Design, installation and preliminary testing of a permeable reactive barrier for diesel fuel remediation at Casey Station, Antarctica

Cold Regions Science and Technology 96 (2013) 96–107

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Design, installation and preliminary testing of a permeable reactive barrier for diesel fuel remediation at Casey Station, Antarctica K.A. Mumford a,⁎, J.L. Rayner b, I. Snape c, S.C. Stark c, G.W. Stevens a, D.B. Gore d a

Department of Chemical and Biomolecular Engineering, University of Melbourne, Australia CSIRO Land and Water, Private Bag No. 5, Wembley, Western Australia 6913, Australia Australian Antarctic Division, Department of Sustainability, Environment, Water, Population and Communities, 203 Channel Highway, Kingston, TAS 7050, Australia d Department of Environment and Geography, Macquarie University, NSW 2109 Australia b c

a r t i c l e

i n f o

Article history: Received 19 January 2013 Accepted 14 June 2013 Keywords: Hydrocarbon capture Bioremediation Zeolite Granulated activated carbon

a b s t r a c t To minimize the environmental impact of a fuel spill a permeable bio-reactive barrier (PRB) was designed and installed at Australia's Casey Station. The PRB was designed to prevent further migration of a decade-old fuel spill during summer melt periods by intercepting catchment flow down-gradient of the spill. Catchment flow was intercepted using a PRB with a funnel and gate design. This is the first time a full-scale PRB has been designed and installed specifically for polar regions. This paper reports on the selection of a location for a PRB, and the subsequent design, installation and testing of the PRB throughout the first summer of operation at Casey Station, Antarctica. The PRB was designed to test five different treatments. Each treatment contained three zones: a zone of slow fertilizer release to enhance biodegradation; a zone for hydrocarbon and nutrient capture and degradation; and a zone for cation capture to contain excess nutrients released in the first zone. The materials used within these zones were required to have no adverse impact on the environment; be permeable enough to capture the entire catchment flow during the peak summer melt period without overtopping; have the ability to deliver nutrients in a controlled way; and have sufficient residence time to fully capture migrating hydrocarbons. The first zone tested different types of slow release fertilizer: MaxBac™, ZeoPro™ and zeolite preconditioned with ammonium. Sand was used for a control. For the capture of hydrocarbons the second zone contained granulated activated carbon and either: Raw St Cloud zeolite, sodium Australian zeolite, or ZeoPro. The capture of cations in the third zone was achieved with sodium Australian zeolite. The grain size of each material was relatively uniform and large enough (c. 0.4 to 3.5 mm) to keep the water holding capacity to a minimum at the end of the melt period, thereby maximizing permeability at the onset of the next season's melt. The PRB was keyed into the permafrost with insulation to limit the potential for flow bypassing the treatment zone, and sized to intercept the maximum flux of melt water through the upper catchment where the spill occurred. Testing of the nutrient delivery systems was performed by pumping contaminated water from a down-gradient melt lake through the PRB. Nutrient sampling indicated that all the nutrient sources chosen were able to supply ammonium to the hydrocarbon capture zone for 4 to 5 years at concentrations >1 mg L−1 (N as NH+ 4 ) and the ion exchange materials (zeolites) were found to maintain ammonium concentrations at a more consistent concentration than the coated nutrient material MaxBac™. Zeolite also effectively prevented off-site migration of ammonium. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Popular belief considers Antarctica to be a land of unspoilt wilderness. While this is true of the majority of the continent, historical environmental contamination surrounds the majority of scientific stations, which are mostly located in the 0.05% of coastal Antarctica that is ice free. These ice-free, coastal areas contain more diverse ecosystems ⁎ Corresponding author. E-mail address: [email protected] (K.A. Mumford). 0165-232X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.coldregions.2013.06.002

than other parts of the Antarctic continent, and hence the impact on biodiversity can be much larger than estimated by land-area alone (Poland et al., 2003). Effective remediation of contaminated sites in polar regions involves a myriad of scientific and engineering challenges. These challenges include, but are not limited to: extremely low temperatures, seasonally frozen ground, highly variable surface and subsurface water flows during summer, and logistical difficulties associated with undertaking large projects in remote locations. Consequently, remediation methods used in temperate climates are not necessarily suited to

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cold, remote environments and often require significant modification for successful implementation in polar regions. Permeable reactive barriers are one technology that has shown significant potential for use in cold environments (Gore, 2009; Snape et al., 2001). PRBs are an in situ passive intervention remediation technology in which contaminated water passes through reactive material that either transforms the contaminant to a less harmful compound or immobilizes it. The contaminant type, choice of reactive media, nutrient availability and microbial activity all influence abiotic and biotic transformation processes. There are many examples of abiotic degradation systems and PRBs. The most successful and widespread of these contains zerovalent iron, which has been shown to treat chlorinated solvents such as trichloroethene (Gillham and O'Hannesin, 1994), trace metals including hexavalent chromium (Pratt et al., 1997) and uranium (Fiedor, Bostick et al., 1998), and inorganic contaminants like nitrate (Huang and Zhang, 2004). Biotic barriers, generally known as permeable bio-reactive barriers, allow a greater scope for transformation of a wider range of compounds. These barriers use microbes to metabolize contaminants by either manipulation of the redox conditions or via provision of substrates or nutrients to promote biodegradation. As such, bioreactive barriers not only have to meet general PRB requirements regarding appropriate selection of grain size, permeability and stability, but they must also ensure optimal conditions for micro-organism growth including appropriate oxygen concentration, nutrient availability, pH and ionic strength at the prevailing soil temperature and moisture content. Many materials have been developed to sorb hydrocarbons from waste water streams (Northcott et al., 2010), but relatively few have been trialed in full-scale permeable bio-reactive barrier systems. Of these, a sequential bio-reactive barrier comprised of sand and granulated activated carbon was used to degrade polycyclic aromatic hydrocarbons (PAH) and BTEX compounds (benzene, toluene,

ethylbenzene and xylene) (Gibert et al., 2007); and a funnel and gate bio-reactive barrier using peat as the reactive medium in addition to an air-sparging system, was used to degrade toluene, ethylbenzene, xylene and n-alkanes (C6–C36) (Guerin et al., 2002). However, no known permeable bio-reactive barriers have been implemented in cold regions where freeze–thaw cycling occurs. A fuel spill occurred at Australia's Casey Station in 1999 (Snape et al., 2006). A PRB was determined to be the most suitable technology to prevent off-site migration. This paper reports on further delineation of the extent of fuel contamination, the selection of a suitable location for a PRB within the catchment, and the subsequent design, installation and testing of the PRB within the first summer of operation. Since this was the first fully operational PRB to be installed in a polar region the PRB was designed to test five different treatments. Each treatment had a zone of slow fertilizer release to enhance biodegradation, a zone for hydrocarbon capture and biodegradation, and a zone for cation capture to contain excess nutrients released in the first zone. 2. Methodology 2.1. Site characterization Casey Station is situated on a coastal, ice-free rock and gravel peninsula in the Windmill Islands, East Antarctica (approximately 66° 17′S, 110° 32′E (Fig. 1). It runs on power provided by diesel powered generators located in the Main Power House (MPH). Following a spill in 1999, the soil surrounding the MPH was contaminated with dieselrange fuel consisting of approximately 80% Bergen distillate and 20% Aviation Turbine Kerosene (ATK). The average annual water-equivalent precipitation at Casey Station is 210 mm, and over the last 14 years has ranged from 150 mm to 350 mm. The sediment or ‘soil’ structure, texture and depth are highly variable (Fig. 2) across the site, consisting of poorly sorted sand, silt and gravel with cobbles, boulders and areas of outcrop. The maximum

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Fig. 1. Location of main power house fuel spill site, new Casey Station (c), windmill islands (b), Antarctica (a).

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2.2. PRB design

Fig. 2. Vertical profile of soil showing the variability in texture and depth. The tape measure is extended to 1 m.

depth of soil is 1 m and underlying this is weathered rock. This mixture of soil materials gives highly variable hydraulic and chemical properties as well as variations in the depth of permafrost. Observations in the field indicate the water conducting zone is much less than 1 m in depth and mostly confined to the top 0.25 m, but only when snow cover has melted. When snow cover is present, the surface soil remains frozen and restricts the downward migration of melt water which moves predominantly as surface run-off with little interaction with the spilt fuel. As the thaw progresses deeper into the soil profile, interflow leads to mobilization and migration of the fuel. This process would be exacerbated during any future excavation and remediation of the source zone; hence the PRB provides an additional safeguard for these activities.

2.2.1. PRB installation The PRB was constructed from five modified cage pallets, with the dimensions of 1.8 L × 1.1 W × 0.75 H m. The size of the reactive zone was designed to intercept the entire catchment flow, with the capacity increased by a factor of three to allow for peak flows caused by the addition of blown snow into the catchment and consecutive days of high snow melt. The annual flux of water through the catchment was estimated from the area of the upper catchment (3800 m2, Fig. 3), and the average annual precipitation rate of 210 mm. This yields approximately 800 ± 200 m3 yr−1. Flow occurs on 30 to 60 days per year based on field observations, giving a flow rate of 13 to 26 m3 d−1. Using five cages with the above dimensions and, from column tests, a measured saturated hydraulic conductivity (Ksat) of the PRB material of 125 m d−1, the expected elevation of water in the PRB was between 0.1 and 0.2 m, therefore occupying the bottom third of the PRB. This estimate is likely to be conservative as it does not account for losses by evaporation or sublimation. To separate each PRB treatment, a 2 mm galvanized steel sheet was placed between each cage. Nylon mesh (400 μm) was stapled to wooden frames, and placed at the entry and exit of each cage to retain granular material but still allow flow through the cells (Bowman et al., 1999). To ensure the PRB thawed prior to the onset of run-off, three 118 m lengths of heat trace were woven on the underside of a square support mesh (50 mm) and placed at 0.2, 0.4 and 0.6 m below the PRB surface. To prevent the permafrost beneath the PRB from thawing and allowing groundwater to flow beneath the treatment zone, 100 and 200 mm thick Styrofoam insulation was placed on the ends and beneath the PRB, respectively. Temperature sensors were placed throughout the barrier at multiple depths, including within and underneath the insulation, to assist in controlling barrier temperature and monitor the integrity of the permafrost beneath

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Fig. 4. Plan view of monitoring array in PRB.

the PRB. The whole system was placed on a 100 mm thick concrete pad to ensure that it was installed level thereby allowing even distribution of flow across each of the treatments. In addition, 40 stainless steel multiports (MP001 to MP040) were used to collect water samples at 700, 500, 300 and 100 mm below the top surface of the PRB media (Figs. 4 and 5). Holes were also cut in the mesh supporting the heat trace alongside each of the multiports to allow coring of the material without damaging heat trace. The PRB was a funnel and gate style (Fig. 6). The funnel is made of 2 mm thick high-density polyethylene impervious membrane which is 0.9 m deep with hydraulic drainage material placed in front directing groundwater into the treatment area. The wings of the funnel have a 1:20 gradient to capture and direct water flow toward the PRB. Drainage material was placed at the entry of the gate to evenly distribute groundwater across the treatment zones. Excavation of the PRB and wings was carried out with a 25 t excavator with 600 mm bucket, pneumatic hammer and single tine ripper. Piezometers were installed in front of the funnel wings and to the front and behind the barrier to measure ground water elevations. In total thirty-three piezometers were installed: P1 to P19 in 2005 and P20 to P33 in 2006 (Fig. 6).

2.2.2. Reactive material The material in each of the five cages had to perform three functions: nutrient delivery, hydrocarbon sorption and removal of excess nutrient cations. To achieve this, each cage was divided into three zones (Fig. 7). The nutrient source was placed in the first zone of each treatment sequence: MaxBac™, ZeoPro™, ammonium Australian zeolite, or sand. The second zone contained hydrocarbon sorption material: Granulated Activated Carbon (GAC) plus Raw St. Cloud zeolite, ZeoPro™ and sodium Australian zeolite. The final zone contained sodium-activated

Depth (m)

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clinoptilolite zeolite to remove excess nutrient cations. This sequence was selected so that soluble nutrients would be supplied to the zone of highest hydrocarbon concentrations and where hydrocarbon degrading microbial communities were expected to develop. An oxygen delivery mechanism is also shown in Fig. 7. This was in the form of 7.5 m of 8 mm silicone tubing (2 mm wall thickness) woven around 50 mm-square steel mesh placed vertically within the cell. In order to measure oxygen concentrations, oxygen sensors (Figaro KE 25) (Patteron and Davis, 2008) were placed either side of this diffuser (Fig. 4). The nominal grain size chosen for all reactive materials used was 0.4 to 3.5 mm to ensure that the gate was more permeable than the surrounding soil both prior to and during the onset of the melt period. The saturated moisture holding capacity of the porous media used in the PRB was determined by estimating the mean pore diameter (dpore) from the mean particle diameter (d50) and applying the capillary rise equation approximated for water as hc = 15/r, where r is the mean pore radius in mm. Dullien (1979) suggested that the mean pore radius is approximately 0.4 d50/2, while Hubbert (1953) estimated this to be 0.125 d50/2. The calculated capillary rise for a range of grain sizes (Fig. 8) shows that for materials with a mean grain size of 0.5 mm, the hc is between 150 and 480 mm and any decrease in grain size below this leads to a rapid increase hc. This implies that the grain size should be coarser than this and relatively uniform in distribution to minimise the amount of water remaining in the PRB at the end of the season requiring thawing, to ensure adequate hydraulic conductivity prior to the onset of the following melt period.

2.2.3. Zone 1: nutrient release 2.2.3.1. MaxBac™ (Cage 1). MaxBac™ (Grace-Sierra Co., Milpitas, CA, USA) is a commercially-available controlled-release fertilizer consisting

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of 12.3% N as ammonium, 9.7% nitrate as N, 5.7% phosphorus as P2O5, 0.6% sulfur as SO4 and 0.5% calcium on a weight basis. It is encapsulated by a vegetable oil based resin coating (9% by weight). Water slowly permeates the coating, releasing nutrients into solution (Newman et al., 2006). The nutrient bearing compounds encapsulated in MaxBac ™ have been investigated, as well as the structural integrity (Gore and Snape, 2008). Previously, it was considered that the polymeric films of MaxBac™ were not suitable for conditions undergoing freeze–thaw processes, i.e. catastrophic failure of resin surface and release of nutrients into solution in an uncontrolled manner. Gore and Snape (2008) found this not to be the case and that moisture alone was sufficient to release nutrients, and the combination with freeze– thaw cycling does not significantly add to nutrient release. However, this also indicates that it is preferable to apply the controlled-release fertilizer to well-drained areas.

and other trace elements into the solution. The released cations exchange with ammonium and potassium located within the pores of the zeolite. The dissolved phosphate is directly available to the micro-organisms (Beiersdorfer et al., 2003; Ming and Allen, 2001). This reaction process is represented by Eqs. 1 and 2.

2.2.3.2. ZeoPro™ (Cages 2 and 3). ZeoPro™ (ZeoponiX Inc., Louisville, USA) is a commercially-available ammonium and potassium loaded zeolite (St. Cloud Mine, Winston, New Mexico) coated with synthetic apatite (calcium phosphate). The material selected was ZeoPro H™ which has a grain size of 8 × 40 mesh (0.4–2.4 mm). In this nutrient release system the apatite coating acts as a slow release fertilizer, dissolving and thereby introducing calcium, phosphorus,

• The mineral form of the apatite, i.e. the pKsp at 25 °C of hydroxyapatite, fluorapatite and brushite is 58, 60 and 6.6 respectively (where Ksp is the solubility product). • pH, the driving force for dissolution being the neutralization reactions between anions produced at the dissolving surface of the calcium phosphate particle and hydrogen ions present in the soil solution.

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Ca10 ðPO4 Þ6 ðOH Þ2 þ 6H2 O⇌10Ca

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2.2.4.2. Raw St. Cloud zeolite (Cages 1, 3, 4 and 5). This material is zeolite from the St. Cloud mine in Winston, New Mexico. It is the same zeolite used to make ZeoPro™. The grain size selected was the same as for ZeoPro H™ being 8 × 40 mesh (0.4–2.4 mm). 2.2.4.3. Sodium Australian zeolite (Cage 2). For details on this material refer to Zone 3: cation capture. 2.2.5. Zone 3: cation capture 2.2.5.1. Sodium Australian zeolite (all cages). Natural Australian zeolite (Castle Mountain zeolite, Quirindi, N.S.W. Australia) was converted into the sodium form prior to use in the PRB to adsorb excess ammonium cations from solution. The selection of sodium as the exchangeable cation was based on previous research. It had been found that the maximum ammonium exchange capacity of zeolite was highest in the sodium form compared to calcium, magnesium and potassium (Jama and Yucel, 1989; Milan et al., 1997). In addition, the kinetics of ammonium exchange with sodium is faster than for ions such as calcium (Hlavay et al., 1982).

Fig. 8. Capillary rise as a function of the mean grain size of porous media.

• Temperature, e.g. for a pH range of 3.7 to 6.7 and a temperature range of 5 to 37 °C, the following correlation for the solubility product of hydroxyapatite has been found valid (McDowell et al., 1977):

log K s ¼

−8219:41 −1:6657−0:098215T T

ð3Þ

2.2.6. Soil sampling The extent of the contaminated sediment was determined in November 2005 by sampling soil across a 40 × 40 m grid down slope of the MPH. The soil samples were sieved on-site to b3.4 mm and stored in brown glass jars with Teflon-lined lids at -18 °C. Results from soil sampling directed the placement of the PRB within the catchment.

• Moisture holding capacity and the availability of a calcium sink. This has been found to be the most important factor, with the zeolite within the ZeoPro™ system acting as a calcium sink. The interaction between calcium, potassium, ammonium and zeolite has been intensively investigated and has been found to be temperature dependent, with zeolite exhibiting an increased preference towards ammonium at low temperatures (Mumford et al., 2008). This results in a reduced rate of nutrient release at low temperatures which is beneficial for PRB systems operating in polar regions.

2.3. Water sampling

2.2.3.3. Sand (Cage 4). The sand was uniform quartz sand, 0.5 to 1.5 mm diameter with b 0.1% organic matter. This material was used as a control to compare the performance of the nutrient delivery materials.

2.3.1. PRB testing Water from a melt lake down-gradient of the PRB was pumped up-gradient to flow through the PRB. This tested the PRB efficacy in a ‘challenge’ test and at the same time treated any contaminated water downstream of the PRB. The cumulative flow of water through the PRB and the times at which water samples were collected for nutrient analysis are shown in Fig. 9.

2.2.3.4. Ammonium zeolite (Cage 5). Ammonium zeolite was prepared using natural Australian zeolite (Castle Mountain Zeolite, Quirindi, N.S.W., Australia) with a nominal 0.5 to 1.5 mm grain size. This zeolite was converted into the ammonium form by washing with 2 M ammonium chloride solution. Nutrient delivery is dependent on the presence of exchangeable cations in the melt water entering the barrier to displace ammonium cations from the pores of the zeolite. This differs from ZeoPro™ in which the calcium phosphate layer provides a source of exchanging cations.

Water samples were taken across the MPH site and from within the barrier periodically via the installed multiports. Due to the low water volume passing through the site, samples were only available to be collected at the lowest depth, i.e. 700 mm below ground surface. The samples were analyzed on-site, immediately after collection for pH, electrical conductivity (EC), and temperature (TPS WP-81 meter) and dissolved oxygen (DO) (TPS WP-82Y meter with YSI 5739 field probe).

2.4. Analytical techniques This section describes the methods employed for the chemical analysis of soil and water samples from the MPH site, and also samples of PRB material collected during the operational lifetime of the barrier. Unless specified, ‘PRB material’ can be substituted for ‘soil’ in the method descriptions.

2.2.4. Zone 2: hydrocarbon capture 2.2.4.1. Granulated activated carbon (all cages). Granulated activated carbon (GAC) derived from coconut husks were used to adsorb hydrocarbon contaminants (Picabiol TE 1.5, Pica USA, Inc., OH, USA). Activated carbon is very effective in the treatment of contaminated ground water. The highly adsorptive properties of GAC are due to a high surface area (500–1500 m2 kg−1) which can be related to its microporous structure, and a high degree of surface reactivity caused by surface oxide groups and inorganic impurities (Yue and Economy, 2005). The grain size selected for this work was 6 × 12 mesh (1.7–3.4 mm).

2.4.1. Total petroleum hydrocarbons (TPH) Hydrocarbons were extracted from wet, crudely homogenized samples of soil or PRB material into an organic solvent. For soil, a 10 g sub-sample was mixed with 10 mL water and 10 mL hexane in a 40 mL glass head-space vial and placed on a spinning wheel at ~ 60 rpm overnight. For the PRB material, a 4 g sub-sample was subjected to Accelerated Solvent Extraction (ASE) using a Dionex DX100 ASE to optimize recovery of analytes. Conditions for extraction were 1500 psi and 125 °C using 1:1 dichloromethane:acetone with Hydromatrix® (flux calcined diatomaceous earth) added as a drying agent. For both types of samples, an internal standard mixture was

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replicate analysis of samples, standard solutions and certified reference materials (PRIMUS multi-element anion and cation standard solutions, Fluka). During the first season of PRB operation, N and P dissolved nutrients (nitrite + nitrate, ammonia, and phosphate) in water samples were measured on-site using a Hach 2700 portable spectrophotometer employing Hach colorimetric methods (Methods 10023, 10031, and 8192) (Hach, 2007). Analyses performed on samples returned to Australia used ion chromatography (IC), colorimetry, flame atomic absorption spectroscopy (AAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). Limits of quantitation ranged from 1 to 5 μg L−1 for ICP-AES; 0.05 and 0.5 mg L−1 for anion and cation IC, respectively; 0.15 mg L−1 for colorimetry; and 0.2–0.4 mg L−1 for AAS. Analytical precision was typically ≤1–2% and the reproducibility of extractions was generally c. 10% or better, depending on sample heterogeneity.

Date (2006) Fig. 9. Cumulative flow through barrier during 2005/06 season.

added to each sample prior to extraction. This was composed of 1 mL dichloromethane spiked with the following compounds: 1,4dichlorobenzene, p-terphenyl and deuterated tetracosane (C24D50) at 50 mg L−1; and bromoeicosane and cyclooctane at 250 mg L−1. Following extraction, samples were allowed to settle (overnight for the ASE) before removal of the organic component. To determine the gravimetric moisture content, the extracted soil sample or a separate sub-sample of PRB material was dried at 105 °C for 24 h. Extracts were analyzed for TPH by gas chromatography using flame ionization detection (GC-FID; Agilent 6890 N with a split/ splitless injector) and an auto-sampler (Agilent 7683 ALS). Separation was achieved using an SGE BP1 column (35 m × 0.22 mm ID, 0.25 μm film thickness). Five microliters of extract was injected (1:5 pulsed split) at 310 °C and with 30 psi of helium carrier gas. After 1.3 min, the carrier gas pressure was adjusted to maintain constant flow at 1.3 mL min−1 for the duration of the oven program. The oven temperature program started at 50 °C (held for 3 min) and increased to 320 °C at 18 °C min−1 (held for 8 min). Detector temperature was 330 °C. TPH concentrations were determined using a calibration curve generated from standard solutions of Special Antarctic Blend diesel (SAB) and standard diesel. TPH was measured using the ratio of the total detector response of all hydrocarbons to the internal standard peak response. 2.4.2. Nutrients, electrical conductivity, PH Water-extractable nutrients in soil were analyzed following a 1:5 w/v aqueous extraction. A 5 g sub-sample of homogenized wet soil was mixed with 25 mL of Type 1 deionized water (Milli-Q, Millipore) in a 50 mL polypropylene centrifuge tube and tumbled for 1 h. The mixture was centrifuged for 10 min at 1000 rpm and the supernatant filtered through a 0.45 μm cellulose acetate-membrane cartridge filter (Minisart NML, Sartorius AG) into a clean tube for storage. An identical procedure, with deionized water replaced by 2 M KCl, was employed to determine KCl-extractable nutrients. The conductivity of water extracts of soil was measured using a WTW 197i conductivity meter calibrated with 0.01 M KCl. The pH of the extracts was measured using a Radiometer PHM 210 pH meter following calibration with standard pH 7 and 4 buffers. A variety of methods were employed to measure nutrient and sodium and calcium concentrations in water samples and in water and KCl extracts of soil. The concentration range of analytes was typically large and often it was necessary to dilute highly concentrated samples with deionized water to allow quantification. Quality control was established by the preparation of duplicate extracts and by

2.4.3. Anions — nitrite plus nitrate, phosphate Analysis of the nutrient anions nitrite, nitrate and phosphate (along with F−, Cl−, Br−and SO2− 4 ) in waters and water extracts of soil was carried out by ion chromatography using a Metrohm 761 Compact IC connected to a 766 IC Sample Processor. Separation of anions was achieved within 10 min by injecting a 20 μL sample onto a Metrosep A Supp 5 column with 3.2 mM Na2CO3/1.0 mM NaHCO3 eluent flowing at 0.7 mL min−1. A conductivity detector calibrated in the range 0–20 mg L−1 was employed following suppression of the background signal, and a Bischoff Lambda 1010 UV–Vis detector − used to quantify the presence of NO− 2 and NO3 in samples. 2.4.4. Cations — ammonium, sodium, calcium Several methods were employed for the analysis of cationic analytes (ammonium, sodium and calcium). For water samples and PRB water extracts collected during years 1 to 3 of the PRB's operation, + and Ca2+ (plus K+ and Mg2+) were determined by nonNH+ 4 , Na suppressed cation ion chromatography with conductivity detection using the IC system described above. A 20 μL sample was analyzed using a Metrosep C2-100 column and 4.0 mM tartaric acid/0.75 mM dipicolinic acid eluent flowing at 1.0 mL min−1. Separation of cations was achieved over 22 min with calibration from 0 to 30 mg L−1. Owing to difficulties in the analysis of high ionic strength KCl extracts by IC, atomic spectrometry and colorimetry were employed to determine cationic analytes in this matrix. The colorimetric method for ammonia is described below. For KCl extracts of PRB material (years 1–3), AAS, performed with a Varian SpectrAA-400 instrument operating under standard conditions, measured sodium and calcium following dilution with deionized water. Subsequently, ICP-AES provided an efficient procedure for the rapid analysis of Na+ and Ca2+ (along with other dissolved cations including Mg, Sr, Ba, Fe and Mn) in water samples and extracts of soil or PRB material. A Varian 720-ES instrument was employed under standard operating conditions recommended by the manufacturer for RF power, argon flow, and signal stabilization and delay times. A cesium chloride matrix modifier (0.75% w/v in 10% v/v nitric acid) spiked with 5 mg L−1 yttrium internal standard was mixed 1:1 with samples in-line prior to nebulization. Calibration was with standard solutions 0–50 mg L−1, and KCl extracts were diluted 1:10 prior to analysis. 2.4.5. Ammonium by colorimetry Ammonium in waters and soil extracts (water and KCl) was determined in the range 0–10 mg L−1 using a Tecan M200 Infinite microtiter plate reader following a procedure based closely on the microphotometric salicylate method of Laskov et al. (2007)). Sample extracts (400 μL) were pipetted onto a 48-well microtiter plate, mixed with 400 μL of buffer/complexing agent (120 mM sodium potassium tartrate/90 mM sodium citrate, pH 5.2), and the background absorbance

K.A. Mumford et al. / Cold Regions Science and Technology 96 (2013) 96–107

0

2005/06

62

48

26

TPH (C9 to C40) ppm 20000 19000 18000 17000 16000 15000 14000 13000 12000 11000 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0

PRB 0

61

48

Northing (m)

26

0

60

48

26

0

59

48

26

103

Road

Contour (1 m interval)

0

8 85

4

26

Sample location

Tank

478670

Fill material

478680

478690

478700

Easting (m) Fig. 10. 2005/06 grid sampling (tph) results and PRB location. Soil sampling depth was 3 to 5 cm below ground surface.

was measured. Then 240 μL of a fresh 2:1 v/v mixture of alkaline 0.5 M sodium salicylate and 0.1% w/v sodium nitroprusside catalyst was dispensed into each well, followed by 160 μL of 16 mM sodium dichloroisocyanurate. The plate was agitated for 10 min and the color developed for a further 50 min before measurement of the absorbance of the blue indophenol dye at 660 nm. A linear calibration (0–10 mg L−1) was constructed for standard solutions to calculate the concentration of NH+ 4 in the extracts. For some samples, the colorimetric analysis of NH+ 4 by the salicylate method was performed using a GBC UV/VIS 916 spectrophotometer. In this case, sample and reagent volumes were scaled up five-fold for reaction in 10 mL polypropylene tubes, and absorbance measured in disposable 1 cm-pathlength plastic cuvettes.

3. Result and discussion 3.1. Soil sampling Analysis of the soil grid samples from 2005 indicates approximately 2000 t of soil was contaminated with petroleum hydrocarbons at concentrations up to 20,000 mg kg−1 (Fig. 10). 0.00

Depth (m)

-0.05

3.2. Water sampling The results for the surface water samples (Table 1) indicate very low nitrogen concentrations in the soil water on-site, which is

-0.10

-0.15 2m 4m 6m 8m

-0.20

-0.25

In designing a remediation system for hydrocarbons it is important to estimate the phase distribution of the fuel in the subsurface environment. Assuming there is limited biological partitioning or enhanced solubilization due to the presence of other chemicals (surfactants, detergents, degreasers etc.), fuel hydrocarbons in the soil will be in one of four phases: dissolved, vapor, adsorbed or as non-aqueous phase liquid (NAPL). Mariner et al. (1997) proposed a NAPL saturation algorithm to predict the occurrence of NAPL, once the capacity of the soil for the other three phases has been exceeded. Following the methods used by Rayner et al. (2007) to predict the distribution of Special Antarctic Blend Diesel (SAB) at Macquarie Island, the soil saturation for the sum of the three phases with respect to diesel fuel for this spill is between 10 and 20 mg kg−1. This assumes the solubility of the fuel is c. 7 mg L−1, the vapor pressure 0.0019 atm and the fraction of organic carbon 0.1% w/w. The implication for these Antarctic soils is that at concentrations greater than approximately 20 mg kg−1 NAPL will be present, and this will constitute the form in which the majority of fuel mass migrates through the catchment at concentrations greater than the residual saturation. The results from the soil sampling were used to locate a suitable site for the PRB that would intercept the majority of the contaminant plume (Fig. 10), while avoiding the large rocks and boulders that exist near the melt lake. Also, elevated hydrocarbon concentrations were measured at a depth of 0.25 m as shown by the vertical profiles measured at distances along the north/south PRB wing (Fig. 11).

0

2000

4000

6000

8000 10000 12000 14000 16000

Ctph (mgkg-1) Fig. 11. Total petroleum hydrocarbon concentrations along the north/south PRB wing. Distances measured from the PRB corner.

Table 1 Characteristics of surface water within main power house catchment. Sample

pH

EC (μS cm−1)

DO (mg L−1)

Temp. (°C)

Ammonium (mg L−1 as N)

Nitrate plus nitrite (mg L−1 as N)

1 2 3 4 5 melt lake

6.29 6.31 6.85 6.81 6.86

123.7 123.2 114.6 116.1 82.1

3.2 10.6 7.9 7.0 11.2

8.1 9.0 11.0 9.3 4.2

0.190 0.312 0.135 0.128 0.253

0.012 0.054 0.016 0.010 0.560

K.A. Mumford et al. / Cold Regions Science and Technology 96 (2013) 96–107

61

5

104

26

48

2005/06 -1

Total Ammonium as N, mg.kg

26

48

61

0

PRB

0

26 60 48 26

48

59

0

26

48

59

5

26

Northing (m)

48

60

5

20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

478680

478690

478700

478710

Easting (m) Fig. 12. 2005/06 grid sampling results (ammonium) and PRB location. Soil sampling depth was 3 to 5 cm below ground surface.

consistent with the low concentrations of nitrogen (ammonium and nitrate) from the soil grid samples (ammonium data shown in Fig. 12). This figure shows that much of the site contains less than 1 mg kg−1 of ammonium as N, particularly in areas showing elevated TPH concentrations (compare with Fig. 10). The exception to this is the area to the east of the PRB which appears as a region of elevated nitrogen and TPH. When considering the soil ammonium, approximately 25% is water soluble and 75% KCl-extractable, and given the low ionic strength of the soil water, not all the soil N will be in solution. Studies have identified that biodegradation of fuelcontaminated soil at Casey Station and subantarctic Macquarie Island is strongly limited by the availability of nitrogen (Walworth and Ferguson, 2008; Walworth et al., 2008). These studies also identify that over-fertilizing hydrocarbon contaminated soil can lead to inhibition of microbial growth due to osmotic effects (Walworth et al., 2007). This indicates that microbial activity is likely to be nutrient limited in the PRB, but that nutrients must be supplied in a controlled

manner. This emphasizes the importance of incorporating controlledrelease nutrient sources within the PRB. The electrical conductivity of water samples is also low (c. 100 μS cm−1) and the pH slightly acidic (6.3 to 6.9) indicating the site surface water consists mainly of melt water (Table 1).

3.3. PRB testing As the melt season progressed, the concentration of nitrogen steadily increased corresponding with an increase in the contribution from soil water as the soil profile thawed. The increase in nitrogen concentrations is illustrated in the water samples extracted from the control cell, Cage 4 (Figs. 13 and 14). Interestingly phosphate concentrations remain fairly constant within this cell (Fig. 15). Ammonium concentrations within the remaining cells are presented in Figs. 16 to 19. As shown, all nutrient delivery systems

0.8 0.7

0.1

0.3 0.2

Fig. 13. Ammonium concentrations in Cage 4 during 2005/06 season.

MP25

Effluent

MP32

MP31

MP30

MP29

MP28

MP27

MP26

MP25

Sampling Position - Cage 4

Influent

0.0

0.0

2 Granulated Activated Carbon 1 Raw St. Cloud mine zeolite

Sand

0.1

Sodium Australian zeolite

Sampling Position - Cage 4 Fig. 14. Nitrate concentrations in Cage 4 during 2005/06 season.

Effluent

0.2

0.4

MP32

0.3

0.5

MP31

Sodium Australian Zeolite

MP30

2 Granulated Activated Carbon 1 Raw St. Cloud mine zeolite

0.6

MP29

Sand

0.4

3

Sampling 3 - 870m 3 Sampling 4 - 1385m 3 Sampling 5 - 2450m 3 Sampling 6 - 4223m

MP28

Sampling 6 - 4223 m3

MP27

Sampling 4 - 1385 m3

MP26

Sampling 5 - 2450 m3

Concentration NO3- (mg.L-1)

Sampling 3 - 870 m3

0.5

Influent

Concentration N-NH4+ (mg.L-1)

0.6

K.A. Mumford et al. / Cold Regions Science and Technology 96 (2013) 96–107

Concentration N-NH+4 (mg.L-1)

2.5

2.0

1.5 Sampling 4 - 1385m3 Sampling 5 - 2450m3 Sampling 6 - 4223m3

1.2

Sampling 5 - 2450m 3 Sampling 6 - 4223m

0.8 0.6 0.4 0.2 Zeopro

2 Granulated activated carbon

Sodium Australian

1 Sodium Australian zeolite

zeolite

Effluent

MP16

MP15

MP14

MP13

MP12

MP11

MP10

Influent

Sampling Position - Cage 2 Effluent

MP32

3

1.0

Sodium Australian zeolite

MP31

MP30

MP28

MP27

MP26

MP25

Influent

0.0

2 Granulated Activated Carbon 1 Raw St. Cloud mine zeolite

Sampling 3 - 870m 3 Sampling 4 - 1385m

0.0

0.5 Sand

3

1.4

MP09

1.0

MP29

Concentration PO43-* (mg.L-1)

3.0

105

Fig. 17. Ammonium concentrations in Cage 2 during 2005/06 season.

Sampling Position - Cage 4

1.8

1.5

Sampling 4 - 1386m3

Sampling 6 - 4223m3

Sampling 5 - 2450m3

Sampling 8 - 10900m3

1.2

0.9

0.6

0.3

Effluent

MP24

Sodium Australian zeolite

MP23

MP22

MP21

MP20

1 Granulated activated carbon 2 Zeopro

MP19

MP17

MP18

1 Granulated activated carbon 6 Zeopro

0.0 Influent

increased ammonium concentrations to above background. Additionally, sodium modified zeolite removed excess ammonium from solution, preventing it from entering into the environment. MaxBac ™ delivered higher ammonium concentrations than the other systems, however, by sampling period 4 (1385 m3) the concentrations had decreased. This observed decrease may be due to one or a combination of reasons, which includes: the nutrient source had become depleted; microbial activity had increased resulting in an increase in ammonium utilization; or, the increase in water flow rate from 1 to 3.5 L s−1 at the time of the fourth sampling (Fig. 9) resulted in the dilution of ammonium concentrations. A similar reduction in ammonium concentrations was not observed in cells where the nutrient release rate relied on an ion exchange mechanism (Cages 2, 3 and 5). This may be due to the increased flow holding exchangeable cations that displaced the ammonium held in the zeolite pores, thereby stabilizing the ammonium concentrations (Mumford et al., 2007 The calcium phosphate layer on ZeoPro™ enabled Cages 2 and 3 to deliver larger amounts of ammonium into solution compared to Cage 5, which contained Australian zeolite treated with ammonium. Although the concentration of ammonium released by MaxBac™ did drop dramatically over the course of the season, concentrations

were still of the order of that released by ZeoPro™. Both MaxBac™ and ZeoPro™ released phosphate throughout the season. As an example the orthophosphate concentrations measured in Cage 2 are in Fig. 20.

Concentration N-NH4+ (mg.L-1)

Fig. 15. Orthophosphate concentrations in Cage 4 during 2005/06 season.

Sampling Position - Cage 3 Fig. 18. Ammonium concentrations in Cage 3 during 2005/06 season.

1.4

3 2 Granulated Activated Carbon 1 Raw St. Cloud mine zeolite

2

Effluent

MP08

MP07

MP06

MP05

MP04

MP03

MP02

MP01

0

Influent

1

Sampling Position - Cage 1

0.8 0.6 0.4 0.2 Ammonium Australian zeolite

0.0

2 Granulated activated carbon 1 Raw St. Cloud zeolite

Sodium Australian zeolite

Sampling Position - Cage 5 Fig. 16. Ammonium concentrations in Cage 1 during 2005/06 season using MaxBac as the nutrient source.

Fig. 19. Ammonium concentrations in Cage 5 during 2005/06 season.

Effluent

4

1.0

MP40

Sodium Australian Zeolite

20 Granulated Activated Carbon 1 Maxbac

Sampling 6 - 4223m3

MP39

Sampling 4 - 1385 m

Sampling 5 - 2450m3

Sampling 4 - 1386m3

MP38

5

3

Sampling 3 - 870m3

MP37

6

1.2

MP36

Sampling 3 - 870 m3

MP35

Sampling 6 - 4223 m3

MP34

Sampling 5 - 2450 m3

Sampling 2 - 695 m3

MP33

Sampling 1 - 50 m3

Influent

7

Concentration N-NH4+ (mg.L-1)

Concentration N-NH4+ (mg.L-1)

8

106

K.A. Mumford et al. / Cold Regions Science and Technology 96 (2013) 96–107

indicating oxygen was not limiting to microbial growth during the first year of PRB operation. The use of water from the melt lake enabled an assessment of the flow regime in the catchment from contouring of site water levels (Fig. 6). The water flows from the pump outlet and then splits at a subsurface rock bar near location P28. Both flow paths, however, are intercepted by the wings directing water to the reactive gate. A tracer test confirmed that the entire flow was captured when released from the pump site indicated on Fig. 6. Also, temperature sensor data in Fig. 21 show that the temperature underneath the barrier (depth of 1.18 m) did not rise above 0 °C even when the temperature within the barrier was above 20 °C, indicating underflow of the barrier was unlikely.

Sampling 4 - 1385m3

4.4

Sampling 5 - 2450m

4.0

Sampling 6 - 4223m3

3

3.6 3.2 2.8 2.4 2.0 1.6 1.2 0.8

4. Conclusion

Effluent

MP16

Sodium Australian zeolite

MP15

MP14

MP13

MP11

MP09

Influent

0.0

2 Granulated Activated Carbon 1 Sodium Australian zeolite

Zeopro

MP12

0.4

MP10

-1 Concentration PO34 (mg.L )

4.8

Sampling Location - Cage 2 Fig. 20. Orthophosphate concentrations in Cage 2 during 2005/06 season.

There are a number of benefits of ion exchange nutrient release systems over soluble fertilizers. For instance, as the thaw develops there is an increase in contaminant load on the PRB and also an increase in the ionic strength of water. The increase in ionic strength results in the release of higher concentrations of nutrients from an ion exchange based delivery system, thereby providing extra nutrients to micro-organisms metabolizing the high hydrocarbon concentrations. Additionally at lower temperatures, zeolite based exchange media exhibit a preference to retaining ammonium cations, resulting in lower ammonium concentrations in the water, which corresponds with lower microbial activities. As a consequence of the fuel existing mainly as NAPL and the highly variable water and contaminant flux, estimation of hydrocarbon capture through sampling the liquid phase was difficult. Therefore, the ability of the PRB to limit fuel migration could only be determined by sampling the PRB material itself. This was not done during the first summer of operation, but was carried out during the subsequent years of the PRBs operation. The oxygen sensors installed in the PRB measured oxygen concentrations at around 21% of saturation

This paper documents the design, installation and preliminary performance of the first full-scale PRB installed in a cold region subject to freeze–thaw. The objective was to control a decade-old fuel spill in a shallow soil ranging from silt sized particles to boulders. Given the highly variable flux of contaminant fuel and melt water through the catchment during the summer period, the PRB provided a means of mitigating and remediating the fuel as well as protecting the receiving environment during planned source zone remediation. To capture the upper catchment flow, a funnel and gate design was employed, consisting of 50 m of impermeable funnel and 5.5 m of reactive gate, both keyed into the permafrost and weathered bedrock to minimize leakage or short circuiting. The materials were chosen to be inert enough to have minimal impact on the environment, have high hydraulic conductivity (>100 m d−1), be freely draining to minimize retained water that would require thawing the following season, adsorb hydrocarbons, supply nutrients in a controlled manner, and capture any excess ammonia not consumed during biodegradation of the hydrocarbons. Data show that the wings effectively directed the catchment flow from the spill area to the PRB; the temperature beneath the PRB remained below freezing indicating there was little migration under the treatment zone. Nutrient concentrations were best controlled through the use of ion exchange media (zeolites) releasing ammonia and phosphate in the presence of melt water, and the sodium

20 0.05 m

15

10

Temperature (oC)

0.70 m

5

0.92 m

0

-5 1.18 m

-10

0.05m

1.02m

0.7m 0.92m 1.02m

-15

1.18m

-20 20/11/2006

18/12/2006

15/01/2007

12/02/2007

Date Fig. 21. Temperature profile within barrier.

12/03/2007

K.A. Mumford et al. / Cold Regions Science and Technology 96 (2013) 96–107

pre-treated zeolite in the down-gradient part of the PRB captured excess ammonia. The performance of the PRB for hydrocarbon capture was not assessed in the first year of operation. The assessment of hydrocarbon capture, biodegradation and longevity of the PRB materials is the subject of further publication. Acknowledgments The authors wish to thank the 2005–06 Casey Crew, Greg Hince for chemical expertise, and Tania Raymond for editing. This research was supported by Australian Antarctic Grants 1163, 2576, and 2570 and Australian Research Council Linkage grant LP0667574. References Beiersdorfer, R.E., Ming, D.W., Galindo, C., 2003. Solubility and Cation Exchange Properties of Zeoponic Substrates. Elsevier Science Bv. Bowman, R.S., Li, Z., Roy, S.J., Burt, T., Johnson, T.L., Johnson, R.L., 1999. Surface Altered Zeolite as Permeable Barriers for In Situ Treatment of Contaminated Groundwater. Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, New Mexico. Dullien, F.A.L., 1979. Porous Media Fluid Transport and Pore Structure. New York, Academic Press, New York. Fiedor, J.N., Bostick, W.D., Jarabek, R.J., Farrell, J., 1998. Understanding the mechanism of uranium removal from groundwater by zero-valent iron using X-ray photoelectron spectroscopy. Environmental Science and Technology 32 (10), 1466–1473. Gibert, O., Ferguson, A.S., Kalin, R.M., Doherty, R., Dickson, K.W., McGeough, K.L., Robinson, J., Thomas, R., 2007. Performance of a sequential reactive barrier for bioremediation of coal tar contaminated groundwater. Environmental Science and Technology 41 (19), 6795–6801. Gillham, R.W., O'Hannesin, S.F., 1994. Enhanced degradation of halogenated aliphatics by zero-valent iron. Ground Water 32 (6), 958–967. Gore, D.E., 2009. Chapter 20: Application of Reactive Barriers Operated in Frozen Ground. Springer-Verlag, Permafrost Soils. R. Margesin. Berlin 303–320. Gore, D.B., Snape, I., 2008. Freeze–thaw cycling, moisture and leaching from a Controlled Release Nutrient source. Cold Regions Science and Technology 52 (3), 401–407. Guerin, T.F., Horner, S., McGovern, T., Davey, B., 2002. An application of permeable reactive barrier technology to petroleum hydrocarbon contaminated groundwater. Water Research 36 (1), 15–24. Hach, 2007. DR 2800 Spectrophotometer. Procedures Manual, Germany, Hach Company. Hlavay, J., Vigh, G., Olaszi, V., Inczedy, J., 1982. Investigations on natural Hungarian zeolite for ammonia removal. Water Research 16 (4), 417–420. Huang, Y.H., Zhang, T.C., 2004. Effects of low pH on nitrate reduction by iron powder. Water Research 38 (11), 2631–2642. Hubbert, M.K., 1953. Entrapment of petroleum under hydrodynamic conditions. Bulletin of the American Association of Petroleum Geologists 37 (8), 1954–2026. Jama, M.A., Yucel, H., 1989. Equilibrium studies of sodium–ammonium, potassium– ammonium, and calcium–ammonium exchanges on clinoptilolite zeolite. Separation Science and Technology 24 (15), 1393–1416. Laskov, C., Herzog, C., Lewandowski, J., Hupfer, M., 2007. Miniaturized photometrical methods for the rapid analysis of phosphate, ammonium, ferrous iron, and sulfate in pore water of freshwater sediments. Limnology and Oceanography: Methods 4, 63–71.

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