Project outline

Murphy was engaged to carry out Phase 2 – soil stabilisation works at the Gas Networks Ireland Limerick Gas Work Remediation site. Phase 1 - pump and treat remediation works, were carried out by a different contractor between 2016 and 2017. Coal gas was manufactured on the 1.4 hectare, city-centre site up until 1974 and contaminated the site with residues of DNAPL. The current works involve site remediation and stabilisation.

Prior to the main stabilisation and remediation works there will be extensive demolition carried out on site. Some of this will involve demolition in proximity to protected structures. This will involve isolating the internal walls from the protected structure in advance of demolition.

During the remediation process the site will be divided into dirty and clean areas with clear demarcation between the two. Personnel will access and leave the site through a decontamination unit.

Key challenges

There are a number of site constraints that require due allowance during the current remediation works. A significant proportion of the boundary walls are considered unstable. These include the Dock Road boundary wall, which is a protected structure in the Limerick City Development Plan. This wall will not be disturbed although excavation works will be undertaken in close proximity. There are brick boundary walls in several locations and these are stabilised by the use of gabion baskets. The O’Curry Street wall acts as a retaining wall to the pavement services on O’Curry Street and a steep slope on the site facing side of this wall has to be replaced. There is a second protected structure on the site, the Generator Building, which also has to be retained while excavation and stabilisation take place in close proximity.

There are houses adjacent to the southern boundary of the site which could be affected by vibration during the works. Excavation and solidification will have to be undertaken adjacent to all the above structures whilst protecting their integrity. There are also former GNI offices on the site which will be retained while remediation takes place in close proximity.

There is restricted access to the site and this will have to be pro-actively managed during the course of the works.

The site is subject to an EPA industrial emissions licence which places emphasis on the controls of emissions such as noise, odour, dust and vibration. Works are planned to minimise emissions and there is strict reporting guidelines to comply with the licence. There is also planning permission from Limerick City Council that will be complied with.

Project delivery/innovations

Coal gas was manufactured on the 1.4 hectare, city-centre site up until 1974 and contaminated the site with residues of DNAPL. The current phase of works (soil stabilisation) involve site remediation and stabilisation. This will be carried out by excavation and treatment of approximately 20,000m³ of contaminated ground. Approximately 3,000m³ of U2 (highly contaminated ground) will be safely disposed of overseas through a licensed waste contractor. Numerous underground tanks on the site will also be broken out. The upper 3m of soil across the site will be excavated and remediated using a cement/GGBS combination. Hard dig materials (concrete) will be crushed on site to form 6F2 which will be used as a capping layer across the site.

The site is operated under an industrial emissions licence issued by the EPA. An extensive pilot study was carried out prior to excavation to develop the remediation process and prove it could be successfully delivered. Extensive ongoing testing is required to prove the process is working. Extensive noise, vibration, dust and odour control and monitoring is also carried out, as detailed in the EPA licence. Two protected structures are present on the site (built heritage and industrial heritage) and require preservation in-situ.

Key facts
  • Coal gas manufactured on the site till 1974, contaminating the site with residues of DNAPL
  • Phase 2 works - site remediation and stabilisation
  • Works carried out under EPA industrial emissions licence
  • Excavation and treatment of 20,000m³ of contaminated ground
  • 3,000m³ of U2 (highly contaminated ground) to be disposed of overseas through a licensed waste contractor
  • Underground tanks to be broken out
  • Upper 3m of soil to be excavated and remediated with cement / GGBS combination
  • Hard dig materials to be crushed on site to form 6F2 to be used as capping layer
  • Ongoing testing
  • Noise, vibration, dust and odour monitoring

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Limerick Gasworks Remediation image.

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