Remediation Actions by a Risk Assessment Approach: A Case Study of Mercury Contamination

Abstract

Abstract. The risk assessment procedure for identifying the remediation actions which may be adopted at a mercury contaminated site, when the plants are upgraded in the future, is proposed. The potentially active exposure/migration pathways in the future arrangement of the area will be due to Hg contaminated subsoil as a primary source (vapor inhalation and groundwater leaching) and to groundwater as a possible secondary source (transport to the point of compliance).The data of mercury concentration in the soil were acquired through environmental monitoring campaigns, and were processed to establish the three-dimensional distribution of contamination in subsoil, to locate sources and to define their geometrical and chemical characteristics. Speciation tests of mercury in the soil indicated that the most abundant species present were poorly leachable under the site-specific environmental conditions, confirming the coefficient distribution value obtained by the leaching tests.Analytical and numerical fate and transport modeling tools were used to locate digging zones in the contaminated subsoil, so as to reduce the possible groundwater contaminant loading and to avoid the down-gradient exceeding the concentration limit according to regulations. Remediation actions additional to civil works were required, which consists of soil digging within one contamination source, for about 22,200 m 3 of soil. In order to evaluate the Hazard Index (HI) for human receptors due to Hg vapor inhalation, the air concentration of volatile mercury at the exposure point was estimated, based on direct measurements carried out at the site. Simulation gave HI values below 1 for all tested scenarios, suggesting that public health is protected without any additional actions to the already scheduled plant upgrading and digging for groundwater protection. Keywords

Risk Evaluation of a Mercury Containment System

“…The Saponaro et al, 2005 study concluded that even the most abundant mercury species in soil are poorly leachable under the site-specific environmental conditions. In general, human health and environmental risk assessments for metals are difficult to estimate because environmental behavior and toxicity depend on metal chemical forms and soil properties, such as pH value and redox potential, and these properties greatly vary in the environment.…”

“…Furthermore, the study concluded that given the serious risks posed by methyl mercury to mink and kingfishers, the next step is to evaluate possible remedial options that could be used to reduce risks to acceptable levels. Saponaro et al, 2005, developed a risk assessment procedure to identify the remediation actions that may be adopted at a mercury-contaminated site. Analytical and numerical fate and transport modeling tools were used to locate digging zones in contaminated subsoil, to reduce the possible groundwater contaminant loading, and to avoid exceeding concentration limits.…”