The Remediation of Chemical Groundwater Contamination at Harwell

The Remediation ofChemical GroundwaterContamination at HarwellReport to the Harwell Chilton CampusLocal Stakeholder Group:March 2009Harwell Groundwater Containment Plant

The Remediation of Chemical Groundwater Contamination at HarwellLSG Groundwater Report ii March 2009

The Remediation of Chemical Groundwater Contamination at HarwellTHE REMEDIATION OF CHEMICAL GROUNDWATERCONTAMINATION AT HARWELLIssue Date Author Checked by Approved byA March 09 Name Jon Blackmore Paul Atyeo Ken HeiderRole Project Manager Senior Project Closure DirectorManagerSignatureDateLSG Groundwater Report iii March 2009

The Remediation of Chemical Groundwater Contamination at HarwellLSG Groundwater Report iv March 2009

The Remediation of Chemical Groundwater Contamination at HarwellEXECUTIVE SUMMARYChemical contamination of groundwater at Harwell was first identified in the late1980s. This contamination, principally by chlorinated organic chemicals, wassubsequently linked to the disposal of waste chemicals in unlined chalk pits atHarwell. These waste disposal pits were located at the Southern Storage Area(SSA), formerly used by the RAF for munitions storage, and the Western StorageArea (WSA). RSRL has subsequently undertaken a major programme of work toinvestigate and deal with the contamination. This report presents developments inrelation to the groundwater programme at Harwell during 2008.The groundwater containment plant (HGCP) continues to maintain effective hydrauliccontainment at the WSA. This was confirmed by the water level measurements madeduring 2008.HGCP has realised improvements over the original plant in terms of health andsafety, energy consumption, waste generation and ease and flexibility of operation.Energy consumption is 30% of that used by the old groundwater plant.Remediation of the unsaturated zone at the WSA has continued during 2008,removing a further 795 kg of contaminants. The total removed by the unsaturatedzone project is now nearly 1.8 tonnes. Up to three further phases of unsaturatedzone remediation are planned.The total mass of contamination removed by the different components of theremediation programme is now estimated to be approximately 11 tonnes.LSG Groundwater Report v March 2009

The Remediation of Chemical Groundwater Contamination at HarwellGLOSSARYAODAquiferBoreholeChlorinatedsolventsGACGroundwaterLevelHGCPRemediationSSASVETEVEUnsaturatedzoneVacuumextractionVOCsWater TableWSAZone ofwater tablefluctuationAbove Ordnance Datum. The height of a point (eg the water table or groundlevel) above mean sea level (the Newlyn datum, since 1921), usually expressedin metres (eg 120 m AOD).An aquifer is a permeable rock that stores and allows groundwater flow readilythrough it.A deep, narrow vertical shaft used for the extraction or monitoring of groundwateror soil vapour. Typically, boreholes drilled at Harwell in relation to the chemicalgroundwater contamination programme are between 50 and 200 mm in diameterand up to 55 metres deep.Liquids used to remove grease from metal components in engineering workshopsand also as laboratory reagents. These were disposed of in large quantities to thewaste pits at the SSA and WSA. The principal groundwater contaminants are allchlorinated solvents:• carbon tetrachloride;• chloroform;• 1,1,1-trichloroethane;• trichloroethene; and• tetrachloroethene.Chlorinated solvents form part of a larger grouping of chemicals called VOCs(see below).Granular Activated Carbon. A product often derived from coal or coconut husks,which readily adsorbs organic chemicals. Widely used in many industries for thetreatment of contaminated liquids and gases.See Water Table.Harwell Groundwater Containment Plant – the replacement water treatment plantat the WSA, which became fully operational in June 2007.In the context of pollution, used to describe works carried out to reduce theimpact of the pollution.Southern Storage Area. The former RAF bomb dump, used for wastemanagement and disposal operations by UKAEA from the 1940s to the 1970s.Soil Vapour Extraction. A technique used for removing VOC contamination fromsoils and rocks, usually above the water table.Thermally enhanced vacuum extraction. Collective term for a group of techniqueswhich use heat energy to improve the rate of contaminant removal using SVE. Inthe case of the WSA project, conductive heating elements are used to heat thechalk above the water table.The part of the aquifer above the water table.See SVE.Volatile Organic Compounds. A broad grouping for a range of different organiccompounds characterised by their readiness to evaporate under normalconditions. Many of the chlorinated solvents fall within this category.That level beneath the land at which the pores of rock or soil become completelyfull of groundwater. Also referred to as the groundwater level.Western Storage Area. Licensed landfill, used for the disposal of chemical wastesfrom the 1970s to 1980s.The part of the chalk that is between the lowest and highest observed water tablelevels. At Harwell, the Chalk water table fluctuates by up to 18 metres, from thelowest to highest levels. Depending on the elevation of the water table, this partof the aquifer may be available for SVE or TEVE.LSG Groundwater Report vi March 2009

The Remediation of Chemical Groundwater Contamination at HarwellCONTENTSEXECUTIVE SUMMARY............................................................................................ 5Glossary ..................................................................................................................... 61 Introduction.......................................................................................................... 12 Groundwater Levels ............................................................................................ 33 Groundwater Containment, Western Storage Area ............................................. 64 Unsaturated Zone Remediation, WSA............................................................... 105 Groundwater Monitoring.................................................................................... 126 Summary ........................................................................................................... 15FiguresFigure 1 Location of the Western and Southern Storage Areas at Harwell ................ 2Figure 2 Geological map of the Harwell Area ............................................................. 2Figure 3 Groundwater levels (“water table”) in the Chalk at Harwell (Borehole HWS9),1991 to 2009 ................................................................................................ 4Figure 4 Annual variation in groundwater levels in Borehole HWS9 during 2007 and2008 in comparison to data since 1991........................................................ 4Figure 5 Map of Harwell site showing groundwater levels and groundwater flowdirections in the Chalk aquifer, April & October 2008................................... 5Figure 6 Schematic representation of the hydraulic containment of groundwatercontamination at the Western Storage Area................................................. 6Figure 7 Annual quantities of groundwater treated and contaminant mass removedby the Western Groundwater Plant .............................................................. 9Figure 8 Total contaminant concentrations in the water pumped into the WesternGroundwater Plant ....................................................................................... 9Figure 9 Illustration of remediation techniques for the unsaturated zone and zone ofwater table fluctuation at the Western Storage Area .................................. 11Figure 10 Installation of conductive heating elements in boreholes for the TEVEsystem........................................................................................................ 11Figure 11 Total contaminant concentrations (CHCs - chlorinated hydrocarbons),April and October 2008 .............................................................................. 13Figure 12 Variation in total contaminant concentration with time in boreholeHWS1 (150 metres north of the WSA) ....................................................... 14Figure 13 Variation in total contaminant concentration with time in boreholeHWS10 (200 metres southeast of the WSA) .............................................. 14Figure 14 Summary of contaminant mass removal by year ................................ 15LSG Groundwater Report vii March 2009

The Remediation of Chemical Groundwater Contamination at HarwellLSG Groundwater Report viii March 2009

The Remediation of Chemical Groundwater Contamination at Harwell1 INTRODUCTIONContamination of the groundwater beneath the Harwell site was first detected in late 1989.Investigations revealed the presence of chlorinated organic solvents in the groundwater,which were linked to disposal of wastes in a number of shallow, unlined pits at theSouthern (SSA) and Western (WSA) Storage Areas (Figure 1). Both disposal sites arelocated on the Chalk aquifer, as indicated by the areas underlain by green shading onFigure 2.The Southern Storage Area (SSA) was the older of the two disposal sites. It was locatedbetween Harwell site and Chilton, and was first used for munitions storage when Harwellwas a Second World War RAF airfield. The SSA was used immediately after the SecondWorld War for the early waste management operations of the former Atomic EnergyResearch Establishment at Harwell. Chemical wastes were disposed of on the site until1970, when operations were transferred to a new site, located on the western boundary ofthe main Harwell site.This second site was the Western Storage Area (WSA), which included a compound with25 unlined pits. The site was originally licensed under the Control of Pollution Act 1974 byOxfordshire County Council. The pits on the site were used for the disposal of variouschemical wastes, including chlorinated solvents and other organic chemicals. Thechlorinated solvent disposals occurred over the period from 1970 to 1977; after this time,wastes were sent off-site for incineration. The site is now licensed as a closed landfill bythe Environment Agency (EA).Following the discovery of the groundwater contamination, a programme of work wasimplemented to delineate, contain and then remediate the groundwater contamination andits sources. An extensive programme of groundwater monitoring is also undertaken, inconjunction with the EA.This report, covering the period January to December 2007, provides an annual update onthe status of the groundwater programme to the March 2009 meeting of the Harwell-Chilton Campus Local Stakeholder Group (LSG).LSG Groundwater Report 1 March 2009

The Remediation of Chemical Groundwater Contamination at Harwell© Crown Copyright 2005. All rights reserved. OrdnanceSurvey Licence Number 10047376.Figure 1Location of the Western and Southern Storage Areas at HarwellFigure 2Geological map of the Harwell AreaLSG Groundwater Report 2 March 2009

The Remediation of Chemical Groundwater Contamination at Harwell2 GROUNDWATER LEVELSThe variation in groundwater levels (the “water table”) with time in the Chalk aquifer underHarwell site is shown in Figure 3. These data relate to borehole HWS9 (Figure 1), whichhas been monitored weekly since 1991. Groundwater levels are relevant to themanagement of groundwater contamination for a number of reasons:1. Historically, as groundwater levels have risen (usually in the late autumn and winter)contamination has been washed out from the Chalk beneath the waste pits at theWSA, resulting in higher contaminant concentrations in the groundwater captured bythe containment plant.2. Away from the WSA, the relationship between groundwater levels and contaminantconcentrations is the opposite. At times of high groundwater levels, concentrations arelowest, because of dilution of the contaminants by rainfall entering the aquifer. Whengroundwater levels are low, contaminant concentrations rise.3. In the Chalk aquifer beneath the northern part of the Harwell site, the direction ofgroundwater flow changes depending on the groundwater levels. At times of highgroundwater levels, water flows from the springs at the top of the Lydebank Brook,resulting in groundwater flows to the north from much of the site. As the groundwaterlevels fall flow from the springs stops and the dominant groundwater flow directionchanges to the east and southeast. Groundwater flows beneath the southern part ofthe Harwell site do not show the same seasonal change in direction.The peak groundwater level recorded in borehole HWS9 during 2008 was 110.8 m AOD,recorded on 25 March (Figure 3). Groundwater levels then dropped until late May/EarlyJune, when groundwater levels rose in response to heavy rainfall. Met Office data forOxford show that the rainfall total for May and June 2008 was 60% above average 1 . Thiswas the second successive year in which summer recharge of groundwater had occurred,something not seen since collection of groundwater level data began at Harwell in 1990.Figure 4 shows groundwater level data for borehole HWS9, re-plotted to allow comparisonof data for each year. During the summer, groundwater recharge usually does not occurbecause rainfall either evaporates from the surface or is utilised by plants. However,Figure 4 shows that groundwater levels increased by 3.2 metres in response to heavyrainfall in July 2007 and by 1.3 metres in June 2008.From July 2008 onwards, groundwater levels fell until early November, when groundwaterbegan to increase.The maps in Figure 5 show groundwater levels in the Chalk in April and October 2008.The solid lines are contours of equal groundwater level. The groundwater flow direction isapproximated by the arrows. These plots coincide with the major six-monthly groundwatersampling events undertaken by RSRL on site. April and October were selected as themain sampling events because they generally coincide with the highest and lowestgroundwater levels respectively.The patterns of groundwater flow seen in 2008 (Figure 5) were similar to those seen in2007. The groundwater level data show that the groundwater plant at the WSA maintainedeffective containment during 2008, continuing to prevent contaminated groundwatermoving away from the WSA.1Based on data for the period 1971-2000LSG Groundwater Report 3 March 2009

The Remediation of Chemical Groundwater Contamination at Harwell120Ground level: approx. 120 mAOD115groundwater level (metres AOD)110105100Total water table range approx. 18 metresWater Table (Chalk Aquifer)95Jan-91Jan-92Jan-93Jan-94Jan-95Jan-96Jan-97Jan-98Jan-99Jan-00Jan-01Jan-02Jan-03Jan-04Jan-05Jan-06Jan-07Jan-08Jan-09Jan-10Figure 3Groundwater levels (“water table”) in the Chalk at Harwell (BoreholeHWS9), 1991 to 2009120115Groundwater levelincrease due to heavyrain, June 200820072008Groundwater Level (m AOD)11010510095Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecFigure 4 Annual variation in groundwater levels in Borehole HWS9 during 2007and 2008 in comparison to data since 1991LSG Groundwater Report 4 March 2009

The Remediation of Chemical Groundwater Contamination at HarwellApril 2008October 2008Figure 5Map of Harwell site showing groundwater levels and groundwater flowdirections in the Chalk aquifer, April & October 2008LSG Groundwater Report 5 March 2009

The Remediation of Chemical Groundwater Contamination at Harwell3.2 Groundwater Plant Operations 2008The groundwater containment plant at the SSA was decommissioned in April 2002, withthe agreement of the EA. This followed the successful completion of the SSA landremediation project.The original hydraulic containment plant at the WSA became fully operational in 1994. Theneed for a replacement plant was identified several years ago because the original planthad reached the end of its design life, and predictions, based on extrapolation of themonitoring data for the original plant, indicated that a containment plant could be neededuntil around 2025.The replacement plant, referred to as Harwell Groundwater Containment Plant (HGCP),has been operating very successfully since June 2007.HGCP uses granular activated carbon (GAC) to remove the contaminants from thegroundwater. GAC is used in domestic water filters, as well as many other applications. Itis very effective at removing organic chemicals from water, and is robust and costeffective.The original groundwater plant at the WSA used GAC to effect water treatment, but inconjunction with a process called air stripping. However, contaminant concentrations in thegroundwater at the WSA have been successfully reduced to a level where liquid phaseGAC treatment alone is viable. This has simplified the design, operation and regulation ofHGCP, resulting in significant cost and environmental benefits. As an example, the airstripping system on the original plant required the operation of a 27 kW heater, and this isnot needed in HGCP.The liquid phase GAC filters themselves are an improvement over those used on theoriginal plant, which were fixed vessels. Removal of the spent GAC filter medium fromthese filters required personnel to enter the vessels. Although these operations werealways managed safely, the opportunity to eliminate industrial hazards such as confinedspace working and working at height was taken with HGCP.When the GAC used on HGCP requires replacement, the entire filter unit is transported ona special lorry to a regeneration plant. Here the GAC is removed without the need forpersonnel to enter the vessel. The GAC is then treated to remove and destroy thecontaminants. The regenerated GAC is returned to the vessel and the vessel deliveredback to the plant at Harwell. No interruption to the operation of HGCP is needed duringthis process, in contrast to the GAC change operation on the old plant, which required ashutdown of up to five days.Overall, the replacement plant offers the following improvements over the original plant:• Industrial safety hazards eliminated (no routine confined space working or working atheight);• Lower energy consumption (the electricity used by HGCP is around 30% of that usedby the original plant);• Minimal waste generation (the GAC is regenerated rather than being sent to landfill);• Ease and flexibility of operation (flows can be precisely specified for each borehole,and the plant can be monitored and operated remotely via a laptop PC).LSG Groundwater Report 7 March 2009

The Remediation of Chemical Groundwater Contamination at HarwellHGCP became fully operational in June 2007 and the original groundwater plant wasdemolished in February 2008.During 2008, HGCP was operational for over 99.5 % of the time, well above the targetfigure of 95 %. Sustained operation of the plant is required to ensure containment of thecontaminated groundwater. The closed contours around the WSA in both plots on Figure 5indicate that HGCP continues to be highly effective in maintaining hydraulic containment.The total volume of water treated by the WSA groundwater plants in 2008 was nearly480,000 m 3 (Figure 7). The total volume of water treated as a result of the WSA hydrauliccontainment operations since 1993 is now 5.6 million cubic metres.The total mass of contamination removed by the plant during 2007 was 71 kg (Figure 7), adecrease over the figure for 2007. Contaminant concentrations in the water treated byHGCP (the red lines on Figure 8) were initially higher than those for the old groundwaterplant, but have now stabilised at levels similar to those recorded in the final period ofoperation of the original plant.Overall, groundwater containment operations have removed 5.75 tonnes of contaminationsince 1993, although it is important to note that the primary role of the plant is containmentof the contaminated groundwater.The groundwater containment operation at the WSA plant forms part of a programme ofworks that UKAEA is carrying out to tackle the contamination. Other components of theprogramme include:• Excavation of the WSA chemical pits. This complex project was safely completed in2004.• Removal of contamination from the Chalk below the pits (“Unsaturated ZoneRemediation”) – see Section 4.• Enhancement of HGCP to facilitate pumping of contaminated groundwater from areasto the north of the WSA, where contaminant concentrations have reduced more slowlythan elsewhere.Operation of HGCP is regulated by the Environment Agency (EA) under the terms of aWaste Management Licence (EA WML 86165), an Abstraction Licence (28/39/18/0097)and a Discharge Consent (CAWM.0231). During 2008/09 applications were submitted totransfer these permits, and the Waste Management Licence for the closed landfill site atthe Western Storage Area (EA WML 86127), from UKAEA to Research Sites RestorationLimited (RSRL). These transfers were all successfully implemented by the EA to takeeffect from 2 February 2009, the date from which RSRL became the legal entityresponsible for these permits.LSG Groundwater Report 8 March 2009

The Remediation of Chemical Groundwater Contamination at HarwellVolume of groundwater treated (m3)500,000450,000400,000350,000300,000250,000200,000150,000100,00050,000Volume of groundwater treated in yearContaminant mass removed in year2,0001,8001,6001,4001,2001,000800600400200Contaminant mass removed (kg)0019931994199519961997199819992000200120022003200420052006200720082009Figure 7Annual quantities of groundwater treated and contaminant massremoved by the Western Groundwater Plant3500030000Old Groundwater Plant Inlet Concentration (ppb)New Groundwater Plant (HGCP) Inlet Concentration(ppb)Total VOC Concentration (ppb)2500020000150001000050000Jan-09Jan-08Jan-07Jan-06Jan-05Jan-04Jan-03Jan-02Jan-01Jan-00Jan-99Jan-98Jan-97Jan-96Jan-95Jan-94Figure 8Total contaminant concentrations in the water pumped into the WesternGroundwater PlantLSG Groundwater Report 9 March 2009

The Remediation of Chemical Groundwater Contamination at Harwell4 UNSATURATED ZONE REMEDIATION, WSAAn important component of the strategy for managing the groundwater contamination atthe WSA is the unsaturated zone remediation project. The unsaturated zone is the part ofthe chalk aquifer that lies above the water table (Figure 6). Several tonnes ofcontamination are known to be trapped in this zone, and this contamination will continue toact as a long-term source of groundwater contamination without remediation.The removal of the wastes from the WSA disposal pits was necessary before remediationof the unsaturated zone could begin. Drilling boreholes through the wastes would havebeen hazardous and could have spread the contamination. The pit contents were removedduring 2004.A very encouraging pilot scale study of various remediation techniques was carried out atthe WSA by AIG Engineering Ltd (“AIG”) in late 2005. The pilot scale study establishedthat a technique called soil vapour extraction (SVE), originally developed in the USA butnow widely applied in the UK, could be successfully used to remove contamination fromthe unsaturated zone.Figure 9 illustrates how SVE works. Using vacuum pumps, air is drawn through cracks andfissures in the chalk via boreholes drilled into the unsaturated zone. Volatile contaminantsare drawn out with the air, and are adsorbed onto GAC filters.In addition to the basic “cold” SVE technique, a trial was carried out of thermally enhancedvacuum extraction (TEVE). In TEVE, electrodes (shown during installation in Figure 10)are used to heat the rock, which can increase the clean up rate and can also accesscontamination that would not be removed without the thermal treatment.As the pilot scale study was very succesful, full scale unsaturated zone remediation wasimplemented in 2006. Three operational phases have taken place to date.Remediation of the unsaturated zone at the WSA has removed nearly 1,800 kg ofchemical contaminants. This material has been recovered from the rock beneath four ofthe twenty-five former disposal pits. Following a review of historical data, and testingcarried out during the past year, it has been established that unsaturated zone remediationat five further pit locations has the potential to recover significant contaminant mass. Up tothree further phases of work are planned to undertake remediation in these areas.It had been planed to install an impermeable cap over the whole of the WSA oncompletion of the remediation works. This requirement is under review with theEnvironment Agency, because the benefits of the cap are not clear if the much of theremaining unsaturated zone contamination has been removed.During 2007, the WSA Unsaturated Zone Remediation project was approved as aTechnology Demonstration Project by CL:AIRE 2 . CL:AIRE is a respected, independentnot-for-profit organisation established to stimulate the regeneration of contaminated land inthe UK by raising awareness of, and confidence in, practical and sustainable remediationtechnologies. A Technology Demonstration Report is currently being finalised on theunsaturated zone remediation work at the WSA and will be published by CL:AIRE later thisyear.2 CL:AIRE - Contaminated Land: Applications in Real EnvironmentsLSG Groundwater Report 10 March 2009

The Remediation of Chemical Groundwater Contamination at HarwellFigure 9Illustration of remediation techniques for the unsaturated zone and zoneof water table fluctuation at the Western Storage AreaFigure 10 Installation of conductive heating elements in boreholes for the TEVEsystemLSG Groundwater Report 11 March 2009

The Remediation of Chemical Groundwater Contamination at Harwell5 GROUNDWATER MONITORINGThe current groundwater monitoring programme undertaken by RSRL at Harwell involvescollection and analysis of groundwater samples on a quarterly basis. In April and October,a site-wide sampling programme is carried out, with samples being taken from eighty fiveboreholes. In January and July groundwater quality is monitored in twenty sevenboreholes, mainly located close to the Western and Southern Storage Areas. Thisgroundwater sampling is co-ordinated with the off-site sampling undertaken by theEnvironment Agency (EA), so that an overall picture of groundwater contamination in thearea is obtained.The results of the site-wide groundwater sampling exercises carried out in April andOctober 2008 are presented in Figure 11. These maps include data collected by both theEA and RSRL.For each location where a sample was obtained, a coloured symbol is shown on the mapat the appropriate location, with the following meanings:• Red symbols: these show sites where at least one of the chlorinated hydrocarbonswas present at concentrations above the relevant drinking water standard;• Amber symbols: these indicate locations where chlorinated hydrocarbons werepresent at concentrations below the drinking water standard, but above the limits ofdetection;• Green symbols: these show sites where no chlorinated hydrocarbons were detected.No notable changes were observed in trends for data collected in either April or October2008. In many parts of the contaminant plume, there continues to be a downward trend inconcentrations, albeit with considerable seasonal variation.Figure 12 and Figure 13 show the variations in the total concentration of contaminants attwo locations downgradient (downstream in terms of groundwater flow) of the WSA. Thesedemonstrate that, although seasonal effects on contaminant concentrations can be seen,the overall trend at these locations is downwards. This is because hydraulic containmenthas prevented contaminated groundwater from moving away from the WSA.Following discussions with the EA, additional monitoring boreholes will be drilled during2009/10. These will be used to refine the conceptual model to the east of the Harwell site.LSG Groundwater Report 12 March 2009

The Remediation of Chemical Groundwater Contamination at HarwellApril 2008October 2008Figure 11 Total contaminant concentrations (CHCs - chlorinated hydrocarbons),April and October 2008LSG Groundwater Report 13 March 2009

The Remediation of Chemical Groundwater Contamination at Harwell45004000Western Groundwater PlantCommissionedHWS1Concentration (parts per billion)3500300025002000150010005000Jan-10Jan-09Jan-08Jan-07Jan-06Jan-05Jan-04Jan-03Jan-02Jan-01Jan-00Jan-99Jan-98Jan-97Jan-96Jan-95Jan-94Jan-93Jan-92Figure 12 Variation in total contaminant concentration with time in borehole HWS1(150 metres north of the WSA)80007000Western Groundwater PlantCommissionedBorehole HWS10: Total contaminant concentrationConcentration (parts per billion)6000500040003000200010000Jan-10Jan-09Jan-08Jan-07Jan-06Jan-05Jan-04Jan-03Jan-02Jan-01Jan-00Jan-99Jan-98Jan-97Jan-96Jan-95Jan-94Jan-93Jan-92Figure 13 Variation in total contaminant concentration with time in boreholeHWS10 (200 metres southeast of the WSA)LSG Groundwater Report 14 March 2009

The Remediation of Chemical Groundwater Contamination at Harwell6 SUMMARY• The groundwater containment plant (HGCP) continues to maintain effective hydrauliccontainment at the WSA. This was confirmed by the water level measurements madeduring 2008.• HGCP has realised improvements over the original plant in terms of health and safety,energy consumption, waste generation and ease and flexibility of operation. Energyconsumption is 30% of that used by the old groundwater plant.• Remediation of the unsaturated zone at the WSA has continued during 2008, removinga further 795 kg of contaminants. The total removed by the unsaturated zone project isnow nearly 1.8 tonnes. Up to three further phases of unsaturated zone remediation areplanned.• The total mass of contamination removed by the different components of theremediation programme to date is summarised in Figure 14.Cumulative VOC Mass Removed (kg)1200011000100009000800070006000500040003000TotalSVE/TEVEWestern Groundwater PlantSSA PitsWSA PitsSouthern Groundwater Plant200010000Pre-941994/951995/961996/971997/981998/991999/002000/012001/022002/032003/042004/052005/062006/072007/082008/09Figure 14 Summary of contaminant mass removal by yearLSG Groundwater Report 15 March 2009