The use of permeable reactive barriers to control contaminant dispersal during site remediation in Antarctica

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<ul><li><p> .Cold Regions Science and Technology 32 2001 157174www.elsevier.comrlocatercoldregions</p><p>The use of permeable reactive barriers to control contaminantdispersal during site remediation in Antarctica</p><p>I. Snape a,), C.E. Morris b, C.M. Cole a,ca Human Impacts Research, Australian Antarctic Diision, Channel Highway, Kingston, Tasmania 7050, Australia</p><p>b Department of Ciil, Mining and Enironmental Engineering, Uniersity of Wollongong, Wollongong, NSW 2522, Australiac DPIWE, GPO Box 44A, Hobart, Tasmania 7001, Australia</p><p>Received 9 October 2000; received in revised form 12 March 2001; accepted 12 March 2001</p><p>Abstract</p><p>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</p><p> .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.</p><p>Keywords: Permeable reactive barriers; Contaminant dispersal; Antarctica</p><p>1. Introduction</p><p>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-</p><p>) Corresponding author. .E-mail address: ian.snape@aad.gov.au I. Snape .</p><p>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</p><p>0165-232Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. .PII: S0165-232X 01 00027-1</p></li><li><p>( )I. Snape et al.rCold Regions Science and Technology 32 2001 157174158</p><p>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.</p><p>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:</p><p> heavy metals associated with abandoned tipswhere petroleum hydrocarbons may be minorconstituents;</p><p> poorly contained petroleum sources e.g. frozen.rusty drums and petroleum-contaminated sedi-</p><p>ments; nutrient-, heavy-metal- andror microbially-</p><p>contaminated wastewater effluent.</p><p>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.</p><p>One methodology that we think will prove valu-able in the remediation of contaminated sites inAntarctica involves the use of permeable reactive</p><p> .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-</p><p>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.</p><p>We began our research and development programon the premise that the main environment- and site-specific limitations to barrier efficacy will be thefollowing:</p><p> Freezing water clogging the outer membraneand inner reactive material of the barrier, therebyreducing permeability. Unfavourable kinetics slowing precipitation re-</p><p>actions andror sorption at low temperatures. Pulsed water and contaminant fluxes during</p><p>diurnal freeze-thaw cycles, and weekly variations inmelting associated with passing weather systems. Low ionic strength melt waters that are weakly</p><p>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-</p><p>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.</p><p>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</p></li><li><p>( )I. Snape et al.rCold Regions Science and Technology 32 2001 157174 159</p><p>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-</p><p> .ment Fig. 1 . Our approach for barrier development .includes both field pilot tests and laboratory test-</p><p>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-</p><p>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.,</p><p>.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</p><p>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</p><p>other components in the PRB design pathway Fig..1 , will be presented in due course.</p><p>2. Site characterization</p><p>2.1. Natural enironment in the Casey region</p><p>Both Old and New Casey Stations are located ona coastal, largely ice-free rock and gravel peninsula .Fig. 2 . Sea ice is usually present in the wintermonths, but melts or is blown out to sea eachsummer. Average windspeed at Casey Station is 18km hy1 in summer and 31 km hy1 in winter, withmean temperatures of ;38C and y208C for the</p><p>summer and winter months respectively Deprez et.al., 1999 . Soil development is generally poor in the</p><p>immediate vicinity of Casey Station, with glacial,fluvial and marine deposits being better described asmineral sediments. However, there are mosses andlichens at Casey that are amongst the most diverse</p><p> .and abundant in Antarctica Smith, 1986 . Nearbyterrestrial areas are breeding and feeding grounds forseals, penguins, and a range of other birds, and</p><p>Fig. 1. Path to permeable reactive barrier design and emplacement. Stages of our work in Antarctica that are presented here are highlighted .in bold US-EPA, 2000 .</p></li><li><p>( )I. Snape et al.rCold Regions Science and Technology 32 2001 157174160</p><p>Fig. 2. Casey, Old Casey and Wilkes Stations in the Windmill Islands, East Antarctica.</p><p>shallow nearshore marine areas are also highly di-verse with biota that include sponges, algae, echino-derms, fish and corals. Coastal outcrops, such asthose near Casey, are examples of only a few Antarc-</p><p> .tic coastal oases see references in Pickard, 1986 ,and the impact we might expect in these areas fromterrestrial contamination is considered disproportion-</p><p>ately large relative to their real extent Snape et al.,.2001b .</p><p>2.2. Origins of site contamination in Antarctica</p><p>Contamination at Antarctic research stations suchas Wilkes and Old Casey occurs through abandon-</p><p>ment of waste such as batteries and fuel drums Fig.. .3a ; through accidental spills Fig. 3b , usually of</p><p>fuel; or by discharge of liquid effluent, which con-tains human waste, but may also include other chem-icals. Although modern management practices nolonger allow abandonment of solid waste as a man-agement option, we are left with a legacy of aban-doned tips and fuel drum caches from times whenenvironmental protection was not considered a prior-ity. Similarly, it is impossible to guarantee that fuelspills will not occur in the future, or that liquidwastes will be treated to a tertiary level beforedischarge.</p><p>2.3. Site inestigations at Casey and Wilkes stations</p><p>A joint study by the Australian Antarctic Divisionand the Tasmanian Department of Environment andLand Management identified 20 sites at both Old andNew Casey Stations as being potentially contami-</p><p> .nated Deprez et al., 1999 . In their report, Deprez et .al. 1999 identified two sites near the Old Casey</p><p>Station; the abandoned Thala Valley tip site and thepetroleum-contaminated sediments near the Mechan-ical WorkshoprPowerhouse, as being the highestpriority for remedial action. From a grid-based geo-</p><p> .chemical survey of Thala Valley, Deprez et al. 1999found that sediments had concentrations of contami-</p><p> .nants, including heavy metals Cu, Pb and Zn , .polycyclic aromatic hydrocarbons PAH , and</p><p>petroleum hydrocarbons, that were significantlyabove background levels. Contaminant concentra-tions for these chemicals also exceeded Environmen-</p><p>tal Investigation Guideline levels ANZECCrNH&amp;. .MRC, 1992 . Deprez et al. 1999 also found that</p><p>Total Petroleum Hydrocarbon concentrations nearthe workshop buildings were 47,600 mg kgy1, thehighest for the Casey region.</p><p>In response to recommendations made by Deprez .et al. 1994, 1999 , clean-up of Thala Valley tip was</p><p>initiated. In 19951996, large rubbish material was</p></li><li><p>( )I. Snape et al.rCold Regions Science and Technology 32 2001 157174 161</p><p> .Fig. 3. Examples of the main hazardous waste types associated with abandoned tips and fuel spills in Antarctica. a shows the front of the .disturbed Thala Valley tip that is in contact with marine waters in Brown Bay in seasons of extensive melt. b illustrates one of the sources</p><p>of petroleum spills at the contaminated Fuel Farm site at the abandoned Wilkes station. Spills of this type are not single catastrophes butrather occur gradually drum-by-drum as the containers rust. It is also important that spills permeate into porous sediments almostimmediately and cannot therefore be simply mopped-up by surface mats after the event.</p><p>extracted from the tip and consigned to a landfill inTasmania. The remaining material in Thala Valley,consisting of small fragments of rubbish and fineloose sediment, was pushed into a stockpile on theedge of Brown Bay until further management action</p><p> .could be decided Snape and Riddle, 1998 .In a post-clean-up assessment of the site, Snape et .al. 1998, 2000, 2001b concluded that the 1995</p><p>1996 remediation works did not remove the bulk ofthe contaminants from the site. Contaminant concen-trations in the active layer are believed to be highernow than before the clean-up attempt. The process ofremoving large waste fragments from the surface haseffectively redistributed and concentrated the mostchemically reactive fines fraction into the activelayer. Snape et al. further concluded that partial</p></li><li><p>( )I. Snape et al.rCold Regions Science and Technology 32 2001 157174162</p><p>removal of the tip material without controlling andtreating the surface and subsurface waters that movedthrough the site would inevitably have caused agreater than normal contaminant flux into BrownBay during the ex...</p></li></ul>

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