Site specific in-situ bioremediation

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

confirmed.

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

contamination.

Natural bacteria

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.