A non invasive sampling and remediation strategy was developed and implemented at shoreline contaminated with spilt diesel. To treat the contamination, in a practical, cost-effective, and safe manner (to personnel working on the stockpiles and their ship loading activity), a non-invasive sampling and remediation strategy was designed and implemented since the location and nature of the impacted geology (rock fill) and sediment, precluded conventional ex-situ and any in-situ treatment where drilling is required. A bioremediation process using surfactant, and added N & P and increased aeration, increased the degradation rate allowing the site owner to meet their regulatory obligations. Petroleum hydrocarbons decreased from saturation concentrations to less than detectable amounts at the completion of treatment.

1. Bioremediation of diesel from a rocky shoreline in an arid tropical
climate
Turlough F. Guerin
Climate Alliance Ltd, c/o 5 Retreat Crescent, Sunbury 3429, Victoria, Australia
a r t i c l e i n f o
Article history:
Received 17 February 2015
Revised 22 July 2015
Accepted 25 July 2015
Available online 30 July 2015
Keywords:
Spill
Marine
Maintenance
Resources
Shoreline
Flushing
Fuel
a b s t r a c t
A non invasive sampling and remediation strategy was developed and implemented at shoreline contam-
inated with spilt diesel. To treat the contamination, in a practical, cost-effective, and safe manner (to per-
sonnel working on the stockpiles and their ship loading activity), a non-invasive sampling and
remediation strategy was designed and implemented since the location and nature of the impacted geol-
ogy (rock fill) and sediment, precluded conventional ex-situ and any in-situ treatment where drilling is
required. A bioremediation process using surfactant, and added N & P and increased aeration, increased
the degradation rate allowing the site owner to meet their regulatory obligations. Petroleum hydrocar-
bons decreased from saturation concentrations to less than detectable amounts at the completion of
treatment.
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
Resource construction, as well as operational mine sites, for
both new and expansion of existing projects, has been a major
contributor to the growth of Australia’s economy in the past two
decades, deploying large numbers of plant and equipment, and
necessitating the transfer and use of large volumes of chemicals
including fuels and lubricants. Despite the strong culture of
compliance of Australian resource companies to the standards gov-
erning the safe handling of hazardous and dangerous goods, loss of
containment occurs on mining and resource construction opera-
tions (Guerin, 2014), in some cases with potentially significant
impacts on aquatic and marine ecosystems, or even human health
(Colombo et al., 2005; Hewstone, 1994; Ismail and Karim, 2013;
Reed et al., 2005; Smith, 1995; Vazquez-Duhalt, 1989). Habitat loss
and its effects on biodiversity are a growing global concern and is a
major cause of the decline of coastal species. Changes in habitat as
a result of petroleum spills is of particular concern (Margesin and
Schinner, 2001; Olagbende et al., 1999), and the region where
the current spill occurred is an important marine conservation area
and is under consideration by regulatory authorities for further
increasing the conservation value of the region.
Mining operations and resource construction with activities
adjoining marine waters, present a particularly high potential risk
to marine pollution, and mine owners and plant operators must be
vigilant to ensure integrity of chemical (fuel, lubricant, hydraulic
fluid) storage tanks, lines, pumps, secondary containment and
wash down facilities (Guerin, 2002, 2009). Operational personnel
must also be trained in the risks and the specific controls to pre-
vent fluid releases and emergency procedures where preventative
measures fail. Problems associated with working close to marine
waters are the risks from loss of containment from such facilities
and the resulting loss of aquatic life and negative impacts on
marine ecosystems. While biodegradable refined products are
increasingly gaining popularity in marine and related applications
(Mercurio et al., 2004), spills into marine waters (regardless of pur-
ported biodegradability), attract heavy fines and pose unacceptable
risks to operator (owner) companies.
Diesel is a ‘‘light oil’’ and small spills of 2–20 kL will usually
evaporate and disperse within a day or less. For larger spills, a resi-
due of up to one-third of the amount spilled will usually remain
after a few days. Diesel will not sink or accumulate on the seafloor,
except as a result of adsorption to sediment, but is considered to be
one of the most toxic oils to water-column organisms and fish kills
are possible if large spills occur in non-readily mixing water. Light
oils contain moderate concentrations of soluble toxic compounds,
and can leave a film or layer in the intertidal zone with the poten-
tial to cause long-term contamination (Anon., 2011).
Heavy fuel oils are typically not very toxic to water column
organisms compared to lighter oil. Diesel on the other hand is
http://dx.doi.org/10.1016/j.marpolbul.2015.07.059
0025-326X/Ó 2015 Elsevier Ltd. All rights reserved.
E-mail address: turlough.guerin@hotmail.com
Marine Pollution Bulletin 99 (2015) 85–93
Contents lists available at ScienceDirect
Marine Pollution Bulletin
journal homepage: www.elsevier.com/locate/marpolbul

2. considered to be one of the most toxic oils to water column organ-
isms, and direct mortalities are possible for fish, invertebrates and
seaweed in direct contact with a spill (Hansen et al., 2013), as well
as algae and plankton (Romero-Lopez et al., 2012; Seuront, 2011).
However, small spills in open water are very rapidly diluted and fish
kills have not been reported in these scenarios. Bioremediation
processes reduce the toxicity of diesel (Hohener et al., 1998;
Molina-Barahona et al., 2005).
Mortality rates for seabirds can be high where populations are
concentrated (for example, during bird migrations), and shorebirds
feeding in intertidal habitats are at risk of sub-lethal effects from
contaminated or reduced prey populations. Direct contact with
diesel can affect marine birds by ingestion during preening and
hypothermia from matted feathers, although the oil evaporates
so rapidly that the number of birds affected is usually small.
Small spills have the potential for serious impact if they occur close
to a large nesting colony or are transported into an area of large
bird population (Brown et al., 2011).
A very effective clean-up is possible for spills of light oil such as
diesel. Diesel is not sticky or viscous in comparison to heavier oils,
and tends to penetrate porous sediments and rocks on the shore-
line but be washed off quickly by waves and tidal flushing, mean-
ing that shoreline clean-up is usually not required. Complete
degradation (of available fractions) by naturally occurring
microbes takes one to several months.
The site on which the current spill study is focused is a small
island off the coast of North West Western Australia which has
been joined by a causeway to another island, which in turn is also
connected to the mainland (Fig. 1). The region is unique within
Australia in that it is the only marine environment adjacent to an
arid tropical terrestrial environment. Rocky shores are the most
common habitat in the region. The coastline is largely
Precambrian igneous rock, but in some areas there is an overlay
of Pleistocene limestone (Jones, 2004).
2. Purpose
Remediation criteria for the pollution of the marine waters
adjoining the spill site, was determined in consultation with the
environmental regulator. The remediation criteria primarily was
Fig. 1. Overview of the location of the spill. (Top Left) Primary (feeder) stockpile of mineral salt in foreground that feeds the stockpile on the island where the spill occurred
and the remediation treatment was setup and showing proximity to the marine environment. (Top Right) Secondary stockpile that is used to load ships located on the island
where the spill occurred and was the source of salt contamination in the spill zone showing dozers in operation. (Middle Left) Secondary stockpile being added to from feeder
(primary) stockpile via a conveyor belt along causeway. (Middle Right) Close view of dozer moving secondary stockpile of salt to hoppers for ship loading. (Bottom Left)
Refueling bay area where spill occurred. (Bottom Right) Refueling hose and crystalline salt on the catchment drain [within the refueling bay area] where salt and fuel mixed
prior to (overflow) release into rockfill area immediately below.
86 T.F. Guerin / Marine Pollution Bulletin 99 (2015) 85–93

3. that there would be ‘‘no visible sheen of petroleum hydrocarbon on
the surface of the marine water body’’. The purpose of the study
was to design, construct and operate a process to remove the spilt
diesel entrapped in the rockfill.
3. Materials and methods
3.1. Site location and assessment
The site was located on a small island connected via a causeway
to the mainland, on a rocky outcrop on the North West Western
Australian coastline, used for loading mined product onto ships
(Fig. 1). The principal product being mined was salt (sodium chlo-
ride) and the operation was undergoing earthworks to expand the
evaporation area of the mine, and to improve roads across the mine
and port loading facilities (Table 1) at the time of the spill. The spill
location was on the top of a rock fill area approximately 8 m above
the low tide mark. The coastline was exposed to a large daily tidal
movement of approximately 5–6 m. During king tide events (1–2
per year) the tidal variation increased to approximately 7–8 m.
3.2. Plant, equipment and spill source
A refueling bay (within concrete secondary containment) was
located on the eastern edge of the island, on top of the rock fill area
(Fig. 1). An above ground diesel storage tank (30 kL) was located in
the refueling area. During the peak of the construction expansion
works, the diesel tank was refilled from a land-based tanker fort-
nightly. A grader and excavators (for road construction), and bull-
dozers (for stockpile movement) were being refueled from the
same refueling bay. Table 2 describes the types of activities across
the entire operation that are potential sources of contamination,
including refueling. Internal investigations (by the site owner)
identified that the cause of the spill was the release of 7000 L of
diesel during the refueling operation of a grader undertaking road
construction activity near the stockpile. It was noted that only at
18–24 months post spill was petroleum hydrocarbons observed
in the water in the lower intertidal area, and only a sheen (not free
product).
3.3. Shoreline sediment and rock fill sampling
After a consideration of the intractability of the shoreline and
above lying rock fill (from an initial site visit and detailed site
inspection), a purposive sampling plan was developed. This plan
required collection of samples from the area immediately below
the spill location (or spill zone), a 40 m2
area including representa-
tive samples from the upper, middle and lower intertidal zones
(Fig. 2). Samples were collected in a directed (purposive) manner
so as to represent the size fraction of À50 mm, and to ensure the
most visibly contaminated material was collected, reflecting the
practical objectives of this study (to ensure cost-effective remedi-
ation of the diesel spill). This sampling (in the depth range of
0–15 cm) included small rocks, stones, sand, fines and the residual
liquor. Liquor samples were collected to assess petroleum hydro-
carbons as a check for the presence of a sheen and were assessed
separately to the solid samples. All samples were collected during
low tide on each sampling day. Sediment and rock fill samples
were collected from the intertidal area up to a distance of 200 m
away from the center of the spill zone.
3.4. Petroleum hydrocarbon analysis
Once the objectives of the clean-up were determined (i.e. no
sheen on marine waters and the source of contamination dispersed
and removed), an analysis regime was developed. Confirmatory
(fingerprinting) analysis showed that the spilled product was die-
sel. The n-alkane/biomarkers ratios, C17/Pristane and C18/Phytane,
were used to identify the extent of weathering and biodegradation,
under the action of natural attenuation (for the period of
0–112 weeks post spill), and throughout the treatment process,
as has been adopted in other bioremediation assessments
conducted by the author (Guerin, 2000). Since contamination
concentrations immediately after the spill were not assessed, rep-
resentative rock fill and sediment samples were saturated with
diesel and free drained, to estimate ‘diesel holding capacity’ (after
1 week from dosing), using conventional instruments for deter-
mining moisture and volumetric properties of soil (Guerin, 1993).
Maximum petroleum hydrocarbon concentrations at week 0
(i.e. at the time of the spill) were extrapolated from this assess-
ment and represented an effective ‘‘field capacity’’ or free drained
concentrations of diesel in samples of the contaminated rock fill
immediately under the spill zone.
3.5. Physico-chemical analysis
Due to the diesel contamination occurring in a marine environ-
ment, with the added contribution of salt from an adjacent salt
stockpile, electrical conductivity (EC) was considered an important
constraint to the likely effectiveness of any microbiological treat-
ment. Given that inorganic nutrients were likely to be limiting in
the intertidal zones, the macro nutrients for biological activity, N &
P (in their available forms), were also assessed throughout the study.
The analyses of pH, EC and available N & P were conducted on solids
and liquors using the conventional methods described previously
and which provide explanatory methodology (Guerin, 1999a,b,
Table 1
Production of mineral salt at the nearby mine and bulk handling at the ship loading
stockpile and treatment site.a
Production parameter Value/description
Production mechanism Solar evaporation
Salt production rates (annual) 4 million tonnes
No. of evaporation ponds 6
Salt production (daily) 40,000 tonnes
Salt harvesting frequency Annual
Salt washing by-product Gypsum
a
Gypsum is used on site for road repairs and other uses.
Table 2
Sources of petroleum hydrocarbon contamination at the mining and ship loading site.
Activity and area Source Types of
contaminants
Product handling and ship
loading activities
Wastewater discharge,
spills from bulk handling
equipment
Fuels, oils,
equipment fluids
(mixed with salt)
Wastewater discharge
from conveyer transfer
point
Fuels, oils,
equipment fluids,
greases (mixed
with salt)
Vehicle and plant
maintenance workshop
(on adjacent production
facility)
Oily water separator
discharge
Fuels, oils, metals,
detergent,
equipment fluids
Refueling bays Oily water separator
discharge (including
product from spill
events)
Fuels, oils,
equipment fluids
Bulk fuel storage Tank and line failure or
filling spill
Fuel (diesel and
petrol)
Vehicle wash-down bays Oily water separator
overflow discharge
Fuels, oils, metals,
detergent,
equipment fluids
T.F. Guerin / Marine Pollution Bulletin 99 (2015) 85–93 87

4. 2001). Particle size fractionation was also conducted using conven-
tional fractionation techniques as described by the particle size anal-
ysis was the Bouyoucos method described in Day (1953). Dissolved
oxygen was measured by an Orion A329 DO meter (Thrermofisher,
Sydney Australia) and calibrated on a daily basis.
3.6. Microbial analysis
Total heterotrophic and petroleum hydrocarbon degrading
microbial populations were determined using a most probable
number (MPN) technique. An increase in the petroleum hydrocar-
bon degrading population (using the MPN method) was considered
to be a key indicator of the success of any bioremediation strategy
selected. This study deployed an enhanced method of petroleum
hydrocarbon MPN which uses resazurin (dye) to make positive
(i.e. growing) wells more clearly observable to the human eye,
overcoming the constraints associated with low turbidity, but
active degrading populations (Guerin et al., 2001).
3.7. Design of treatment methodology
A contamination model (or conceptual model of the contamina-
tion at the site) was developed based on all the data available,
including the limited subsurface data, and was used to inform
the design and construction of the treatment strategy.
Acceptance of the model by the site owner and government
regulator meant that a non-invasive clean-up strategy, would be
acceptable as a practical solution for the spill’s remediation. The
design would also need to prevent further discharges to sea,
remove residual diesel from the rock fill and enhance natural
biodegradation processes already present (albeit limited) in the
shoreline rock fill and sediments.
Fig. 2. Salt-imapcted, intractable rock fill, sediment and shoreline. (Top Left) Rockfill from an adjacent area without any fuel or salt contamination. (Top Right) Image showing
contamination source area at the top of rockfill area. (Middle Left) Immediately below source zone showing salt overflow onto rockfill from bulk handling of stockpile.
(Middle Right) Middle intertidal zone showing fuel contamination. (Bottom Left) Lower intertidal zone showing boom in place to capture free product entering the marine
waters. (Bottom Right) A pre-spill photograph (no concrete refueling bay in place) used here to illustrate the treatment and monitoring zone of the spill including steep
rockfill face (see the bottom right hand corner of this image).
88 T.F. Guerin / Marine Pollution Bulletin 99 (2015) 85–93

5. The design involved shallow drilling (15–20 cm) and creation of
channels through the concrete secondary containment where the
diesel spill occurred, on top of the rock fill, and placing agricultural
(perforated) drain pipe in place in the top of the subsurface, to
allow the delivery of a mixture of surfactant and water soluble
nutrients to infiltrate through contaminated rock fill and the lower
intertidal sediments (Fig. 3).
3.8. Treatment implementation and operation
The flushing of surfactant and nutrients was initiatedat week 112
(i.e. just over 2 years after the initial spill event). A floating absorbent
boom was put in place to minimize the escape of mobilized diesel
(from the rock fill) to the sea. Surfactant and soluble N & P nutrient
formula were also sprayed over the rocks and sediments in the inter-
tidal zone with a knapsack, and in addition, MaxBac Slow Release
(5–6 months) N & P granules (Scotts, Sydney Australia), were dis-
tributed to all accessible areas of sediment, an area representing
the contaminated zone (Fig. 3) approximately 8 m  25 m, as well
as the smaller spill zone (40 m2
). Rock fill flushing was repeated at
weeks 121, 131, 177 and 183, with shoreline spraying of the
surfactant and nutrient placement (soluble and granular N & P
formulations) at week 132, 173, 177 and 183. Treatments were
interspersed with sampling and analyses to monitor progress of
diesel removal in the rock fill and intertidal sediments.
4. Results and discussion
4.1. Assessment of the site and regional characteristics impacting the
environmental sensitivity and nature of contamination and treatment
The geology and other geographic information on the site and
the surrounding region was reviewed in order to develop the
model for the site’s contamination and subsequent treatment
strategy. The contaminated zone was represented by large igneous
rocks and smaller rocks down to the size of silt (Fig. 2). The geology
and the severe climatic conditions are the most significant con-
straint to establishing and implementing a successful remediation
program at the site.
4.2. Development of the contamination model
The spill occurred along the coastline such that the diesel was
released slowly and intermittently into the lower sand and sedi-
ment (at low tide) when high and king tides occurred, as observed
by the presence of a slight sheen as seen by operators who were
working at the contaminated site area (prior to treatment inter-
vention) during the period of 18–24 months post-spill. The high
and king tides caused the residual diesel in the rock fill to become
mobile, causing a distinct sheen in the lower lying marine water.
This bleed or release behavior (of the entrapped diesel) can be
explained by the presence of perched diesel in free product form
(Fig. 4). This slow release of diesel over the 2 years leading up to
the initiation of the remediation strategy was contributing to the
ongoing observation of a sheen on the rock fill/sediment surface
at mid and low tide, as well as the presence of a sheen on the
marine waters at the initiation of the remediation works and the
23 weeks immediately after the surfactant flushing events
(Figs. 4 and 5). Salt may also have had the effect of preserving
the diesel in situ for the two years where no degradation was
observed, in addition to the oxygen-limited environment, and
low concentrations of available N & P.
A proportion of diesel (approximately 10% or 700 L) was
estimated to have moved through the rock fill all the way to the
bottom of the rock fill, exiting into the sand and sediment at the
low tide mark into the ocean, as evidenced from the observations
Fig. 3. Establishment of the infiltration treatment system. (Top Left) Agricultural drain pipe entering into the base of the refueling bay for evenly distributing the aerated mix
of surfactant, water and soluble nutrients to the contaminated zone in the rockfill immediately below. (Top right) Large 600L plastic tubs for mixing surfactant and soluble
nutrients used in the flushing process. (Bottom Left) View of the southernmost area of the refueling bay showing proximately to marine water. (Bottom Right) Surfactant and
soluble nutrient mix undergoing aeration to saturation prior to flushing events. This aeration was conducted 24–48 h prior to each flushing event (to ensure super-saturation
with oxygen).
T.F. Guerin / Marine Pollution Bulletin 99 (2015) 85–93 89

6. provided by the operators and environmental personnel on the site
who had been monitoring the spill since it occurred. An additional
10% (or 700 L) was estimated to have migrated directly into the
subsurface below the rock fill without migration into the ocean.
A further 10% (or 700 L) was estimated to have dissipated into
the marine water and lost via evaporative processes. This left an
estimated residual volume of approximately 4800 L in the rock fill
and sediment (including in any underlying perched diesel) and
throughout the vadose zone, including the amount that could have
been expected to have been sorbed onto the rock and sediment in
the contaminated zone.
4.3. An assessment of remedial options
The main options reviewed for the remediation were removal
and treatment ex-situ, bioventing and sparging (combined), and
flushing with a surfactant to enhance dispersion and biodegrada-
tion. Removal and treatment ex-situ was eliminated because of
the extremely high cost of excavation due to the extensive
distribution of diesel into the underlying rock fill. Bioventing and
sparging were technically feasible options, both introducing
oxygen to enhance the natural biodegradation processes in the
subsurface, however the main constraint was the costs of estab-
lishing the required wells in a safe manner. Finally flushing using
a surfactant was considered the most technically feasible and cost
effective as it allowed required oxygen to be introduced (via a sat-
urated solution and by increasing the surface area of diesel held in
the rock fill and sediment as free product) (Khalladi et al., 2009;
Lee et al., 2005; Mena et al., 2015), as well as dissolved nutrients,
and surfactant to release the sorbed and entrapped diesel (Mao
et al., 2015; Martienssen and Schirmer, 2007; Mulligan et al.,
2001; Zhou et al., 2005). The flushing action would also transfer
the sorbed diesel into the lower intertidal areas, exposing the
entrapped diesel to further wave action and tidal activity, which
in time would increase aeration, which in turn increases biodegra-
dation. Such an intervention would avert the need for extensive
earthworks and drilling which was unlikely to have been effective
in such a heterogeneous subsurface.
4.4. Physico-chemical characteristics of the rock fill and intertidal
zones at start of treatment strategy
Numerous physico-chemical parameters, particularly those rel-
evant to supporting biodegradation, were assessed as part of the
treatment program. These results are presented and summarized
in this section.
Analysis of macro nutrients required for biological degradation
indicated their status was limiting, with measurements reporting
<3.4 mg available N per kg and <0.8 mg available P per kg.
Typically for biodegradation processes to be effective, these values
should be in the minimum range of at least 10–50 mg/kg, depend-
ing on the corresponding quantities of petroleum hydrocarbon to
be biodegraded. The measured concentrations were reflective of
the characteristics of an intertidal zone where soluble chemicals
were susceptible to leaching leaving little or no soluble nutrients.
Ratios of C:N:P of 100:10:1 provide a useful rule of thumb for
Refuelling
Spill zone
Rocky outcrop
Low Ɵde
Contaminated
(vadose) zone
High Ɵde
Perched
diesel plume
Sheen
(A) PracƟcal exclusion zone
Refuelling
InfiltraƟon
system
acƟvated with
surfactant and
nutrients
(B)
Sheen
Refuelling
Diesel released,
migrates toward
ocean
(C)
Soap/Foam
Traces
Fig. 4. Model of diesel plume migration during treatment with surfactant and
nutrients (A) diesel remains in situ in perched location in rock fill 2 years after spill.
Minor sheen evident at the shoreline in the period 18–24 months post spill; (B)
oxygenated solution of surfactant, N & P infiltrate into the source (perched diesel),
dispersing the plume and making it more susceptible to wave, tidal and microbi-
ological processes at 112–115 weeks post spill; (C) mobilized diesel further
disperses and biodegrades under influences of wave and tidal action both of which
in turn further increase aeration and aerobic biodegradation at 180 weeks post spill.
0
5000
10000
15000
20000
25000
30000
0 20 40 60 80 100 120 140 160 180 200
Petroleumhydrocarbons(mg/kg)
Time aŌer spill (weeks)
Individual Samples
Sampling Time Means
(a)
(b)
(c)
Fig. 5. Diesel removal from rockfill after spill and surfactant infiltration. Three distinct degradation phases (a) slow natural attenuation post-spill, (b) fast enhanced
biodegradation, and (c) slow, asymptotic decay. Arrows show dates of interventions.
90 T.F. Guerin / Marine Pollution Bulletin 99 (2015) 85–93

7. ensuring nutrients are not limiting, though wider ratios may still
allow an effective bioremediation process.
The pH of sediments was alkaline, reporting values between 8.5
and 9.2. Biological degradation processes are usually optimized in
the neutral pH zone. It is likely that pH has limited biodegradation
of the spilt diesel since the time of the spill. No further modifica-
tion of the pH of the contaminated zone was attempted. The addi-
tion of soluble nutrients had the effect of lowering pH to
approximately 7.5.
The EC varied markedly with the sediment particle size and
type, but were typically in the range 1100–5000 lS/cm. The rela-
tively high EC values reflected the fact that stockpiling of the salt
for shipment had progressively lead to salt being pushed over onto
the rock fill as a result of normal loading operations, thus con-
tributing to the already saline liquors in the intertidal zone.
Highly saline environments are known to limit biodegradation
however the adaptive potential of indigenous microorganisms is
high are previously reported (Margesin and Schinner, 2001).
Oxygen in the liquors collected (prior to any flushing events were
initiated), as measured by dissolved oxygen, was relatively low at
ranging from <2 to 5 ppm. The low levels of dissolved oxygen were
consistent with the odors that emanated from the rock fill which
was a sulfur-based smell of a ‘‘rotten egg gas’’ (hydrogen sulfide)
smell. These odors of hydrogen sulfide and petroleum product ema-
nating from the spill area indicated that anaerobic processes were
occurring at the site, and were likely to be influencing the biodegra-
dation processes degrading the residual diesel, at least to some
extent.
4.5. Distribution of petroleum hydrocarbons across the intertidal zones
at start of treatment strategy
At week 112 post-spill, petroleum hydrocarbon concentrations
at the high tide mark were in the range of 15,000–27,500 mg/kg.
These fractions were in the range of C10–C36, reflecting the compo-
sition of slightly weathered diesel. These petroleum hydrocarbon
concentrations had not decreased over 112 weeks, indicating die-
sel was still being released from the rock fill into the high tide zone
sediments. The period from 0 to 112 weeks post-spill represented
the effect of natural attenuation processes in a predominantly
anaerobic (or at least an anoxic) environment.
4.6. Changes in degradation rates in response to addition of surfactant
and macro-nutrients
The progress of petroleum hydrocarbon degradation over the
190 weeks since the spill, is represented in Fig. 5. The degradation
curve followed a predictable tri-phasic pattern. This pattern
illustrates how the inherent (initial) slow rate of degradation,
attributable to natural attenuation (under anaerobic/anoxic condi-
tions), was improved by the treatment strategy (intervention) of
flushing the contaminated zone with surfactant and nutrients.
Microbiological changes in the sediment (from the rock fill area
and intertidal zone) provided verification that a biostimulation
process was occurring as a result of the added surfactant and
nutrients described in the following paragraphs.
Table 3
Summary of Microbiological Monitoring in sediment and rock fill solid material samples pre-Infiltration and post Infiltration with surfactant and nutrients.
Sample No. Petroleum degraders (cfu range
per gram at weeks post spill)
Sample descriptions Biostimulation
response
112 121 180
1 ? 3 104
–105
107
–108
105
–106
Representative of high tide in the contamination zone; wide range of particle sizes; visibly
contaminated with diesel fuel at Week 112, 121, and 180 post-spill
Strong
4 104
–105
108
–109
104
–105
Representative of mid-tide in the contamination zone; wide range of particle sizes; visibly
contaminated with diesel fuel at Week 112, 121, and 180 post-spill
Strong
5 104
–105
109
–1010
102
–103
Representative of shoreline; predominantly sand and rocks to À20 mm; no contamination
evident (though sheen had been observed by site personnel in period 6–18 months post-spill
Strong
6 103
–104
<102
<102
Background sample (taken 100 m away from source of contamination); predominantly sand
and rocks to À20 mm
No response
7 102
–103
<102
<102
Background sample (taken 150 m away from source of contamination); predominantly sand
and rocks to À20 mm
No response
8 109
–1010
108
–109
109
–1010
Background sample (taken 200 m away from source of contamination) + spiked with diesel oil
and BioSolve; predominantly sand & rocks to À20 mm
Strong
(a) Biostimulation tests were conducted in the laboratory to determine response of samples to aeration and nutrient addition (80 ml diesel/500 ml of soil sample) and 1% (v/v)
BioSolve solution.
(b) ANOVA analyses showed that there were significant differences between Sample 8 and each of the other samples 1–7 at weeks 112 & 180.
(c) The data ranges represented the data from 3 separate measurements. The standard errors were relatively high due the heterogeneous nature of the sediment particles of
the means varied from 18% to 45%.
(d) Scale of responses: None, weak, moderate and strong.
Table 4
Phases of the petroleum hydrocarbons removal in the contaminated rock fill spill model with perched diesel.
Phase of spill remediation Degradation
rate (mg/
kg/day)
Qualitative
removal
rate
Proposed
mechanisms
Evidence for proposed mechanism Biodegradation
conditions
Pre-treatment (0–2 years post
spill)
0 Slow,
asymptotic
decay
Natural
attenuation
Low DO; absence of a measurable petroleum hydrocarbon
degradation rate; only traces of sheen observed on shoreline; H2S
odors mixed with diesel
Anoxic,
potentially
anaerobic
Initial treatment interventions
(surfactant, nutrient
flushing)
170 Fast Enhanced
aerobic
biodegradation
High DO; high petroleum hydrocarbon degradation rate; high
petroleum hydrocarbon degrader populations; Distinct sheen on
shoreline
Aerobic
enhanced by
surfactant
Late treatment interventions
(ongoing surfactant,
nutrient flushing)
12 Slow,
asymptotic
decay
Enhanced
aerobic
biodegradation
High DO; high petroleum hydrocarbon degrader populations Aerobic
enhanced by
surfactant
T.F. Guerin / Marine Pollution Bulletin 99 (2015) 85–93 91

8. In the initial phase, the total heterotrophs, reflective of the
intrinsic total aerobic microflora in the sediment and rock fill
2 years after the spill, and petroleum hydrocarbon degraders, were
estimated to be in the order of 104
–105
cfu per gram at 112 weeks
post-spill, that is, before the remediation strategy was imple-
mented. It was noted that there was no significant difference
between the total heterotrophic and petroleum hydrocarbon degra-
ders that were enumerated. This range (i.e. 104
–105
cfu per gram) is
low for soil and sediments that are contaminated with petroleum
hydrocarbons in aerobic environments (Guerin, 1999c; Guerin
et al., 2001) this nevertheless reflects a positive presence for petro-
leum hydrocarbon biodegradation capability in the intertidal zone
samples tested. The low oxygen levels in the rock fill are consistent
with relatively low numbers of aerobic microflora. It appears from
the degradation rate in this initial phase, where natural processes
were the predominant ones at work, that the rate was severely lim-
ited by the depleted nutrient status of the sediments, including oxy-
gen, and their near saturation with contaminant.
During the second stage of degradation of the diesel (Fig. 5), the
rate was considerably higher, mostly due to dispersal, coupled
with enhanced biodegradation. This rate was calculated at
170 mg/kg/day. This is fast when considered relative to petroleum
hydrocarbon biodegradation on other projects such as in biovented
processes where rates can reach 250 mg/kg/day or more. The sur-
factant is likely to have successfully dispersed the petroleum
hydrocarbons more uniformly throughout the surrounding sedi-
ments, making them more available to the weathering action of
the waves and rising (and falling) tides and intrinsic microbial pop-
ulations, stimulated by greater nutrient availability and oxygen.
This second and most rapid degradation stage was mostly due to
dispersal processes that released entrapped diesel to undergo
enhanced degradation in the intertidal zone. The surfactant suc-
cessfully dispersed the petroleum hydrocarbons more uniformly
throughout the surrounding sediments, making the petroleum
hydrocarbons more available to the weathering action of the rising
tides and intrinsic microbial populations, stimulated by greater
nutrient availability and oxygen. The microbial count at this stage
was increased up to 106
–107
and 108
–109
cfu per gram of sediment
(solids), respectively for total heterotrophs and petroleum hydro-
carbon degraders (Table 3). These changes indicated, when corrob-
orated with other parameters assessed in this study including DO
readings, changes in pristine and phytane ratios, and high contam-
inant degradation rates, that a very effective biostimulation pro-
cess had occurred (Tables 4). The dispersive influence of the
surfactant was verified by the presence of traces of soap (foam)
on the low tide mark, beginning several weeks after the first flush
(of surfactant) (Table 5).
The biomarker ratios changed during the treatment process
from 2–3:1 in samples from 112 weeks post-spill, to <1:1 at week
121 and 165, further indicating a biological process was occurring.
The third stage, between week 121 and 165 post spill, exhibited
a slow removal rate of 12 mg/kg/day. No treatments occurred
between week 132 and 173 due to a labor shortage (because of
the remote location) to undertake the flushing or sample collec-
tion. Activity between weeks 173 and 183, featured further rock fill
flushing with surfactant, leading to mobilization of diesel by,
which further enhanced biodegradation.
After 170–190 weeks post-spill, petroleum hydrocarbon con-
centrations reduced to 23–190 mg/kg, with many of the sampling
sites reaching ‘not detected’ limits in the sediment. The remaining
petroleum hydrocarbons were determined to be within the C15–C36
n-alkane fraction, the least biodegradable fraction of diesel, and
was typical of a residual quantity remaining after an effective
bioremediation process.
4.7. Review of the effectiveness of the treatment
Table 5 summarizes the changes in the intertidal zone during
the course of treatment. There was a clear biostimulation response
after the flushing intervention reflected in the increase in the
number of petroleum hydrocarbon degraders and in the reduction
of petroleum hydrocarbon concentrations in the rock fill and
sediment in the intertidal zone. The regulatory requirements to
eliminate the sheen on the marine waters at the shoreline and
remove the source of ongoing diesel were met through the applied
interventions. There was evidence of a reduced sheen observed
after the second flushing event and the diesel had been flushed
from the upper rock fill areas.
4.8. Remediation cost analysis
Tight budgetary constraints at the operation precluded ready
availability of funds to remove the contaminated rock fill, and
any residual sources, and treat these materials ex-situ. Such an
extensive excavation which would have to be conducted using civil
Table 5
Petroleum hydrocarbon sheen and odors in the intertidal zone.
Observations in intertidal zone Weeks post-spill
0 115 122 169 180
Presence of sheen À ++ + À À
Odor (H2S + diesel) ++ +++ + À À
Soap discharge (foam) À À ++ + À
Table 6
Licence conditions for the site relevant to petroleum hydrocarbon release and
management developed as a result of the spill.a
Regulated environmental
activity
Specific site requirement
Pollution control
equipment
Be maintained and operated to manufacturer’s
specification or to an effective internal
management system
Hazardous goods
management
All such chemicals to be stored in accordance
with the WA Code of Practice for Storage and
Handling of Dangerous Goods
Spill management The Licensee shall immediately recover or
remove and dispose of spills of
environmentally hazardous chemicals (if spill
occurs outside of an engineered secondary
containment area)
Stormwater management The licensee shall implement all practical
measures to prevent stormwater run-off from
becoming contaminated by site activities
The licensee shall treat contaminated or
potentially contaminated stormwater as
necessary prior to being discharged (to the
environment, offsite)
Discharge limits for total petroleum
hydrocarbons (US EPA 3550) is set at 15 mg/L
for the designated wastewater discharge
points
Information and training The licensee shall ensure that any person who
performs tasks on the site is informed of all the
conditions of the licence that relate to the tasks
which that person is performing
Auditing, reporting and
government
notifications
The Licensee shall complete an annual
compliance audit indicating the extent to
which the licence conditions have been met
including
Contaminated sites investigations underway
and related monitoring or remediation
[treatment] works underway (during the
previous 12 month period)
Breaches of any limits specified in the licence
or failure of any pollution control equipment
or any incident that may cause pollution
a
There were no discharge limits set on contaminants entering groundwater.
92 T.F. Guerin / Marine Pollution Bulletin 99 (2015) 85–93

9. earthworks plant and equipment including a specialized long arm
excavator, over several weeks, which would have cost up to an
estimated AUD500,000, excluding any surfactant, nutrients, or
monitoring (and analyses). Comparison with other researchers
suggests remediation costs can vary from at least $50–200/t for soil
washing and or flushing. The total labor and materials cost for the
clean-up of this contaminated zone and intertidal shoreline, was in
the order of AUD25,000 and as such, this biostimulation strategy
was a cost effective solution to what would otherwise have been
a major disruption to the refueling bay and large expense item
for the operation.
5. Conclusions
The clean-up of the spill was achieved with evidence that bios-
timulation was a key underlying process responsible for diesel
degradation. A pronounced increase in the petroleum degrading
microflora, as a result of the flushing of surfactant, nutrients, and
increased oxygen, verified that the biodegradation processes had
been increased in the contaminated rock fill and intertidal zone.
A demonstration of the evidence for biostimulation from the flush-
ing treatment interventions and reduction in petroleum hydrocar-
bons, met the regulator’s requirements for the clean-up endpoints.
A modified license was subsequently put in place that now pro-
vides greater protection for this sensitive tidal marine environment
(Table 6).
The selection of remediation technology and treatment design
was fit for purpose with mine production and ship loading able
to continue during the entire treatment period. The practical,
cost-effective treatment design also kept costs to a minimum,
making the clean-up project acceptable to the management team
responsible for meeting the legal obligations for the site. The
design also allowed for a minimum exposure of unsafe conditions
and behaviors to site personnel involved in the process or working
in the area, as an intrusive civil earthworks program was avoided.
This practical, surfactant-enhanced biostimulation approach
can be applied to other intractable spill sites where access to the
spill and contaminated zone is restricted and unsafe for trafficking
with excavation and earthworks equipment.
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