industries Database will highlight all the industries located in that suburb.

Figure 8: Single search showing which industries potentially drain to Sebokeng WWTW, with the associated information highlighted in all linked tables.

An example will now be discussed.

• all the suburbs where such industries are;
• the corresponding industries with their details; and
• the type of potential effluent .

• the chosen WWTW with its associated sample points at the works and down stream;
• only the suburbs which effluent drains to that chosen WWTW;
• the corresponding industries in those specific suburbs or industrial areas with their contact details, and
• type of potential effluent and all other relevant effluent information in the Effluent Database.

Details of all the result information in the tables are shown in Figure 14. Highlighted search results in tables showing the industries' contact details (2nd table), then the potential effluent which could be expected from dairies as well as their industrial classification. At the bottom the drainage database showing the suburb with its associated WWTW, catchment sample points and sewage sample points.

A direct link would be established between the laboratory data and the sample points (in WWTW and in rivers) through the usage of SDE. These results would be available to users more regularly, easily and timeously through ArcIMS. In this way decisions for water quality management could be done pro-actively.

In future the census population numbers could be linked to the WWTW as the number of people in an area is an indication of the COD to be expected at that WWTW. If the COD load from households is a given to be expected, everything above that value will have come from industries.

After using the system and clients experience the benefits of it, more needs will develop. As the basic important data sets with the necessary links exist, future expanding and updating will be quite easy. Different kinds of queries are possible because the links exist in multiple tables.

When high values of certain variables occur at a certain sample point or WWTW (according to a graph for that point), it is now possible to:

• Trace the origin of variables back to specific industries
• Show their location on a map and contact details can easily be shown – because the source can be found easily.
• Even when certain variables have a high trend at a sample point the source can easily be found and therefore decisions can be made to launch proactive action.
• The controlling of pollution incidents can now be dealt with efficiently and the catchment can be managed in an effective manner.
• In this way potable water resource protection can be done better.
• Manage the WWTW in an effective manner to protect the river source water quality.

• Celéne Davidson, Catchment Advisor, Rand Water for editorial comments and initial laboratory data abstraction through computer systems.
• Sanitation Section, Rand Water (Michel van der Schyff and Danie Nel) for practical information and expectations.
• Romana Kalas of Johannesburg Waste Water GIS Section for data (Location of WWTW and their drainage areas).
• Paul Strydom of Johannesburg Unicity (old Midrand City Council GIS Section) for converting data to other map projection - when the anti-virus program interfered with the Projection Utility of ArcView.

Marna Swart

GIS Specialist

Water Treatment and Technology,

Rand Water

PO Box 1127

Johannesburg

2000

South Africa

Tel +27 11 682-0736

Fax +27 11 682-0733

Esri Users Conference 10 July 2001, San Diego, CA, USA