Hydrochemical monitoring of GRES power plant

. Cooling ponds are an important part of the complex of thermal power plant facilities. However, with their economic use, there are needs for environmental monitoring and environmental assessment to predict the condition and assess their effectiveness. In this research, first, the issues of hydrochemical monitoring are considered; second, an ecological analysis of hydrochemical indicators is carried out. The research showed that during the year an unsatisfactory condition is observed according to biochemical parameters, and the content of basic ions is within the normal range. The results of research expand knowledge in the field of environmental monitoring and can be useful in design and survey activities.


Introduction
The Iset lake-type reservoir is located in Verkhniaia Pyshma district in the north of Yekaterinburg, its distance from the latter is 37 km (by road) and has good access roads. Iset is a shallow, well-heated reservoir, used as a cooler for Sredneuralskaya GRES [1][2][3][4]. Geomorphologically, the reservoir is located in the forest zone of the Trans-Urals, on an abrasive-erosive platform characterized by hilly relief in the western part and billowy in the eastern part. Soils of podzolic type are of predominant importance in the zone, there are outcrops of massively crystalline blocks. Swamp soils have a significant distribution. Vegetation is mainly represented by pine and secondary birch-aspen forests.
The climate of the area is continental. The temperature regime is characterized by low average annual and winter temperatures. The average annual air temperature is about 1°C, with an annual absolute maximum of +34°C, an absolute minimum of -48°C. The average temperature in January is -15.5°C, the average temperature in July is 17.2°C. The average duration of the frost-free period is 102 days. The sum of the average daily temperatures for the growing season is quite high, above +10 o , is 1778 o .
The prevailing winds are western. The average annual precipitation is 465 mm with seasonal distribution: winter -58 mm; spring -88 mm; summer -214 mm; autumn -105 mm.
The territory belongs to the zone of sufficient moisture, the average annual amount of precipitation is 450-550 mm, of which 47% falls in the summer period. The height of the snow cover is 0.4-0.6 m.

Materials and methods
The work objective is to collect and analyze data from hydrochemical monitoring of the reservoir to control the water quality of the Iset reservoir and the discharge channel of the Sredneuralskaya power plant (SUGRES).
Chemical analysis of water samples from the Iset reservoir was carried out in accredited laboratories. The author's team carried out analytical processing of research results.

2.1
Research Object The Iset reservoir was chosen as the object of research.
Reservoir at the source of the lake Isets-r. Iset was created in 1725. The average annual amplitude of water level fluctuation is 41 cm, in certain years it reaches 90 cm.
The main parameters of the reservoir are as follows: NWL -249.5 m The total volume at NWL -67.0 million m 3 The mirror area at NWL -2440 ha Length -8.5 km The maximum width -4.5 km Maximum depth-3.5 m Average depth -2.8 m Water mass volume -67.0 million m3 According to operating conditions of GRES, the water level in the reservoir should be maintained at the level of NWL, if possible.
Water collection area of the lake Iset is 618.0 km 2 . Peat-swamp soils prevail in the water collection area and forest podzols are common, it is dissected by rivers (Chernaya, Mulyanka, Kedrovka, Kalinovka, Lebyazhya, Zhuzhelka, Shitovskoi Source), with a total length of 226 km. There are lakes in the collection area: Shity, Vashty, Shchuchye, Chernovskoye, two Karasiye. The Iset river flows out of the reservoir. The reservoir carries out long-term and annual regulation of the flow of the Iset river.
Iset lake has a hydrological connection with other reservoirs -above the river Shitovskoi Source are located the lakes of Shity and Vashty, which lie below the river Iset reservoirs -Lake Melkoye and Upper Iset pond.
The basin of the lake is of tectonic origin; it is characterized by the presence of rocky ridges, islands (Solovetskiye, Krasnenkiy, Korablik) at the bottom. Freeze-up occurs in late October-early November, reservoir break-up -in late April-early May. Typical soils: dark gray silts, sand, silted sand, rocky.
Since 1936, when SUGRES appeared on the shore of the lake Iset, the reservoir turned into a cooling pond. Further on, its hydrochemical and hydrological regimes were determined by the nature of the reservoir use for its main purpose -technical water supply of Sredneuralskaya GRES and Yekaterinburg. The flow of heated discharge waters of the GRES into the reservoir forms a specific thermal regime. Part of the water area, about 300 hectares, does not freeze throughout the winter, and part is covered with ice much later than in an area with a natural temperature regime. The average annual water temperature in the discharge channel of SUGRES is 7-8°C higher than at the water intake and 5.5-10.5°C higher than in the zone of reservoir dam. In winter, the discharge of heated water affects the thermal regime of the lake only in a limited area, with an area of about 1 km 2 , in summer, heating extends to all active zones of the reservoir.
Along the coastal slopes of the reservoir basin, including the islands, silty deposits are insignificant. The bottom is formed by clastic material, less often by sand or gravel. The capacity of silty bottom sediments at the water intake structures of SUGRES is 0.

Results and discussion
In the spring-summer-autumn period, hydrochemical samples, samples for toxicity analysis by biotesting, chemical indicators were taken in the Iset reservoir. A total of 117 samples were taken at 9 sampling points during the observation period for hydrochemical studies [10,11]. The reservoir condition was assessed following the current taxation rules and regulations for fisheries waters and modern ecological and sanitary classifications. They are presented in Tables 1 and 2.

Conclusion
According to research results, toxicity index of all studied samples does not exceed the norm. The indicators of COD, BOD 5 and permanganate index were exceeded in all water samples. The maximum values of these indicators were found in the area of BNS-1 water intake, the mouth of discharge channel, the mouth of the Chernaya river, dam area. The indicators in water samples taken to the biomodule are comparable with the indicators of samples taken after the biomodule. Excess of COD, BOD 5 and permanganate index indicates both the presence of natural and anthropogenic pollution of the reservoir. It is necessary to conduct additional research to establish the reasons that led to the deviation of indicators from the standards.