Subsurface Contamination Research Articles

Testing an Analytical Model for Predicting Subsurface LNAPL Distributions from Current and Historic Fluid Levels in Monitoring Wells: A Preliminary Test Considering Hysteresis

Knowledge of subsurface light nonaqueous phase liquid (LNAPL) saturation is important for developing a conceptual model and a plan for addressing LNAPL contaminated sites. Investigators commonly predict LNAPL mobility and potential recoverability using information such as LNAPL physical properties, subsurface characteristics, and LNAPL saturations. Several models exist that estimate the LNAPL specific volume and transmissivity from fluid levels in monitoring wells. Commonly, investigators use main drainage capillary pressure–saturation relations because they are more frequently measured and available in the literature. However, main drainage capillary pressure–saturation relations may not reflect field conditions due to capillary pressure–saturation hysteresis. In this paper, we conduct a preliminary test of a recent analytical model that predicts subsurface LNAPL saturations, specific volume, and transmissivity against data measured at a LNAPL contaminated site. We call our test preliminary because we compare only measured and predicted vertical LNAPL saturations at a single site. Our results show there is better agreement between measured and predicted LNAPL saturations when imbibition capillary pressure–saturation relations are employed versus main drainage capillary pressure–saturation relations. Although further testing of the model for different conditions and sites is warranted, the preliminary test of the model was positive when consideration was given to capillary pressure–saturation hysteresis, which suggests the model can yield reasonable predictions that can help develop and update conceptual site models for addressing subsurface LNAPL contamination. Parameters describing capillary pressure–saturation relations need to reflect conditions existing at the time when the fluid levels in a well are measured.

Numerical Modeling of Multiphase Extraction (MPE) Aiming at LNAPL Recovery in Tropical Soils

Subsurface contamination by light non-aqueous phase liquids (LNAPL) is a widespread global problem that requires appropriate techniques to remediate soil and groundwater. In this paper, the subsurface transport over multiple phases (STOMP) model was used to simulate LNAPL multiphase flow and transport during multiphase extraction (MPE) application in two Brazilian tropical soils (silty sand and oxisol) contaminated by diesel. The model was applied to a hypothetical contamination site, with the initial LNAPL thickness observed in well extraction. The first part consisted of the MPE system sensitivity analysis, varying the applied vacuum and tip tube position. The Van Genuchten α parameter and hydraulic conductivity were the properties that most affected LNAPL saturation and fluid extraction volumes. Suitable applied vacuum and tip tube position parametrization was imperative for the efficiency of LNAPL extraction. After the definition of an appropriate MPE system configuration, simulations demonstrated that the immobile LNAPL saturation affected fluid extraction and diesel oil concentrations in aqueous and gas saturation. The model applied is able to predict LNAPL contaminant behavior in porous media during MPE technique application.

Research of natural remediation of the subsurface contaminated with petroleum products

Remediation of the subsurface contaminated with petroleum products is the ecological problem on a world scale and a foreground direction of geoecological research in Ukraine. Remediation of contaminated vadose zone can be provided with the activity of microorganisms, mainly micromycets, whose features of location and vital activity depend on a depth, the level of contamination, aerobic conditions, etc. Practically, it is complicated to use artificial microbiological methods and natural remediation of contaminated subsurface due to microorganisms should be taken into consideration. Microorganisms oxidizing hydrocarbons are of particular interest. Field investigations were carried out within the fuel storage of the Boryspil airport where subsurface contamination with petroleum products was revealed in 1998. The research included sampling at contaminated and uncontaminated sites, quality analysis of petroleum product contains in soils and determination of the species composition of micromycets. Soil samples were taken in three wells at different depths – in the center of the contamination source at the depths of 0,1 m and 2,0 m (unsaturated zone) and 4,0 m (saturated zone), in the northern part of the fuel storage in the unsaturated zone at the depths of 0,1 m and 1,0 m, and out of the contamination source in the unsaturated zone at the depth of 3,7 m. Fungus culture determination data in soil samples indicate that variety of their forms depends on a contamination degree, a depth of sampling, lithology and water saturation. Regular monitoring should be carried out including soil sampling and determination of petroleum product contains to specify conclusions about natural remediation of contaminated soils due to life activity of microorganisms oxidizing hydrocarbons.

An approach to optimize the location of LNAPL recovery wells using the concept of a LNAPL specific yield.

Leakage of hydrocarbon fuel (light nonaqueous-phase liquid, LNAPL) from petroleum processing facilities and storage tanks may result in significant subsurface contamination. Remediating the contaminated areas represent considerable challenges, especially when remediation resources are limited and site data are incomplete. A reasonable management strategy under this scenario may be to identify sites where LNAPL recovery operations should be located that would provide the largest LNAPL recovery initially while minimizing the LNAPL remaining in the subsurface (entrapped and residual LNAPL), which may serve as future sources for groundwater contamination. To accomplish this objective, we use estimates of subsurface recoverable and total LNAPL specific volumes and LNAPL transmissivities to generate GIS maps that can be combined to highlight locations where to develop LNAPL recovery operations. When the approach is applied to a LNAPL-contaminated area in Iran, we were able to narrow the locations for potential LNAPL recovery operations. Specifically, we combine maps of the LNAPL specific yield, an introduced term, and the LNAPL transmissivity where the LNAPL specific yield is the ratio of the recoverable to total LNAPL specific volumes. The LNAPL specific yield is a relative measure of the amount of LNAPL that potentially can be recovered while minimizing residual LNAPL in soils. The approach can be applied to sites where the recoverable and total LNAPL specific volumes and LNAPL transmissivities can be estimated using data from boreholes in the contaminated area.

Mapping of subsurface contamination zone using 3D electrical resistivity imaging in Hilla city, Iraq

Electrical resistivity imaging (ERI) method is very useful in mapping subsurface contamination zones. In this study, 3D ERI is used to identify the distribution and depth of subsurface soil contamination zone near Al_Furat state company for chemical and pesticides industries in Hilla city, Iraq. A 3D pure image of electrical resistivity distribution is obtained from a perpendicular square grid (80 × 80 m) which consists of three parallel and three perpendicular lines. The electrical resistivity values range from < 1 to 21 O.m, and the total root mean square (RMS) after four iterations is about 7%. The image gives eight different depth slices for the estimated model with a depth interval of about 1 m. The maximum depth of investigation is 13.7 m. The results mapped the contamination zone, where high electrical resistivity values (about 21 O.m) are observed possibly due to accumulation of alkaline waste disposed from the company. The ERI results show that the subsurface layers up to a depth of 4.99 m are of moderate-to-high electrical resistivity values. The study reveals that 3D ERI is an effective tool for subsurface contamination zone mapping in various depths, which extends in this study from the near-surface to a depth of about 5 m below the ground level.

Vapor intrusion evaluation for redevelopment of former industrial facilities

Former industrial facilities in our cities are finding new life as they are repurposed for use as nonindustrial commercial or even residential spaces. Often, these buildings are brownfield properties, complicating redevelopment because of past industrial uses that led to soil and/or water contamination at the site. In case site contaminants include volatile chemicals (VCs), concerns about air quality at the site may arise. VCs can vaporize from the subsurface and migrate through soil to outdoor air or into indoor spaces of overlying buildings, where they may accumulate.Vapour intrusion is a relevant problem especially at sites where building modernization and revitalization is to be carried out, as environmental investigations may be complicated by the structure of the built environment, and the contamination may remain undetected. Moreover, upgrading structures to meet building codes and energy conservation requirements can create tight buildings that may enhance the effects of vapor intrusion.For accurately predicting whether indoor air quality is being or will be adversely affected by subsurface contaminations a multiple lines of evidence approach should be used. Many issues can in fact introduce uncertainty in predicting indoor air concentrations related to vapor intrusion, including i) sampling and analytical methods ii) modelling of fate & transport from subsurface into building, iii) indoor/ambient background sources.This work refers about the risk management strategy at a site in Milan (Italy) where soil remediation (excavation and off-site disposal) left a residual volume of soil polluted with petroleum-derived hydrocarbons next to redeveloped buildings. Furthermore, the site was also affected by an extended plume of chlorinated solvents in groundwater from an unknown source, likely external to the site. Indoor air, outdoor air, crawl-space air and soil gas samplings were carried out to collect robust information for evaluating decisions points in the vapor intrusion process. Despite few ambient air and crawl-space measurements resulted in episodic high values, as a general trend, the average outdoor and indoor concentrations did not differ significantly from the background values, suggesting other sources than soil pollution were affecting the quality of the air at the site. Although not strictly necessary in terms of time-averaged health risk, a mitigation system of the residual soil contamination was, however, installed to prevent future uncontrolled exposure.

Biochar Effects on Mineral Nitrogen Leaching, Moisture Content, and Evapotranspiration after 15N Urea Fertilization for Vegetable Crop

Globally, mineral nitrogen (N) losses as nitrate leaching (NL) are a substantial portion of applied fertilizer and cause surface and sub-surface water contamination. To precisely measure NL and its interlink parameters, biochar soil amendment was tested in this study. Three treatments—biochar (BC), without biochar (WB) with 15N urea (300 kg/ha), and control (no fertilization)—were tested in soil-filled lysimeters (circular PVC (Polyvinyl Chloride) tank of 30 cm diameter and 35 cm height) equipped with moisture content sensors and weighing assembly for the consecutive two cropping of Brassica Camprestis Var. Chinensis. The 15N-urea in the first season and the poultry manure in the second season were applied, but the fate of the 15N was examined in leachate, dry matter, and soil. As compared to WB, BC significantly decreased mineral N leaching, including nitrate levels (35%), increased electrical conductivity (68.5%), and water availability (20% inches per foot), while there was a non-significant increase in biomass per plant (2.84%), evapotranspiration (8.33%), dry matter (6.89%), and a decrease in mean leachate volume (7.63%). Moreover, BC accumulated values were higher than WB, as N uptake (38%), water use efficiency (12.24%), maximum fresh weight (11.4%), and soil N retained (185%) after cropping. The soil pH, the bulk density, and the total nitrogen were changed but presented non-significant differences. Therefore, biochar can increase soil N retention and available water to improve water use efficiency and decrease potential N leaching.

Sensitivity of advective contaminant travel time to the soil hydraulic parameters in unsaturated heterogeneous soils

This study deals with the sensitivity of advective contaminant travel time to soil hydraulic parameters through a heterogeneous soil profile, which is often required in many applications such as designing a monitoring network, developing a remediation strategy for contaminated sites, and determining the associated risks of subsurface contamination. The main objective is to determine relative contributions to the output uncertainty of advective travel time from individual input stochastic hydraulic parameters. A new approach is developed to examine the sensitivity of advective contaminant travel time to saturated hydraulic conductivity and macroscopic capillary drive as a result of infiltration from a wet and contaminated surface source. The approach can be applied to both non-stationary layered formation and stationary soil profile. The results demonstrate that the advective contaminant travel time is sensitive to the layers with small saturated hydraulic conductivity and small macroscopic capillary drive values. Larger uncertainty of saturated hydraulic conductivity and macroscopic capillary drive shifts the sensitive layers to the advective travel time to deeper layers. Correlation range of saturated hydraulic conductivity and macroscopic capillary drive has less significant impact on the sensitivity of advective contaminant travel time than the standard deviation. In the stationary saturated hydraulic conductivity and macroscopic capillary drive profile, although the advective contaminant travel time increase significantly for fine textured soil compared to coarse textured soil, the fractional contribution of spatial locations to the overall uncertainty of total advective travel time is virtually identical for both fine textured and coarse textured soils.

Quantitative decision making for a groundwater monitoring and subsurface contamination early warning network

With the increased development of oil and gas activities in northern Colorado, public concerns over the environmental impacts associated with well drilling and hydraulic fracturing have continued to rise. Issues such as leakages of “toxic” products from oil and gas operations to the subsurface environment (such as groundwater contamination) have led to community action and state regulations related to the establishment of groundwater quality monitoring sites in oil and gas activity areas, particularly those adjacent to urban development. Colorado Water Watch was a groundwater quality monitoring network comprised of seven monitoring wells in northern Colorado to monitor groundwater quality near oil and gas wells and give early warnings of contamination. Our study is aimed at developing a quantitative methodology to find ideal monitoring locations as well as evaluate them. We utilized hydraulic and geological data to select the most preferred sites to monitor groundwater quality, understand the temporal trends and identify unique anomaly signals in the oil and gas active area (Wattenberg field, northern Colorado). In addition to the site selection methodology, water quality data from Colorado Water Watch over 2 years is used to do evaluate the performance using entropy information and Principal Component Analysis. The analysis indicates that the earliest functional monitoring site (CHILL) is the most informative monitoring well, and the most recently installed monitoring sites (Gilcrest and LaSalle) are the least informative and least important stations due to their low data efficiency.

Impact of Forest Combustion on Soil Contamination by PAHs Using QuEChERS and GC-MS/MSTQD

The present study was conducted in one of the most dense forest area of Asir region located in the southwest of Saudi Arabia to study the Impact of Forest Combustion on surface and subsurface soil contamination by Poly Aromatic Hydrocarbons (PAHs). The major toxic effects of PAHs including cancers, immunity suppression, loss of fertility, mutagenic and cardiovascular diseases. The extraction and analytical methods, have been developed and validated for quantification of trace levels of 17 PAHs namely, Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, Anthracene, Fluoranthene, Pyrene, Retene, Benzo [b+j] fluoranthene, Benzo (a)pyrene, Benzo [k] fluoranthene, 3-methylchol-anthrene, Dibenz [a,h] acridine, Indeno [1,2,3-cd]pyrene, Dibenz [a,h] anthracene and Benzo [ghi] perylene. Surface and subsurface soil samples were collected from Alsaqa and Murir post-fire forests in Asir Province, Saudi Arabia, and extracted by Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) and analyzed by Gas Chromatography-Mass Spectrometry Triple Quadrupole (GC-MS/MSTQD). The experimental results of 17 compounds of PAHs were highly satisfactory linearity, recovery and precision, especially with the tested soil samples. Recovery % ranged from 96.48±2.19 to 105.61±3.21%., the limit of detection (LOD) ranged from 3.71 to 6.77 µg kg-1. Meanwhile the limit of quantification (LOQ) for the analyzed PAHs were in the range of 10.47 to 16.42 µgkg-1. This method featured good sensitivity, lower quantification limits and the precision of the analyzed 17 PAHs. The calibration curves were linear over wide concentration ranges with correlation coefficients (r2) 0.7478 to 0.9822 for 17 PAHs analyzed by GC-MS/MSTQD. The concentrations of the investigated PAHs in Alsaqa forest surface (S) and subsurface (SS) soils ranged from F24.81±4.29 to 57.28±3.56 and 24.10±2.31to 55.47±4.15 mg kg-1dry weight respectively. Meanwhile, the PAHs concertation in Murir surface and subsurface soils ranged from 12.48±2.37 to 28.83±3.35 and 12.83±1.37 to 25.59±4.31 mg kg-1 dry weight respectively. Retene compound was detected in Alsaqa, and Murir forest investigated surface, and subsurface soil sample ranged from 57.28, 55.47, and 28.83, 25.59 mg/kg-1(ppm) respectively. Meanwhile, Retene was not detected (ND) in the control surface and subsurface soil sample. The detected PAHs by applying the modified QuEChERS and GC-MS/MSTQD method were applied successfully for the extraction and determination of the 17 PAHs in burned forest soil samples.

Artificial neural network prediction models of heavy metal polluted soil resistivity

Heavy metal contaminated soil is on the rise in the whole world with the boost of industrialisation and urbanisation. As such, the heavy metal pollution in lands is of attracted considerable concern to professionals and planners. The detection of contaminant plumes in the subsurface is an important aspect of geotechnical and geo-environmental engineering practice. In this regard, a commonly used method involves conducting electrical resistivity measurements is employed to qualitatively delineate suspected contaminated sites subsurface contamination. However, resistivity measurements alone will lead to some degree of ambiguity in the results, and give only qualitative information about the changes in the chemical composition of the soil-pore fluid. In order to generate much confidence in using the resistivity, the better computational algorithms (viz. artificial neural networks) that should be capable of incorporating the interdependence of several parameters must be employed. Artificial neural network (ANN) presents an oversimplified simulation of the human brain and is accepted as a reliable data modelling tool to capture and represent complex relationships between inputs and outputs. With this in view, efforts were made to develop ANN models that can be employed for predicting electrical resistivity by employing different soil properties such as contaminants, ionic concentrations (n), moisture content (w), porosity (φ) and saturation (S r). To demonstrate the efficiency of the ANN models, the results obtained were compared with those obtained from experimental investigations and empirical relationships, which are reported in the literature. In addition, the performance indices such as coefficient of determination, root mean square error, mean absolute error and variance were used to assess the performance of the ANN models.

Shear rheological properties of composite fluids and stability of particle suspensions: Potential implications for fracturing and environmental fluids

Composite fluids are comprised of particles and polymers and are used for fracking and the in‐situ treatment of subsurface contaminants. This study investigates the correlation between the shear viscoelasticity of guar aqueous solutions and their effectiveness in suspending sand, which is a common fracking proppant. In the absence of a crosslinker, the shear viscous modulus (G”) of 5 g/L guar solutions was greater than the shear elastic modulus (G’). When the crosslinker borax was added, the guar solutions behaved as yield stress fluids (G’ &gt; G”). Sand was well‐suspended in the crosslinked guar solutions but settled in non‐crosslinked fluids. Similar results were obtained with fenugreek gum. This study also investigates the correlation between particle settling and the effect of particle addition on the rheology of the fluids. Granulated activated carbon (GAC) particles are utilized to remediate polluted sites and were used as model particles. Guar and xanthan effectively suspended the GAC. Anionic polyacrylamide effectively suspended the GAC but not after soaking in sodium dodecyl sulphate. Zetag 8167 did not effectively suspend the GAC. The addition of 10 g/L of GAC did not affect the shear rheology of the fluids that suspended them, but decreased the shear viscoelastic moduli of the polymeric fluids that could not suspend them.

Current Insights into the Effectiveness of Riparian Management, Attainment of Multiple Benefits, and Potential Technical Enhancements.

Buffer strips between land and waters are widely applied measures in diffuse pollution management, with desired outcomes across other factors. There remains a need for evidence of pollution mitigation and wider habitat and societal benefits across scales. This paper synthesizes a collection of 16 new primary studies and review papers to provide the latest insights into riparian management. We focus on the following areas: (i) diffuse pollution removal efficiency of conventional and saturated buffer strips, (ii) enhancing biodiversity of buffers, (iii) edge-of-field technologies for improving nutrient retention, and (iv) potential reuse of nutrients and biomass from buffers. Although some topics represent emerging areas, for other well-studied topics (e.g., diffuse pollution), it remains that effectiveness of conventional vegetated buffer strips for water quality improvement varies. The collective findings highlight the merits of targeted, designed buffers that support multiple benefits, more efficiently interrupting surface and subsurface contaminant flows while enhancing diversity in surface topography, soil moisture and C, vegetation, and habitat. This synthesis also highlights that despite the significant number of studies on the functioning of riparian buffers, research gaps remain, particularly in relation to (i) the capture and retention of soluble P and N in subsurface flows through buffers, (ii) the utilization of captured nutrients, (iii) the impact of buffer design and management on terrestrial and aquatic habitats and species, and (iv) the effect of buffers (saturated) on greenhouse gas emissions and the potential for pollution swapping.

Evaluation of methods for water and non-volatile LNAPL content measurement in porous media

Proper characterization of contaminants in subsurface helps to clean up effectively the contaminated sites. In this study, different methods were used to quantify non-volatile light non-aqueous phase liquid (LNAPL) and water from sample columns subjected to different water to LNAPL ratios. The objective of the study was to evaluate methods for porous media water and LNAPL contents analysis. The liquids were sampled from the sample columns using activated carbon pellets (ACP). Sample columns water content was also measured using soil moisture sensors. Dielectric mixing model (DMM) was evaluated for the estimation of LNAPL content after water and LNAPL contents of the sample columns were determined through gravimetric analysis method. The result shows that it was possible to sample both water and LNAPL using ACP proportionally but with high standard deviations. It also shows that more liquid was sampled from sample columns subjected to only one liquid compared to sample columns subjected to two liquids. On the other hand, analysis of water and LNAPL using gravimetric analysis method gave the best result although the presence of LNAPL resulted in underestimation of water content at higher LNAPL contents. Meanwhile, the presence of LNAPL modified the bulk relative permittivity (ε&lt;sub&gt;a&lt;/sub&gt;) of the sample columns and resulted in overestimation of water contents measured using soil moisture sensors at higher LNAPL content. The modification of ε&lt;sub&gt;a&lt;/sub&gt; was used for the estimation of LNAPL using DMM. The evaluation of the model with known water and LNAPL contents and in estimating the LNAPL content of the other sample columns shows that the model could be used for the proper estimation of LNAPL in porous media.

In situremediation of subsurface contamination: opportunities and challenges for nanotechnology and advanced materials

Engineered nanomaterials alone or in combination with other technologies may improvein situsubsurface remediation of legacy and emerging contaminants.

A POD Coupled Adaptive DEIM (POD-ADEIM) Reduced-Order Model for Incompressible Multiphase Flow in Porous Media

The multiphase fluid flow in porous media is one of the most fundamental phenomena in various physical processes, such as oil/gas flow in reservoir, subsurface contamination dispersion, chemical separation, etc. Due to its importance, the efficient and accurate solution and prediction of multiphase flow in porous media is highly required in engineering applications and mechanism studies, which has been a research hot spot with increasing interest in recent years. However, the strong nonlinearity implicated in the multiphase flow model has brought great challenges for the computation and analysis. In addition, the permeability in Darcy-type pressure equation is always represented as a high contrast coefficient, which further complicates the simulation difficulty especially for high fidelity prediction and decision-making process. In this study, we attempt to apply one popular global model reduction method, namely Proper Orthogonal Decomposition (POD), to accelerate the simulation of incompressible multiphase flow in porous media. The cornerstone of POD is processing information from a sequence of snapshots (or instantaneous solutions) to identify a set of basis functions to construct a low-dimensional space, the most energetic part of these basis functions is then selected to represent the solution of the original system. In our work, one key point is how to establish the accurate POD reduced order model (ROM) for incompressible mul-tiphase porous flow problems. According to Li et al. [1], the traditional Galerkin projection method (directly project the original governing equation into the low-dimensional space spanned by basis functions) is incapable of introducing the fluid saturation and permeability located on the cell face in POD-ROM for incompressible multiphase flow whether in homogeneous or heterogeneous porous media, thus we adopt the matrix operation method (project the discrete governing equation instead of the original governing equation into the low-dimensional space spanned by basis functions) to build the POD-ROM in this study. Based on the proposed POD-ROM framework, we use the implicit method to solve the (non-) wetting-phase pressure and saturation equations. However, in the implicit solution of the pressure and saturation equations, the standard POD-ROM alone sometimes cannot yield an expected acceleration owing to two main reasons: (1) the nonlinearity between pressure and saturation is sensitive, thus the saturation would change largely even with slight pressure change. And the small error of pressure results would lead to a large deviation of saturation, which in turn exerts negative impacts on the computation of pressure; (2) the complexity for computing a projected nonlinear term in POD-ROM still depends on the dimension of the original full-order system, it is unavoidable in conventional POD-ROM. Therefore, more POD modes are needed to be used in order to achieve the prescribed numerical accuracy, which could worsen the speed up efficiency of proposed POD-ROM. To further reduce the computational complexity of POD-ROM to speed up the implicit solution of pressure and saturation equations, another model reduction method called Discrete Empirical Interpolation Method (DEIM) [2] is applied to treat the projected nonlinear term in the proposed incompressible multiphase porous flow POD-ROM. Different from previous studies, we develop an adaptive DEIM (ADEIM) in this work to achieve a more flexible selection of the interpolation points. Combined the POD-ROM with ADEIM, a POD-ADEIM-ROM for incompressible multiphase flow in porous media is established. The computational efficiency and numerical accuracy of the proposed model is validated through several representative numerical examples. Numerical results indicate that an outstanding acceleration (2~3 orders of magnitude faster) without sacrificing numerical accuracy significantly is obtained from the proposed model when comparing to the traditional solution method that without any acceleration technique. In addition, the effects of POD mode number, the distribution of permeability field, and the mesh density on the overall performances of the proposed model are investigated in detail.

Applying a Modular PET System to Investigate Bioremediation of Subsurface Contamination: A Proof-of-Principle Study

Remediation of subsurface contamination using microbial consortium can be less toxic to the environment and ecosystems than using chemical dispersants or physical measures. But bioremediation involves complex and dynamic processes in a visually opaque medium, which can be difficult to monitor. Positron emission tomography (PET), which reveals the dynamic distribution of labeled molecules, offers a means to probe into the bioremediation process. This study evaluates and verifies the feasibility of employing a freely-rearrangeable modular PET system (BioPET) in combination with a generic tomographic image reconstruction platform, CASToR, for tracking fluid transport, as well as metabolic activities, occurrence, and distribution of subsurface microorganisms. This enables quantitative imaging of bioremediation processes in high resolution with further expanding the flexible modular system and refining the data processing algorithms.

GEOCHEMICAL REACTIVE MODELING OF FLOW AND TRANSPORT PROCESS AT A MINE SITE IN NORTHERN TERRITORY, AUSTRALIA

Subsurface contamination of metals and radionuclides are common problems in abandoned mine sites. Metals and radionuclides are likely to occur in the mobile phase or may bind to soil particles and geologic framework. The transport process for reactive contaminants also include chemical reactions in groundwater aquifers, which are complex physical and biogeochemical processes. Accurate tools to reliably predict the movement and changes in concentration of metals and their daughter products (radionuclides) formations in the subsurface environment is important for decision makers to analyze impact, and to evaluate the effectiveness of remediation strategies. An advanced numerical model can provide such useful direction of predictions. A 3-D contaminant transport model for fluid flow, hydrogeologic transport, and biogeochemical kinetic and equilibrium reactions in saturated and unsaturated media was calibrated, validated and implemented to model the hydrogeochemical processes that occur in the subsurface at such a complex contaminated site, consisting of waste rock dumps and flooded mine pits of this abandoned uranium mine site. The developed flow and transport simulation model for no longer in use mine site in Northern Territory of Australia is discussed.

Technogenic hydrocarbon reservoirs and geoenvironmental issues in the city of Grozny

This paper is devoted to the history and current state of the issue of pollution of the geological environment and formation of technogenic petroleum reservoirs in the territory of the city of Grozny as a consequence of petroleum-related industrial activities. The area of Grozny was analyzed for subsurface contamination with petroleum products. Recommended actions for the remediation of the geological environment from petroleum contaminants are provided.

Multi-year CO2 efflux measurements for assessing natural source zone depletion at a large hydrocarbon-impacted site

The changing landscape of fuel consumption related, in part, to increased engine efficiency and the inexpensive supply of natural gas, has led to the closure of multiple refineries. As the operational lifetime of many refineries exceeds 100 years, historical releases of oil and refined products is common. To evaluate remediation and rehabilitation options, there is a need to understand the rate and distribution of natural hydrocarbon mass losses across these large properties. Here, surficial CO2 flux measurements were used to evaluate naturally occurring hydrocarbon mass losses at a large-scale former refinery that has been closed since 1982. Natural source zone depletion (NSZD) rates over a five-year period (2012–2016) were derived from surficial CO2 efflux measurements on a high-resolution grid (N > 80). Results demonstrate substantial variations of mass loss rates across the site. Average site-wide mass loss rates ranged from 1.1–5.4 g TPH m−2 d−1 as C10H22 with a multi-year average of 4.0 g TPH m−2 d−1 as decane (C10H22), consistent with observations at other sites. Statistical analysis demonstrated that the same average mass loss rates would have been obtained with fewer measurement locations (N = 20–30). Comparing NSZD rates to site metadata show CO2 fluxes to be a reasonably good proxy for zones of subsurface hydrocarbon contamination – particularly with respect to vadose zone impacts. It is hypothesized that the observed decline of NSZD rates over the study period is related to rise of groundwater levels, leading to increased submergence of the smear zone. Overall, mass loss rates calculated from CO2 fluxes show NSZD can result in substantial contaminant removal, which may rival that obtained from engineered remediation, under some conditions.