Remediation works (Hub & Cluster) involving the treatment of contaminated soils from a residential development for use at an adjoining site requiring fill material
Site Background & History
Remediation works to address contaminated soils in residential gardens.
Earth Science Partnership had undertaken site investigation of capping soils at a social housing estate in Llanelli (historically the site was used as a saw mill and timber yard prior to redvelopment in the 1990’s). The resultant analysis suggested that the soils exceeded human health criteria for a number of parameters, namely arsenic, lead and polycyclic aromatic hydrocarbons (particularly Benzo(a)Pyrene) and presented a Significant Potential of Significant Harm to site users.
Much of the analysis suggested the soils to be hazardous and without any hazardous landfill in Wales to except the soils, disposal costs were considered to be very high. A number of remediation options were considered including a novel remedial strategy (Cluster-Hub-Receiver) strategy which enabled re-use of treated excavated soils on a nearby development project. This stratgey would not only satisfy the remediation requirements but result in a significant cost saving to the client.
At the time of this project the Cluster-Hub-Receiver approach was very new, such that Earth Science Partnership organised a tour of the project for local Local Authority and NRW officers, with presentation by both Envirotreat and Earth Science Partnership.
Remedial Works
The proposed remedial works comprised the removal of the 600mm upper soil horizon from front and rear garden and landscaping areas followed by subsequent reinstatement with an underlying geotextile layer and clean soils to return the garden / landscaping areas to previous levels. The shared landscaping areas were also capped.
Excavated soils were transfer to the Treatment Area where they were treated ex-situ. A total volume of 3,789m3 of soils were treated over a 19 week period.
Validation
Samples of treated soils were leach tested and compared with the Environmental Quality Standards leachate target criteria for the identified contaminants of concern. In total 30 composite samples were tested to demonstrate compliance of the treated material with the agreed remediation criteria for the Receptor Site. The validated and treated [recovered] material was deposited at the Receptor Site.
Excavation of top 600mm from residential front / rear gardens (Donor site)
Stockpiled soils awaiting treatment a Hub Site
Soil treatment by E-Clay stabilisation at Hub site
Deposition of treated / validated soils at the Receiver site
Conclusions
The remediation strategy implemented by Envirotreat represented a significant cost saving to the client in terms of saving costly hazardous waste disposal associated with the donor site and and import costs associated with the receiver site.
The Cluster-Hub-Receiver site is much more widely accepted now and is one of the principle solutions under the C:AIRE Code of Practice Definition of Waste guidance
