Best use of chemical systems - winner : Hyder Consulting and May Gurney
22 September 2006, News release from Hyder Consulting Ltd
May Gurney Ltd and Hyder Consulting applied an ex-situ stabilisation/solidification (s/s) solution to deal with heavy metal contamination in the bed of Newlyn Harbour to enable the construction of a series of floating pontoon moorings to facilitate safe berthing at the harbour.
The cost - effectiveness of the treatment selected meant that the project was able to go ahead; the reuse of treated materials has meant that pollution has been reduced without generating waste; and treatment has been carried out according to best practice techniques.
In order to build the new facility, dredging of the harbour bed and the treatment of the contaminated silts found there was required. The contamination is thought to have arisen through the use of organic tin compounds (TBT) in anti-fouling paints applied to boat hulls.
Disposal via landfill was not considered to be sustainable; the nearest suitable facility is located 200 miles from Newlyn, and the cost of dig - and - dump would have added a prohibitive £2m to the project budget. S/s treatment was projected to cost just £200,000, keeping the overall project cost within budget.
In late 2005 May Gurney undertook an s/s treatability study to demonstrate that the technique would substantially reduce the leachability potential for the contaminants. Trials and tests on treated and untreated silts and leachates led to the proposal of a specific 'mix'. This was designed to meet Environmental Quality Standards for sea water, measuring a variety of metallic contaminants in addition to organotin.
Reuse of treated materials
Environment Agency approval was secured in mid - February 2006; this included the granting of a Section 19 Exemption enabling the treated materials to be reused as improvement fills for the adjacent area of Sandy Cove, which is to be developed as a boat maintenance facility and therefore requires the raising of land levels in order to comply with flood risk regulations. The project has brought the joint benefits of reducing pollution in the harbour and improving flood risk in Sandy Cove. This also meant that no contaminated materials were transferred to another location and the impact of the works on the local community was minimised.
Both the treatability study and the early improvement of the EA meant that project approval was gained in time to take advantage of the low spring tides to facilitate excavation and dredging works - enabling timely progress of the project.
Silts were excavated and stockpiled while awaiting treatment on a prepared area of the development site, enabling construction of the floating pontoon mooring to proceed.
Reduction of pollution
Batch treatment of the contaminated silts took place during February and March 2006, with a total of 7,300m3 of contaminated soils stabilised during that period. These were then placed onto the future car park area to be allowed to cure and later topped off with uncontaminated materials arising from the project earthworks.
After treatment, testing showed that leachability was reduced by 90%, and that the majority of leachable contaminants had been reduced by over 99% of their pre - treatment levels.
To date there has been little application of this type of clean - up in the UK, but the project has demonstrated that the s/s technology could have widespread use in remediation of harbours around the UK.
"This represents a remediation solution spawned from the limitations of the Landfill Directive - and that is good news" Tony Uppington
"Stabilisation has been around for a while but what is really positive in this instance is that all the work was staged on site, offering a total solution within one location" Phil Crowcroft
For further information please email Hyder Consulting Ltd