Sergey A. Kozlov

Far East State Regional Center of Geomonitoring, 20-b, Industrial street, Khabarovsk, 680009, Russia

Abstract:Peculiarities of the Middle-Amur artesian basin ground-water formation were revealed after investigation of various natural and human related factors. Ground waters in natural environment conditions and those used for water supplies were probed. As a result, the so-called hydro-geochemical provinces characterized by a higher concentration of Fe, Mn, Si, Ba, and Li where established within the artesian basin boundaries. Importance of ground water as a source of water for large human settlements instead of polluted water of Amur river is emphasized.

Key words: Hydro-geochemical provinces, Amur, artesian basin, ground-water, Fe, Mn.

The Middle-Amur artesian basin (Fig. 1) is located at the middle and downstream of Amur river and associated with the depression of the same name which has an area of about 55000 squared kilometres. This basin is the northern part of Sungari-Amur basin which southern part is situated on the territory of China. Middle-Amur basin's western and eastern boundaries are Burein heights and Sihote-Aline mountain range correspondingly.

The Middle-Amur basin is characterized by a regional ground-water flow. An overall thickness of deposits which form the basin is up to 2000m with hydro-geologically studied part limited by 300m while ground waters from depth of 100m or less are in practical use. The basin is formed by sediments, volcanic and metamorphic rocks of Paleozoic era to Pleistocene era. Litologically these are mainly siltstones, clays, loams, clay sands, sands, and gravel sediments which contain main ground water resources. Ground waters are fresh with concentration of minerals of 0,2 - 0,3 g/l having tendency to increase slightly at a depth of more than 100 meters.

The total amount of ground water reserves of the Amur valley is estimated to be 754 m³ per second. The total amount of ground water reserves of the main aquaifer (of pliocene-quaternary epochs) of the Middle-Amur basin is equal to 150 m³ per second, and a module of reserves accessible for exploitation is 3,7 l/(s*km²). The water extraction is on average 105 m³/day.

Artesian water formation is affected by a climate, geological structure, hydro-dynamical and geo-morphological and other factors. Simultaneous influence of these factors is resulted in a quite complicated pattern of iron distribution in the ground water. Distinctive features of the Middle-Amur basin's ground water chemical composition formation is oxigen free environment and a relatively high content of Fe and Mn in water bearing rocks. The amount of Fe in ground waters is increasing from basin boundaries towards its center reaching 20-30 mg/l (80 mg/l at some places). In accordance to that process transition from hydro-carbonate sodium waters at the basin boundaries through hydro-carbonate magnesium-sodium waters to hydro-carbonate calcium-iron waters at the center occurs.

Vertical zoning exits in Fe and Mn concentration dependence from the ground water depth. The Middle-Amur basin artesian water contains dissolved oxygen, carbon dioxide, and nitrogen only at depths less than 10-15m. Below that depth the carbon dioxide, methane, and nitrogen zone is located. Changes in the ground water chemical composition (main aquaifer of pliocene-quaternary epochs) happen mainly due to presence of the iron.

Figures 2-3 below show examples of the vertical hydro-geochemical profile for two large groundwater deposits of the basin: Tunguss deposit near city of Khabarovsk (reserves of 500000 m³/day) and Sendendeposit near Amursk town (reserves of 100000 m³/day).

Basin's environment is favourable for formation of higher concentration of iron and  manganese as well as some other elements. Territories where ground waters have locally higher (relative to the Maximum Allowed Concentration) content of controlled elements are divided into hydro-geochemical provinces. Our research made possible to locate and qualitively characterize several such provinces in the Middle-Amur artesian basin. These provinces (which overlap with each other) determine main anomalies in the ground water quality. Table 1 shows provinces characterized by a higher concentration of Fe, Mn, Si, Ba, and Li in the groundwater.

Despite of problems with the ground water quality large deposits ready for industrial usage were discovered. These deposits are sufficient for daily life and industrial needs of a city with a population of more than 500 000 people. Example of such ground water deposit is Tungus deposit near city of Khabarovsk. For its development we plan to use modern techniques of Fe and Mn content reduction directly in the aquaifer. Benzolpollution of river Sungari in November 2005 has been shown the importance of the groundwater supplies for the human settlements along the Amur river. Therefore, studies of quality and hydro-geochemical processes leading to modification in the ground water chemical composition become tasks of current importance. Research conducted by the author reveals the nature of ground-water chemical content formation. This  resultallows to discover main problems related to ground water quality of the basin, predict existence of hydro-geochemical provinces in other Far East regions, and determine main directions of future research in the Middle-Amur artesian region.

Table1 The characteristics of natural hydro-geochemical provincesof the Middle-Amur artesian basin (The Far East of Russia)