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ABSTRACT Centrifuge model tests were carried out to observe LNAPL transportation in a sand deposit. The LNAPL infiltrated into the partly saturated sand deposit and was transported along the surface of the groundwater table by an induced horizontal flow. A floating type impermeable sheet was inserted in an attempt to stop the transportation of LNAPL. It appeared that the sheet was unable to stop the transportation of LNAPL. However, the sheet wall caused the LNAPL to accumulate at a certain location. It was investigated whether the accumulation might facilitate efficient extraction of the LNAPL from the sand deposit. INTRODUCTION The number of underground storage tanks that have been constructed for hazardous chemicals in chemical plants, gasoline stations and other facilities runs into the millions. The tanks carry some risk of geoenvironmental damage caused by leaks. An important part of evaluating soil remediation technologies understands the transportation behavior of substances in the ground after a spill. Many approaches have been developed for quantifying the transportation behavior using mathematical and physical modeling. A disadvantage of large scale model tests is the large amount of time and money they consume. Fortunately, a convenient and efficient alternative physical modeling technique for these problems is available in the form of a geotechnical centrifuge. This study used a light non-aqueous phase liquid (LNAPL) as the chemical substance. There have already been several centrifuge studies of multiphase transportation in porous media. Arulanandan et al. (1988) developed one of the earliest applications of centrifuge modeling for studying contaminant transport problems. They showed that the length scale and modeling time could be reduced by subjecting models to centrifuge acceleration. Scaling laws previously developed by other researchers (e.g., Cooke and Mitchell, 1991; Mitchell and Stratton, 1988) were used to establish the model dimensions.
Detection of organic contaminants such as an light nonaqueous phase liquid (LNAPL) in the subsurface by using In April 10, 1996, a rice field in Nankan county, northwestern geophysical methods has been subjected to considerable Taiwan, was flooded a lot of light non-aqueous phase liquid interest among geophysicists in recent years (e.g., Campell et (LNAPL) as a result of a leakage from an underground al., 1996; Sauck et al., 1998).
- Asia > Taiwan (0.26)
- North America > United States > Texas > Ellis County (0.25)
Analytical Solutions for Free-Hydrocarbon Recovery using Skimmer and Dual-Pump Wells
Obigbesan, A.B. (The University of Texas at Austin) | Johns, R.T. (The University of Texas at Austin) | Lake, L.W. (The University of Texas at Austin) | Bermudez, L. (The University of Texas at Austin) | Hassan, M.R. (The University of Texas at Austin) | Charbeneau, R.J. (The University of Texas at Austin)
Abstract Accidental release of petroleum hydrocarbons to the subsurface may occur through spills around refineries, leaking pipelines, storage tanks or other sources. If the spill is large, the hydrocarbon liquids may eventually reach a water table and spread laterally in a pancake-like lens. Hydrocarbons in the aquifer that exist as a separate phase are termed free product or light nonaqueous phase liquids (LNAPL). This paper presents new analytical solutions for the effective design of long-term free-product recovery from aquifers with skimmer-, single- and dual-pump wells. The solutions are derived for steady-state flow based on the assumption of vertical equilibrium, and include the effect of coning of LNAPL, air, and water on flow. The results show how to estimate the maximum rate of inflow of LNAPL for skimmer wells, i.e. wells in which LNAPL is recovered with little or no water production. The paper also shows how to calculate the increase in LNAPL recovery when water is pumped by single or dual-pump wells. A simple equation is given that can be used to adjust the water rate to avoid smearing of the LNAPL below the water table. Introduction Petroleum hydrocarbon liquids generally are less dense than water, which implies that such liquids would float on the water table of a groundwater aquifer. If large amounts of petroleum hydrocarbon liquids are spilled they will depress the water table and cause a hydrocarbon liquid lens to spread laterally across the water table in a pancake-like lens. Petroleum hydrocarbons are examples of a "light" nonaqueous phase liquid (LNAPL), which means that they are lighter than and immiscible with water. Equivalent acronyms are "free product" or OIL, which stands for an organic immiscible liquid. Effective cleanup of an aquifer requires a) timely removal of LNAPL while b) limiting additional spreading of the contaminant and c) minimizing excessive pumping of the aqueous phase. Lowering the water table near the well can increase the LNAPL flow rate into the well. While small water pumping rates may lengthen remediation times, large rates may cause hydrocarbon to be smeared into soils below the original water table, perhaps soils that were originally uncontaminated. When smearing occurs, there is an increase in the volume of soil that contains residual hydrocarbon contamination. Smearing can result in a reduction in the volume of recoverable free hydrocarbon, which may increase long-term remediation costs. Excessive pumping also produces large volumes of water that must be treated and discharged (Fig. 1). Thus, a tradeoff exists between pumping too much water and recovering of the LNAPL at too small of a rate. Many free-product recovery systems in operation today employ either single- or dual -pump recovery wells, such as that shown schematically in Fig. 1. Skimmer wells, which produce LNAPL with little or no water production, are also used but these are not as efficient as single- or dual-pump wells. Currently, limited guidance is available regarding how best to operate these wells for optimum long-term free-product LNAPL recovery. As a result, prolonged remediation times and unnecessary expenditures may be needed. Numerical simulation models have been developed to analyze and design LNAPL migration and recovery. These models generally assume vertical equilibrium of the associated fluids, and simulate LNAPL recovery with two-dimensional models rather than in three-dimensions.
Abstract Groundwater and soil contamination resulted from light nonaqueous phase liquids (LNAPLs) spills and leakage in petroleum industry is currently one of the major environmental concerns in the North America. Numerous site remediation technologies, generally classified as ex-situ and in-situ remediation techniques, have been developed and implemented to clean up the contaminated sites in the last two decades. One of the problems associated with ex-situ remediation is the cost of operation. In recent years, in-situ techniques have acquired popularity. However, the selection process of the desired techniques needs a large amount of knowledge. Insufficient expertise in the process may result in large inflation of expenses. In this study, petroleum waste management experts and Artifical Intelligence (AI) researchers worked together to develop an expert system (ES) for the management of petroleum contaminated sites. Various AI techniques were used to construct a useful tool for site remediaiton decision-making. This paper presents the knowledge engineering processes of knowledge acquisition, conceptual design, and system implementation in the project. The case studies have indicated that the expert system can generate cost-effective remediation alternatives to assist decision-makers. Introduction Automation of engineering selection is important for tbe petroleum industries in which decision for a desired remediation technology at a contaminated site is critical for ensuring safety of the environment and the public. A variety of remediation methods/technologies are available. However, different contaminated sites have different characteristics depending on pollutants' properties, hydrological conditions, and a variety of physical (e.g. mass transfer between different phases), chemical (e.g. oxidation and reduction), and biological processes (e.g. aerobic biodegradation). Thus, the methods selected for different sites vary significantly. The decision for a suitable method at a given site often requires expertise on both remediation technologies and site hydrological conditions (Sims, 1992). In general, soil and groundwater remediation techniques can be divided into two classes depending on whether the pollutant is directly removed/degraded in-place or not, i.e. in-situ or ex-situ. One of the main problems associated with ex-situ remediation is its high operating cost for activities like soil excavation and groundwater pumping. In recent years, in-situ techniques have become popular. However, with in-situ remdiation methods, knowledge on processes and factors controlling the results is lacking, which translates to much inflated expenses. Several mathematical models have been proposed to furnish representations as close as possible to reality of the effects of widely known remediation techniques. Some quantitative models have also been proposed for coupling multiphase flow and transport in a porous medium, with consideration of various remediation strategies such as water pumping, vapor and air venting, and steam injection. All of these techniques rely on human intervention for removing the contaminant. These techniques are fast, but costly. Moreover, most of them are too complex and not easily comprehensible for managers and engineers in industries and government. Therefore, a new approach is needed for developing useful, cost..effective, and user friendiy systems which can be readily adopted by industry and/or government to support decision-making on site remediation techniques.
Use of Surfactants to Recover Oils From Groundwater
Jayanti, Shekhar (The University of Texas) | Pope, Gary A. (The University of Texas) | Weerasooriya, Vinitha (The University of Texas) | Zhong, Lirong (The University of Texas) | Varadarajan, Dwarakanath (Duke Engineering and Services, Austin) | Taimur, Malik (Duke Engineering and Services, Austin)
Abstract Laboratory phase behavior and soil column experiments were conducted using branched alcohol propoxy sulfate surfactants to evaluate their effectiveness in removing gasoline and diesel range hydrocarbons from contaminated groundwater. Very low residual oil saturations were achieved with a much smaller amount of surfactant than typically required in surfactant enhanced aquifer remediation (SEAR). This type of surfactant has been shown to be both robust and efficient even when used at low temperatures and without co-solvent. Introduction The contamination of groundwater by nonaqueous phase liquids (NAPLs) is a widespread problem. The NAPL moves through the subsurface due to gravity forces and is trapped in pores by capillary forces. The trapped NAPL can persist in the soil for many decades (1). Large volumes of water can be contaminated and migrate long distances as the contaminants dissolve into the water and form a dissolved phase aqueous plume. Most of the contaminant mass remains in the NAPL, so it must be removed or it will continue to feed the plume. The conventional remediation method of pump and treat involves pumping of contaminated water followed by treatment at the surface by air stripping, steam stripping, activated carbon filtration and various other means. The hydraulic force imposed upon the NAPL as a result of pumping alone is usually insufficient to lower the residual NAPL saturation to acceptable levels. The limitations of pump and treat are well known (1–4). Surfactants can be used to vastly increase the solubility of the NAPL constituents in water (5,6). Surfactants also lower the interfacial tension at the water-NAPL interface. Ultra-low interfacial tension can reduce the capillary forces and cause mobilization and the formation of an oil bank at sufficiently high capillary numbers. Some surfactants are also biodegradable and can be used as a substrate to promote biodegradation in the aqueous phase once the NAPL is removed. Some of the early studies of surfactants to remediate light nonaqueous phase liquids such as gasoline and diesel can be found in references 7–14. These early studies made relatively little use of the extensive literature on surfactant enhanced oil recovery (15–17). In recent years, vast improvements have been made in SEAR due to a better understanding of surfactants and microemulsions and better formulations based upon phase behavior experiments (18–32). Elliott (30) and Jayanti (31) have shown the effectiveness of alcohol propoxy surfactants in recovering tetrachloroethene (PCE). Surfactant flooding has been recently demonstrated at several field sites (33–41). Both of the surfactant floods in the DNAPL pool of Operable Unit 2 at Hill AFB, Utah, resulted in final average DNAPL saturations in the swept volumes of each wellfield on the order of only 0.0003 (33–35,40). A thermally enhanced surfactant flood using a propoxy sulfate surfactant at 50°C was conducted at a field site and found to perform extremely well with 88% removal of a fuel oil with 1000 cp viscosity (41–43). The use of alcohol cosolvents to improve the performance of surfactant enhanced oil recovery has been known for a long time. In general the need for cosolvent is greater for lower temperatures typical of groundwater aquifers than for oil reservoirs. The addition of a suitable cosolvent improves the fluidity of the microemulsion-NAPL interfaces, prevents the formation of gels and/or liquid crystals and induces macroemulsions to equilibrate to stable microemulsions faster. Dwarakanath and Pope (44, 45) report similar benefits for SEAR. However, the use of alcohol cosolvents increases the cost of treating the effluent from SEAR and has other disadvantages.
- Materials > Chemicals > Specialty Chemicals (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)