Life cycle assessment of active and passive groundwater remediation technologies

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  • evaluated by focusing on the main technical elements and their significance with respect to resource

    funnel construction and by minimising the steel consumption for the gate construction. Granular activated

    carbon (GAC) is exclusively considered as the treatment material, both in-situ and on-site. Here it is

    Journal of Contaminant Hydrology 83 (2006) 171199

    www.elsevier.com/locate/jconhyddepletion and potential adverse effects on ecological quality, as well as on human health. Seven impact

    categories are distinguished to address a broad spectrum of possible environmental loads. A main point of

    discussion is the reliability of technical assumptions and performance predictions for the future. It is

    obvious that a high uncertainty exists when estimating impact specific indicator values over operation times

    of decades. An uncertainty analysis is conducted to include the imprecision of the underlying emission and

    consumption data and a scenario analysis is utilised to contrast various possible technological variants.

    Though the results of the study are highly site-specific, a generalised relative evaluation of potential

    impacts and their main sources is the principle objective rather than a discussion of the calculated absolute

    impacts. A crucial finding that can be applied to any other site is the central role of steel, which particularly

    derogates the valuation of FGS due to the associated emissions that are harmful to human health. In view of

    that, environmental credits can be achieved by selecting a mineral-based wall instead of sheet piles for theLife cycle assessment of active and passive groundwater

    remediation technologies

    Peter Bayer *, Michael Finkel

    Center for Applied Geoscience, University of Tuebingen, Sigwartstrasse 10, 72076 Tuebingen, Germany

    Received 17 June 2005; received in revised form 28 October 2005; accepted 10 November 2005

    Available online 27 December 2005

    Abstract

    Groundwater remediation technologies, such as pump-and-treat (PTS) and funnel-and-gate systems

    (FGS), aim at reducing locally appearing contaminations. Therefore, these methodologies are basically

    evaluated with respect to their capability to yield local improvements of an environmental situation,

    commonly neglecting that their application is also associated with secondary impacts. Life cycle assessment

    (LCA) represents a widely accepted method of assessing the environmental aspects and potential impacts

    related to a product, process or service. This study presents the set-up of a LCA framework in order to

    compare the secondary impacts caused by two conceptually different technologies at the site of a former

    manufactured gas plant in the city of Karlsruhe, Germany. As a FGS is already operating at this site, a

    hypothetical PTS of the same functionality is adopted. During the LCA, the remediation systems are0169-7722/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

    doi:10.1016/j.jconhyd.2005.11.005

    * Correspond

    E-mail address: peter.bayer@uni-tuebingen.de (P. Bayer).ing author. Tel.: +49 7071 2973178; fax: +49 7071 5059.

  • identified as an additional main determinant of the relative assessment of the technologies since it is

    continuously consumed.

    D 2005 Elsevier B.V. All rights reserved.

    Keywords: Life cycle assessment; Funnel-and-gate; Pump-and-treat; Remediation; Groundwater; Uncertainty; Monte

    Carlo; Weighting triangle

    1. Introduction

    Groundwater is one of the most valuable natural resources. Beside its central position for

    terrestrial and aquatic ecosystems, groundwater is essential for drinking and industrial water

    abstraction. It represents by far the largest reservoir of fresh water, with stored volumes over fifty

    times greater than the amount of surface water. Growing populations, continual urbanisation and

    industrialisation are increasing the risk of groundwater contamination, while simultaneously, the

    living standards and demands on our natural environment are rising. Hazardous waste disposal

    facilities, oil refineries and chemical plants are typical sources of waste streams, which can reach

    the aquifer and produce long-term contaminations in the subsurface. Most contaminant sites in

    industrialised countries are characterised by the occurrence of hazardous organic chemicals in

    the underground. They can form separate, nonaqueous phases in the subsurface, which

    continuously feed the passing groundwater with contaminants. Downgradient of these source

    zones, plumes develop with significant concentrations of the contaminants dissolved in the

    groundwater. Contaminants can also slowly diffuse into the low permeable aquifer matrix and,

    because of the small mass transfer rates into groundwater, stay there as long-term secondary

    sources (Grathwohl, 1998; Fetter, 1999). These aspects substantiate the importance of the

    protection of groundwater from pollution and the control of already contaminated aquifer zones.

    However, the considerably low mobility together with a typically high persistency of organic

    contaminants is the crux for the development of suitable groundwater remediation technologies.

    A still common and conventional bcleanupQ practice is pump-and-treat, meaning the pumpingof contaminated groundwater followed by on-site treatment. Pumping wells are installed in or in

    the vicinity of the source or plume area in order to hydraulically capture the critical aquifer

    zones. Experience shows that due to the limited mass transfer rates, aquifer restoration by

    conventional pump-and-treat systems is, for the most part, not achievable within reasonable

    timeframes (Eberhardt and Grathwohl, 2002; Stroo et al., 2003). Though the use of pump-and-

    treat systems (PTS) is not the only technological option, it still seems to be the most favourable

    because of the experience in appropriate hydraulic design, as well as its flexibility and simplicity

    (US EPA, 1996; Bayer, 2004).

    Meanwhile, permeable walls (PRBs) are a widely accepted alternative for long-term plume

    management. Continuously or locally reactive vertical walls are installed in-situ for down-

    gradient capture and treatment of the contaminated plume (US EPA, 2002). Funnel-and-gate

    systems (FGS Starr and Cherry, 1994) are a variant based on the combination of impermeable

    walls (funnels) and reactive zones (gates). Adjusted to the regional groundwater flow regime, the

    funnels direct the contaminated water through the in-situ treatment facilities within the gates.

    Compared to PTS, FGS and continuous permeable walls are denoted as bpassiveQ systems since,after proper installation of the technological devices, no active work, such as pumping, is

    needed.

    P. Bayer, M. Finkel / Journal of Contaminant Hydrology 83 (2006) 171199172In the presented study, the focus is set on the comparison of PTS and FGS, as typical active

    and passive groundwater remediation options, in terms of their environmental impacts. Similar

  • to wastewater treatment or recycling techniques, the achievement of a local environmental

    benefit, i.e. the control and removal of contaminants, is compromised by certain environmental

    burdens caused during the construction, installation and maintenance of the technologies. These

    so-called secondary impacts (Volkwein et al., 1999) can reach significant levels depending on

    the type of materials and energy used, the size of the treatment system and its time of operation.

    A life cycle assessment (LCA) framework is used to contrast the potential impacts in different

    categories reflecting the inherent adverse effects on ecology, human health as well as the

    depletion of energy resources. LCA considers the potential impacts associated with the supply

    chains throughout a products (i.e. here, technologys) life cycle from raw material acquisition

    through production, use and disposal (ISO, 14040, 1997).

    2. Previous work

    The most comprehensive approaches for using LCA to environmentally rate impacts from

    remediation of contaminated sites have been presented by Beinat et al. (1997), Volkwein et al.

    (1999) and Diamond et al. (1999). Sue`r et al. (2004) give a brief literature review of the few

    available studies in this area. The REC method presented by Beinat et al. (1997) is a streamlined

    decision support system for estimating the relevance of environmental impacts of technological

    alternatives within a risk assessment framework. Volkwein et al. (1999) emphasize a difference

    in their UVA approach to REC: While the REC tool can be applied to derive suitable clean-up

    levels, the levels have to be assigned a priori when using the UVA method. Aside from this,

    UVA is a more detailed and elementary approach, which operates on generic datasets processed

    in over 50 modules (LfU, 1998). Volkwein et al. (1999) show the application of their method in

    accessing the impacts caused by partial soil excavation, on-site ensuring and surface sealing.

    Bender et al. (1998) also discuss the suitability of the UVA tool for analysing the impacts caused

    by a number of different groundwater remediation technologies, such as long-term extraction of

    groundwater, in-situ bioremediation and soil vapor extraction. Though their case study does not

    exhibit a detailed site and inventory data description and no information is given on how the site

    data is processed within the LCA framework, general conclusions are derived when comparing

    the different remediation technologies. For example, they identified energy consumption as the

    major cause of environmental impact when long-term groundwater extraction is considered. This

    is supported by the findings of Vignes (2001).

    The life cycle management approach of Diamond et al. (1999) is intended as a systematic

    concept for deriving qualitative comparisons of selected soil and groundwater remediation

    options within a decision making process. It is complemented by a LCA step for a detailed

    investigation of the environmental burdens associated with the technologies. The generic

    remediation options highlighted were excavation and off-site disposal, in-situ bioremediation,

    soil washing, vapor extraction and no action. The utilisation of the conceptual outline presented

    by Diamond et al. (1999), for a quantitative inspection of associated environmental burdens, is

    shown in a case study on soil remediation of a PAH contaminated site in Ontario, Canada (Page

    et al., 1999). During the examined time horizon of 75 weeks, contaminated soil and sludge was

    discarded at nearby disposal facilities. Since no long term measurements such as post-site

    processing and maintenance of waste landfill were investigated, the main emissions were

    controlled by material transport. The creation of solid waste and land use was accounted for in

    separate life cycle impact categories. Soil remediation is also subject to the LCA presented by

    P. Bayer, M. Finkel / Journal of Contaminant Hydrology 83 (2006) 171199 173Blanc et al. (2004), where four technologies are compared in terms of their environmental

    impacts and the related energy consumption to clean-up a sulfur contaminated site in France.

  • The four remedial actions work with soil excavation, followed by on-site treatment, backfill and/

    or disposal.

    3. LCA framework

    3.1. Overview

    The structural and procedural components of LCA are determined by the international

    standard series ISO 1404043 (1997, 1998, 2000a,b). Mandatory initial steps include the

    definition of goal and scope, functional unit as well as system boundaries. The overall goal for

    this study is the comparison of the environmental performance of two different long term

    groundwater remediation technologies. A premise for a valid comparison is to presume an equal

    functionality of both approaches, i.e. to define the functional unit so that it provides a reference

    to which the inputs and outputs can be related (Rebitzer et al., 2004). This is addressed by

    analysing an existing case, the former manufactured gas plant site of the city of Karlsruhe in

    southern Germany (site description given in Table 1). In 2000, a FGS (Fig. 1) was installed

    (Schad et al., 2000), which will subsequently be judged against a hypothetical PTS. The latter is

    Table 1

    Technical specifications of Karlsruhe site and key elements of FGS and PTS subject to LCA

    Site parameterformer gas plant Karlsruhe

    Width of contamination 210 m

    Hydraulic conductivity log mean 3.9E03 m/sHydraulic conductivity log variance 1.31

    Regional gradient 0.070.135% gradient direction

    (25% seasonal variation) NW/WNW

    Contaminant concentrations Acenaphthene 400600 ug/l

    Averaged total flow rate through FGS 10 l/s

    P. Bayer, M. Finkel / Journal of Contaminant Hydrology 83 (2006) 171199174FGS

    Funnel depth 17 m

    Funnel length 240 m

    Gates depth 17 m

    Gate borings diameter 2.50 m

    Gate casings diameter 1.80 m

    Steel/gate 812 tGravel/gate (50 m3/gate; 1.6 t/m3) 880 tClay/gate (8 m3/gate; here 2 t/m3) 816 tGAC/gate (25 m3/gate; 0.6 t/m3) 815 tLifetime (regeneration interval) 5 years

    PTS

    Number of wells 10

    Installation depth 17 m

    Pumping rate 18 l/s

    PVC conduits 100 m

    HDPE container (5 cm wall) max. 20 m3 each

    GAC refill interval 1 year

    GAC volume per fill 2443.2 t/fillLifetime of conduits, pumps, vessels 10 years

  • P. Bayer, M. Finkel / Journal of Contaminant Hydrology 83 (2006) 171199 175configured assuming equivalent remediation goals, i.e. the long term hydraulic containment of

    the contaminated plume emanating from the upgradient source zone. Based on the site-specific

    results of the LCA, the goal is to identify crucial and environmentally sensitive technical design

    elements, as well as to derive suggestions for technological enhancements for the particular site

    and in general. The exact definition of functional unit used for this study is explained in detail in

    the following section.

    The system boundaries for the LCA are set based on the characteristics of the site, focusing

    on the environmental burden related to major technological elements, which will be delineated in

    Fig. 1. Scheme of funnel-and-gate system as installed at the former gas plant Karlsruhe-Ost. Vertical sheet piles act as

    funnels that direct the contaminated groundwater into (in total 8) gates. In these gates, perforated steel cylinders are filled

    with GAC that is regenerated every 5 years.detail after the subsequent description of the site. The presented study is not limited to the

    analysis of the installed FGS and a hypothetical PTS. Several modifications of the reference

    scenario are formulated during the evaluation of the results in order to investigate the role of

    assumptions made for the technological elements and to develop system alternatives with

    decreased environmental impact. An overview is in Table 2. The scope of these scenarios is

    illustrated in Fig. 2.

    After the initial phase of the LCA, which is crucial to establish the context in which the

    evaluation is to be made, the ensuing steps are inventory analysis, impact assessment and

    interpretation. The inventory analysis (LCI) examines and compiles all relevant energy and

    material inputs and outputs of processes during the life cycle of a...

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