Migration of acidic groundwater seepage from uranium-tailings impoundments, 3. Simulation of the conceptual model with application to seepage area A

Abstract. Groundwater-dependent ecosystems (GDEs) have important functions in all climatic zones as they contribute to biological and landscape diversity and provide important economic and social services. Steadily growing anthropogenic pressure on groundwater resources creates a conflict situation between nature and man which are competing for clean and safe sources of water. Such conflicts are particularly noticeable in GDEs located in densely populated regions. A dedicated study was launched in 2010 with the main aim to better understand the functioning of a groundwater-dependent terrestrial ecosystem (GDTE) located in southern Poland. The GDTE consists of a valuable forest stand (Niepolomice Forest) and associated wetland (Wielkie Błoto fen). It relies mostly on groundwater from the shallow Quaternary aquifer and possibly from the deeper Neogene (Bogucice Sands) aquifer. In July 2009 a cluster of new pumping wells abstracting water from the Neogene aquifer was set up 1 km to the northern border of the fen. A conceptual model of the Wielkie Błoto fen area for the natural, pre-exploitation state and for the envisaged future status resulting from intense abstraction of groundwater through the new well field was developed. The main aim of the reported study was to probe the validity of the conceptual model and to quantify the expected anthropogenic impact on the studied GDTE. A wide range of research tools was used. The results obtained through combined geologic, geophysical, geochemical, hydrometric and isotope investigations provide strong evidence for the existence of upward seepage of groundwater from the deeper Neogene aquifer to the shallow Quaternary aquifer supporting the studied GDTE. Simulations of the groundwater flow field in the study area with the aid of a 3-D flow and transport model developed for Bogucice Sands (Neogene) aquifer and calibrated using environmental tracer data and observations of hydraulic head in three different locations on the study area, allowed us to quantify the transient response of the aquifer to operation of the newly established Wola Batorska well field. The model runs reveal the presence of upward groundwater seepage to the shallow Quaternary aquifer of the order of 440 m3 d−1. By the end of the simulation period (2029), with continuous operation of the Wola Batorska well field at maximum permissible capacity (ca. 10 000 m3 d−1), the direction of groundwater seepage will change sign (total change of the order of 900 m3 d−1). The water table drawdown in the study area will reach ca. 30 cm. This may have significant adverse effects on functioning of the studied GDTE.

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Geochemical evolution of inactive pyritic tailings in the Elliot Lake uranium district

Canadian Geotechnical Journal ◽

10.1139/t85-011 ◽

1985 ◽

Vol 22 (1) ◽

pp. 110-128 ◽

Cited By ~ 52

Author(s):

N. M. Dubrovsky ◽

J. A. Cherry ◽

E. J. Reardon ◽

A. J. Vivyurka

Keyword(s):

Heavy Metals ◽

Water Table ◽

Ferric Hydroxide ◽

Low Ph ◽

Geochemical Evolution ◽

Geochemical Data ◽

Secondary Aluminum ◽

Tailings Impoundments ◽

High Concentrations ◽

Uranium Tailings

Geochemical data obtained between 1979 and 1983 from a network of piezometer nests and cores from three inactive uranium tailings impoundments in the Elliot Lake district indicate that oxidation of pyrite taking place in the shallow part of the zone above the water table is causing the chemistry of the pore water above and below the water table to change. A two-layer hydrochemical zonation has developed in which infiltration water from rain and snow has resulted in an upper zone of low-pH water with high concentrations of SO4, Fe, and heavy metals. This zone is gradually expanding downward at rates generally between 0.2 and 2 m/year, causing displacement of the original mill process water, which has neutral pH and low concentrations of heavy metals. High concentrations of Fe(III) at shallow depth in the zone above the water table indicate that ferric iron is an important oxidizer of pyrite in the presence of free oxygen.The pe of the groundwaters is controlled by the ferric–ferrous redox couple, and trends in the data indicate iron solubility control by siderite at high pH, by ferric hydroxide at moderate to slightly acid pH values, and possibly by jarosite at low pH. Aluminum solubility controls are complex, and precipitation of amorphous aluminum hydroxide, allophane, and basic aluminum sulfates may occur over different pH ranges. Transport of low-pH conditions is retarded relative to the rate of groundwater flow in the tailings, because of the buffering effect of small amounts of carbonate minerals added during tailings neutralization; primary aluminosilicates such as sericite; and secondary aluminum hydroxides.Field data show that the flux of dissolved iron from the vadose zone to the groundwater zone in the Nordic Main tailings has been decreasing in recent years. However, mass-balance calculations indicate a potential for the generation of high-Fe groundwater for several decades to several hundred years. A long-term potential for acid and iron production is also shown by data from two tailings impoundments that have been inactive 8–10 years longer than the Nordic Main area. Presently only a small portion of the Nordic Main and West Arm tailings areas has become acidic through the entire tailings thickness; however, under existing infiltration conditions more extensive acidification will occur in future decades.

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