Life-cycle assessment of in situ thermal remediation

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  • REMEDIATION Autumn 2012

    Life-Cycle Assessment of In Situ ThermalRemediation

    Angela Fisher

    A detailed cradle-to-grave life-cycle assessment (LCA) of an in situ thermal treatment remedy for

    a chlorinated-solvent-contaminated site was performed using process LCA. The major materials

    and activities necessary to install, operate, monitor, and deconstruct the remedy were included

    in the analysis. The analysis was based on an actual site remedy design and implementation

    to determine the potential environmental impacts, pinpoint major contributors to impacts, and

    identify opportunities for improvements during future implementation.

    TheElectro-ThermalDynamic Stripping Process (ET-DSPTM) in situ thermal technology coupled

    with a dual-phase extraction and treatment system was evaluated for the remediation of 4,400 yd3

    of tetrachloroethene- and trichloroethene-impacted soil, groundwater, and bedrock. The analysis

    was based on an actual site with an estimated source mass of 2,200 lbs of chlorinated solvents.

    The remedy was separated into four stages: remedy installation, remedy operation, monitoring,

    and remedy deconstruction. Environmental impacts were assessed using Sima Pro software, the

    ecoinvent database, and the ReCiPe midpoint and endpoint methods.

    The operation stage of the remedy dominated the environmental impacts across all categories

    due to the large amount of electricity required by the thermal treatment technology. Alternate

    sources of electricity could significantly reduce the environmental impacts of the remedy across all

    impact categories. Other large impacts were observed in the installation stage resulting from the

    large amount of diesel fuel, steel, activated carbon, and asphalt materials required to implement

    the technology. These impacts suggest where opportunities for footprint reductions can be found

    through best management practices such as increased materials reuse, increased recycled-content

    materials use, and clean fuels and emission control technologies. Smaller impacts were observed

    in the monitoring and deconstruction stages. Normalized results show the largest environmental

    burdens to fossil depletion, human toxicity, particulate matter formation, and climate-change cate-

    gories resulting from activities associated with mining of fossil fuels for use in electricity production.

    In situ thermal treatment can reliably remediate contaminated source areas with contaminants

    located in low-permeability zones, providing complete destruction of contaminants in a short

    amount of time, quick return of the site to productive use, and minimized quantities of hazardous

    materials stored in landfills for future generations to remediate. However, this remediation strategy

    can also result in significant emissions over a short period of time. It is difficult to quantify the overall

    value of short-term cleanups with intense treatment emissions against longer-term cleanups with

    lower treatment emissions because of the environmental, social, and economic trade-offs that need

    to be considered and understood. LCA is a robust, quantitative tool to help inform stakeholder

    discussions related to the remedy selection process, trade-off considerations, and environmental

    footprint-reduction opportunities, and to complement a broader toolbox for the evaluation of

    sustainable remediation strategies. Oc 2012 Wiley Periodicals, Inc.

    c 2012 Wiley Periodicals, Inc.Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/rem.21331 75

  • Life-Cycle Assessment of In Situ Thermal Remediation

    INTRODUCTION

    Many professionals within the remediation community have come to understand thatwhile the cleanup of a contaminated site should inherently have positive environmentalimpacts, many activities conducted for site cleanup generate environmental burdensthemselves. Consequently, the tendency to invoke a more holistic view of siteremediation, sustainable remediation, has emerged (Sustainable Remediation Forum[SURF], 2009, Interstate Technology & Regulatory Council [ITRC], 2011a). Althoughformal definitions have not yet been accepted throughout the remediation community, theconcept is to attain a balance among the environmental, social, and economic benefits of aremediation project while minimizing the negative impacts to the local, regional, andglobal environment, communities, and economy. For these types of balancing andtrade-off decisions to be properly informed, the remediation community needs additionaldata and quantitative results about the impacts of remediation technologies to determinewhere, how, and when opportunities for improvements can be made.

    Life-cycle assessment (LCA) is an International Organization for Standardization(ISO) standardized and widely accepted method for identifying and calculatingenvironmental impacts across the life cycle of products and services (such as remediationprojects). It includes the definition of the goal, scope, functional unit, and systemboundary, followed by the inventory analysis, impact assessment, and interpretation (ISO,2006). Application of LCA in the field of soil and groundwater remediation technologiesis beginning to increase, has been evaluated in two recent literature reviews (Lemminget al., 2010a; Suer et al., 2004), and can be traced back to as early as the late 1990s(Bender et al., 1998; Page et al., 1999; Volkwein et al., 1999). Not only is LCA a robusttool for quantifying the potential environmental impacts of remediation projects across avariety of impact categories, but it can also identify opportunities within specific processesor phases of the remedy to meaningfully reduce the remedys environmental footprint.

    Not only is LCA a ro-bust tool for quantifyingthe potential environmen-tal impacts of remediationprojects across a variety ofimpact categories, but itcan also identify opportu-nities within specific pro-cesses or phases of theremedy to meaningfully re-duce the remedys environ-mental footprint.

    Early LCA studies focused mainly on ex situ remediation methods, while in morerecent years, LCAs for in situ remediation technologies have been published. Recent in situremediation LCAs include comparative studies of permeable reactive barriers versuspump and treat (Higgins et al., 2009; Mak & Lo, 2011), capping options for sedimentremediation (Sparrevik et al., 2011); electron donors for in situ bioremediationapplications (Hong & Li, 2012); and in situ bioremediation versus in situ thermaldesorption versus excavation and disposal (Lemming et al., 2010b).

    Within the remediation-LCA framework, environmental impacts have beencategorized into the following: those resulting from local impacts of the residual sitecontamination (primary impacts); those resulting from the actual remediation activities(secondary impacts); and, in one study, those consequences associated with future reuse ofthe site or avoided use of greenfield sites (tertiary impacts) (Lesage et al., 2007). The aimof the study discussed in this article is to use LCA for a detailed cradle-to-grave analysis ofthe secondary environmental impacts of an in situ thermal remediation technology for thetreatment of a tetrachloroethene- (PCE) and trichloroethene- (TCE) contaminated sourcearea. Primary environmental impacts in groundwater are neglected due to the ability ofthe thermal technology to rapidly remove contamination from the source area. Tertiaryimpacts have also been excluded because the site reuse after remedy completion willremain commercial/industrial and, therefore, is expected to have no net change in service.

    76 Remediation DOI: 10.1002/rem c 2012 Wiley Periodicals, Inc.

  • REMEDIATION Autumn 2012

    A methodology to conduct LCAs for remediation projects (Favara et al., 2011) wasfollowed for this analysis. It should be noted that LCA is an effective quantitative tool foridentifying potential environmental impacts of remedial projects, but from the perspectiveof sustainability, social and economic impacts should also factor into the decision-makingprocess. The integration of methods such as life cycle costing, cost-benefit analysis, andsocial LCA with environmental LCA may provide avenues to explore the more holisticview of impacts and provide additional insight for decision making. An extensive list ofsustainability metrics applicable to remediation projects was compiled by SURF (Butleret al., 2011) and ITRC (2011b).

    This work was motivated by a desire to provide the remediation community with anobjective demonstration of the process and capabilities of LCA to identify and quantify theoverall environmental impacts of a site remedy. Additional detailed, quantitativeenvironmental impact information about the technologies employed is necessary forremediation professionals to more wholly evaluate the relative sustainability of technologyoptions. Fully informed remedy-selection discussions, trade-off considerations, andidentification of improvement opportunities can only proceed after a more holisticunderstanding of the relevant environmental impacts and magnitude of emissions has beenachieved.

    METHODOLOGY

    Thermal Remedy Overview

    The Electro-Thermal Dynamic Stripping Process (ET-DSPTM) is an in situ thermal soil andgroundwater remediation technology that combines the three dominant heat-transfermechanisms of electrical heating, conductive heating, and convective heat transfer.ET-DSPTM uniformly heats the subsurface and volatilizes the contaminants for recoveryusing standard vacuum extraction techniques. This process involves heating soil withinand across both saturated and unsaturated zones by passing electrical current viaelectrodes placed at calculated depths and distances (Exhibit 1). Water is also circulatedthrough the electrodes to assist with convective heat transfer. The combination ofheat-transfer mechanisms is intended to address contamination in both low- andhigh-permeability zones (McMillan-McGee Corporation, 2011). Dual-phase extraction(DPE) wells are installed within the target treatment area to recover volatilized VOCs andgroundwater. The wells in this case study also recover residual mass in the aqueous phasefor aboveground treatment and reinjection into the formation. The recovered vapor andliquid are separated and treated with activated carbon prior to reinjection or discharge.

    Site Overview

    The remediation site is located in the northeastern United States in a mixed commercial,light industrial area. The in situ thermal remedy was chosen based on an evaluationthat compared short-term effectiveness, long-term effectiveness, implementability,community impact, sustainability, time frame, and cost. Elevated source areaconcentrations, low-permeability materials, and short cleanup time frames weremajor contributors to the remedy selection. Destruction of contaminants, low risk of

    c 2012 Wiley Periodicals, Inc. Remediation DOI: 10.1002/rem 77

  • Life-Cycle Assessment of In Situ Thermal Remediation

    Exhibit 1. Diagram of ET-DSPTM thermal remedy (McMillan-McGee Corporation, 2011)

    failure, cost, minimization of long-term storage in a landfill, and rapid reuse of the sitewere also important stakeholder objectives.

    Goal, Scope, and System Boundary

    The goal of this study was to evaluate the potential environmental impacts from theapplication of an in situ thermal remedy for the destruction of contamination in twochlorinated solvent source areas. The functional unit was defined as the treatment of4,400 yd3 of contaminated media via ET-DSPTM thermal technology for the removal ofgreater than 99 percent of the estimated 2,200 lbs of source mass. The duration of theremedy was estimated to be 180 days, followed by two years of performance monitoring.

    The scope of this study included the major inputs and emissions related to the in situthermal technology, including raw materials acquisition, materials processing, transport(labor, equipment, and wastes), resource use (electricity and water), monitoring(transport and sample analysis), and waste treatment and disposal. Exhibit 2 presents thesystem boundary (shown as a process map). For discussion and optimization purposes, theremedy was separated into four life-cycle stages: remedy installation, remedy operation,monitoring, and deconstruction (waste transport and disposal).

    Pre-remedy site activities not considered in this study included: initial sitegroundwater, soil, bedrock, and surface water investigation; monitoring well installation;hydrogeologic evaluation; and the tracer study that was conducted to evaluate thefeasibility of other in situ remedies. The study also excluded relocation of undergroundutilities because it was outside the scope of this analysis.

    Given that the remedy-volatilized chlorinated VOCs from soil and groundwater tosoil vapor, measures were developed to mitigate the potential for vapor migration toimpact outdoor air and the indoor air quality (of an adjacent building). These measuresincluded repaving the treatment area to serve as a cap for vapor migration, and using DPE

    78 Remediation DOI: 10.1002/rem c 2012 Wiley Periodicals, Inc.

  • REMEDIATION Autumn 2012

    Exhibit 2. Process map depicting the remedy life-cycle stages and activities within each stageincluded in the thermal remedy LCA

    points and shallow vapor-extraction points to extract vapors generated during remedyoperation. Additional shallow vapor-extraction points were installed near the building toprovide adequate vapor recovery. In addition, subsurface vacuum/pressure measurementswere collected to confirm the extent of capture and outdoor and indoor air sampling wasconducted to monitor air concentrations during the remediation.

    Inventory

    An inventory of materials and processes included in this study were separated into specificphases of the remedy as depicted in the process map. The majority of the inventory datawas compiled from the remedy design and cost report provided by the technology vendorand is described in Exhibit 3. Additional data were obtained via communications with thesite consultant, contractors, and vendors. This primary data-collection effort wassupplemented with data from the ecoinvent 2.2 database for background processes(ecoinvent Centre, 2010).

    Remedy Installation

    All major materials and activities related to the construction and implementation of thethermal technology were included in the remedy installation stage. This included: drilling(extraction, electrode, reinjection, and sensor wells), the ET-DSPTM system (electrodes,power control system, electronic control and safety system, water recirculation system,sensors, and conducting fixtures), and the DPE system (extraction wells, asphalt vaporcap, liquid and vapor treatment equipment, and treatment consumables).

    Much of the equipment for the electrical, recirculation, and power controlcomponents of the ET-DSPTM system as well as the DPE system can be reused onadditional sites and, therefore, only a percentage of their impacts (percentage of theequipment materials) were allocated to the inventory. The evaluation...

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