VULNERABILITY ASSESSMENT INDEX OF GEOMEDIA AGAINST SPILLED ACIDS

Acid spill accidents are frequently occurring in Korea with increased production, use, storage, and transport of acids accompanied by the growth of related industries. The spilled acids would have negative impacts on geo-ecosystems. We expect that the spilled acids will be neutralized eventually in subsurface, but the spatial and temporal range of acid impacted areas before the eventual neutralization will vary depending on the characteristics of geomedia. However, lack of understanding of geomedia’s responses to the spilled acids has hampered the development of proper response strategies and selection of optimal remediation techniques. Here, we designed a vulnerability index assessment scheme for geomedia against sulfuric acid. First, we defined the vulnerability index as the reciprocal of geomedia’s acid neutralization capacity against the moving acid front. We operationally defined the acid impacted volume as the volume of the geomedia that reaches pH 2 after 48 hours from the spill event such that the vulnerability index is proportional to the acid impacted volume. Second, we identified essential factors and corresponding sets of input data required by each factor to include in the vulnerability scoring scheme. We considered acid spill scenarios, physicochemical properties of the acid and geomedia, amount and concentration of the spilled acid, mineral composition, permeability and hydraulic conductivity, etc. We identified permeability of geomedia, contents of reactive primary and secondary minerals, and size fractionation as the most important factors, despite the complexity of geomedia and interdependency among each factor. Third, we added the weighted score for each factor to get the final vulnerability indices. The acid neutralizing capacity of the mineral components and geomedia were obtained either from laboratory experiments or literature survey. We plotted the score for each factor on a target geographic area and added the multiple layers of the score plots after multiplying by weighting factors. The vulnerability indices will give rough yet useful information in selecting proper counteraction measures depending on the location of a future acid spill accident, in estimating the impacted area, and in deciding when to end the active remedial measure or pH monitoring.