Soil and Groundwater Remediation
1. Natural Attenuation and Fate Processes in Groundwater and Vadose Zone Soils
A range of studies have been carried out to determine the natural attenuation and fate of petroleum hydrocarbons, solvents, munition compounds and pesticides, in groundwater and soils:
Natural attenuation studies were carried out at the Eden Hill site in Perth, Western Australia, where a gasoline spill had contaminated groundwater in a sandy aquifer with BTEX (benzene, toluene, ethylbenzene, xylene) compounds and other soluble components. Over a 7 year period, groundwater was sampled from transects of multi-level samplers to monitor the contaminant plume in three dimensions along with principal electron acceptors and the products of mineralisation (e.g. oxygen, sulphate, sulfides, methane, iron) to determine the natural attenuation of the BTEX compounds. Background groundwater was anaerobic and sulphate-rich, with a variably-cemented ‘coffee rock’ layer in the zone of water table fluctuation consisting of iron oxy-hydroxides coating the aquifer sediments. Soil cores were recovered in the source regions to determine the vertical gasoline NAPL distribution and composition. A tracer test using deuterium-labeled contaminants was carried out within the plume to obtain direct estimates of degradation rates for benzene, p-xylene, toluene and naphthalene. Degradation rates were also inferred from modelling of plume extent. Microbiological studies were carried out to determine the principal microbes responsible for apparent biodegradation occurring at the site. The studies indicated that: benzene was persistent within the plume; toluene (and other component) plumes were stable from year to year; and monitoring at individual boreholes could be quite misleading due to seasonal recharge and other controls on groundwater and plume dynamics. Coupled hydrogeological, geochemical and microbiological modelling of the data from the site was also undertaken and is described separately below.
Key contact: Greg Davis
Davis, G.B. 1996. Intrinsic (natural) attenuation of gasoline compounds in groundwater. Proc. Third Nat. Haz. and Solid Waste Convention, Sydney, Australia, AWWA and WMAA, 531 - 537.
Franzmann. P.D., Patterson, B.M., Power, T.R., Nichols, P.D. and Davis, G.B. 1996. Microbial biomass in a shallow, urban aquifer contaminated with aromatic hydrocarbons: analyses by phospholipid fatty acid content and composition. J. Applied Bacteriology 80, 617 - 625.
Davis, G.B., Barber, C., Power, T.R., Thierrin, J., Patterson, B.M., Rayner, J.L. and Qinglong Wu. 1999. The variability and intrinsic remediation of a BTEX plume in anaerobic sulphate-rich groundwater. J. Contaminant Hydrology 36(3-4), 265-290.
Davis, G.B., Power, T.R., Briegel, D., and Patterson, B.M. 1999. Natural attenuation of BTEX compounds in groundwater and soil environments: evidence and uncertainties. Contaminated Site Remediation: Challenges Posed by Urban and Industrial Contaminants (Ed. C.D. Johnston). Proc. 1999 Contaminated Site Remediation Conference, Fremantle, Western Australia, 21-25 March 1999, 343-350.
Franzmann, P.D., Robertson, W.J., Zappia, L.R. and Davis, G.B. 2002. The role of microbial populations in the containment of aromatic hydrocarbons in the subsurface. Biodegradation 13(1), 65-78.
Two projects have been carried out to investigate and model the behaviour of hydrocarbon plumes as they move towards, and potentially discharge to river and marine environments. The two studies were carried out at field sites in Perth, Western Australia to determine the natural attenuation and biodegradation potential of hydrocarbon compounds at the groundwater/estuarine water and groundwater/marine water interface, and in the hyporheic mixing zones.
At one site adjacent to the Canning River, fine-scale depth profile sampling and analysis of groundwater was carried out to map the three dimensional features of a dissolved gasoline plume as it moved towards a tidal river. Sampling of multilevel groundwater samplers and spear probing in the sediments of the river indicated that groundwater (and the contaminant plume) discharged near the shore and extended less than 10 m beyond the shoreline beneath the river sediments. Little evidence of hydrocarbon compounds above background concentrations was observed in river water. The river water was aerobic and sulfate-rich potentially providing electron acceptors for biodegradation and mineralisation of the petroleum hydrocarbon compounds. In the core of the plume, sulfate was depleted, and biocarbonate increased indicating that biodegradation and natural attenuation of hydrocarbons was likely to be occurring under sulfate-reducing conditions. Modelling and monitoring showed significant near-shore vertically-focused groundwater discharge (seepage) into the river, with an increased groundwater velocity. Seasonal and tidal changes in hydrocarbon distributions and groundwater discharge were observed.
At a second site, the natural attenuation of petroleum hydrocarbons in groundwater close to a marine environment was studied. The zone of discharge was complicated by hydraulic transients due to wave, tidal and seasonal fluctuations as well as the intrusion of the salt water wedge into the aquifer and geochemical mixing and reactions. An investigation was carried out in the near-beach region at a field site with a spill of gasoline 70 m from the beach front in a sand aquifer. Multi-level groundwater samplers were installed in a transect towards the beach from the source area to determine a depth section of hydrocarbon concentration changes towards the marine environment. Spear probe sampling of the aquifer was also carried out in transects across the groundwater flow path - both near the source and on the beach front. On-line water level logging was carried out with intensive tidal period sampling to assess tidal flushing of the beach front. There was an abundance of BTEX (benzene, toluene, ethylbenzene, xylene) range compounds at shallow depths near the spill while concentrations were much reduced on the beach. However, ethylbenzene was persistent. Transient monitoring of water levels and electrical conductivity changes indicated the dynamics of the marine water/groundwater interface at a range of temporal scales and showed an increased zone of sulfate-rich marine water overtopping the zone of plume discharge on the beach face. Modelling is underway to couple density transients to biodegradation and chemical aspects to further quantify the potential attenuation.
Key contact: Greg Davis
Westbrook, S., Davis, G.B., Rayner, J.L., Fisher, S.J. and Clement, T.P. 2000. Initial site characterisation of a dissolved hydrocarbon groundwater plume discharging to a surface water environment. Contaminated Site Remediation: From Source Zones to Ecosystems (Ed. C.D. Johnston). Proc. 2000 Contaminated Site Remediation Conference, Melbourne, 4-8 December 2000, 189-196.
Westbrook, S.J., Rayner, J.L., Davis, G.B., Clement, T.P., Bjerg, P.L., and Fisher, S.J. 2004. Interaction between shallow groundwater, saline surface water and contaminant discharge at a seasonally- and tidally-forced estuarine boundary. J. Hydrology (submitted).
A series of projects have been carried out
to quantify the fate and biodegradation of
hydrocarbon vapours in sandy and clayey vadose
zone soils and to determine the impact of dwellings
on vapour distribution and attenuation in the
subsurface. The objectives of the projects
were to estimate biodegradation rates for BTEX
(benzene, toluene, ethylbenzene, xylene) vapours
in gasoline impacted vadose zones; test methods
for estimating BTEX vapour biodegradation;
provide tools for understanding BTEX vapour
fate processes; determine the effects of house
structures on vapour behaviour and the potential
for vapour movement through cracks in a simulated
house slab. Laboratory, field and modelling
studies have been carried out, with field sites
in a number of states of Australia including
Western Australia, Victoria, New South Wales
and Queensland. These studies have shown that
the penetration of hydrocarbon vapours from
a sub-surface source to the ground surface
is critically dependent on oxygen ingress into
the profile to support aerobic biodegradation,
soil layers restricting gaseous diffusion and
surface coverings. Typically, where oxygen
was present, vapours readily biodegraded. Penetration
of vapours to the ground surface varied seasonally
due to changes in soil moisture but where no
ground cover was present, hydrocarbon vapours
typically did not reach the ground surface.
Hydrocarbon vapour biodegradation rates were
found to be in the range 1-30 mg/kg soil/day,
but were highly dependent on modelling assumption
used to calculate the degradation rates. Estimation
of biodegradation rates from static oxygen
profiles was found to be problematic due to
the presence of stratigraphic zones of high
moisture content. These zones were found to
dominate vapour behaviour and confound biodegradation
rate estimates. Sequential field experiments
involving flushing of the vadose zone with
nitrogen to generate anaerobic soil profile
conditions, and oxygen to create aerobic soil
profile conditions were also carried out to
provide independent measures of biodegradation.
Separate experiments showed that vapours accumulated
under the centre of a house pad over a sandy
soil profile where oxygen ingress was limiting,
but that no vapours were seen to accumulate
beneath a house slab above a layered, sand-over-clay
profile. A further project also is being carried
out to determine the behaviour of vapours in
the presence of a house slab with cracks. The
study is investigating the potential for vapour
and oxygen exchange through such cracks to
help determine if this poses an unacceptable
Davis, G.B., Power, T.R., Briegel, D.and Patterson, B.M. 1998. BTEX vapour biodegradation rates in the vadose zone initial estimates. Groundwater Quality: Remediation and Protection (Proceedings GQ’98 Conference, Tubingen, Germany, September 1998). IAHS Publ. no. 250, 300-303.
Franzmann, P.D., Zappia, L. R., Power, T.R., Davis, G.B. and Patterson, B.M. 1999. Microbial mineralisation of benzene and characterisation of microbial biomass in soil above hydrocarbon contaminated groundwater. FEMS Microbial Ecology 30, 67-76.
Davis, G.B., Rayner, J.L., Fisher, S.J. and Patterson, B.M. 2000. Soil profile layering and seasonal effects on the fate and biodegradation of gasoline vapours in a sandy vadose zone. Contaminated Site Remediation: From Source Zones to Ecosystems (Ed. C.D. Johnston). Proc. 2000 Contaminated Site Remediation Conference, Melbourne, 4-8 December 2000, 391-398.
Davis, G.B., Trefry, M.G., Öhman, J. and Rayner, J.L. 2001. Nitrogen and air flushing field experiments to determine the natural biodegradation of gasoline vapours in a sandy vadose zone. First European Bioremediation Conference, Chania Crete, Greece, 2-5 July 2001, 9-12.Davis, G.B., Rayner, J.L., Trefry, M.G., Fisher, S.J. and Patterson, B.M. 2004. Measurement and modelling of seasonal hydrocarbon vapour behaviour in a layered soil profile. Vadose Zone J. (in preparation).
Davis, G.B., Trefry, M.G. and Patterson, B.M.
2004. Petroleum and solvent vapours: quantifying
their behaviour, assessment and exposure. CSIRO
Land and Water Report to the Western Australian
Department of Environment.
Research on the retention and movement of NAPL has included site characterisation to determine the distribution of non-aqueous phase liquids at contaminated sites, laboratory studies of the retention and movement of non-aqueous phase liquids in soil materials and modelling studies. Fine-scale measurements of grain size, saturated hydraulic conductivity, saturation-capillary pressure relationships (retention characteristics) and residual NAPL contents have been made to explain distributions of NAPL in a layered sandy aquifer. Field work has been conducted at sites contaminated by weathered diesel and gasoline. Work was also undertaken to relate three-phase fluid pressures to NAPL mobility and thickness in screened boreholes. A field site was instrumented with hydrophillic and hydrophobic tensiometers to determine fluid pressures while potentiometric head and NAPL thicknesses were automatically measured in monitoring bores. Pressures and NAPL thicknesses were also related to NAPL content in cores collected form the site. As an adjunct to the field studies, laboratory column experiments examined the movement of NAPL in response to varying water tables. This was in order to study the role of entrapped NAPL as a source of dissolved organic contamination. Other work has looked at the effect of antecedent water contents on residual (entrapped) NAPL contents. More recent work examined the infiltration and redistribution of NAPL (diesel and Otto fuel) and the possible impacts on groundwater from spills and leaks from storage facilities. This work has encompassed laboratory column experiments and modelling. The dissolution of single- and multi-component NAPL petroleum hydrocarbons has also been conducted at the laboratory scale. Equilibrium dissolution (interphase mass transfer) was identified in these systems at the groundwater flow velocities expected at field sites. These studies also demonstrated the preferential dissolution of benzene from gasoline NAPL. Partitioning tracers and interfacial tracers were used to characterise the residual NAPL during dissolution. Partitioning inter-well tracer tests (PITT) have also been applied at the field scale to characterise the distribution of LNAPL petroleum hydrocarbons (weathered gasoline) during remediation.
Key contact: Colin Johnston
Johnston, C.D. and Patterson, B.M., 1994. Distribution of nonaqueous phase liquid in a layered sandy aquifer, In Hydrocarbon Bioremediation R.E. Hinchee, B.C. Alleman, R.E. Hoeppel and R.N. Miller (Editors) (Lewis Publishers, Boca Raton), 431437.
Johnston, C.D. and Rayner J.L., 1996. Preferential dissolution of benzene from a residual multi component non aqueous phase liquid (Extended abstract). First International Conference on Contaminants and the Soil Environment in the Australasia-Pacific Region, 18-23February 1996, Adelaide, South Australia.
Johnston, C.D. and Rayner, J.L., 2000. Investigation of the fate of Otto fuel in the soils and aquifers of Garden Island, Western Australia. HMAS Stirling Environmental Working Paper No. 15, (Garden Island Environmental Advisory Committee, HMAS Stirling, Rockingham, Western Australia) 78pp.
Rayner, J.L., Johnston, C.D. and Rao, P.S.C., 2000. Characterising residual NAPL using partitioning and interfacial tracers and implications for interphase mass transfer. In: Contaminated Site Remediation: From Source Zones to Ecosystems (ed. by C.D. Johnston). Proc. 2000 Contaminated Site Remediation Conference, Melbourne, Victoria, 4-8 December, 2000, 613-620.
Steffy, D.A., Johnston, C.D. and Barry, D.A., 1994. A field study of the vertical immiscible displacement of LNAPL associated with a fluctuating water table. Int. Conf. on Groundwater Quality: Remediation and Protection(CQ 95, IAHS), Prague, Czech Republic, May 15-28, 1995.
Steffy, D.A., Johnston, C.D., and Barry, D.A., 1995. A field study of the vertical immiscible displacement of LNAPL associated with a fluctuating water table. Groundwater Quality: Remediation and Protection. IAHS Publ. no. 225, 49-57.
Steffy, D.A., Barry, D.A. and Johnston, C.D., 1997. Improved scaling technique for two-phase pressure-saturation relationships, J. Contam. Hydrol., 28, 207-225.
Steffy, D.A., Barry, D.A. and Johnston, C.D., 1997. Influence of antecedent moisture content on residual LNAPL saturation. J. Soil Contam., 6, 113-147.
Steffy, D.A., Johnston, C.D., and Barry, D.A., 1998. Numerical simulations and long-column tests of LNAPL displacement and trapping by a fluctuating water table. J. Soil Contam., 7, 325-356.
The fate and behaviour of non-aqueous phase liquids in heterogeneous and structured aquifer materials is being investigated in laboratory and modelling studies. This research has arisen in conjunction with field remediation studies and is particularly focussed on the recovery of light non-aqueous phase liquids (LNAPLs) from aquifers. Our particular interests are in granular aquifers which exhibit heterogeneity as horizontal layering as well as structured materials which contain secondary porosity (fractures and other macroporosity). Monte Carlo analyses are being conducted using a three-dimensional, variably-saturated, multiphase simulator to predict LNAPL extraction during dual-phase recovery in the presence of layer variability. The variability is approximated as discrete layers with the permeability of individual layers log-normally distributed. These have shown that even for a moderate variance in Log permeability, substantial variance in LNAPL recovery is predicted. We have also shown that this variance is dependent on the initial volume of LNAPL in the aquifer. For the structured materials we have undertaken laboratory experiments measuring the NAPL transport characteristics (permeability) of single fractures. Using these single-fracture characteristics we are modelling the recovery of LNAPL from simple fracture networks. These are showing the extent to which spilled LNAPL may be recovered from such system.
Key contact: Colin Johnston
Mobility and biodegradation of low concentrations of pesticides and hydrocarbons through surface soils
The natural attenuation of the munition compounds Nitroluene (NT), Dinitrotoluene (DNT), Trinitrotoluene (TNT) and RDX, were investigated in the fractured basalt aquifer underlying Melbourne, Australia. Groundwater at the former Albion Explosives Factory site was impacted via release of the munitions and other organic and inorganic compounds from the manufacturing of explosives over a considerable period of time. The project sought to (i) estimate the natural degradation rate of munition residues dissolved in groundwater, and to identify the bacteria or other microbial consortia degrading these compounds; (ii) establish the sorption/desorption characteristics of munition residues onto soils and aquifer media from the site, for model parameterisation; (iii) develop models of the movement and degradation of dissolved munition residues in groundwater; and (iv) provide guidance for enhancing the degradation of munition residues in groundwater, should remediation be necessary. Field and laboratory investigations included recovery of intact cores for lithological description, sorption and biodegradation studies, the conduct of a deuterium-labelled TNT, DNT, NT and RDX forced gradient tracer test, and modelling to describe plume behaviour. Natural degradation was found to occur, with enhanced remediation apparent when amendments were used in laboratory microcosms, but hazardous intermediates were observed to occur. TNT was found to be the most degradable of the munition compounds.
Key contact: Greg Davis
Patterson, B.M., Davis, G.B., Zappia, L., and Power, T.R. 1996. Sorption of munition compounds in a weathered basalt aquifer material from Victoria, Australia. Environmentally Responsible Defence (P.Crabb, J. Kesby, L. Olive - Eds), Australian Defence Studies Centre, Canberra, Australia, 361-370.
Toze, S., Zappia, L. and Davis, G.B. 1996. Microcosm experiments to determine the bioremediation potential of munition compounds in a fractured basalt aquifer. Environmentally Responsible Defence (P.Crabb, J. Kesby, L. Olive - Eds), Australian Defence Studies Centre, Canberra, Australia, 417-424.
Powell, S., Franzmann, P.D., Cord-Ruwisch, R. and Toze, S. 1998. Degradation of 2 nitrodiphenylamine, a component of Otto Fuel II, by Clostridium spp. Anaerobe 4(2), 95-102.
Toze, S., Zappia, L. and Davis, G.B. 2000. Determination of the potential for natural and enhanced biotransformation of munition compounds contaminating groundwater in a fractured basalt aquifer. Land Contamination & Reclamation 8(3), 225-232.
Davis, G.B., Patterson, B.M., Thierrin, J. and Benker, E. 2000. Deuterated tracers for assessing natural attenuation in contaminated groundwater. Tracers and Modelling in Hydrogeology (Proceedings. TraM’2000 Conference, Liege, Belgium, 23-26 May 2000). IAHS Publ. no. 262, 241-247.
The mobility of trichloroethene (TCE) in groundwater was investigated at the Jolimont site in Perth, Western Australia. The sand aquifer at the site had very low organic carbon content and the retardation and degradation of TCE was investigated to determine its long-term behaviour, in the core of the plume several hundred metres down gradient of the presumed source region. Multi-depth sampling of groundwater, soil coring, batch and column sorption studies and a deuterium-labelled tracer test were carried out to map the plume cross-section and to determine at batch, column and tracer test scale the relative magnitude of sorption in retarding TCE movement in the plume. Traditional scaling equations based on the fraction of organic carbon (foc) in soil were shown to be unreliable in predicting retardation at such low foc values found in the aquifer. Batch and column experiments showed that retardation was very small. The tracer test showed coincident breakthrough of bromide and the deuterium-labelled TCE, indicating little or no sorption, and little or no biodegradation in the core of the plume.
Key contact: Greg Davis
Benker, E., Davis, G.B., and Barry, D.A. 1995. Using deuterated trichloroethene (TCE) in a tracer test to estimate the transport characteristics of a TCE plume. Groundwater Quality Remediation and Protection, Prague, Czechoslovakia, 18-25 May 1995, IAHS Publication No. 225, 61-69.
Benker, E., Davis, G.B., Appleyard, S., Barry, D.A. and Power, T.R. 1996. Trichloroethene (TCE) contamination in an unconfined sand aquifer underlying a residential area of Perth, Western Australia. Hydrogeology Journal 4(1), 20-29.
Benker, E., Davis, G.B. and Barry, D.A. 1997. Factors controlling the distribution and transport of trichloroethene in a sandy aquifer: hydrogeology and results of an in situ transport experiment. J. Hydrology 202(1-4), 315-340.
Benker, E., Davis, G.B. and Barry, D.A. 1998. Estimating the retardation coefficient of trichloroethene for a sand aquifer low in sediment organic carbon - a comparison of methods. J. Contaminant Hydrology 30(1-2), 157-178.
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