Evaluation of Remediation Approaches for Contaminated Groundwater in Metal-rich Geological Settings

A petroleum–chemical contaminated groundwater aquifer influenced by geological features of nickel-rich basalt was studied with geochemical simulation that employed the PHREEQC program. The parameter settings were based on local geological characteristics and the conditions of the real groundwater. Previous laboratory results were employed for model calibration, and model validation was conducted with real groundwater monitoring data to construct the site specific geochemical model. The simulation results indicate that both pH and ethylenediaminetetraacetic acid (EDTA) were controlling factors for the release of nickel from the basalt. Injection of chemicals transformed the groundwater body into an extreme environment; however, the groundwater returned to its former state after injection was terminated. Because EDTA played a role of a stabilizer for aqueous metal species in the groundwater, it is believed to be a sensitive controlling factor on the release of nickel from basalt rocks in this region. In the future, this model can be used to analyze alternatives of pollution remediation approaches when other metal-rich regions are encountered. The simulations of several treatment approaches for the removal of nickel in the groundwater revealed that chemical treatment by injecting a Ca(OH)2 solution is an appropriate approach. When combined with pump-and-treat method, the treatment can prevent spreading of pollutants during the injection. However, care should be taken for the planning of the location and number of pumping and injecting wells.