When a non-electrolyte solution, such as an organic substrate solution used in thermally enhanced bioremediation is injected into the ground, it is necessary to control a predetermined concentration in-situ. However, since the solution is non-electrolyte, continuous measurement, control and management of the concentration in situ is difficult. In this study, a fluorescent dye was mixed with the organic substrate solution and injected into the ground. Fluorescent dyes can be measured in situ and have been widely applied as tracers for groundwater flow investigations.
A previous study confirmed that the fluorescent dye moves with the non-electrolyte solution in the ground. In this study, we attempted to indirectly evaluate the behavior of the organic substrate using the fluorescent dye tracer and found a significant correlation in the concentrations of the fluorescent dye and the organic substrate solution.
The purpose of this study was to confirm whether fluorescent dyes can be applied as a tracer for evaluating the concentration of the non-electrolyte solution. A field experiment was carried out in silty fine sand in Japan. The aquifer at the test site extended from 10m below ground level and was partly surrounded by sheet piling to a length of 9.2m, a width of 10m, and a depth of 16m. Water circulation was controlled by two injection wells and two pumping wells. The fluorescent dye Eosin Y and the organic substrate solution were injected into the ground at a constant flow rate for over 80 days. Groundwater was periodically sampled from multiple observation wells to measure the concentration of Eosin Y and the total organic carbon, as the concentration of the organic substrate solution.
In this study, we show that the behavior of a fluorescent dye and non-electrolyte solution in the ground is highly correlated. The viability of using a fluorescent dye to indirectly assess the concentration of the non-electrolyte solution was demonstrated.
In addition, the difference in arrival time of the fluorescent dye and the non-electrolyte solution at the observation points were discussed, focusing on their adsorption and decomposition characteristics as well as the heterogeneity of the ground.