the use of permeable reactive barriers to control contaminant dispersal during site remediation in...
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.Cold Regions Science and Technology 32 2001 157174www.elsevier.comrlocatercoldregions
The use of permeable reactive barriers to control contaminantdispersal during site remediation in Antarctica
I. Snape a,), C.E. Morris b, C.M. Cole a,ca Human Impacts Research, Australian Antarctic Diision, Channel Highway, Kingston, Tasmania 7050, Australia
b Department of Ciil, Mining and Enironmental Engineering, Uniersity of Wollongong, Wollongong, NSW 2522, Australiac DPIWE, GPO Box 44A, Hobart, Tasmania 7001, Australia
Received 9 October 2000; received in revised form 12 March 2001; accepted 12 March 2001
When used as part of an integrated contaminated sites remediation program, permeable reactive barriers are a valuabletechnological application that can remove, retain or treat contaminated waters in seasonally frozen ground in remote areas.The main advantages of permeable reactive barriers for application in remote cold regions are that they are passivelow-technology systems that do not require power to operate; they can be left at short notice during extreme weather events;and most importantly, they have a minimal impact on the environment as they can be completely removed at the end of siteoperations. However, barrier technology was originally developed for use in temperate regions and site-specific adaptationsare required to ensure effective deployment and recovery from seasonally frozen ground. Experience gained from testing avariety of fill materials on site at Casey Station, Antarctica, indicates that fine-grained reactive materials are less suitable
.than coarse-grained free-draining materials. Preliminary results from simple field trials using granular activated carbonindicate that a significant improvement in water quality is possible for waters that contain high concentrations of petroleumhydrocarbons and heavy metals. For remote area deployment, barriers are best pre-assembled in modular form to allow rapidemplacement in frozen ground before seasonal melting begins. Future developments that are needed for efficient applicationin cold regions include the need to quantify reactionradsorption rates at low temperatures for fill media and to establishbreakthrough curves for promising materials. q 2001 Elsevier Science B.V. All rights reserved.
Keywords: Permeable reactive barriers; Contaminant dispersal; Antarctica
In-situ and on-site remediation of contaminatedsites associated with scientific research stations inAntarctica offers significant environmental and fi-nancial benefits when compared with the more tradi-tional management practices of excavation and re-
) Corresponding author. .E-mail address: firstname.lastname@example.org I. Snape .
moval or the do nothing option. However, develop-ing methodologies that are suitable for use in Antarc-tica requires considerable process-oriented researchand applied engineering. To be effective in Antarc-tica, remediation methodologies must be capable ofoperating under challenging environmental condi-tions. In summer, most coastal Antarctic stationsexperience a short but very dynamic melt period thatconsists of diurnal freezing and thawing in periods offine weather, interspersed with blizzards, high windsand fresh snow accumulations. Therefore, suitable
0165-232Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. .PII: S0165-232X 01 00027-1
( )I. Snape et al.rCold Regions Science and Technology 32 2001 157174158
remediation methodologies must be robust and capa-ble of operating at full capacity in fine-weatherwindows, but must also be designed in a manner thatwill allow the system to be left unattended for anextended time at short notice. The techniques chosenshould ideally require few people to install andoperate, have low energy and infrastructure require-ments and, above all, must have minimal impact onthe environment.
To develop techniques suitable for in-situ or on-site remediation in Antarctica, or more generally forArctic and High Alpine areas that have similar sitecharacteristics to those in Antarctica, our investiga-tions focused on how contaminants interact in theenvironment through physical, chemical and biologi-cal processes that are potentially unique to, or signif-icantly altered by, cold climates. The contaminatedsites we have studied in Antarctica contain one ormore of three main contaminant suites:
heavy metals associated with abandoned tipswhere petroleum hydrocarbons may be minorconstituents;
poorly contained petroleum sources e.g. frozen.rusty drums and petroleum-contaminated sedi-
ments; nutrient-, heavy-metal- andror microbially-
contaminated wastewater effluent.
The control and treatment of wastewater is arelatively straightforward process that can be per-formed using traditional methods in heated buildings,and thus is not part of our present research. Success-ful technologies for treating heavy metals andpetroleum hydrocarbons have been developed for usein temperate climates, and we are currently focusingon modifying these for use in the Antarctic.
One methodology that we think will prove valu-able in the remediation of contaminated sites inAntarctica involves the use of permeable reactive
.barriers PRBs to remove contaminants from sur-face and subsurface waters. Such barriers can poten-tially contribute to the management of most of thecontaminants found in the sites we studied, althoughwe are not considering using barriers as the solelong-term treatment strategy. As part of an integratedcontaminated site remediation program, PRBs mayreduce environmental risks associated with contami-
nated sites, especially where the contaminant trans-port mechanism is via flowing water. We foreseethat the main use for PRBs will be during theremoval of heavy-metal contaminated solid waste,drums that are leaking hydrocarbons, and during theremediation of contaminated soils. This is primarilybecause heavy metal and petroleum contaminantswill inevitably be released through the disturbanceassociated with the excavation and removal of tipmaterial, and when tilling or digging is undertaken toremediate contaminants in situ or on site. For PRBsto work effectively in Antarctica, they must be de-signed for the types of contaminants they will berequired to remediate, the local site characteristicsand conditions, and the discharge rates and volumesof water that will move through them.
We began our research and development programon the premise that the main environment- and site-specific limitations to barrier efficacy will be thefollowing:
Freezing water clogging the outer membraneand inner reactive material of the barrier, therebyreducing permeability. Unfavourable kinetics slowing precipitation re-
actions andror sorption at low temperatures. Pulsed water and contaminant fluxes during
diurnal freeze-thaw cycles, and weekly variations inmelting associated with passing weather systems. Low ionic strength melt waters that are weakly
carbonic, have few dissolved complexes or ligands,and low buffering capacity. These features mean thatmelt waters are efficient cation scavengers and thusthe solubilities of heavy metals within them tend tobe high. A mixed cocktail of polar and non-polar con-
taminants ranging from solvents, fuels and oils, toPCBs and heavy metals. Such a range and mixture ofcontaminants must be considered when designing thesorbent qualities of material that will retain them.
In this paper we describe how we envisage usingPRBs to reduce contaminant dispersal during reme-diation and rehabilitation of contaminated sites atCasey Station and the nearby abandoned WilkesStation, both in Australian Antarctic Territory. Theobjectives of our study are to provide a preliminaryindication of how PRBs might be usefully deployed
( )I. Snape et al.rCold Regions Science and Technology 32 2001 157174 159
in the Casey region, and how these barriers mightfunction in Antarctic conditions. By determiningwhich of the many limiting factors are dominant, wehope to focus future research to improve barrierperformance. The US-EPA has identified a researchand development path for PRB design and emplace-
.ment Fig. 1 . Our approach for barrier development .includes both field pilot tests and laboratory test-
ing. However, for the first phase of investigation .reported here , we felt that extensive bench-topexperiments were unwarranted, as a considerableamount of information is already available on thegeneral chemical performance of barrier fill materi-
als e.g. Blowes et al., 1998; Gharaibeh et al., 1998;Johns et al., 1998; Knappe et al., 1998; Ouki andKavannagh, 1999; Bailey et al., 1999; Cooney et al.,
.1999a,b . In this contribution, we present an overviewof site characterisation data, some conceptual mod-els and preliminary designs, and preliminary resultsfrom the first pilot tests. Five small pilot tests havebeen initiated at Casey to examine various aspects ofthe conceptual models described in this paper. Threeof these are long-term multiyear trials where chemi-cal validation is not yet available. Results for twoshort-term trials, and the first summers results froma 4-year trial, all using granular activated carbon as areactive medium, are presented here. These results,and our experiences with other fill media, are then
considered in the general context of barrier perfor-mance and design for contaminant mitigation inAntarctica. Laboratory testing, final design and val-idation of full-scale emplacement performance, the
other components in the PRB design pathway Fig..1 , will be presented in due course.
2. Site characterization
2.1. Natural enironment in the Casey region
Both Old and New Casey Stations are located ona coastal, largely ice-free rock and gravel peninsu