A DEMONSTRATED METHODOLOGY JUSTIFYING A MASS TRANSFER LIMIT IN RBCA HYDROCARBON INHALATION CALCULATIONS

The use of the Atlantic Risk Based Corrective Action (RBCA) tool kit is endorsed by the provincial regulators in Atlantic Canada for evaluating human health risk and hazard potentials. The tool can also be used to calculate site specific hydrocarbon concentration goals, for the soil and groundwater on a property. Atlantic RBCA is another local variation of the jurisdiction specific RBCA tool kits used across North America, as developed by GSI Inc. of Texas.

Geoscientists in Atlantic Canada are often the official project "Site Professional" under the applicable provincial guidelines for the management of contaminated sites. For sites where gasoline and furnace oil impacts exist under a building, the vapour inhalation exposure route calculations are among the most significant and influential on the resulting conclusions and recommendations.

The Atlantic RBCA spreadsheet tool calculates the hydrocarbon intake by humans through the vapour inhalation exposure route. This calculation applies a linearly proportional Henry's Law partitioning relationship, to the user supplied hydrocarbon concentrations in the soil and water. The application of this relationship is not always valid. Applying Henry's Law to user supplied hydrocarbon concentrations that exceed the compound specific solubility limit, results is an overestimation of the vapour based mass transfer, which is reflected in the resulting human exposure conclusions.

Atlantic RBCA spreadsheet tool users can better understand and justify the application of a methodology that takes this into account, by referencing this document. The methodology is presented in this document, and its appropriateness is demonstrated by including supporting detailed backup calculations.