HR: 15:25h
AN: B43B-02    [Abstracts]
TI: Sources and Transport of Arsenic Contaminating Shallow Groundwater in the Historical Industrial Zone of Monterrey City, Nuevo León, México
AU: Romero, F M
EM: fmrch@geol-sun.igeolcu.unam.mx
AF: UNAM, Instituto de Geologia, Mexico, DF 04510, Mexico
AU: * Gutierrez-Ruiz, M E
EM: ginny@servidor.unam.mx
AF: UNAM, LAFQA, Instituto de Geografia, Mexico, DF 04510, Mexico
AU: Villalobos, M
EM: marvilla@igg.unam.mx
AF: UNAM, LAFQA, Instituto de Geografia, Mexico, DF 04510, Mexico
AB: Arsenic contamination has been detected in a shallow aquifer of the geographical center of Monterrey City, in the Northeast of Mexico, and where the historical industrial zone of the city is located, reaching concentrations of up to 3.1 mg/L. A metallurgical plant that operated more than a 100 years and closed down in 1999 is identified as a possible pollution source because it deposited arsenic-rich wastes in the fields adjoining it, showing total arsenic contents that reach up to 1-2 % As in weight. We deem arsenic transport through the soil profile as highly unlikely based on the following experimental and field evidence: water-soluble arsenic contents in 1:20 soil:water extracts of both surface and subsurface samples is very low, showing values in a majority of samples below 1 mg As/L; the unsatured zone under the inactive plant is characterized by the presence of two impermeable clay layers (hydraulic conductivities of 2.1 x 10-8 cm-1 to 8.4 x 10-8 cm-1), the first one occurring at 0.6 to 1 m below the surface, and the second one at approximately 17 m below the surface; arsenic analyses of several core samples from boreholes 40 m deep show that As released at the soil surface is completely retained in the upper clay layer. Nevertheless, the highest dissolved arsenic concentrations (1.1 to 3.1 mg/L) were found in wells from shallow groundwater from active industries located to the north of the inactive plant. The groundwater flux in the area goes in a direction west to east, therefore, the source of these arsenic levels cannot come from the inactive plant premises and indicates the occurrence of additional sources of arsenic groundwater contamination. The evidence points to the fact that the most likely cause of shallow groundwater contamination inside the inactive plant is via surface runoff of deposited wastes during the rainy season, into drilled boreholes in the area. This is supported by a 10-year semester analysis database. Therefore, the authors recommend a suitable and immediate closure of these boreholes.
DE: 0478 Pollution: urban, regional and global (0345, 4251)
DE: 0486 Soils/pedology (1865)
DE: 1865 Soils (0486)
SC: Biogeosciences [B]
MN: 2007 Joint Assembly