Push-Pull Tests to Support In Situ Chemical Oxidation System Design

ISCO;Push-pull test;Civil Engineering

Mathai, Ashley

University of Waterloo

关键词: ISCO;    Push-pull test;    Civil Engineering;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/6474/1/Mathai_Ashley.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

The problems associated with the contamination of groundwater environments by non-aqueousphase liquids (NAPLs) such as chlorinated solvents, gasoline and manufacturing gas plant(MGP) residuals, including their distribution and persistence, are well accepted. The treatmentof groundwater by in situ chemical oxidation (ISCO) relies on the oxidation potential ofchemical reagents to destroy harmful organic compounds. The interaction of these oxidants withtarget and non-target compounds in the subsurface will help determine effectiveness andefficiency of an ISCO treatment system. Push-pull tests (PPTs) have the utility to estimate keyproperties in situ and allow for sampling a larger volume of aquifer to yield more representativeestimates as compared to conventional bench-scale tests. The scale and cost-effectiveness of aPPT make it an ideal tool to collect valuable information on subsurface system behaviour so thatuncertainties can be minimized. The use of PPTs to provide insight into treatment expectationsor to support the design of an ISCO system requires a suitable interpretation tool.A multi-species numerical model (;;PPT-ISCO’) in a radial coordinate system was developed tosimulate a PPT with the injection of a conservative tracer and oxidant (persulfate orpermanganate) into the saturated zone of a porous medium environment. The pore space maycontain variable amounts of immobile, multicomponent, residual NAPL. The aquifer materialcontains a natural organic matter (NOM) fraction and/or other oxidizable aquifer material(OAM) species. The model is capable of simulating mass transport for an arbitrary number ofconservative and reactive tracers and NAPL constituents subjected to chemical reactions.The ability of PPTs to capture the in situ natural oxidant interaction (NOI) was tested with PPTISCO.Breakthrough curve (BTC) data collected from permanganate and persulfate PPTsconducted in the field were compared to simulated BTCs by assigning the same field operationalparameters to the model and applying NOI kinetic information obtained from batch tests. Thesetests confirmed the usability of the model and PPTs to obtain the NOI kinetics from PPT BTCs.The sensitivity of PPT BTCs to variations in the field operating and NOI parameters wereinvestigated. The results of varying the field operating parameters indicated that the oxidantBTCs could be scaled to match varying injection and extraction flow rates. Variations in NOIparameters revealed that the permanganate BTC is primarily controlled by the permanganate fastreaction rate coefficient and the quantity of OAM present in the aquifer. The spatial profiles ofOAM across the test zone revealed that the majority of the OAM consumption is from the fastfraction and occurs in the vicinity of the well where the permanganate concentration is greatest.An estimate of the permanganate fast reaction rate coefficient can be obtained from apermanganate PPT BTC by employing the model to simulate the PPT with the operationalparameters (used in the field) and literature estimates of the remaining NOI parameters.Calibration between the simulated and observed BTCs can be undertaken to adjust thepermanganate fast reaction rate coefficient to fit the permanganate PPT BTC.Persulfate NOI sensitivity investigations revealed that persulfate PPT BTCs can be characterizedby a concentration plateau at early times as a result of the increased ionic strength in the areaaround the injection well. The ionic strength is primarily controlled by the injected persulfateconcentration, and as persulfate degrades into sulphate and acid, the ionic strength is enhanced.Graphical analysis of the BTC revealed that an underestimated value of the persulfatedegradation rate coefficient can be obtained from the PPT BTC. A more representative estimateof the persulfate degradation rate coefficient can be achieved after fitting the field BTC to thesimulated results, applying the underestimated value as a starting point.PPTs investigating ISCO treatability have the ability to provide insight into the effect of the NOIon the oxidation of target compounds, site-specific oxidant dosage requirements and NAPLtreatment expectations. NAPL component BTCs from treatability PPTs are primarily controlledby the mass in the fast region, and the fast region mass transfer rate coefficient. Oxidationestimates extracted from NAPL component BTCs were shown to accurately approximate themass of each NAPL component oxidized when compared to model calculations. The mass ofNAPL oxidized for each of the components yields a site-specific oxidant dosage. This estimateexceeds what is prescribed by the stoichiometry between permanganate and the contaminant ofconcern due to the effect of the NOI.The utility of PPTs to study and quantify the interaction between injected oxidants and theaquifer material has been demonstrated with PPT-ISCO. In addition, PPT-ISCO has revealed thattreatability PPTs can be tailored to investigate the dosage requirements and treatmentexpectations of residual NAPLs. Results from this effort will be used to support ongoing fieldresearch exploring the use of PPTs to assist in understanding the competing subsurface processesaffecting ISCO applications.