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This article was downloaded by: [University of New Mexico] On: 27 November 2014, At: 10:01 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Energy Sources, Part A: Recovery, Utilization, and Environmental Effects Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ueso20 Remediation of Petroleum-contaminated Sites through Simulation of a DPVE-aided Cleanup Process: Part 2. Remediation Design Y. F. Huang a , G. H. Huang b c , H. N. Xiao d e , A. Chakma f , Q. G. Lin c & H. Xu g a State Key Laboratory of Hydroscience and Engineering , Tsinghua University , Beijing, China b Key Laboratory of Energy Security and Clean Utilization, Sino-Canada Center of Energy and Environmental Research , North China Electric Power University , Beijing, China c Environmental Systems Engineering Program, Faculty of Engineering , University of Regina , Regina, Saskatchewan, Canada d State Key Lab of Pulp and Paper Engineering , South China University of Technology , Guangzhou, China e Department of Chemical Engineering , University of New Brunswick , Fredericton, NB, Canada f Department of Chemical Engineering , University of Waterloo , Waterloo, Ontario, Canada g MOE Key Laboratory of Condition Monitoring and Control for Power Plant Equipment , North China Electric Power University , Beijing, China Published online: 07 Oct 2010. To cite this article: Y. F. Huang , G. H. Huang , H. N. Xiao , A. Chakma , Q. G. Lin & H. Xu (2007) Remediation of Petroleum- contaminated Sites through Simulation of a DPVE-aided Cleanup Process: Part 2. Remediation Design, Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 29:4, 367-387, DOI: 10.1080/15567030600904460 To link to this article: http://dx.doi.org/10.1080/15567030600904460 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions

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Page 1: Remediation of Petroleum-contaminated Sites through Simulation of a DPVE-aided Cleanup Process: Part 2. Remediation Design

This article was downloaded by: [University of New Mexico]On: 27 November 2014, At: 10:01Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Energy Sources, Part A: Recovery, Utilization, andEnvironmental EffectsPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/ueso20

Remediation of Petroleum-contaminated Sites throughSimulation of a DPVE-aided Cleanup Process: Part 2.Remediation DesignY. F. Huang a , G. H. Huang b c , H. N. Xiao d e , A. Chakma f , Q. G. Lin c & H. Xu ga State Key Laboratory of Hydroscience and Engineering , Tsinghua University , Beijing, Chinab Key Laboratory of Energy Security and Clean Utilization, Sino-Canada Center of Energy andEnvironmental Research , North China Electric Power University , Beijing, Chinac Environmental Systems Engineering Program, Faculty of Engineering , University of Regina ,Regina, Saskatchewan, Canadad State Key Lab of Pulp and Paper Engineering , South China University of Technology ,Guangzhou, Chinae Department of Chemical Engineering , University of New Brunswick , Fredericton, NB,Canadaf Department of Chemical Engineering , University of Waterloo , Waterloo, Ontario, Canadag MOE Key Laboratory of Condition Monitoring and Control for Power Plant Equipment , NorthChina Electric Power University , Beijing, ChinaPublished online: 07 Oct 2010.

To cite this article: Y. F. Huang , G. H. Huang , H. N. Xiao , A. Chakma , Q. G. Lin & H. Xu (2007) Remediation of Petroleum-contaminated Sites through Simulation of a DPVE-aided Cleanup Process: Part 2. Remediation Design, Energy Sources, Part A:Recovery, Utilization, and Environmental Effects, 29:4, 367-387, DOI: 10.1080/15567030600904460

To link to this article: http://dx.doi.org/10.1080/15567030600904460

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Page 2: Remediation of Petroleum-contaminated Sites through Simulation of a DPVE-aided Cleanup Process: Part 2. Remediation Design

Energy Sources, Part A, 29:367–387, 2007Copyright © Taylor & Francis Group, LLCISSN: 1556-7036 print/1556-7230 onlineDOI: 10.1080/15567030600904460

Remediation of Petroleum-contaminated Sitesthrough Simulation of a DPVE-aided Cleanup

Process: Part 2. Remediation Design

Y. F. HUANG

State Key Laboratory of Hydroscience and EngineeringTsinghua University, Beijing, China

G. H. HUANG

Key Laboratory of Energy Security and Clean UtilizationSino-Canada Center of Energy and Environmental ResearchNorth China Electric Power University, Beijing, ChinaandEnvironmental Systems Engineering Program, Faculty of EngineeringUniversity of Regina, Regina, Saskatchewan, Canada

H. N. XIAO

State Key Lab of Pulp and Paper EngineeringSouth China University of Technology, Guangzhou, ChinaandDepartment of Chemical EngineeringUniversity of New Brunswick, Fredericton, NB, Canada

A. CHAKMA

Department of Chemical EngineeringUniversity of Waterloo, Waterloo, Ontario, Canada

Q. G. LIN

Environmental Systems Engineering Program, Faculty of EngineeringUniversity of Regina, Regina, Saskatchewan, Canada

H. XU

MOE Key Laboratory of Condition Monitoring and Control forPower Plant Equipment

North China Electric Power University, Beijing, China

Address correspondence to Dr. G. H. Huang, Sino-Canada Center of Energy and EnvironmentalResearch, North China Electric Power University, Beijing, China 102206. E-mail: [email protected]

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Abstract Remediation of petroleum-contaminated sites is usually a challenging task.It is hard to identify and customize a desired remediation technique or technique-combination into specific on-site conditions due mainly to the difficulties in gaininginsight into the complex source and medium conditions in aquifer systems. More-over, it is exigent to remediate sites where low-permeability soil layers exist. Thisstudy presents an integrated approach based on the simulation of a DPVE-aided(dual-phase vacuum extraction aided) remediation process for the identification andcustomization of desired remediation techniques, as well as its application to a sitelocated in western Canada. Data of the specific site conditions, the forecasted resultsof contaminant transport, and the scenarios of remediation techniques with differenttreatment efficiencies are examined. Then the proposed approach was applied to de-sign six remediation alternatives based on combinations of several technologies andthe provision of analyses for system designs and costs. The study will help providedecision support for further remediation actions to be taken at the site.

Keywords DPVE-aided, groundwater pollution, remediation design, western Canada

Introduction

Remediation of petroleum-contaminated sites has been a challenge for environmentalengineers. Clean-up efficiencies of such sites are related to conditions of pollution sources,aquifer characteristics, and treatment technologies. It is even more exigent to remediatesites with low temperature and low soil permeability. Presently, a number of techniquesare available to cleanup contaminated oil and groundwater (Roy F. Weston Inc. andUniversity of Massachusetts, 1990; Freeman and Harris, 1995; Nyer, 1998). However, dueto complexities of aquifer systems, it is hard to identify a desired remediation techniqueor technique-combination. Even after a technique is determined, customization of it intospecific on-site conditions may remain to be another challenging issue, due mainly to thedifficulties in gaining insight into the complex source and medium conditions.

During the past decade, many approaches were undertaken for site remediation tech-niques design, which mainly included site installation, construction design through siteinvestigation, numerical modeling (USEPA, 1997; Christ et al., 1999; Miller et al., 2000;Johnson et al., 2001; McGovern et al., 2002; Liu et al., 2003; Maqsood et al., 2004;Liu, 2005) and site operation strategy design through mathematical optimization (Sawyeret al., 1995; Rizzo and Dougherty, 1996; Mylopoulos et al., 1999; Huang et al., 2003).Only a few approaches have been reported on how to screen efficient remediation tech-niques for the sites to answer the questions such as what remediation technologies aresuitable and cost-effective for a contaminated site (Medd et al., 1993; Loncar et al., 1994;Brendon, 1995; WTIC, 1997; Lamberti and Nissi, 2005). For example, Powell (1994)presented a general guide for selecting innovative cleanup technologies based on theanalysis of site conditions; however, no practical applications have been published. TheSite Remediation Technology Database (REMTEC) provided information for site reme-diation technologies (Brendon, 1995); the expert system of REMTEC was developed tohelp the users to locate particular remediation technologies and provide a directory ofinnovative site remediation methodologies based on the characteristics and conditions ofthe site. However, all those approaches on identification and customization of remediationtechniques depended on how experts tackle the problem according to the site characteris-tics. There has been no such kind of effort in developing an integrated modeling systemto (1) clarify the mechanism of contaminant fate and transport, (2) predict contaminantdistribution in subsurface under various remediation options, and (3) identify desiredremediation techniques based on comprehensive information of site characteristics andsimulation results.

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Remediation of Petroleum-contaminated Sites: Part 2 369

In the companion paper (Huang et al., 2006), a hybrid modeling system for simulatingDPVE-aided remediation and contaminant transport (DRCT) at petroleum-contaminatedsites was developed. In this second part of research, an integrated modeling and de-sign system will be proposed for identification and customization of desired remediationapproaches. Investigation of site characteristics, forecasting of contaminant transport,and simulation of the remediation process will be incorporated within a general frame-work. The designed system will be applied to a petroleum-contaminated site in westernCanada. Tasks of simulation of dual-phase vacuum extraction, forecasting of contaminanttransport, identification of potential remediation techniques, and design of cleaning uppractices will be undertaken.

Fate of Contaminants under Different Remediation Options

Several scenarios were studied to predict temporal and spatial distributions of the con-taminants under different remediation options. In general, the following questions areaddressed by assuming that a 60-day DPVE program will be continued after 2001:

(a) Without other remediation actions, what will happen 10, 20, 40, 60, 80, and 100years later?

(b) If a further remediation action with 60% efficiency is undertaken in 2002 to2003, what will happen 10, 20, 40, 60, 80, and 100 years later?

(c) If a further remediation action with 90% efficiency is undertaken in 2002 to2003, what will happen 10, 20, and 40 years later?

Option (a): A 60-day DPVE Program Only

Figure 1 shows the predicted free product thickness at the site with a 60-day DPVEprogram after October 2001. The maximum thickness was predicted to be 786.1 mm.This information was useful for the multiphase compositional model in predicting spatial

Figure 1. Predicted free-product thickness distribution with DPVE remediation.

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(a)

(b)

Figure 2. (a) Predicted benzene concentrations (ppb) in groundwater after 10 years under option a.(b) Predicted benzene concentrations (ppb) in groundwater after 20 years under option a.

and temporal variations of contaminant concentrations. Figure 2 shows distributions ofbenzene concentrations in the groundwater 10, 20, 40, 60, and 80 years later, with peakconcentrations being 403.0, 406.1, 306.6, 87.1 and 1.7 µg/L, respectively. Figure 2cshows the peak 40 years later will not have decreased significantly since hydrocarbonsstill exist in the unsaturated zone and will thus continuously move into the groundwater,

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(c)

(d)

Figure 2. (c) Predicted benzene concentrations (ppb) in groundwater after 40 years under option a.(d) Predicted benzene concentrations (ppb) in groundwater after 60 years under option a.

but the plume boundary will start to shrink. As shown in Figure 2d, the peak 60 years lateris higher than the regulated 5 µg/L in the local Potable Groundwater Quality Guidelines(SERM, 1999). The peak 80 years later would decrease significantly due to naturaldispersion, biodegradation, and no further hydrocarbon moving into the groundwaterfrom the unsaturated zone (Figure 2e). The proportion of concentration reduction within

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(e)

Figure 2. (e) Predicted benzene concentrations (ppb) in groundwater after 80 years under option a.

the last 20 years (from 2062 to 2082) will be 98.0%. In general, with a continued 60-dayDPVE program only after October 2001, the existence of benzene will keep posing threatseven 60 years later, but no effect after 80 years.

Option (b): A Continued 60-day DPVE Program Followed by a Remediation Actionof 60% Efficiency

Figure 3 shows distributions of benzene concentrations in the groundwater 10, 20, and40 years later, with peak concentrations being 162.5, 101.3, and 0.28 µg/L, respectively.These are lower than the regulated 300 µg/L in the local Aquatic-Use GroundwaterQuality Guidelines (SERM, 1999); however, the peak 20 years later will still be muchhigher than the regulated 5 µg/L in the local Potable Groundwater Quality Guidelines(SERM, 1999). The peak of 0.28 µg/L 40 years later will be much lower than theregulated 5 µg/L in the local Potable Groundwater Quality Guidelines (SERM, 1999).In general, with a continued 60-day DPVE program after October 2001, followed by aremediation action of 60% efficiency, the existence of benzene will keep posing threatseven 20 years later, but no effect after 40 years.

Option (c): A Continued 60-day DPVE Program Followed by a Remediation Actionof 90% Efficiency

Figure 4 shows distributions of benzene concentrations in the groundwater 10 and 20years later, with peak concentrations being 24.4 and 1.30 µg/L, respectively. The peak10 years later will be much lower than the regulated 300 µg/L in the local Aquatic-Use Groundwater Quality Guidelines (SERM, 1999), however, higher than the regulated5 µg/L in the local Potable Groundwater Quality Guidelines (SERM, 1999). The peak

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(a)

(b)

Figure 3. (a) Predicted benzene concentrations (ppb) in groundwater after 10 years under option b.(b) Predicted benzene concentrations (ppb) in groundwater after 20 years under option b.

20 years later will be lower than the regulated 5 µg/L in the local Potable Ground-water Quality Guidelines (SERM, 1999). In general, with a continued 60-day DPVEprogram after October 2001, followed by a remediation action of 90% efficiency, theexistence of benzene will keep posing threats even 10 years later, but have no effect after20 years.

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(c)

Figure 3. (c) Predicted benzene concentrations (ppb) in groundwater after 40 years under option b.

Identification of Desired Remediation Techniques

The previous remedial efforts at the site include a manual bailing program conductedduring 1998 to 1999. Approximately 2,300 L of hydrocarbons in naphtha range wererecovered during that period. An initial DPVE program was operated during April 2000 toSeptember 2000; in that period, a total of 7,800 L of hydrocarbons in naphtha range wererecovered. As part of a continuing effort for remediation, an additional DPVE programwas operated in 2001. Although the DPVE technique was effective for reducing free-product thickness, its capability for enhancing in situ biodegradation was insignificant.This was demonstrated by the fact that the O2 and CO2 concentrations in the DPVEexhaust remained similar to those in the normal atmosphere. At the same time, the totalvolume of hydrocarbons recovered from the groundwater throughout the DPVE operatingperiod was extremely low (only a few liters). The simulation results also indicated thatfurther remediation actions are needed for the groundwater. Therefore, it is necessary toidentify an effective approach to tackle contaminants in both soil and groundwater.

Due to the existence of various remediation technologies, a screening effort is neededfor identifying applicable options. This should be based on explication for a number offactors such as:

• Subsurface conditions, e.g., soil type, subsurface hydrology, geological condition,homogeneity (in vadose and saturated zones), and soil permeability;

• Groundwater conditions, e.g., elevation of groundwater table, depth of saturatedaquifer, and hydraulic conductivity;

• Contaminant type and its physical and chemical characteristics, such as concen-tration, solubility, density, and volatility;

• Extent of contaminant plume including depth in vadose zone, depth in saturatedzone, and area of contamination;

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(a)

(b)

Figure 4. (a) Predicted benzene concentrations (ppb) in groundwater after 10 years under option c.(b) Predicted benzene concentrations (ppb) in groundwater after 20 years under option c.

• Adjacent surface conditions, such as size of operating property, conditions abovecontaminated zone (open space, tanks, pipes, paving, structures), and open spaceavailable for treatment;

• Permitting requirements including clean-up criteria;• Other factors, such as long-term real estate planning, and decisions of future land-

use modification.

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In this study, the REMTEC (Brendon, 1995) is employed as one of the measuresfor identifying initial technology candidates based on site investigation and numericalsimulation. The key factors that need to be evaluated include: (1) type of hydrocarbonsrequiring remediation, (2) behavior of hydrocarbons, (3) volume of contaminated soil,(4) depth of groundwater table, (5) quality of groundwater, (6) availability of remediationtechnologies, (7) applicability to the site, (8) performance of remediation technologies(efficiencies and costs), and (9) future real estate considerations. Based on a series ofsite-condition investigation, subsurface simulation, technical analysis and literature sur-vey, applicable remediation techniques are further identified. These technologies and theircombinations are then examined in detail to generate desired approaches. Several tech-niques are initially deemed feasible for enhancing the existing DPVE program and/orfurther cleaning up the site using the existing equipment and installation, shown asfollows:

• pneumatic fracturing (PF)• dual phase vacuum extraction (DPVE)• vacuum enhanced recovery (bioslurping)• air sparging (AS)• bioventing (BIOV)• in-situ bioremediation (ISB)• surfactant-enhanced aquifer remediation (SEAR)

Analysis of Technology Feasibility and Applicability

Due to low permeability of the site in both vertical and horizontal directions, the widelyused soil vapor extraction (SVE) technology is not directly suitable. Therefore, theDPVE technique has been used for recovering free products. Following the DPVE pro-gram, bioventing, air sparging, and bioslurping technologies associated with pneumaticfracturing could be applicable for cleaning up the soil zone. These technologies canalso be combined to generate more cost-effective alternatives. For treating the con-taminated groundwater, enhanced in-situ biodegradation (EISB) combined with SEARcan result in improved removal efficiency. Air sparging (AS) associated with SVE andbioslurping can also effectively remove hydrocarbons within the capillary fringe and thegroundwater.

Dual Phase Vacuum Extraction and Pneumatic Fracturing

DPVE provides airflow through unsaturated zone to remediate volatile organic compounds(VOCs) and fuel contaminants by vapor extraction and/or bioventing. The airflow alsoextracts groundwater for treatment above ground. The screen in the two-phase extractionwell is positioned in both unsaturated and saturated zones. A vacuum applied to the well,using a drop tube near the water table, extracts soil vapor. The vapor movement entrainsgroundwater and carries it up the tube to the surface. The potential limitations of suchprocesses include: (a) subsurface heterogeneity can interfere with uniform collection ofcontaminated groundwater and aeration of contaminated soil; (b) combination with com-plementary technologies (e.g., pump-and-treat) may be required to recover groundwaterfrom high-yield aquifers; and (c) two-phase extraction requires both water and vaportreatment.

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Pneumatic fracturing is a recognized method adapted from petroleum industries thatinduce fractures to improve the performance of oil extraction or injection wells. Thistechnology involves the injection of either gases (typically air) or fluids (either water orslurries) to increase the permeability of soil around an injection well, thereby resultingin increased removal/degradation of contaminants and improved cost-effectiveness forsite remediation. It is most applicable to low-permeability geologic formations, such asfine-grained soils (including silt, clay, and bedrock). This technique has also been widelyused for enhancing performance of many other remediation processes, such as dual-phaseextraction (DPE), in-situ bioremediation, thermal treatment (e.g., hot gas injection), andgroundwater pump-and-treat systems. Factors that may limit the applicability of suchprocesses include: (a) the technology should not be used in areas of high seismic activityafter the fracturing operation; (b) fractures will close in non-clay soils; (c) investigationof possible underground utilities, structures, or trapped free products is required; and(d) there are risks of opening new pathways for unwanted spread of contaminants.

Air Sparging

Air sparging (AS) can enhance the removal of chemicals with low volatility and/orthose that are tightly sorbed. It can also enhance biodegradation of contaminants. AS isimplemented by injecting pressurized air into a contaminated aquifer so that air streamstraverse horizontally and vertically through the soil column, creating an undergroundstripper that removes contaminants by volatilization. This technique operates at highflow rates to maintain increased contact between groundwater and soil, and to stripmore groundwater by sparging. Combined with other fracturing measures, AS can beused at sites with heterogeneous and low-permeability soils. Its potential limitationsinclude (a) subsurface heterogeneity can interfere with uniform air distribution; (b) low-permeability of soils will hinder airflow transport; and (c) contaminants with low Henry’slaw constants are difficult to treat.

In-situ Bioremediation

Enhanced in-situ biodegradation is used in conjunction with groundwater pumping andsoil flushing systems to circulate nutrients and oxygen through a contaminated aquifer andassociated soils. The process usually involves introducing aerated and nutrient-enrichedwater into the contaminated zone through a series of injection wells or infiltration trenchesand recovering the down-gradient water. The amendments are circulated through the con-taminated zone to provide mixing and intimate contact between the oxygen, nutrients,contaminant, and microorganisms. The recovered water can then be treated and reintro-duced into the subsurface onsite.

Bioventing (BIOV) is another in-situ technique. During such a process, the oxygenconcentration in soil gas is increased by injecting air into the contaminated zone throughdrilled wells. Air extraction wells may be used to control vapor migration. In contrastto soil vapor extraction, BIOV uses low airflow rates to provide only enough oxygento sustain microbial activity. Oxygen is commonly supplied by directing airflow throughresidual contamination in soil. In addition to degradation of adsorbed fuel residuals,volatile compounds are biodegraded when vapors move slowly through biologically activesoil. For the study site, part of DPVE infrastructure can be used for facilitating the BIOVpractice. This in-situ bioremediation process can be primarily controlled by the following

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factors: (a) presence of nutrients (nitrogen and phosphorous), (b) moisture availability,and (c) oxygen content.

Surfactant-Enhanced Aquifer Remediation (SEAR)

SEAR facilities the removal of residual nonaqueous-phase liquids (NAPLs) that aretrapped in pore spaces of the aquifer. It enhances the remediation by increasing theeffective aqueous solubility of NAPLs and reducing the interfacial tension between waterand NAPLs. SEAR is conducted by injecting a surfactant solution into the contaminatedzone while simultaneously extracting groundwater to control the movement of the surfac-tant solution and the mobilized contaminants. Potential limitations include: (a) subsurfaceheterogeneities can interfere with the delivery and recovery of the surfactant solution andmay require additional mobility-control measures; (b) low-permeability soils are difficultto handle; (c) residual surfactants in the subsurface may have toxic effects; (d) surfactantflow may mobilize contaminants deeper into the aquifer or off site if inadequate hydrauliccontrol is maintained.

Vacuum-Enhanced Recovery (Bioslurping)

Bioslurping (BIOS) supplies vacuum to extraction wells using above-ground vacuumpumps, such that LNAPLs and groundwater are removed from the wells by air entrain-ment. The negative pressure established in the wells depends on the air withdrawal rateand the permeability of the surrounding formation. Biological degradation of hydrocar-bons will be enhanced as a result of the introduction of air into the unsaturated zone. BIOScan be operated as a conventional system for the remediation of unsaturated-zone soils.Potential limitations include: (a) large volumes of water extracted may need to be treatedwith special oil/water separators and other treatment methods; (b) subsurface heterogene-ity can limit LNAPL flow to the wells and affect uniform aeration of the contaminatedsoils; (c) low-permeability soils may affect mobilization of free products to the extrac-tion wells; and (d) off-gas from the system requires treatment before being discharged.

Design of Remediation Alternatives

The remediation process at the study site can be divided into two steps. The first isfor free-product recovery, while the second is for remediation of contaminated soil andgroundwater after the free products have been recovered. Currently, DPVE techniqueassociated with pneumatic-fracturing enhancement is running at the site to recover thefree products. Since the monitoring results show that the free-product thickness is stillhigh, an integrated DPVE-PF approach is desired.

After the amount of free products become low enough, an integrated remediationcan be initiated for further cleaning up of the contaminated soil and groundwater. Giventhe complexities at the site, an integrated approach that combines several technologieswithin a general system is desired, since no single technique can efficiently clean upthe site. Such an integrated approach should be desired based on in-depth examinationof contamination situation, applicable technology, and infrastructure availability. The re-sulting approaches for contaminated soil and groundwater are: (1) contaminated soils:bioventing, air sparging, and vacuum-enhanced recovery (bioslurping), and (2) contam-inated groundwater: Enhanced in-situ biodegradation and surfactant enhanced aquiferremediation.

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The DPVE infrastructure can be re-used for facilitating bioventing. A combina-tion of air sparging with pneumatic fracturing is for sites with heterogeneous and less-permeable soils. The infrastructure of vacuum-enhanced recovery can be also re-used forconventional bioventing. Moreover, soil permeability needs to be improved to enhanceeffectiveness of the selected technologies. Considering these factors, six alternatives arerecommended.

Alternative 1: Integrated Air Sparging, Pneumatic Fracturing Enhancement, andEnhanced In-situ Biodegradation (AS-PFE-EISB)

Generally, a combination of air sparging (AS) with pneumatic fracturing can deal withcontaminated soils with low permeability within capillary fringe and/or below ground-water table. Figure 5 shows locations of wells for pneumatic fracturing. Among the wells,four are new and need to be drilled, while two are existing ones that were used for testingthe efficiency of pneumatic fracturing. The air sparging system contains extraction andinjection wells as well as a blower system (Figure 5), which is specified as follows:

Among the 9 injection wells, four need to be drilled (AIW1, AIW2, AIW5, andAIW9), while the others are based on the existing ones (AIW3, AIW4, AIW6, AIW7,and AIW8).

• For the extraction wells, there are five new wells (BH11, BH18, BH201, BH202,and BH203) that must be drilled, as well as six existing ones (BH108, 9, BH401,BH103, BH101, BH115, and BH105).

• The air-water treatment facilities consist of a water/air separator, a vacuum blowerand an off-gas treatment system. Facilities of the existing DPVE system can beused for facilitating the air sparging.

Figure 5. The in-situ remediation system (alternative 1) for the site.

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380 Y. F. Huang et al.

Figure 5 presents a schematic diagram of the enhanced in-situ biodegradation (EISB)system. The system contains extraction and injection wells, an integrated tank system,a pipeline system, and monitoring wells. The following are its details:

• The design includes six extraction wells. Only one of them (EW3) needs to bedrilled. The others are based on the existing wells, including EW1, EW2, EW4,EW5, and EW6.

• Among the eight injection wells, IW1, IW2, IW4, and IW6 are the existing bore-holes, while IW3, IW5, IW7, and IW8 are new ones.

• The integrated tank system consists of 4 subsystems, including biological inocu-lum fermentation, nutrient feeding, oxygenation, and chemical/biological additivecontrol.

The estimated costs for the air sparging system are shown in Table 1. The total costis estimated to be in the range of $170,000 to 300,000. The costs are for supporting:(a) site preparation, including well drilling and preparation, utility connection, and systeminstallation; (b) capital requirement, including vacuum pump, and blower; (c) consumableinvestment; (d) utilities; (e) shipping and handling of residuals and wastes; and (f) labor.In general, in-situ biodegradation is considered to be a relatively low-cost technology.For the enhanced in-situ biodegradation, its expenses are mainly for supporting sitepreparation, facility design/construction and system operation. The detailed costs for thissystem are presented in Table 1, with a total estimated cost of $140,000 to $270,000.For the pneumatic fracturing enhancement system, its cost is $9 to $13 per metric tonof soil treated (or $8 to $12 per ton). The detailed costs for this system are presented inTable 1, with a total cost of $120,000 to $270,000. Expenses for pneumatic fracturingare mainly for labor, equipment, off-gas treatment, site preparation, residual disposal, andsystem operation and maintenance. Table 1 also presents the total cost of this integratedAS-PFE-EISB system, amounting to $330,000 to $660,600.

Alternative 2: Integrated Bioventing, Pneumatic Fracturing Enhancement, andEnhanced In-situ Biodegradation (BIOV-PFE-EISB)

In alternative 2 for the enhanced in-situ biodegradation (EISB) system, injection andextraction wells as well as an integrated tank system are all the same as those in alter-native 1. A combination of bioventing (BIOV) with pneumatic fracturing can deal withbiological active soils with low permeability. The bioventing system contains extractionand injection wells as well as a blower system (Figure 6). Considering the combinationwith EISB, the air injection wells of BIOV are placed at the periphery of the site, whilethe extraction wells are placed in the center of the contaminated area. The following areits details:

• Among the 9 injection wells, four need to be drilled (BIW1, BIW2, BIW5, andBIW9), while the others are based on the existing ones (BIW3, BIW4, BIW6,BIW7, and BIW8).

• For the extraction wells, there are two new wells (BEW3 and BEW4) that mustbe drilled, as well as three existing ones (BEW1, BEW2, and BEW5).

The estimated costs for bioventing system are shown in Table 1. The total cost isestimated to be in the range of $80,000 to $170,000. The total costs for enhanced in-situbiodegradation system is estimated to be in the range of $120,000–$270,000. The costfor pneumatic fracturing system is the same as that of alternative 1 (Table 1). Table 1 also

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Tabl

e1

App

roxi

mat

eco

sts

(×$1

03)

ofre

med

iatio

nal

tern

ativ

esfo

rcl

eani

ngup

the

site

Cos

tA

ltern

ativ

e1

Alte

rnat

ive

2A

ltern

ativ

e3

Alte

rnat

ive

4A

ltern

ativ

e5

Alte

rnat

ive

6

Site

prep

arat

ion

cost

10–2

010

–20

10–2

010

–20

10–2

010

–20

Faci

lity

desi

gn/c

onst

ruct

ion

cost

30–6

020

–50

20–5

030

–60

20–5

020

–50

Ope

ratio

nco

st90

–140

50–1

0050

–120

90–1

4050

–120

50–1

00A

bove

-gro

und

trea

tmen

tco

st40

–80

N/A

N/A

40–8

0N

/AN

/AV

apor

trea

tmen

tco

stN

/AN

/A40

–60

N/A

40–6

0N

/ASu

b-to

tal

170–

300

80–1

7012

0–24

017

0–30

012

0–24

080

–170

Enh

ance

din

situ

biod

egra

datio

nSi

tepr

epar

atio

nco

st10

–20

10–2

010

–20

N/A

N/A

N/A

Faci

lity

desi

gn/c

onst

ruct

ion

cost

30–8

030

–80

30–8

0N

/AN

/AN

/AIn

vest

men

tco

st30

–70

30–7

030

–70

N/A

N/A

N/A

Ope

ratin

gco

st50

–100

50–1

0050

–100

N/A

N/A

N/A

Sub-

tota

l12

0–27

012

0–27

012

0–27

0N

/AN

/AN

/ASu

rfac

tant

enha

nced

aqui

fer

rem

edia

tion

Site

prep

arat

ion

cost

N/A

N/A

N/A

10–4

010

–40

10–4

0Fa

cilit

yde

sign

/con

stru

ctio

nco

stN

/AN

/AN

/A80

–150

80–1

5080

–150

Inve

stm

ent

cost

N/A

N/A

N/A

60–1

6060

–160

60–1

60O

pera

ting

cost

N/A

N/A

N/A

80–2

0080

–200

80–2

00A

bove

-gro

und

trea

tmen

tco

stN

/AN

/AN

/A10

0–18

010

0–18

010

0–18

0Su

b-to

tal

N/A

N/A

N/A

330–

730

330–

730

330–

730

Pneu

mat

icfr

actu

ring

Site

prep

arat

ion

cost

5–10

5–10

5–10

5–10

5–10

5–10

Faci

lity

desi

gn/c

onst

ruct

ion

cost

10–2

010

–20

10–2

010

–20

10–2

010

–20

Ope

ratin

gco

st25

–60

25–6

025

–60

25–6

025

–60

25–6

0Su

b-to

tal

40–9

040

–90

40–9

040

–90

40–9

040

–90

Tota

lco

st(×

$103

)33

0–66

024

0–53

028

0–60

054

0–1,

120

490–

1,06

045

0–99

0

N/A

=no

tap

plic

able

.

381

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382 Y. F. Huang et al.

Figure 6. The in-situ remediation system (alternative 2) for the site.

presents the total cost of this integrated BIOV-PFE-EISB system, amounting to $240,000to $530,000.

Alternative 3: Integrated Pneumatic Fracturing Enhancement, Vacuum-enhancedExtraction, and Enhanced In-situ Biodegradation (PFE-BIOS-EISB)

In alternative 3, vacuum-enhanced extraction (BIOS) is combined with pneumatic frac-turing to clean up contaminated soils. It functions as a replacement of the bioventingsystem to deal with the unsaturated zone in alternative 2. Figure 7 presents a schematicdiagram of the integrated PFE-BIOS-EISB system. The injection and extraction wells aswell as an integrated tank system of the enhanced in-situ biodegradation system are thesame as those in alternative 1. Vacuum-enhanced extraction system can simultaneouslyrecover free products while cleaning up the unsaturated zone. Therefore, it can be startedup before free products being completely recovered from soils. The vacuum-enhancedextraction system contains extraction wells and a vacuum pump system, as well as anoff-gas treatment system, which includes air/liquid separation and oil/water separatorsystem (Figure 7). No new wells are needed for the vacuum-enhanced extraction system.Eleven existing wells are utilized including (BH9, BH11, BH18, BH101, BH103, BH105,BH108, BH115, BH202, BH203, and BH401). Facilities of the existing DPVE systemcan be used for facilitating the vacuum-enhanced extraction.

The estimated costs for the vacuum-enhanced extraction system are shown in Table 1.The total cost is estimated to be in the range of $120,000–$240,000. The total cost forenhanced in-situ biodegradation system is estimated to be in the range of $120,000–$270,000 (Table 1). Table 1 also presents the total cost of this integrated PFE-BIOS-EISBsystem, amounting to $280,000 to $600,000.

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Figure 7. The in-situ remediation system (alternative 3) for the site.

Alternative 4: Integrated Pneumatic Fracturing Enhancement, Air Sparging, andSurfactant-enhanced Aquifer Remediation (PFE-AS-SEAR)

Figure 8 presents the schematic design of PFE-AS-SEAR system. Surfactant-enhancedaquifer remediation (SEAR) is used to deal with contaminated groundwater. Since theair sparging and pneumatic fracturing are similar to those in alternative 1, only thesurfactant-enhanced aquifer remediation is analyzed. The surfactant-enhanced aquiferremediation system contains injection, extraction and hydraulic control wells as well as atank system that includes surfactant preparation and surfactant solution treatment system(Figure 8). The injection wells are located in the center of contaminants plum, whileextraction wells are located at upstream and downstream of the plum. The following arethe details: (1) among the 5 injection wells, only one needs to be drilled (IW2), whilethe others are based on the existing ones (IW1, IW3, IW4, and IW5); and (2) amongthe 11 extraction wells, four need to be drilled (EW2, EW6, EW8, and EW10), whilethe others based on the existing ones (EW1, EW3, EW4, EW5, EW7, EW9, and EW11).The costs of the surfactant-enhanced aquifer remediation system are for supporting welland pump installation, labor, chemical, operation, and aboveground wastewater treatment.The estimated costs for this system are shown in Table 1. The costs for air sparging andpneumatic fracturing systems are presented in Table 1. Table 1 also presents the totalcost of this integrated PFE-AS-SEAR system, amounting to $540,000 to $1,120,000.

Alternative 5: Integrated Vacuum-enhanced Extraction, Pneumatic FracturingEnhancement, and Surfactant-enhanced Aquifer Remediation (BIOS-PFE-SEAR)

In alternative 5, vacuum-enhanced extraction (BIOS), pneumatic fracturing (PF), andsurfactant-enhanced aquifer remediation (SEAR) are integrated together to clean up the

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384 Y. F. Huang et al.

Figure 8. The in-situ remediation system (alternative 4) for the site.

Figure 9. The in-situ remediation system (alternative 5) for the site.

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Remediation of Petroleum-contaminated Sites: Part 2 385

contaminated soil and groundwater (Figure 9). The vacuum-enhanced extraction andpneumatic fracturing systems in this alternative are similar to those in alternative 3, whilethe surfactant-enhanced aquifer remediation system is similar to that in alternative 4. Onlythe number and location of extraction wells are different from those in alternative 4.Considering the vacuum-enhanced extraction system can also remediate contaminants ingroundwater, there are totally 10 extraction wells in alternative 5. There are five newwells (EW1, EW2, EW5, EW6, and EW10) that must be drilled, as well as five existingones (EW3, EW4, EW7, EW8, and EW9). Compared with that in alternative 4, thedifference is not significant. Therefore, the estimated costs for the surfactant-enhancedaquifer remediation system in alternative 4 are directly used for alternative 5. Table 1presents the total cost of this integrated BIOS-PFE-SEAR system, amounting to $490,000to $1,060,000.

Alternative 6: Integrated Bioventing, Pneumatic Fracturing Enhancement,Surfactant-enhanced Aquifer Remediation (BIOV-PFE-SEAR)

Figure 10 presents a schematic diagram of this integrated BIOV-PFE-SEAR system.Bioventing, pneumatic fracturing, and surfactant-enhanced aquifer remediation are in-tegrated together to clean up the contaminated soil and groundwater. The bioventingand pneumatic fracturing systems in this alternative are the same as those in alterna-tive 2, while the surfactant-enhanced aquifer remediation system is the same as that inalternative 4. Table 1 presents the total cost of this integrated BIOV-PFE-SEAR system,amounting to $450,000 to $990,000.

Figure 10. The in-situ remediation system (alternative 6) for the site.

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Conclusions

(1) An integrated design system was proposed for identification and customization ofdesired remediation approaches. Investigation of site characteristics, forecastingof contaminant transport, and simulation of remediation process was incorporatedwithin a general framework. The designed system was applied to a petroleum-contaminated site in western Canada, where conditions of low temperature andlow hydrological conductivity existed.

(2) Six remediation alternatives were recommended, including (a) integrated airsparging, pneumatic fracturing enhancement, and enhanced in-situ biodegra-dation, (b) integrated bioventing, pneumatic fracturing enhancement, and en-hanced in-situ biodegradation, (c) integrated pneumatic fracturing enhancement,vacuum-enhanced extraction, and enhanced in-situ biodegradation, (d) integratedpneumatic fracturing enhancement, air sparging, surfactant-enhanced aquifer re-mediation, (e) integrated vacuum-enhanced extraction, pneumatic fracturing en-hancement, and surfactant enhanced aquifer remediation, and (f) integratedbioventing, pneumatic fracturing enhancement, and surfactant enhanced aquiferremediation. These recommended alternatives are helpful for the decision makersto select cost-effective actions for cleaning up the contaminated site.

(3) The integrated approach can also be extended to other sites to supply decisionsupport for site remediation. The site investigation and numerical simulationefforts can help provide in-depth understanding of the site characteristics andcontaminant conditions.

(4) Although extensive investigations were conducted for the site in the past years,further studies through pilot testing and/or field work are desired for optimizingcrucial remediation parameters before actual actions are undertaken.

Acknowledgments

The authors would like to thank the anonymous reviewers for their insightful commentsand suggestions that were helpful for improving the manuscript. Thanks are also dueto the National Natural Science Foundation of China (No. 50509010), and the NationalBasic Research Program of China (No. 2005CB724202 and 2005CB724200).

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