Case Study; Integrated phys/chem/bio remediation system closes site early

1.
Figure 1. Service Station Site Map
Integrated Physical – Chemical – Biological Remedial Strategy
for TPH Impacted Groundwater
Service Station, Hertfordshire, UK
Historical operations at a service station in Hertfordshire resulted in petroleum hydrocarbon contamination in
soil and groundwater. The site was demolished and was to become a residential development with
underground parking. Shallow soil samples and groundwater monitoring were conducted to determine the
extent of total petroleum hydrocarbon (TPH) contamination. Shallow soils impact was associated with a former
tank farm and was limited to the northern portion of the site. A TPH concentration of 3,600 milligrams per
kilogram (mg/kg) was observed in the vicinity of borehole WS1 (<0.5m bgl). The maximum TPH concentrations
observed in groundwater were 53 milligrams per liter (mg/L) and 34 mg/L at locations MW4 and MW1,
respectively (Figure 1).
Remedial Strategy
The remedial objective was to reduce concentrations of
TPH and benzene in soil and groundwater to the site
specific target level (SSTL) of 10 mg/L. However, due to
the presence of a chalk formation underlying the site, a
significant proportion of the identified contamination
would persist as a result of the dual porosity nature of
the chalk formation. For this reason, the most effective
remedial solution was determined to be groundwater
abstraction using a down‐well pump and treat (P&T)
system, in combination with RegenOx™ augmentation
to address the sorbed material. A phased remedial
approach optimised treatment whereby the Phase 1
P&T removed the bulk of the impact from the fractures.
However, post pumping rebound resulted from the
hydrocarbons in the formation pore spaces coming into
solution. RegenOx was used to target the hydrocarbon
contamination by chemical oxidation whilst also making it more available for removal during the second phase
of the P&T operation. ORC Advanced® was used as a polishing step to aerobically degrade any remaining
petroleum hydrocarbon contamination to the SSTL.
System Augmentation using RegenOx™
RegenOx™ is a proprietary two‐part chemical oxidation product developed and sold by Regenesis for in situ
groundwater treatment. It combines the use of a controlled‐release percarbonate‐based oxygen compound
with a proprietary multi‐part catalyst to generate surface‐mediated free‐radical generation and contaminant
oxidation (e.g. perhydroxyl radical, hydroxyl radical and superoxide radical), with reactive power comparable
to that of Fenton’s reagent but with much easier handling and subsurface delivery / longevity (up to 30 days).
This provides an effective contaminant oxidation reaction without violent exothermic reaction, and can
therefore be handled using a wide range of standard field equipment (e.g. direct push injection rigs) or applied
directly to excavations.
WS1
WS6
WS8
WS2
WS3
WS5
WS4
WS7
WS9
WS10
WS11
WS12

2.
Augmentation of the P&T system using chemical oxidation allowed for enhanced recovery of petroleum
hydrocarbons from soil and groundwater. This occurs as a result of the powerful desorption‐surfactant effect
of RegenOx (principally the catalyst) that draws the contaminant off the soil surface and into solution. The
contaminant then reaches the catalytic surface where localised free‐radical generation occurs, leading to
focused contaminant destruction. This restricts
the oxidant losses onto tightly bound and
heavier soil organics such as humic, roots, and
other natural or immobile fractions. As a result
of the above processes, RegenOx‐desorbed
contaminant mass and partially oxidised (more
soluble) organic species are recovered via
groundwater abstraction using the existing P&T
system, whilst further contamination is
destroyed in situ by oxidation. Enhanced
biodegradation using ORC Advanced, as a
polishing step, was applied following the
RegenOx treatment to target residual dissolved
phase contamination and reach the SSTL.
RESULTS
Initial pumping/free product removal activities
proved very successful, having achieved a 60%
reduction in average total TPH concentration
within the first four months of operation.
However, upon shutdown of the P&T system,
rebound was observed at all locations (MW1 to
MW6) as a result of desorption. The system was
then augmented using RegenOx to target the sorbed phase.
Shortly following augmentation of the P&T system, an anticipated increase in dissolved phase TPH was
observed. Following this increase, the P&T system was switched on and the ‘rebound’ abstracted, thus making
the physical removal of the TPH impaction much more effective.
The RegenOx applications were repeated approximately 2‐4 times, depending on location, between April 2008
and July 2008. Once the dissolved phase contamination was reduced to a level suitable for aerobic
bioremediation, an ORC Advanced injection was completed in all wells to target residual TPH concentrations in
groundwater.
The combined P&T, RegenOx and ORC Advanced treatment was effective at reducing TPH to below the SSTL of
10 mg/L in all wells. An average 99% reduction in average Total TPH was reported in September and October
2008. No further rebound was observed after this time. In addition, the combined treatment approach
reduced the time taken to achieve the remedial targets from an estimated 12 months using P&T alone to 6
months using a combined treatment approach.
Table 1. Subsurface Details
Soil Type Glaciofluvial clays and chalk
Depth to Groundwater 10m
Treatment Area 300 m2
Treatment Thickness 3m
Table 2. RegenOx Application Details
Application Type
Fixed point – through P&T
abstraction points
Application Rate (avg)
RegenOx Part A – 16.4 kg/m
RegenOx Part B – 16.4 kg/m
Table 3. ORC Advanced Application Details
Application Type Fixed point
Application Rate 9.07 kg/m
TOTAL REGENOX
MATERIAL COST
<£9,000
TOTAL PROJECT COST ~£80,000

3.
CONCLUSIONS
As a result of the integration of RegenOx and ORC Advanced with a physical treatment system, petroleum
hydrocarbon concentrations were reduced quickly and cost effectively. RegenOx augmentation of the pumping
system on site allowed for reduced pumping time and faster decommissioning. It is estimated that the
combined treatment approach allowed for the entire treatment time frame to be reduced from 12 months
using P&T alone to 6 months with the RegenOx & ORC‐Advanced material costs totaling approximately only
10% of the total project costs.
The ORC Advanced application enhanced the biodegradation of the residual contamination and effectively
reduced TPH concentrations to the target goal. An average 99% contaminant reduction was reported across
the treatment area and concentrations of TPH were reduced to below the SSTL of 10 mg/L in all wells of
concern. Successful regulatory sign off was achieved due to the overall reduction in TPH concentrations.
WD Environmental
Simon Ware
+44 (0) 1442 825570
sware@wdenvironmental.com
www.wdenvironmental.com
Land Clean Ltd
Mark Swanston
+44 (0) 1730 23478
mark.swanston@landclean.net
www.landclean.net
Regenesis Ltd
Gareth Leonard
+44 (0) 1833 630411
gleonard@regenesis.com
www.regenesis.com
Pumping
RegenOx
ORC Adv
Remedial
Target