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This study concerns a roughly 20-acre parcel located in the Honolulu Harbor area.  The site has more than 100-year history of various petroleum operations, and portions of the site are underlain by a NAPL plume, some 2.5 million liters in volume.  One of the key questions at this site is whether or not the NAPL plume is mobile or stable.   If it is still mobile - and therefore still moving toward the Harbor – then relatively more aggressive actions need to be taken to contain the plume.  On the other hand, if the NAPL plume has stabilized, then relatively less aggressive actions may be sufficient, to slowly recover and manage the NAPL plume in place.

The study site, located in a coastal area, is tidally influenced.  The frequent wetting and re-wetting of the pore spaces with water should theoretically impede the movement of the NAPL.  As a result, tides might act as a partial down gradient barrier to the continued movement of the NAPL plume toward the harbor. Because of the complicated nature of the tidal fluctuations, the effects of the tides on the movement of the NAPL plume are difficult to quantify.  A conservative approach is therefore typically adopted, which assumes that the tides do not impede the movement of the NAPL plume and that can overestimate the impact on the harbor. The research will involve collecting old and new data from existing wells; experimental work involving the use of a fluorescent tracer to measure the movement of the light NAPL plumes; and numerical modeling through the use of multiphase numerical models that include capillary effects and the effects of actual tidal fluctuation data. The fluorescent tracer will be adopted for use under tidal conditions through the use of both laboratory and field experiments. Preliminary bench experiments have shown success of the methodology. The use of both cross-sectional and vertically integrated models will be assessed. Data collected will be used to calibrate and validate the models which will be used for designing remediation strategies.  It is expected that the techniques employed in this work, would be applicable to other NAPL sites in granular lithology, tidal settings, both elsewhere in the Hawaiian Islands, as well as on the Mainland.