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ASSESSMENT OF MERCURY POLLUTION TO THE IRTYSH RIVER IN PAVLODAR, KAZAKHSTAN
ILYUSHCHENKO, M., E. LAPSHIN, R. KAMBEROV, A. AKHMETOV, P. RANDALL, AND T. TANTON. ASSESSMENT OF MERCURY POLLUTION TO THE IRTYSH RIVER IN PAVLODAR, KAZAKHSTAN. Presented at American Institute of Chemical Engineers 2005 Annual Meeting, Cincinnati, OH, October 30 - November 04, 2005.
To address four scenarios (no change in the direction of the contaminated mercury plume; constructing a impermeable screen around building 31, which is the main source of mercury contamination spread; containment of pollution, which will eliminate the groundwater contamination; and changes of hydrogeological conditions in the northern industrial area of Pavlodar) to produce a forecast of Hg transport with groundwater.
The threat of polluting the river Irtysh by mercury was caused by high losses of Hg during 1975-1993 during chlor-alkali production at the former PO "Khimprom", Pavlodar, North-East Kazakhstan (at present JSC "Pavlodar Chemical Plant"). These losses were the highest among similar factories in the former USSR. On average, they could be estimated as 1.6 kg Hg per ton of produced caustic soda (total losses could be estimated as 1310 tons of those 1100 tons were non-counted mechanical losses of metal mercury). The majority of this mercury was concentrated beneath the electrolysis factory (building #31) and formed the hotspot of groundwater contaminated by soluble mercuric chloride. The other adverse effects that took place include: losses of Hg-contaminated wastewater from plant drain; contamination of topsoil within industrial site #1 and around lagoons for mercury waste; and contamination of surface water in wastewater storage-lake Balkyldak (having capacity more than 80 million m3). The closest sites subject to risk of mercury pollution are the village Pavlodarskoye (having 200 ha of groundwater fields) and the river Irtysh, located in 3-5 km to the west from chlor-alkali prodution. The original design of the clean-up was developed in 1995, based on small-scale investigations conducted during the Soviet period. The scope of designed works included the following activites: (i) demolishing of building #31; (ii) excavation and thermal treatment of concrete floors; (iii) selected excavation of contaminated soil from beneath of building 31 and its treatment by soil washing technique; (iv) construction of impermeable screen (so called "cut-off wall") around building 31 which is the main source of mercury contamination spread; and (v) construction of underground landfill for IV hazardous class waste in 50 m to the south from building 31 for further disposal of materials with low Hg content. Several large hotspots were revealed where the threshold value for Hg in soil (2.1 mg/kg) was exceeded by 500 times and more. Four hotspots were located within the industrial site #1 and were related to the building #31 and facilities for regeneration of solutions, wastewater storage and treatment facilities. One hotspot was located on the bank of lake Balkyldak and was related to the lagoons used for storage of mercury waste. The volume of soil contaminated above 10 mg/kg in top 0-0.5 m layer was estimated as well as amount of mercury deposited in this soil (excluding Hg deposited underneath building 31 and within the lagoons for Hg waste). These estimates give 19263 m3 of contaminated soil and 2931 kg of Hg for the industrial site #1, and 79542 m3 of contaminated soil and 16022 kg of Hg for the area between industrial site of former PO "Khimprom" and lake Balkyldak. Sampling and analysis of groundwater from the existing network of boreholes and newly established ones (in total more than 200 boreholes) revealed the plume of Hg-contaminated groundwater spreading from the main source (building 31) and secondary source of pollution (pumping station for wastewater) in north-north-west direction almost in parallel to river Irtysh. The maximum width of the plume is 350 m and its length - more than 2 km. The contaminated groundwater is spreading above basalt clays of Pavlodar assisted at the depth 6-14 m depending on landscape. Within the major Hg concentration in the groundwater reached 150 µg/L (near the building 31) and 120 µg/L (near the wastewater pumping station). Concentration decreased with the distance from hotspots reaching after every 300 m 45 µg/L, 0.8 µg/L, 1.1 µg/L, 0.9 µg/L and 0.4 µg/L, correspondently. Using groundwater modeling software GMS 3.1 it was determined that existing direction of groundwater plume is caused by a combination of natural and man-made factors. Four scenarios were addressed to produce a forecast of Hg transport with groundwater until 2030. In the case of a zero-change scenario, the contaminated plume will continue to spread in a north-north-west direction above basalt clays at the depth 5-15 m. Thus, if the direction of plume does not change mercury will not pose a serious threat for Palvodarskoye village and river Irtysh. At the same time limited amount of Hg might enter the emergency canal going from lake Balkyldak to the west. The second scenario assumes the construction of cut-off wall around building 31. It will not solve the problem of water quality due to the presence of other sources of pollution near the wastewater pumping station, though the latter sources are less intensive. The third scenario assumes containment of both sources of pollution, which ultimately will eliminate the groundwater contamination. The fourth scenario assumes changes of hydrogeological conditions in the northern industrial area of Pavlodar depending on industrial development or degradation. The results will be discussed.