Integrated Modeling of Cadmium and Zinc Contamination in Groundwater and Surface Water of t

Abstract: Regional modeling of subsurface cadmium and zinc transport in a diffusely polluted area in the south of the Netherlands is the subject of this study. The atmospheric deposition of cadmium and zinc was caused by three zinc-ore smelters (point sour

Integrated Modeling of Cadmium and Zinc Contamina-tion in Groundwater and Surface Water of the Kempen

Region, The Netherlands

Bas van der Grift, Hilde Passier, Joachim Rozemeijer and Jasper Griffioen Netherlands Institute of Applied Geoscience TNO - National Geological Survey, Utrecht, The Netherlands

(h.passier@nitg.tno.nl)

Abstract: Regional modeling of subsurface cadmium and zinc transport in a diffusely polluted area in the south of the Netherlands is the subject of this study. The atmospheric deposition of cadmium and zinc was caused by three zinc-ore smelters (point sources of emission). Agriculture and other sources of heavy metals are small compared to the atmospheric deposition in the vicinity of the smelters. A coupled unsaturated and saturated zone flow and transport model was used to assess and predict reactive transport of cadmium and zinc in three different catchments in the area. For cadmium an extensive set of modeling results is presented, for zinc only preliminary results. The modeling started with a spatial reconstruction of the historic atmos-pheric deposition followed by an unsaturated zone transport model to calculate cadmium leaching to groundwater. After this, a 3-dimensional reactive transport model was used for the saturated zone. The calcu-lated cadmium concentrations were compared with two datasets of shallow groundwater analyses for valida-tion of the model. The range of modeled and measured concentrations is the same. The modeling results indi-cate that the amount of cadmium in the groundwater has been doubled in the past twelve years. In the satu-rated zone, cadmium becomes strongly retarded, despite the low reactivity of the sandy sediments. The maximum depth of modeled and measured concentrations is about 20 meter beneath surface level. In 2002 about 10% of the total estimated leached cadmium has been discharged in seepage areas. The integrated modeling system developed here can be used to run future scenarios to predict resulting concentrations in groundwater and surface water.

Keywords: groundwater; modeling; cadmium; zinc; Netherlands

1.INTRODUCTION

In the border region of Belgium and the Nether-lands, three zinc-ore smelters are located within 10 km from each other and a fourth was shut down in 1973. Exhaust fumes from these smelters have emitted oxides of heavy metals during about one century, which have reached the soil either by dry deposition or with rainfall. As a result of this, the soils in the Kempen are heavily contaminated with cadmium and zinc on a large regional scale (Fig. 1) (Sonke, 2002, Harmsen, 1977; Boekholt, 1992). Since the seventies, the cadmium and zinc emis-sions have been greatly reduced, so the pollution of the soil of this region is of a historical nature. Leaching of heavy metals from the topsoil is a major risk for groundwater contamination. The soils of the Kempen region are developed in poor aeolic drift sands and are vulnerable for leaching due to the acidifying conditions (Wilkens & Loch, 1997). The saturated zone consists of unconsoli-dated sandy Pleistocene deposits.

Regional modeling of subsurface cadmium and zinc transport in the diffusely polluted area is the subject of this study. A coupled unsaturated and saturated zone groundwater flow and transport was used for three different catchments the area (Fig.

1) to assess and predict:

?leaching of metals from unsaturated zone to groundwater;

?the development of the metal concentrations in shallow and deeper groundwater;

?the metal loads of the surface water drainage network.

This paper focuses on the Beekloop-Keersop, Bu-ulder Aa and Tungelroijsche Beek catchment. The approach (Fig. 2) started with a spatial reconstruc-tion of the historic atmospheric deposition fol-lowed by an unsaturated zone transport model to calculate metal leaching to groundwater. Agricul-ture and other sources of heavy metals were also

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