THE CHALLENGE:
The Chrisp St Regeneration Scheme is a mixed-use redevelopment to create ~18,000m2 of commercial space and 212 residential properties. Site investigations by Ramboll confirmed a source area of elevated Trichloroethene (TCE) concentrations. Accumulation of its associated daughter product cis-DCE and low Vinyl Chloride (VC) concentrations confirmed that natural conditions had ‘stalled’. Remedial Criteria following DQRA had set stringent targets, due to the sensitive Secondary ‘A’ aquifer and potential vapour risks associated with VC, where retrofitting of vapour protection measures in nearby commercial properties was undesirable.
Additional logistical challenges were presented by significant in-ground live services, members of the public accessing the centrally located Market District and clearance / demolition works ongoing nearby.
OUR SOLUTION:
Targeted source injection using direct-push techniques to promote accelerated breakdown of TCE and daughter products through combination of biotic and abiotic (chemical processes) to achieve enhanced reductive de-chlorination (ERD):
- Colloidal micro-scale Zero-valent Iron (ZVI) was injected in 9nr evenly spaced locations to promote rapid chemical reduction of TCE and create strong reductive conditions favourable to anaerobic biodegradation; and,
- A controlled-release substrate, 3D Microemulsion (3DMe) and Bio-Dechlor Inoculum Plus (BDI+) was also co-injected with the ZVI. 3DMe enhances de-chlorination of the plume and BDI+ promote bioaugmentation and the breakdown of both TCE and daughter products within the source area and down-gradient plume.
Post-injection monitoring carried out by Ramboll on behalf of the client confirmed strong reducing conditions persisted. Concentrations of TCE, DCE and VC all rapidly fell to below the stringent remedial criteria within both the source zone and down gradient, including a target of <2ug/l for VC. This objective was achieved (and thereafter sustained) within 8 months of injection.
