Environmental Engineering Reference
In-Depth Information
Food and produce markets
Nitrate, phosphate
Home industries
Transition metals, ammonia, TDS
Urban agriculture
Nitrate, phosphate, potassium
types: standard pit latrines, ventilated improved pit latrines (known in Zimbabwe as
“Blair toilets”), pourflush pit latrines or, occasionally, septic tanks.
Bacteria and viruses may be transported with percolating effluent into the
groundwater. Many pathogens, especially coliform bacteria, can survive in shallow
groundwater for longer than two months (McCarthy et al . 2004), and these organisms
may be ingested causing infection. Whether or not an individual will become infected
will depend on the concentration and persistence of the pathogen in groundwater and the
infectious dose required to initiate disease (Feachem et al . 1981). Infectious waterborne
diseases such as diarrhea-type diseases, dysentery, cholera and hepatitis are almost
endemic in many rural and informal urban areas (Manase 2001). Children under the age
of five years of age living in settlements with no access to safe water are the most
susceptible (Obi et al . 2004). These factors clearly indicate the major problem that poor
sanitation in informal settlements presents to water supply for the same settlements.
Home industries, which are also a source of diffuse pollution in informal settlements,
are small-scale industries such as panel-beating, brick-making, painting, leather craft and
grain milling. They are widespread in both high-density formal residential areas and in
informal settlements in many cities in Zimbabwe (including the study area), with no
zoning controls in the latter case. The operations of these small industries has been
associated with release of a number of metals (Mvungi et al. 2003), and their impact on
surface water has been discussed in Chapter 5.
Produce markets are found to occur at irregular intervals in most informal settlements,
either as small “commercial centers” or as aggregations of two or three traders at bus-
stops, cross-roads or other places where people congregate (Kyessi, in press). They are
associated with nutrient contamination-and also coliform bacteria at markets large
enough for public urination to become a nuisance.
Urban agriculture is widespread in informal and semi-formal settlements, as residents
grow staple crops or vegetables to augment their diet and/or income (Kyessi, in press,
Lynch et al . 2001). This can be either on the land they own or occupy for residential
purpose, or distant from their dwellings, in open spaces-either unusable for housing
development or simply not yet occupied. Figure 6.1 illustrates the urban agriculture
practice and in this case it is practiced within a residential dwelling. Note the monitoring
borehole in the foreground. The pit latrine on the right was constructed after the borehole
was drilled.
Some residents also raise small or large livestock, as medium term investments, or for
milk production (Losada et al . 2000). Agriculture can contaminate shallow groundwater
with potassium, nitrate, nitrite, phosphate, dissolved organic carbon and salinity (Conrad
et al . 1999), although most of these parameters only become elevated when fertilizers or
manure are applied.
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