Environmental Engineering Reference
In-Depth Information
to some extent regarding TP, but would not influence the pollution loads regarding
dissolved constituents as ammonia and nitrates. Therefore, biological treatment methods
should be applied as pollution abatement measures.
3.6
Spatial variation of water quality
The comparison of the variation of water quality with respect to the different points,
based on Figure 4.2, shows that at SP2, the mean values of TSS, TDS, TP, ammonia,
nitrates and Pb were higher compared to the rest of the points. This indicates a
considerable contribution of pollutants from the industries located in this area. Data sets
for this point show high fluctuation of results, which is typical of runoff water quality in
general, but at this specific location could also be associated with possible informal
discharges from industrial enterprises. Correspondingly, this is reflected in the statistical
analysis and the statistical significance of the difference between mean values. However,
the suggested contribution with respect to SP2 is supported by the fact that at this point,
the dissolved contaminants as nitrate, ammonia and TDS were much higher compared to
the other sampling locations. Pollutant concentrations at SP3 are lower than the ones at
SP2, which could be attributed to dilution due to the additional and less polluted runoff
from DR3.
The spatial variation of runoff characteristics were examined based on the statistical
analysis for a significant difference of data sets (“t-test”). All data sets for the individual
sampling points were compared individually for a statistically significant difference of
their mean values with respect to all parameters. For data sets with high variability,
logarithmic transformations were applied, which did not show any difference, compared
to the “t-test” results obtained from the actual values. The results, with respect to
statistically significant difference of the mean values (+) between the different locations,
are presented in Table 4.4. The parameters, which are not included in the table, did not
show a statistically significant difference of mean values. There was no statistically
significant difference between SP1-SP4, and SP1-SP3 with respect to all parameters
tested.
SP1 and SP4 are characterizing the water quality of runoff from Harare's City center.
The difference between the land use patterns of both drainage areas is that at SP1 the
impermeable cover area forms a higher percentage of the total area. The density of the
building construction is higher and includes high story buildings. The SP4 drainage area
includes some medium density residential areas in addition to commercial and
institutional developments, and the population density is lower. The results obtained did
not show a considerable and statistically significant difference in the water quality from
both areas, which
Table 4.4. Results of the test for a statistically
significant difference of mean water quality
characteristics.
Parameter
SP1-SP2
SP3-SP2
SP3-SP4
SP4-SP2
COD
+
+
