Flux based site assessment and design of an integrated remediation system
The applicability of contaminant flux and mass discharge as tools for site characterization and remediation design was evaluated through field experiments and modeling analyses. This is in contrast with traditional approaches that use maximum concentration levels (MCLs) to guide remedial choice. The need to couple source and plume treatment for optimal remediation design was recognized and flux distribution across the source control plane flux distribution was identified as a metric that links source to plume. It was observed (through numerical studies and assessment of existing field data) that, for flushing based source depletion technologies, the coefficient of variation of the source distribution increases with time, but, that of the flux distribution remains constant. Also, 'hot-spots' or high flux zones persist through the treatment process and targeted source treatment would increase efficiency.
In order to design such targeted treatment system, field-scale measurement of contaminant fluxes is required. Groundwater and contaminant fluxes were measured at three sites in the US, two TCE plumes and one MTBE plume using an innovative technology, the passive flux meter (PFM). Flux measurements, using PFM, compared well with existing site characterization data. A confounding factor in PFM measurements lies in the estimation of the groundwater flow convergence/divergence factor (α). A new inverse technique used for estimation of α corresponded well with the conventional technique, while providing additional depth information. The importance of depth delineation increases with increasing site heterogeneity.
Site data from two TCE plumes, one in U.S.A. (where fluxes were measured using PFM) and another in Australia (where flux measurements are scheduled) were used to demonstrate the impact of site characteristics on remedial choices. Estimates of the source strength, degradation rate and other site attributes were used in an analytical modeling approach to assess the expected outcomes from several remediation options. At the US site the source flux was larger but so was the degradation rate. Thus, source treatment was found to be more important at the US site, while plume treatment was more important at the Australian site.
0775: Environmental engineering