Environmental Engineering Reference
In-Depth Information
(natural) water quality. In addition, both programs do not envisage and control sources of
diffuse pollution from agricultural activities.
The analytical methods applied to determine specific water quality characteristics
should be validated with respect to accuracy, precision, range, sensitivity and selectivity
(UN/ECE Task Force 1996). It is advisable for all laboratories in the country to apply the
Zimbabwe standard test procedures (SAZ), as prescribed in the regulations, and
correspondingly, they should be equipped with the necessary resources to implement this
requirement. In many cases, this is not applied in practice, which reflects on the level of
enforcement of the regulatory documents. A central water quality laboratory, as the city
of Harare's one, is required to execute a very wide and diverse scope of water quality
monitoring, with a minimum of technical instrumentation, which is old and worn out. In
order to provide a reliable data, there is an urgent need for upgrading this laboratory with
new technical equipment, which should correspond to the requirements and objectives of
the monitoring programs performed.
The necessity to validate the methods applied and to achieve comparability of results
obtained in different laboratories is of utmost importance in terms of the optimal use of
the resources available and the correct and meaningful data interpretation. In order to
emphasize the importance of this point, a comparison between results obtained on the
same site location and at approximately the same time by the monitoring programs of the
city of Harare and DWR was made. Measurements of pH give a deviation of about 0.5 to
1 unit, which could be attributed to a systematic technical fault of the pH meter. The
results of the municipal program are more consistent compared to those of the DWR one.
Big differences were found regarding DO measurements, but a more detailed validation
of results is necessary in order to determine the specific reason for that. It should be noted
that DO concentrations could vary due to water temperature changes and due to the
conditions at the specific sampling site (depth and flow velocity). It is also possible that
these differences might be due to the improper sampling procedure or malfunctioning of
the equipment used for the analysis (DO-sensors). The phosphate measurements are
comparable in some cases only, while the results of nitrate concentrations show a very
systematic and well-defined difference, which most probably is due to a discrepancy in
the methods and analytical procedures applied. The comparison shows that the reasons
for fault data might be different and not only due to the analytical methods applied.
Problems with the quality assurance of test data regarding water quality are common for
almost all the countries in the region. Therefore, specific attention should be given to the
following factors:
• The analytical procedures applied and equipment used should be well defined and
described and an attempt should be made to use comparable methods of testing in all
water quality laboratories.
• An experienced officer should make a detailed validation of the data obtained, before it
is stored in the record archive.
• A regular and systematic quality assurance program of the sampling procedure and the
analytical methods applied should form an indispensable part of any monitoring
program. It should include internal laboratory procedures as: instrument condition,
maintenance activities, reference sampling, blanks and spiked samples, as well as
external control methods, like inter-laboratory tests.
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