CHEMICAL AND PHYSICOCHEMICAL ASSESSMENT OF SOIL AND GROUNDWATER IN AN AREA IMPACTED BY LEACHATE FROM URBAN SOLID WASTE AND METAL SCRAP

Abstract

The inadequate disposal of municipal solid waste and the historical presence of scrap metal generate complex environmental liabilities in urban areas, requiring an integrated interpretation of soil, groundwater, and soil gas data. This article reassesses an area located in the Cantagalo neighborhood, municipality of Guarujá, São Paulo State, Brazil, with a history of irregular waste disposal and scrap metal storage, based on the integration of field environmental data, accredited laboratory analyses, and bench-scale physicochemical tests. The study was organized into two complementary stages: a field stage, including a soil gas survey, installation of monitoring wells, soil and groundwater sampling, and analyses performed by an accredited laboratory; and a bench-scale stage, including gravimetric moisture, total carbon, and grain-size distribution tests at high vertical resolution. Within the evaluated dataset, soil did not show the most representative analytical response to the impact regarding volatile organic compounds (VOC), semivolatile organic compounds (SVOC), total metals, and total petroleum hydrocarbons (TPH). In contrast, groundwater showed a more consistent hydrogeochemical signature in the dissolved fraction, with the highest concentration values mainly observed for barium and cobalt. The exposure units were treated as compartments for assessment and spatial organization of the site, allowing the relationship between land-use scenarios, comparative values, and plume distribution. Barium showed a more localized distribution in wells PM-14, PM-13, and PM-05, whereas cobalt showed a broader distribution, especially in wells PM-01, PM-05, PM-08, PM-09, PM-12, PM-13, and PM-14. Methane readings remained below the lower explosive limit during the monitored period, although spatial coverage was limited due to non-operational wells. The bench-scale tests confirmed the heterogeneity of the porous medium, with predominance of sandy material, low fine-particle content, abrupt moisture oscillations, and strong variability in total carbon, conditions consistent with a greater expression of the environmental signal in the dissolved phase. Overall, these results reinforce that the integration of stratigraphy, soil physicochemical properties, and analytical groundwater responses is essential to reduce interpretative uncertainties, refine the site conceptual model, and support the direction of technical actions for environmental monitoring and management.