Developing operational site-specific groundwater trigger levels and remediation criteria at an alumina refinery

Site-Specific Trigger Levels (SSTLs) and Remediation Criteria values for signature chemicals in groundwater have been developed for a coastal Alumina Refinery. The values have been developed to protect sensitive receptors in the adjacent ocean in the following manner: SSTLs are to be applied to sentinel wells (located near the site boundary on the groundwater migratory path to the respective marine receiving environments). Remediation criteria are to be applied at the source zone wells. In order to achieve the above outcomes, the following steps were undertaken: Modelling the fate and transport rates of signature chemicals from the source to the sentinel wells, and from the sentinel wells to the ocean, and calculating a diffusion, dispersion and advection coefficient. Measuring the geochemical interactions of the impacted groundwater with the saline intrusion zone boundary (by direct laboratory experimentation) to assess the magnitude of chemical precipitation, followed by calculating a precipitation coefficient for each signature chemical. Using an existing hydrodynamic model to understand the tidal and current effects on discharged chemicals in conjunction with flux rates from the fate and transport modelling and conceptual site model to calculate the reduction in concentrations between the seabed at the point of discharge and the receptors at the point of exposure. Establish acceptable site-specific ecotoxicological and human health exposure levels in the adjacent marine environment. Using the various attenuation coefficients, back-calculating the signature chemical concentrations in the sentinel wells and source wells that would attenuate to an acceptable level prior to discharging into the receiving marine environment. (author)