Studies of the chemical composition of groundwater for providing sustainable urban development (for the Moscow urban agglomeration as an example)
O. M. ROZENTAL, N. D. DUBOV
Institute of Water Problems, Russian Academy of Sciences, Moscow, Russia
Keywords: groundwater, DTW algorithm, urbanised territories, chemical analytical monitoring, correlation analysis, toxic substances, dispersion analysis
Abstract
A comparison of the time series of concentrations of substances predominantly of anthropogenic origin polluting the groundwater of several large territories of the Moscow urban agglomeration in aquifers located at a depth from 3 to 50 m has been performed. It has been found that not all controlled indicators tend to decrease steadily with an increase in depth, the observed changes of parameters are often insignificant, and the concentration of petroleum products, for example, increases by several times when passing to deeper horizons. This makes the notion of deep-lying water as a strategic resource ensuring the sustainable development of a city unreasonable. To identify the sources from which impurities enter deeply located horizons, the causal relationships between the chemical analytical data for groundwaters were analysed using correlation and variance analyses. To measure the similarity of these series, the dynamic time scale transformation (DTW) algorithm was applied because the time series of data for different horizons experience shifts that change over time, so that their rhythms may differ. A significant similarity in the time series of water pollutant concentrations in different aquifers has been established. On this basis, it is concluded that the rock layers separating the aquifers in the territories under consideration are permeable, which provides the possibility of the vertical migration of pollutants to deeper bedded groundwaters. This conclusion is not cancelled by relatively large DTW distances found in some cases, meaning that some additional decrease in water quality is possible due to mass transfer of impurities between neighbouring geological provinces. Based on the results of the work, it is recommended to expand the programme of hydrogeochemical monitoring of pollution over the districts of Moscow in combination with the formation of a currently missing reliable profile of groundwater composition, in particular in relatively deep aquifers.
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