Environmental Engineering Reference
In-Depth Information
usage of unprotected wells (less than 40%). Ward 5 (Chinamano Extension) has the worst
situation with almost 80% of respondents supplied with water from unprotected wells and
all respondents using Blair toilets or pit toilets. Ward 6 (Overspill) has the best water
supply and sanitation picture with less than 20% of respondents supplied with water from
unprotected wells and 25% using flush toilets rather than Blair toilets or pit toilets.
3.2
Groundwater Quality
The results of the groundwater quality study are given in Table 6.5.
There is a substantial variation in nitrate, phosphate and coliform distribution. All
these parameters peak around boreholes EPZ4 and 5 (see Figs. 6.6 and 6.7) - which are
located close to a “dambo” (seasonal wetland). Shallow aquifers collect water from
rainfall events and slowly release excess water into dambos (Mharapara 1995).
Therefore, local groundwater flow should be towards the dambo, accordingly,
accumulation of nitrate, phosphate and coliforms is to be expected in such a downflow
site.
Nitrate concentration is below risk level of 10 mg/l (WRC 1998) or 6 mg/l (DWAF
1996) except for boreholes EPZ4 and 5 (Fig. 6.6), which are located in the dambo. The
elevated nitrate levels could be related to urban agriculture or to pit latrines, or to a
combination of these.
Drinking water standards (WHO 1993) require no fecal coliforms in samples.
However, water in boreholes EPZ3, 4, 5, 6 and 8 contained fecal coliforms (Fig. 6.7).
Figure 6.5. Shallow well (on left) in
close proximity to a pit latrine (on
right).
