Brent E Sleep

University of Toronto | U of T · Department of Civil Engineering

Hormoconis resinae (or Cladosporium resinae ), colloquially known as the kerosene fungus, is predominantly found in fuel tanks (Rafin and Veignie 2018). Its occurrence in fuel tanks was first reported in early 1960s. Since then, it has been considered as a serious threat by the petroleum industry for bio-deteriorating fuel quality, corroding storag...

Mathematical models in engineering play an important role in understanding and predicting the behavior of a system. A mechanistic coupled liquid water, water vapor and heat transfer model incorporating kinetic phase change accounting for real‐time interfacial area between water and gas phases was developed to predict coupled subsurface processes an...

In situ chemical reduction of chlorinated volatile organic compounds (cVOCs) by nano zero-valent iron (nZVI) has been widely applied in the past 20 years, but with limited effectiveness for bare nZVI due to rapid particle settling, short lifespan, and low reactivity. Stabilization and sulfidation of nZVI have improved its mobility and longevity, in...

Here, we review the contributions of Professor Barbara Sherwood Lollar to Compound Specific Isotope Analysis (CSIA) in contaminant hydrogeology and environmental chemistry. We first discuss the seminal work by Professor Sherwood Lollar’s lab on establishing CSIA as a quantitative tool for contaminant (bio)transformation at contaminated groundwater...

Our study has thoroughly investigated the complete mineralization of toluene in water via heat-activated peroxydisulfate (PDS) by: (1) monitoring concentrations/peak areas of various intermediates and CO2 throughout the reaction period and (2) identifying water-soluble and methanol-soluble intermediates, including trimers, dimers, and organo-sulfur...

Non‐aqueous phase liquids (NAPLs), such as toluene, often contaminate the subsurface. In this study, we focus on the transformation of toluene NAPL trapped in a single glass replica of a rock fracture via in situ chemical oxidation (ISCO) with ferrous activated persulfate. The trapped toluene consisted of a main trapped blob surrounded by smaller b...

When not properly treated, nitrate and phosphate present in groundwater can damage human health and environments. In this study, laboratory column experiments were performed for sequential treatment of nitrate and phosphate in groundwater. Two columns were set up and connected: one to treat nitrate with organic carbon materials (i.e., woodchips) an...

Frequent use of persulfates as oxidants, for in situ chemical oxidation and advanced oxidation processes, warrants the need for developing a fast and efficient method for measuring persulfate concentrations in aqueous samples in the lab and on site. Here, we propose a modified method, based on Liang et al.’s (2008) spectrophotometric method, for me...

The transport of cationic amine-modified latex (AML) and anionic carboxylate-modified latex (CML) microspheres through a discrete sandstone fracture with mineralogical heterogeneity and roughness was studied. Two microsphere sizes (200 nm and 1000 nm), two ionic strengths (5 mM and 10 mM), and two specific discharges (0.35 mm.s-1 and 0.70 mm.s-1) w...

Research on electrokinetics-permeable reactive barrier (EK-PRB) remediation to date has mainly focused on homogeneous soils or soils with micro-scale heterogeneities. The potential impact of macro-scale physical heterogeneities, such as stratified layers or lenses, on EK-PRB remediation has not received much attention. This study investigates the e...

Bioremediation of groundwater is a widely applied method for remediation of contaminated groundwater. Microbial growth and biogenic gas accumulation are common during anaerobic bioremediation. These two processes can alter groundwater flow patterns and affect the ability to deliver electron donors or acceptors to target zones through changes in sub...

Chlorinated ethanes are environmental pollutants found frequently at many contaminated industrial sites. 1,1,1-Trichloroethane (1,1,1-TCA) can be dechlorinated and detoxified via abiotic transformation or biologically by the action of dechlorinating microorganisms such as Dehalobacter (Dhb). At a field site, it is challenging to distinguish abiotic...

Injectable filters permeable to water but impermeable to non-polar solvents were developed to contain non-aqueous phase liquids (NAPL) in contaminated aquifers, hence protecting downstream receptors during NAPL remediation. Filters were produced by injecting aqueous solutions of 0.01% chitosan, hydroxyethylcellulose and quaternized hydroxyethylcell...

The injection of nanoscale zero-valent iron (nZVI) can be an effective technique for the treatment of groundwater contaminants, including chlorinated solvents. However, its effectiveness can be limited by natural reductant demand (NRD) reactions, including the reduction of water resulting in the production of hydrogen gas. This study presents resul...

Co-locating green roof (GR) systems with photovoltaic panels (PV) can allow optimal use of roof space for energy production as well as stormwater management. Models for evapotranspiration from integrated Green Roof Photovoltaic Systems (GR-PV) are needed for the design of GR-PV systems. Existing evapotranspiration models can not be used for this pu...

The injection of nano-scale zero-valent iron (nZVI) is a remediation technique for the treatment of organic and metal contamination in soil and groundwater. The hydrogen gas (H2) produced during the reaction of nZVI and excess sodium borohydride (NaBH4) used in nZVI synthesis with water can inhibit nZVI transport in the subsurface, potentially limi...

The process of water infiltration into initially dry sand was studied in horizontal sand columns under various airtight conditions. To investigate the interrelations among water inflow behavior, air pressure, air confinement effect, and vent effectiveness in unsaturated porous media experiencing dynamic infiltration, a total of five dynamic infiltr...

Core Ideas Aqueous relative permeability experiments followed gas exsolution and trapping. Hydrogen gas was produced by the reaction of sodium borohydride and water. Internal drainage, external drainage and imbibition, and dissolution were compared. Trapped gas saturations were higher following internal drainage. Aqueous relative permeability was s...

This study investigated the potential effect of shear rheology and humic acids (HA) on the subsurface transport of polymeric fluids used for the remediation of contaminants. Polymeric fluids were prepared with guar, scleroglucan, and carboxymethyl cellulose (CMC). Guar fluids can be used to suspend reactive particles for contaminant degradation. Fl...

Core Ideas Green roofs comprise a soilless medium over an atmospheric equilibrated space. Green roofs represent microcosms of capillary fringe and vadose zone hydraulics. Bulk properties come from the interparticle voids and the intraparticle pores. Capillary retention is fundamental for water storage in a green roof system. Design specifications f...

In this article, the influence of multiscale roughness on transport of a conservative solute through a self-affine fracture was investigated. The fracture roughness was decomposed into two different scales (i.e., a small-scale stationary secondary roughness superimposed on a large-scale non-stationary primary roughness) by a wavelet analysis techni...

Chlorinated ethanes, such as 1,1,1-trichloroethane (1,1,1-TCA), are environmental pollutants frequently found in soil, groundwater and the atmosphere, and are commonly identified in many industrial contaminated sites. Removal of 1,1,1-TCA can be achieved via abiotic transformation or biodegradation by dechlorinating organisms such as Dehalobacter (...

The remediation of per‐ and polyfluoroalkyl substances by injection of colloidal activated carbon (CAC) at a contaminated site in Central Canada was evaluated using various visualization and modeling methods. Radial diagrams were used to illustrate spatial and temporal trends in perfluoroalkyl acid (PFAA) concentrations, as well as various redox in...

This chapter provides an overview of environmental restoration efforts involving the application of NZVI. The chapter focuses on the novel application techniques aimed at improving the delivery, characterization, and effectiveness of NZVI, drawing on over two decades of peer-reviewed literature. Stressing a base of knowledge through detailed site c...

The reaction of nanoscale zero-valent iron (nZVI) with water, as well as the reaction of sodium borohydride used during nZVI synthesis with water, can produce hydrogen gas during the injection of nZVI for the remediation of chlorinated solvents and other volatile organic compounds (VOCs) in groundwater. If trapped in the pore space, this gas has th...

In recent decades, urbanization has led to more frequent flood events in urban areas. Several studies have shown the promise of green roof technology for storm water reduction. However, limited studies have assessed water retention performance of green roofs in a range of climates. To investigate the retention performance of a green roof in various...

The hydrology and stormwater management benefits of green roofs (GRs) when integrated with photovoltaic (PV) arrays are currently not well understood. This study is the first quantitative study of an integrated full-scale GR-PV system in Canada. In this project, two GR-PV systems, with low (0.6 m) and high (1.2 m) differential height (LDH and HDH)...

In this work, the influence of the Hurst exponent and Peclet number (Pe) on the temporal mixing behavior of a conservative solute in the self-affine fractures with variable-aperture fracture and constant-aperture distributions were investigated. The mixing was quantified by the scalar dissipation rate (SDR) in fractures. The investigation shows tha...

Trapping and treating Cr(VI) is of great importance to environmental applications. In this work, the natural polymer scleroglucan and the reducing agent sodium thiosulfate were used to produce a water-based polymeric fluid to simultaneously trap and treat Cr(VI) in the subsurface. The thiosulfate reduced toxic Cr(VI) to less toxic Cr(III), as was a...

Many metropolitan cities around the world are promoting the implementation of Green Roofs (GR) as effective stormwater management systems to mitigate adverse effects of urbanization. Hourly water balance calculations are necessary for accurate prediction of the antecedent soil moisture conditions of a GR, a key parameter for rainfall-runoff modelin...

In this article, the influence of multiscale roughness on transport of a conservative solute through a self-affine fracture was investigated. The fracture roughness was decomposed into two different scales (i.e., a small-scale stationary secondary roughness superimposed on a large-scale non-stationary primary roughness) by a wavelet analysis techni...

In Canada alone, petroleum hydrocarbons have been found in groundwater and soil at approximately 1400 and 4000 sites, respectively. In situ chemical oxidation (ISCO) is a remediation technology that delivers oxidants to the subsurface to mineralize the contaminants. A typical oxidant is permanganate, which generates carbon dioxide (CO2) as gas and...

Aqueous phase diffusion-related isotope fractionation (DRIF) was investigated through modelling to determine under what subsurface conditions carbon isotope DRIF effects would be observable using typical sampling approaches. A dispersive enrichment factor was defined based on heavy and light isotopologue dispersion coefficients. For a given ratio o...

The use of a deep geological repository (DGR) for the long-term disposal of used nuclear fuel is an approach currently being investigated by several agencies worldwide, including Canada's Nuclear Waste Management Organization (NWMO). Within the DGR, used nuclear fuel will be placed in copper-coated steel containers and surrounded by a bentonite cla...

Roofs are important components of buildings and can be designed and/or retrofitted with photovoltaic (PV) and green-roof (GR) systems to produce energy and to improve stormwater management. Traditionally, GRs and PVs have been viewed as direct competitors vying for the same roof space. However, with correct design, synergy effects arise when combin...

This study presents a set of laboratory-scale transport experiments and numerical simulations evaluating carboxymethyl cellulose (CMC) polymer stabilized nano-scale zero-valent iron (nZVI) transport. The experiments, performed in a glass-walled two-dimensional (2D) porous medium system, were conducted to identify the effects of water specific disch...

This study assesses the relative influence of four independent variables on green roof hydrological performance under rainstorm conditions. Twenty-four extensive green roofs representing all combinations of the following four design factors were used: native meadow species versus Sedum; mineral-based versus biologically derived planting medium; 10-...

The Canadian Nuclear Waste Management Organization (NWMO) has chosen a used fuel container (UFC) design that consists of an inner steel core and outer copper coating that resists corrosion in the anaerobic underground. However, in these anaerobic conditions, microbiologically influenced corrosion (MIC) can contribute to UFC corrosion if sulphides a...

Back diffusion of contaminants from low permeability strata has inhibited site remediation and closure due to an inability to deliver remediants into these strata. This study demonstrates the potential of electrokinetics (EK) to significantly reduce back diffusion of chlorinated compounds from low permeability porous media. Experiments were conduct...

Gases are commonly introduced into the subsurface via external displacement (drainage). However, gases can also be produced by internal drainage (exsolution). One example is the injection of reactive solutions for in situ groundwater remediation, such as nanoscale zero-valent iron (nzvi), which produces hydrogen gas (H2). Effective implementation o...

The effect of roughness on flow in fractures was investigated using lattice Boltzmann method (LBM). Simulations were conducted for both statistically generated hypothetical fractures and a natural dolomite fracture. The effect of increasing roughness on effective hydraulic aperture, Izbash and Forchheimer parameters with increasing Reynolds number...

Thirty-three extensive green roofs in southern Ontario were surveyed and samples of planting media recovered for hydrological laboratory analyses. The resulting data demonstrate a significant dominance of the role of organic matter in the physical and chemical properties of the media. This is very apparent owing to the local practice of basing some...

Nanoscale zero valent iron (nZVI) is an emerging technology for the remediation of contaminated sites. Howeverthere are concerns related to the impact of nZVI on in-situ microbial communities. In this study, the microbial community composition at a contaminated site was monitored over two years following the injection of nZVI stabilized with carbox...

Aqueous phase diffusion-related isotope fractionation (DRIF) for carbon isotopes was investigated for common groundwater contaminants in systems in which transport could be considered to be one-dimensional. This paper focuses not only on theoretically observable DRIF effects in these systems but introduces the important concept of constraining “obs...

Organic matter content is a key indicator for water retention in green roof planting media.  Highly organic materials are not correlated with loss of the planting medium in roofs aged up to 17 years. Higher organic matter content in the planting medium is associated with more extractable phosphorous.

Two low cost solid organic materials, sawdust and peat, were tested in laboratory batch microcosm and flow-through column experiments to determine their suitability for application in permeable reactive barriers (PRBs) supporting biodegradation of trichloroethene (TCE). In microcosms with peat, TCE (∼30μM) was sequentially and completely degraded t...

Nano-scale zero valent iron (nZVI) has been used at a number of contaminated sites over the last decade. At most of these sites, significant decreases in contaminant concentrations have resulted from the application of nZVI. However, limited work has been completed investigating nZVI field-scale mobility. In this study, a field test was combined wi...

Dense nonaqueous phase liquid (DNAPL) accumulation and recovery from wells cannot be accurately modeled through typical pressure or flux boundary conditions due to gravity segregation of water and DNAPL in the wellbore, the effects of wellbore storage, and variations of wellbore inflow and outflow rates with depth, particularly in heterogeneous for...

The distribution of biofilm thickness on individual sand grains in a two-dimensional sand-filled cell maintained under anaerobic conditions was investigated. The cell was inoculated with a mixed microbial culture fed with methanol. Concentrations of biomass attached to the sand and suspended in the water in the cell were determined by protein analy...

The assumption that gas is infinitely mobile, moving without viscous pressure drops, is common in studies of unsaturated flow in porous media. The objectives of this work were to use experimental measurements to examine that assumption in systems experiencing rapid drainage and to explore the extent to which observed pressure drops could be describ...

A pilot scale injection of nanoscale zerovalent iron (nZVI) stabilized with carboxymethyl cellulose (CMC) was performed at an active field site contaminated with a range of chlorinated volatile organic compounds (cVOC). The cVOC concentrations and microbial populations were monitored at the site before and after nZVI injection. The remedial injecti...

The practical finite analytic (PFA) method was applied to the solution of the one-dimensional advection equation with scale-dependent dispersion equation (ASDE) for solute transport in porous media under advection-dominated (high Peclet number) conditions. A triangular explicit PFA (EPFA) with three different approaches (EPFA 1, 2 and 3) and the Cr...

The practical finite analytic (PFA) method was applied to the solution of the one-dimensional advection–dispersion equation (ADE) for solute transport in porous media under advection-dominated (high Peclet number) conditions. Several PFA spatial-temporal computational molecules were developed for Cauchy and pulse loading boundary conditions. The PF...

Simulation of flow and transport through rough walled rock fractures is investigated using the lattice Boltzmann method (LBM) and random walk (RW), respectively. The numerical implementation is developed and validated on general purpose graphic processing units (GPGPUs). Both the LBM and RW method are well suited to parallel implementation on GPGPU...

The occurrence of subsurface buoyant flow during thermal remediation was investigated using a two dimensional electro-thermal model (ETM). The model incorporated electrical current flow associated with electrical resistance heating, energy and mass transport, and density dependent water flow. The model was used to examine the effects of heating on...

The introduction of nanoscale zero valent iron (nZVI) into the subsurface has recently received significant attention as a potentially effective method for remediation of source zones of chlorinated solvents present as dense nonaqueous phase liquids (DNAPL). One of the challenges in the deployment of nZVI is to achieve good subsurface nZVI mobility...

Many studies over the past four decades have observed that capillary pressure-saturation (Pc-Sw) relationships are often different when measured dynamically under rapidly changing pressure inputs. This phenomenon has been referred to as a dynamic capillary effect, and its magnitude is often quantified by the dynamic capillary coefficient, τ. Experi...

Analytical upscaled models that can describe the depletion of dense non-aqueous-phase-liquids (DNAPLs) and the associated mass discharge are a practical alternative to computationally demanding and data-intensive multiphase numerical simulators. A major shortcoming of most existing upscaled models is that they cannot reproduce the non-monotonic, mu...

Significant advances have produced source zone remediation modeling tools of real practical value. These advances include improved understanding of the physics and biogeochemistry of DNAPL source zones, more rigorous mathematical descriptions of the relationships between multiphase flow, groundwater flow, contaminant transport, mass transfer and sp...

Nanoscale zero valent iron (nZVI) particles were injected into a contaminated sandy subsurface area in Sarnia, Ontario. The nZVI was synthesized on site, creating a slurry of 1 g/L nanoparticles using the chemical precipitation method with sodium borohydride (NaBH4) as the reductant in the presence of 0.8% wt. sodium carboxymethylcellulose (CMC) po...

Atomic force microscopy-based force spectroscopy (AFM) was employed to investigate the forces of interaction between aluminum silicates (mica and a synthetic aluminum-silicate) and iron particles, both bare and coated with carboxymethyl cellulose (CMC) polymer. Experiments were conducted in water and salt solutions (100mM NaCl and 100mM CaCl2) at p...

In this work, the influence of wettability on the fluid–fluid interfacial area (anw)anw) in a three-dimensional (3D) self-affine rough fracture during non-wetting phase invasion was studied using the lattice Boltzmann method (LBM). The capillary pressure (Pc)Pc)-saturation (Sw)Sw)-interfacial area (Pc–Sw–anw)Pc–Sw–anw) relationship, irreducible wat...

A three-dimensional multiphase numerical model was used to simulate the infiltration and dissolution of a dense nonaqueous phase liquid (DNAPL) release in two experimental flow cells containing different heterogeneous and well-characterized permeability fields. DNAPL infiltration was modeled using Brooks-Corey-Burdine hysteretic constitutive relati...

Atomic force microscopy-based force spectroscopy (AFM) was employed to probe the forces of interaction between iron oxide (magnetite) surfaces and fresh zero-valent iron particles, either bare or coated with carboxymethyl cellulose polymer. Experiments were conducted at different pH values (4, 5.5 and 8), ionic strengths (water, 100 mM NaCl and 100...

Nano-scale zero valent iron (nZVI) particles have significant potential to remediate contaminated source zones. However, the transport of these particles through porous media is not well understood, especially at the field scale. This paper describes the simulation of a field injection of carboxylmethyl cellulose (CMC) stabilized nZVI using a 3D co...

The attachment of the sodium salt of carboxymethyl cellulose (CMC) onto iron oxide and various silicate substrates in aqueous solution as a function of salt concentration and pH was studied by atomic force microscopy-based force spectroscopy (AFM) and quartz-crystal microbalance with dissipation monitoring (QCM-D). Both ionic strength and cation va...

Key Points Bacteriophage and microsphere transport studied in dolomite fracture Bacteriophage and microsphere transport are quite different Two site kinetic model used to model transport

Since the late 1990s, the use of nano zero valent iron (nZVI) for groundwater remediation has been investigated for its potential to reduce subsurface contaminants such as PCBs, chlorinated solvents, and heavy metals. nZVI shows tremendous promise in the environmental sector due to its high reactivity and as such, numerous laboratory and field stud...

The interactions between a silica substrate and iron particles were investigated using atomic force microscopy-based force spectroscopy (AFM). The micron- and nano-sized iron particles employed were either bare or coated with carboxy-methyl cellulose (CMC), a polymer utilized to stabilize iron particle suspensions. The effect of water chemistry on...

Nano-scale zero valent iron (nZVI) has received significant attention because of its potential to rapidly reduce a number of priority source zone contaminants. In order to effectively deliver nZVI to the source zone the nZVI particles must be stable. Previous laboratory studies have demonstrated the mobility of polymer modified suspensions of low c...

This study presents analytical solutions of the three-dimensional groundwater flow to a well in leaky confined and leaky water table wedge-shaped aquifers. Leaky wedge-shaped aquifers with and without storage in the aquitard are considered, and both transient and steady-state drawdown solutions are derived. Unlike the previous solutions of the wedg...

The effects of fracture characteristics, specific discharge, and ionic strength on microsphere transport in variable-aperture dolomite rock fractures were studied in a laboratory-scale system. Fractures with different aperture distributions and mineral compositions were artificially created in two dolomite rock blocks. Transport tests were conducte...

The transport of particles through groundwater systems is governed by a complex interplay of mechanical and chemical forces that are ultimately responsible for binding to geological substrates. To understand these forces in the context of zero valent iron particles used in the remediation of groundwater, atomic force microscopy (AFM)-based force sp...

Electrokinetics (EK) has been used extensively to remove heavy metals from low permeability porous media. Electrokinetics (EK) or more specifically electrophoresis (EP) has also been proposed to enhance transport of nanoscale zero valent iron (NZVI) in fine grained porous media in the subsurface. However, increased dissolved oxygen and lower pH, du...

The success of enhanced bioremediation of dense non-aqueous phase liquids (DNAPLs) relies on accelerating contaminant mass transfer from the organic to the aqueous phase, thus enhancing the depletion of DNAPL source zones compared to natural dissolution. This is achieved by promoting biological activity that reduces the contaminant's aqueous phase...

Nanometals have received significant attention in recent years due to their ability to rapidly destroy numerous priority source zone contaminants in controlled laboratory studies. This has led to great optimism about the potential of nanometal injection for insitu remediation. However, rapid nanometal settling, reportedly due to the ferromagnetic a...

Fractured rock aquifers are frequently used for water supply for human consumption. In many instances the fractured rock aquifers are vulnerable to contamination by pathogens, including viruses, due to co-location of on-site septic systems, wastewater discharges, biosolids and agricultural activities. Approximately half of the illnesses associated...

Zero-valent iron particles are employed to remediate subsurface areas contaminated by chlorinated compounds, degrading them into less harmful substances. An aspect of major importance when assessing the viability of the technology is the ability of the particles to migrate in the subsurface reaching the contaminant source zone. Particle transport i...

Nano-scale zero valent iron (nZVI) has been applied as a remediation technology at sites contaminated with chlorinated compounds and heavy metals. Although laboratory studies have demonstrated high reactivity for the degradation of target contaminants, the success of nZVI in the field has been limited due to poor subsurface mobility. When injected...

Experiments were conducted with two laboratory-scale variable-aperture dolomite rock fractures (named F1 and F2) to evaluate effects of water specific discharge, ionic strength and composition on the transport of submicron-sized colloidal particles. Fractures were induced along stylolites in two 0.28 x 0.21 x 0.08 m dolomite rock blocks. From hydra...

Laboratory scale continuous-flow-through chambers (flow cells) facilitate the observation of microbes in a controlled, fully hydrated environment, although these systems often do not simulate the environmental conditions under which microorganisms are found. We developed a flow cell that mimics a subsurface groundwater-saturated rock fracture and i...

The effects of subboiling electrical resistance heating (ERH) on subsurface flow and transport were examined in a series of two-dimensional tank experiments, with temperatures reaching 50°C. To analyze the experiments and determine the dominant mechanisms affecting flow and transport, a fully coupled two-dimensional finite difference electrothermal...