Environmental Impacts of Remediation of a Trichloroethene-Contaminated Site: Life Cycle Assessment of Remediation Alternatives
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Environmental Impacts ofRemediation of aTrichloroethene-Contaminated Site:Life Cycle Assessment ofRemediation AlternativesG I T T E L E M M I N G , * ,
M I C H A E L Z . H A U S C H I L D ,
J U L I E C H A M B O N , P H I L I P J . B I N N I N G ,
C E C I L E B U L L E , M A N U E L E M A R G N I ,
A N D P O U L L . B J E R G
Department of Environmental Engineering, TechnicalUniversity of Denmark (DTU), DK-2800 Lyngby, Denmark,
Department of Management Engineering, Technical Universityof Denmark (DTU), DK-2800 Kgs. Lyngby, Denmark, and
The Interuniversity Research Centre for the Life Cycle ofProducts, Processes and Services (CIRAIG), Ecole Polytechniquede Montreal., P.O. Box 6079, Montreal,Quebec H3C 3A7, Canada
Received June 14, 2010. Revised manuscript receivedOctober 20, 2010. Accepted October 25, 2010.
The environmental impacts of remediation of a chloroethene-contaminated site were evaluated using life cycle assessment(LCA). The compared remediation options are (i) in situbioremediation by enhanced reductive dechlorination (ERD),(ii) in situ thermal desorption (ISTD), and (iii) excavation of thecontaminated soil followed by off-site treatment and disposal.The results showed that choosing the ERD option will reduce thelife-cycle impacts of remediation remarkably compared tochoosing either ISTD or excavation, which are more energy-demanding. In addition to the secondary impacts of remediation,this study includes assessment of local toxic impacts (theprimary impact) related to the on-site contaminant leaching togroundwater and subsequent human exposure via drinkingwater. The primary human toxic impacts were high for ERD dueto the formation and leaching of chlorinated degradationproducts, especially vinyl chloride during remediation. However,the secondary human toxic impacts of ISTD and excavationare likely to be even higher, particularly due to upstream impactsfrom steel production. The newly launched model, USEtox,was applied for characterization of primary and secondary toxicimpacts and combined with a site-dependent fate model ofthe leaching of chlorinated ethenes from the fractured clay tillsite.
Chlorinated ethenes, such as perchloroethene (PCE) andtrichloroethene (TCE), are among the most frequent con-taminants found in soil and groundwater due to their
extensive and widespread use as cleaning agents and metaldegreasers (1). In the 2004 U.S. National Priority Listchlorinated ethenes were by far the most common group oforganic contaminants at sites prioritized for remediation (2).Remediation methods for chlorinated ethenes can be eitherex situ methods, where contaminated soil/groundwater isexcavated/pumped to the surface and treated on- or off-site,or they can be in situ methods that remove contaminantsvia mass transfer or mass removal by targeting them at theiractual location in the subsurface.
Life cycle assessment (LCA) is an ISO standardized andwidely used method for environmental assessment ofproducts and services. It has also been applied in the fieldof soil and groundwater remediation to compare theenvironmental impacts of remediation alternatives as re-ported in two recent literature reviews (3, 4). Existing studieshave, however, focused mainly on ex situ remediation andcontaminants such as metals, PAHs, and hydrocarbons (3).LCA studies addressing chlorinated solvent remediation (5, 6)focus on the comparison of groundwater plume remediationtechniques e.g. in situ permeable reactive barriers andconventional pump-and-treat systems, whereas in situmethods for source zone remediation of chlorinated etheneshave not yet been a focus of published LCA studies.
Environmental impacts from remediation can be dividedinto primary and secondary impacts (see e.g. refs 7 and 8).Primary impacts are the local toxic impacts from the residualsite contamination, whereas secondary impacts are impactson the local, regional, and global scale generated by theremediation activities. In addition, a study introduced theterm tertiary impacts to describe impacts associated withthe postremediation fate of a brownfield (9), but these arenot considered here. Existing studies that include primaryimpacts use generic characterization factors that do not takethe site-specific contaminant fate and exposure into con-sideration and furthermore focus on impacts in surface wateror soil (7-9). Although highly relevant for remedial actions,primary impacts in groundwater have not been targeted inexisting studies. This may be because of the fact that thegroundwater compartment is not included as emission orimpact compartment in the applied models for life cycleinventory (LCI) and life cycle impact assessment (LCIA).
The aim of this study is to use LCA for a comparison ofprimary and secondary environmental impacts of threealternative technologies for remediating a TCE-contaminatedsource zone. Site-generic characterization factors for toxicemissions do not adequately represent the fate of chlorinatedethenes at contaminated sites because they disregard deepersoil layers and groundwater causing the main part of thecontamination to end up in the atmosphere (10). Further-more, they do not include the formation of metabolites duringbiodegradation of chlorinated ethenes, of which particularlyvinyl chloride is problematic due to its toxic and carcinogeniceffects (10). Therefore a site-dependent assessment is usedhere, taking into account the site-specificity of the fate of thecontaminant including formation of metabolites. In addition,site-dependent exposure parameters are used for calculationof exposure concentrations and the exposed number ofpeople. In this case the primary impacts are related to humanexposure via ingestion of groundwater due to on-site leachingof contaminants and are evaluated using a site-specificleaching model. Primary ecotoxic impacts in groundwaterare neglected, and no discharge to surface water is includedbecause the groundwater plume is assumed to be fullyabstracted by the downstream drinking water well. Thecompared remediation technologies are as follows: (i)
* Corresponding author phone: (+45) 4525 1595; fax: (+45) 45932850; e-mail: firstname.lastname@example.org.
DTU Environment. DTU Management Engineering. CIRAIG.
Environ. Sci. Technol. 2010, 44, 91639169
10.1021/es102007s 2010 American Chemical Society VOL. 44, NO. 23, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 9163Published on Web 11/05/2010
enhanced reductive dechlorination (ERD) which is an in situbioremediation method employing bioaugmentation andbiostimulation; (ii) in situ thermal desorption (ISTD) whichis a physical remediation method deploying thermal con-ductive heating of the contaminated soil; and (iii) excavationof the contaminated soil followed by off-site treatment andfinal disposal in a landfill.
Based on the LCA results the environmental impacts ofthe three remediation alternatives are compared. Environ-mental hotspots of each technology are identified andimprovement options suggested.
Materials and MethodsCase study. A TCE-contaminated site in central Copenhagenis situated within the catchment of a water supply that extractsdrinking water for approximately 44,000 people located2000 m down gradient from the site. The site was used as ametal shop, boilermaker shop, woodcutting shop, etc. until1986. A conceptual sketch of the contaminated site is shownin Figure 1. The contamination is located mainly in a fracturedclay till and partly in a sand layer embedded in the clay till.The contaminated source zone extends vertically from 3 to8 m below ground surface and has a horizontal cross-sectionalarea of 140 m2. The estimated mass of TCE in the ap-proximately 700 m3 of contaminated soil is 40 kg. The claytill overlies a regional limestone aquifer used for drinkingwater extraction.
The goal of the LCA is to compare three options forremediating the contaminated source zone. In addition tothe three remediation scenarios the assessment includes ano action scenario, in which no active remediation takes
places and monitoring of the naturally occurring degradationis the only activity included. The no action scenario isincluded as a reference scenario only and cannot be seen asa viable management scenario comparable to the threeremediation scenarios.
The functional unit provided by all options compared inthis study is the treatment of the 700 m3 of contaminated soilwith a 98% removal of the contaminant mass within thisvolume. This remediation target was chosen as it reducesthe mass discharge to the groundwater sufficiently to ensurethat the Danish groundwater quality criterion (1 g/L) forchlorinated ethenes is not exceeded. The timeframe for theLCI is unrestricted in order to capture both short- and long-term impacts.
The scope of the LCA is to include all important activitieson site and off site (see overview in Table 1 and a morecomplete listing in the Supporting Information (SI) TableS1) of each scenario, i.e. covering raw materials acquisition,materials production, use stages, and end-of-life processes.Primary data regarding energy and material consumptionfor the different remedial activities is collected from the actualconsultants, contractors, or producers likely to undertakethe work. Inventory data for the background system (pro-duction of steel, electricity, plastic, asphalt, lorry transport,etc.) were based on average technology data from theecoinvent life cycle unit process database version 2.0 (11).These generic data are supported by a collection of specificdata for remediation-related processes for which no data arefound in ecoinvent or other general LCA databases (produc-tion of bioculture and activated carbon, laboratory analysesof soil and groundwater). Electricity used in the operation
FIGURE 1. Conceptual model of the contaminated site and placement of the micr