Site specific in-situ bioremediation
The application of a bioremediation strategy tailored to a specific contaminated site is reported to have speeded up development of a residential project, whilst retaining a responsive, sustainable and added value solution
Response Bioremediation Contracting
(a division of Response Environmental Services Ltd) was commissioned in
November 1999 by A P Geotechnics Ltd, the independent consultant appointed
by Michael Shanly Homes, to provide as site-specific bioremediation strategy
to remediate an area of petroleum contaminated ground as a development site
in High Wycombe.
The site investigations conducted by AP Geotechnics revealed the nature and
extent of the contamination on the site. The main contaminant identified was
1,1,1 Trichloroethane with concentrations recorded at 212.66mg/kg to 2.9
metres depth. Investigations identified a variable sequence of strata,
typically 0.7 metres of fill material over 9.3 metres of stiff brown, silty
clay with some gravel over chalk.
In light of the proposed residential end use, the sensitivity of the
location and the major chalk aquifer beneath the site, the remediation
strategy had to be both responsive and sustainable.
Consultation on strategy
Following consultation with the local authority, NHBC and the Environment
Agency, including the National Groundwater and Contaminated Land Centre,
both the remediation strategy and the remediation target values of 10mg/kg
for total VOCs
and 5mg/kg for 1,1,1 Trichloroethane, as principal contaminant, were
Response Bioremediation Contracting reports that it responded to the
requirements of the project by engineering a site-specific and risk-based,
in-situ bioremediation strategy which utilised Precision Injection
Technology, incorporating Response Bio-Gel. The material is stated to be a
non-toxic, non-corrosive and organic food grade substance found in most
foods and used commonly within the pharmaceutical industry. The bio-gel
itself is used as a carrier, an insulator and an initial source of
nourishment for the bacteria used in the bioremediation of soils and water
that contains elevated concentrations of petroleum hydrocarbon
Site-specific Response Bio-Gel contains the optimum composite of
non-pathogenic, naturally occurring bacteria, found naturally in soils
(including facultative anaerobes), nutrients and dissolved oxygen, to
maximise the interface of bacteria and contaminant.
This promotes the development/colonisation of biomass and therefore
facilitates bioremediation. As part of the colonisation process the bio-gel
is consumed and converted into carbon dioxide and water. Response
Bio-Gel is specifically engineered to respond to the site-specific ground
conditions and contaminant properties, including risks pertaining to
contaminant mobilisation, both laterally and vertically.
Accordingly, the composition of Response Bio-Gel and the technology
selected to deliver the product to the contamination zone is engineered to
suit each project.
The in-situ bioremediation works were executed in November 1999. Response
Bio-Gel was injected manually into the target area of contamination
utilising 19mm diameter injection lances under positive pressure in a
regular grid pattern with injection points at 0.75 metre spacings. The
bacteria within the Response Bio-Gel follow the contaminant front in all
directions throughout the contaminated material.
In accordance with the agreed bioremediation strategy Response undertook a
programme of treatment method validation.
Soil samples were retrieved using a window sampler at week 6 and 11 after
the bioremediation injection process. All samples were entered into a
laboratory chain of custody and despatched to a NAMAS Accredited laboratory
(Environmental Analysis Ltd) for chemical analysis. During the course of the
works visual and olfactory evidence of TPH contamination was encountered.
This was sampled and despatched for analysis accordingly.
Response Bioremediation Contracting reports that the chemical analysis
results confirmed that the in-situ bioremediation treatment process has
effectively reduced the elevated concentrations of VOCs and TPH as the site
within an 11 week period. These results also confirmed that the remediation
target values of 10mg/kg for Total VOCs and 5mg/kg for 1,1,1 Trichloroethane
as principal VOC contaminant have been achieved, with maximum concentrations
being recorded at 1.54mg/kg and <0.02mg/kg, respectively. The chemical
analysis results also confirmed that the TPH contamination has been
remediated to <5mg/kg, states Response.