Environmental Engineering Reference
In-Depth Information
pollution loads, which contribute to the mobilization of these elements at these specific
sites, but their movement within the aquifer is relatively low. In contrast, nitrate
variations show a gradual increase from G1 to G3, where the highest concentrations were
measured and a considerable decrease at GW4, which could be explained by the higher
mobility of this element within the aquifer and in the direction of the main flow. The
observed TKN concentrations are very high, and even at the control point, a
concentration of 2.5 mg/l was measured, which could not be explained and might be due
to a systematic error during the testing procedures, but the pollution pattern with respect
to this element is pronounced as well. The environmental risks with respect to nitrate and
phosphorous could be evaluated as low to medium, while ammonia concentrations
exceed the high hazard values up to two times.
The ground water at Imbwa farm shows an indication of microbiological pollution as
well, with FC in the range of 20-50 counts in the irrigated sites. Again, the sprinkler
irrigated site showed higher counts. The TC showed the same trend. A point to be noted
is the relatively high difference between FC and TC, which could be associated with the
presence of animal excreta on the pastures. Westcot (1997) reported that cattle feces
contain 0.23 × 10
6
indicator micro-organisms/g and that a single cow can contribute 5400
× 10
6
of indicator organisms/24 hours. This could have had an effect on groundwater
close to the watering points. Under a system of rotational grazing in open pastures, such a
type of contribution could be minimal. At present, the ground water has not being used
for beneficial purposes, but the evidence of fecal contamination should be recorded in
terms of future use. Under normal uniform conditions, Papadopoulos (1995) reported that
the horizontal travel of microorganisms rarely exceed 20 m except in karstic formations.
Todd (1980) observed that most pollutants (except those which are conservative) tend to
be reduced in concentration with time and distance traveled, through attenuation
processes such as infiltration, sorption and chemical processes, microbiological
decomposition and dilution with the native groundwater.
Thus, it could be considered that the microbiological contamination observed during
this study, does not pose a significant public health hazard, but it does not allow the
ground water to be used for direct potable consumption. The level of contamination in
terms of fecal coliforms observed was much lower compared to Crowborough farm
(Chapter 9). From an environmental perspective the ground water is considered safe with
respect to FC.
6 CONCLUSIONS
WSPS proves to be a viable option for wastewater treatment in the region and the effluent
produced is suitable for irrigation. Under proper conditions of design and operation, this
treatment option could cause problems with respect to an increased soils' salinity and, in
some cases, ground water pollution and toxic metals contamination. However, in order to
reduce at a minimum level such risks, the beneficial reuse of the effluent should be
considered during the design stage and the WSPS should be designed in conjunction with
the corresponding irrigation facility, after a thorough examination and careful
consideration of the geological and climatic conditions, available and future quantities
