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Annex 3. Methods on Assess of Water Quality and Transboundary Load
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Annex 3.
METHODS ON ASSESS OF WATER QUALITY AND TRANSBOUNDARY LOAD
Water Contamination Index
The WCI can be calculated by the following formula:
,
which sums up the ratios of the observed concentrations of contaminants to their respective maximum permissible levels (MPLs).
The TMP uses a modified version of this assessment, in which two indicators – BOD5 and dissolved oxygen – are held constant, while four others are chosen from among indicators that have the highest ratios of their magnitude to their MPL.
In assessing the state of a watercourse section at a given observation post based of the WCI, the following steps are to be made:
(1) WCI is calculated for each water sample;
(2) based on the WCI, quality class is determined for each sample and the number of times MPLs were exceeded;
(3) statistical data of several observations over a period of study is assessed – minimum and maximum values, average and standard deviations and quantiles.
The table given below helps in interpreting the index obtained in this manner
Quality classes and contamination indices of water
|
Water-quality class |
Class characteristic |
WCI quantity |
|
1 |
Very pure |
Not more than 0.3 |
|
2 |
Pure |
From 0.3 to 1 |
|
3 |
Moderately contaminated |
From 1 to 2.5 |
|
4 |
Contaminated |
From 2.5 to 4 |
|
5 |
Dirty |
From 4 to 6 |
|
6 |
Very dirty |
From 6 to 10 |
|
7 |
Extremely dirty |
More than 10 |
Mass Transfer Assessment
The method of proportions is used as a basic calculation technique, with stratification of the original set of data by dates[6]. The first proportion is formed by data obtained for March, April and May of a given year, the second proportion – by data obtained for the rest of the months.
For indicators that do not correlate with flow rates[7], the following formula is used:
, (1)
where L is the mass transfer volume to be found; N
is the number of days in a year; L1 is the average daily mass
transfer determined as a product of measured concentrations and the
corresponding volumes of flow on a given day; 
is the
daily flow rate averaged over a year; 
is the average daily flow rate in the days of
sampling.
In the case of a significant correlation between flow rates and concentrations, the following formula is used:
, (2)
where 
;
;
= mass
transfer measured at a time of sampling 
;
Cov() = sampling covariance;
Var() = sampling variance;
n = number of samples;
other variables are same as in (1).
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[6] Determination of a data stratification technique, which is optimal from the point of view of validity of the observed values of mass transfer, requires the conduction of a special study. Until the desired results are obtained, it is recommended that assessments be carried out on the basis of several variants of calculation.
[7] Determination of a critical level of correlation significance requires the conduction of additional special studies. Until the desired results are obtained, it is recommended that the assessment be carried out based on two variants of calculation.
