A large-scale permanganate-based in-situ chemical oxidation (ISCO) effort has been conducted over the past ten years at a federal Superfund site in Tucson, AZ, for which trichloroethene (TCE) is the primary contaminant of concern. Remediation performance was assessed by examining the impact of treatment on contaminant mass discharge, an approach that has been used for only a very few prior ISCO projects. Contaminant mass discharge tests were conducted before and after permanganate injection to measure the impact at the source-zone scale. The results indicate that ISCO caused a significant reduction in mass discharge (approximately 75%). The standard approach of characterizing discharge at the source-zone scale was supplemented with additional characterization at the plume scale, which was evaluated by examining the change in contaminant mass discharge associated with the pump-and-treat system. The integrated contaminant mass discharge decreased by approximately 70%, consistent with the source-zone-scale measurements. The integrated mass discharge rebounded from 0.1 to 0.2 Kg/d within one year after cessation of permanganate injections, after which it has been stable for several years. Collection of the integrated contaminant mass discharge data throughout the ISCO treatment period provided a high-resolution, real-time analysis of the site-wide impact of ISCO, thereby linking source-zone remediation to impacts on overall risk. The results indicate that ISCO was successful in reducing contaminant mass discharge at this site, which comprises a highly heterogeneous subsurface environment. Analysis of TCE sediment concentration data for core material collected before and after ISCO supports the hypothesis that the remaining mass discharge is associated in part with poorly-accessible contaminant mass residing within lower-permeability zones.
Human enteric viruses can be highly
infectious and thus capable of causing disease upon ingestion of low
doses ranging from 10
0
to 10
2
virions. Norovirus
is a good example with a minimum infectious dose as low as a few tens
of virions, that is, below femtogram scale. Norovirus detection from
commonly implicated environmental matrices (water and food) involves
complicated concentration of viruses and/or amplification of the norovirus
genome, thus rendering detection approaches not feasible for field
applications. In this work, norovirus detection was performed on a
microfluidic paper analytic device without using any sample concentration
or nucleic acid amplification steps by directly imaging and counting
on-paper aggregation of antibody-conjugated, fluorescent submicron
particles. An in-house developed smartphone-based fluorescence microscope
and an image-processing algorithm isolated the particles aggregated
by antibody–antigen binding, leading to an extremely low limit
of norovirus detection, as low as 1 genome copy/μL in deionized
water and 10 genome copies/μL in reclaimed wastewater.
The objective of this study was to characterize the temporal behavior of contaminant mass discharge, and the relationship between reductions in contaminant mass discharge and reductions in contaminant mass, for a very heterogeneous, highly contaminated source-zone field site. Trichloroethene is the primary contaminant of concern, and several lines of evidence indicate the presence of organic liquid in the subsurface. The site is undergoing groundwater extraction for source control, and contaminant mass discharge has been monitored since system startup. The results show a significant reduction in contaminant mass discharge with time, decreasing from approximately 1 to 0.15 kg/d. Two methods were used to estimate the mass of contaminant present in the source area at the initiation of the remediation project. One was based on a comparison of two sets of core data, collected 3.5 years apart, which suggests that a significant (~80%) reduction in aggregate sediment-phase TCE concentrations occurred between sampling events. The second method was based on fitting the temporal contaminant mass discharge data with a simple exponential source-depletion function. Relatively similar estimates, 784 and 993 kg, respectively, were obtained with the two methods. These data were used to characterize the relationship between reductions in contaminant mass discharge (CMDR) and reductions in contaminant mass (MR). The observed curvilinear relationship exhibits a reduction in contaminant mass discharge essentially immediately upon initiation of mass reduction. This behavior is consistent with a system wherein significant quantities of mass are present in hydraulically poorly accessible domains for which mass removal is influenced by rate-limited mass transfer. The results obtained from the present study are compared to those obtained from other field studies to evaluate the impact of system properties and conditions on mass-discharge and mass-removal behavior. The results indicated that factors such as domain scale, hydraulic-gradient status (induced or natural), and flushing-solution composition had insignificant impact on the CMDR-MR profiles and thus on underlying mass-removal behavior. Conversely, source-zone age, through its impact on contaminant distribution and accessibility, was implicated as a critical factor influencing the nature of the CMDR-MR relationship.
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