Rosehill Industrial Estate, Carlisle (Phase 1)

DESIGN

Working with our directly employed designers, R.G.Parkins from Kendal, a remediation and enabling strategy was produced which resulted in us appointing two specialist subcontractors.  

The first specialist appointed subcontractor was appointed to remediate the existing ground with a cement adding mixing system that increased the strength of the existing ground to allow the construction of a concrete raft foundation for the new buildings. This method was used so as not to run the risk of penetrating the existing aquafer which is situated directly under the site

The second specialist appointed subcontractor was appointed to carry out a general remediation and enabling strategy method for the entire site.

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SITE HISTORY

The site had been partially excavated during the 1920’s for clay extraction associated with a nearby brick and tile factory. The site was subsequently filled with household waste, ash and carcasses from the 1967 foot & Mouth outbreak.

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GROUND CONDITIONS

The ground investigation showed that there was made ground 5.5m below existing ground levels. Asbestos was found to be present within the landfill site and within the hardcore capping layer. Localised cyanide and naphthalene hot spots were identified.  There were also elevated levels of ammonia, hydrocarbons, carbon dioxide and methane. An underground Aquafer was also present.

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CHALLENGES

• The site had to be designed to take light industrial units. The building foundations traditionally on this type of site would require piling. However, this had to be discounted as there was a danger of the piles puncturing into the underground aquafer resulting in contaminated leachate entering the groundwater system. The ground under the buildings therefore had to be stabilised. The solution was soil mixing - which involved mixing cement with the existing landfill to create a solid base to build up from.
• Identifying hazardous hotspots and removing safely from site.
• Removal of asbestos from site and coming up with a strategy to prevent fibre release during the work.
• Removing the minimum of contaminated material from site as this was a major cost component to the budget.
• Strategy for removal of invasive weeds such as Japanese Knotweed
• Pollution risk control measures required to protect the adjacent watercourse and aquafer
• Assessment of groundwater and surface water quality over an extended period of time to determine the risk to the adjacent Durranhill Beck.

WORKS INCLUDED

• Hazardous hotspots were removed to landfill
• Asbestos was also removed to landfill. Air monitoring stations were installed around the perimeter of the site to detect any fibrous material in the air.
• Ground improvement with cement soil mixing below new building footprints
• Contaminated materials were processed on site and mixed with imported hardcore. This then lowered the trigger levels for contamination to the required acceptable levels
• Site won materials were screened and regraded and were reused on site as capping layer beneath paved areas
• Implement all works in strict accordance with UK Environmental Permitting and Local Planning Authority Requirements
• Continual testing of the site won material and new mixed material

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LESSON LEARNT DURING STAGE 1 DESIGN

• As the ground beneath the new buildings were to be solid concrete following the soil mixing, a strategy had to be implemented for getting the drainage and utilities coming into the buildings
• Expect the unexpected
• Concrete is inhibited from setting when mixed with certain chemicals
• DEFRA had to be informed of the potential Foot & Mouth on site. They must be contacted early within the process to allow a mitigation strategy to be approved

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SUCCESSFUL OUTCOMES

• All remediation was completed in line with the agreed strategy and to the stipulations set out by the Local Authority as part of the Planning Conditions.
• The project was delivered with zero reportable Health & Safety incidents.
• The project was delivered with zero environmental notices issued.
• No customer or third-party complaints
• The final amount of material that had to go to landfill was well below the initial estimated amount
• Following the completion of the remediation works a report was compiled by the Environmental Consultant detailing all site enabling works that were undertaken, waste consignment notes and all site investigations, laboratory test certificates and validation testing undertaken
• Early contractor involvement was essential for a successful outcome of the scheme for buildability and budget constraints

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BUILDING WORK

To view the work carried out by our Building department on this project (Phase 2), click here.