Reasons for Non-Compliance With the Maximum Permissible Concentrations of Hazard Class 4e Substances in the Small River Control Point – Drainage and Waste Water Receivers

Abstract

Purpose: to determine the reasons of non-compliance with the maximum permissible concentration of the hazard class 4e substances for water bodies of fishery significance (MPCfs) in the small rivers control point – receivers of drainage and waste waters (DWW). Materials and methods. The research object is the Salt river Semikarakorsk district Rostov region, the catchment area of which is an anthropogenically transformed agricultural landscape. As background concentrations, the data from official certificates on background concentrations in the investigated water body in the section 500 m above the DWW outlet are used. Results. The processes of salt-forming ions dilution belonging to the hazard class 4e substances in the aquatic environment of the Salt river when DWW enter it at the release site to the control point according to the method of A. V. Frolov – I. D. Rodziller were modified. It has been found that important characteristics of dilution processes are the ratio of the flow rates of the river and in the reservoir, as well as the background (Cf) and maximum permissible concentration of the substance. So, for the calcium ion Cf = 105 mg/dm³, MPCfs = 180 mg/dm³, the concentration of the substance in the most polluted jet from the release site to the control point varies from 180 to 107.8 mg/dm³. For sulfate ion Cf = 385 mg/dm³, MPCfs = 100 mg/dm³, the concentration varies from 100 to 232.5 mg/dm³. Conclusions. It has been found that the reasons for non-compliance with the maximum permissible concentrations of the hazard class 4e substances in the control point of small rivers are a high background concentration of salt-forming ions belonging to the 4e hazard class, comparable flows of rivers and DWW. The reasons for the weak dilution are the shallow depth of the river, low flow velocity, as well as high initial mineralization of natural water. Therefore, it is necessary to amend the Russian legislation in terms of regional permissible concentrations in water bodies, taking into account the regional characteristics of the hydrochemical regime of water bodies, river runoff, and the hydrochemical composition of the upper horizons of groundwater.