Entec & Vertase FLI won Best use of a single remediation treatment technique at the BB RIA awards for remediating an active production facility near Newcastle
An active production facility near Newcastle-upon-Tyne was the focus of one of a limited few full-scale successful UK applications of in-situ enhanced anaerobic degradation of a source term, using an emulsified vegetable oil to assist the biological degradation.
The main contaminants on the 3ha site were trichloroethene (TCE), daughter products of dichloroethene isomers (DCE) and vinyl chloride (VC). Historically, uncontrolled releases of TCE to ground and groundwater occurred beneath the northern end of the factory.
The site did not need immediate action, the Environment Agency and local authority found, but was voluntarily cleaned up to levels significantly below the risk assessed requirement, to a "minimal environmental risk" level, at the insistence of the client.
Best practice
Contamination was restricted to the shallow aquifer present within a sandy horizon and the rate of flow through it was considered relatively slow.
A plume of contaminated water within the sandy horizon was well defined as part of site characterisation works and covered an area of 800-1000m2. This accurate delineation played a large part in the success of the treatment, allowing detailed design of the location and type of remediation wells.
Enhanced in-situ anaerobic bioremediation was chosen for its sustainability, low energy costs, natural process and ability to remediate even sites with limited access.
The final system was designed to inject directly under pressure an emulsified vegetable oil and sodium lactate into an area of the plume where access was restricted to hand held tools only, using special injection rods developed by VertaseFLI. The remainder of the treatment was undertaken via the installation of 50mm and 150mm abstraction and re-injection wells across the plume, installed via a sonic rig and conventional cable percussion techniques.
As well as chemical testing an ORP and DO condition survey was taken across the plume to establish baseline conditions. Background microbial populations were established using a new technique that allows assessment of the presence of live dehalococcoides (biobeads) as well as the more traditional heterotrophic and total DNA counts which count both viable and non-viable cells.
A VertaseFLI abstraction, dosing, fermentation and reinjection system was used, along with 15m3 of emulsified vegetable oil, over eight weeks. The system began with abstraction from the first cells, from which water was transferred to the fermentation tank and sodium lactate added to ensure that the water was anaerobic for re-injection. This was then re-injected into the same cell area via the dosing system which added a dose of emulsified oil.
"It was cost effective going further than the initial remedial goals in the longer term with the Water Framework Directive requirements on diffuse pollution coming in." Jonathan Atkinson
