Environmental Engineering Reference
In-Depth Information
2.8.2
Data analysis
The analysis of stored data would help to reach decisions regarding the status of pollution
of the water body under consideration and to identify measures for its reduction, if
necessary. Statistical tools are used to reach sound results and to demonstrate the trends.
Data collected and stored may form the basis for the application of models describing
different aspects of the pollution transport and transformation processes. Models help to
simulate different scenarios and conditions or to predict events, and are very powerful
tools for the decision making process in water quality management.
Water quality assessment is one important form of monitoring data analysis. In many
cases the objectives of the program are associated with the evaluation and assessment of
the current status or trends in the variation of different water quality characteristics. The
term could be defined as follows (Novotny 2003):
To assess water quality means to evaluate the physical, chemical and biological
characteristics of the body, which has been monitored, in relation to natural
(background quality), health effects and intended beneficial use.
The data analysis stage of the monitoring process, together with the following stage - the
preparation of the report, is an essential last step of the monitoring cycle, in which data
obtained is structured, analyzed and conclusions drawn with respect to available
regulatory instruments. It is also important in this stage to make trend analysis of water
quality on a yearly basis. Regarding the assessment of the status of the examined body,
by means of comparison with regulatory instruments, it should be remembered that
stipulated values and criteria in the regulatory instruments should not be considered to be
rigid values, but statistical variables. Well-designed regulatory instruments provide for
flexibility by quoting statistical parameters as “percentiles”. A 90
th
percentile
concentration of 0.5 mg/l of any constituent, represented by a water quality data set,
indicates that this concentration is exceeded in only 10% of the monitoring data. A more
detailed discussion in this respect is presented in Chapter 12.
To enable a simpler analysis and interpretation of monitoring data, specifically
regarding surface natural water quality, the use of water quality indices is often applied.
Regarding physical and chemical parameters, the indices are based on lumping together
different parameters. There are many different indices applied worldwide (Chapman
1998, Ellis et.al. 1993).
2.8.3
The reporting stage
The monitoring cycle aims at the generation of reliable data, which must be processed
and presented in a way that is clear and understandable by non-specialists. Very often,
water quality data is buried in annual reports, with data presented in tabular form only,
without statistical assessment, interpretation or graphical presentation. Comparison with
regulatory instruments should be made only after the statistical analysis of the data
obtained has been done. In addition to the assessment of the status of the examined body,
appropriate abatement measures and activities to be undertaken should be prescribed as
well. Polluters should not be confined to a very strict scenario of pollution abatement
