Limerick Gasworks Remediation Limerick, Ireland by WSP
Shortlisted for Category 7 - Best Re-use of Materials and Category 9 - Best International Project
This unique and complex project has been 25 years in the making! WSP (formerly Mouchel) were originally commissioned by Gas Networks Ireland (GNI) back in 1995 to prepare a Desktop Study of the former Dock Road Gasworks site in Limerick. Due to several difficult-to-resolve constraints in relation to Limerick, WSP proceeded with the remediation of Clonmel, Cork, Dublin and Waterford gasworks while these issues were addressed. The remediation strategy adopted at Limerick differed from the other Irish gasworks remediation projects which essentially comprised the removal of all contaminated soil from site for treatment overseas. At Limerick, an innovative combination of in-situ and ex-situ technologies were adopted to achieve a sustainable and economic solution to a grossly contaminated site; the largest undeveloped site in Limerick City situated in a prime location on the banks of the River Shannon.
WSP’s approach was based on two phases of remediation:
Phase 1 works utilised innovative in-situ Pump & Treat technologies to remove mobile Dense Non-Aqueous Phase Liquids (DNAPL), essentially free phase coal tar from underground structures and features at depth.
Phase 2 works commenced in January 2019 and utilised ex-situ Stabilisation/ Solidification techniques where specialist binders were designed to ensure that both leachability and strength requirements were achieved.
WSP was appointed by GNI to mitigate environmental liabilities associated with its former gasworks site in Limerick. GNI own and operate the natural gas network in Ireland and managing their environmental impact is a key activity for GNI, and includes reducing their carbon footprint where possible. GNI is committed to implementing the principles of sustainable development across all aspects of their operations and in particular in the remediation of the former gasworks site. The site will, when fully remediated, be suitable for future redevelopment and facilitate its reintegration to Limerick City. Ervia (Major Projects), a sister company of GNI, acted in a project management capacity in respect to the remediation project.
The former Dock Road gasworks site in Limerick covers an area of 1.4 hectares and is located approximately 100m south-east of the River Shannon. The site was formerly a limestone quarry prior to first being developed as a gasworks in the 1830’s. Gas production from coal ceased
in the 1960s, where naphtha was then used, which continued until 1989, when natural gas arrived in Limerick.
Historical site investigations undertaken in the early 1990’s had identified significant quantities of DNAPL within soils, groundwater and contained in underground structures. WSP carried out a comprehensive ground investigation in 2011 to fully characterise the contamination across the site. The previous investigations were of limited value as the techniques employed had not been able to penetrate through considerable underground obstructions including basement slabs, foundations etc. WSP adopted a Sonic Drilling technique, not previously used in Ireland for characterising contamination, which proved to be very successful with over 130 boreholes being drilled on a 10 x10m grid to rockhead across the whole site without any refusals. A Detailed Quantitative Risk Assessment (DQRA) was subsequently completed by WSP which identified potential risks to surface water, groundwater and to human health from typical gasworks contaminants within soils including PAHs, TPH, BTEX, heavy metals, sulphur, cyanide and ammonia. A Remediation Options Appraisal and Remediation Strategy were then developed which identified a combination of in-situ and ex-situ remediation technologies as being the most cost-effective and sustainable solutions. The remediation works were designed to remove the main mobile DNAPL sources and effectively immobilise contaminants within soils. The selected approach combined an initial phase of in-situ Pump & Treat, to remove as much of the primary DNAPL source from within below ground tanks and at depth within the soil profile as possible, followed by a phase of excavation and ex-situ treatment by Stabilisation/ Solidification and re-use of soils. The results of the DQRA were used to derive site specific Remedial Target Values (RTV’s) for soil and leachate which were agreed with the Irish Environmental Protection Agency (EPA). The carbon
footprint was calculated for all remediation techniques considered.
The detailed information from the high-density investigation allowed effective mapping of the distribution of DNAPL and bedrock level, to a high degree of resolution. This allowed locations where the Pump & Treat would be most effective to be identified during the Phase 1 works and allowing target depths for excavation to be pre-determined, enabling excavations to be quickly infilled with treated stabilised material, avoiding delays while awaiting basal verification results.
Risk Communication Liaison was carried out with local residents and businesses throughout the whole remediation works by means of information evenings, stakeholder meetings, leaflet drops and face to face meetings. WSP/ Ervia explained the risks associated with the works in a non-technical manner to residents and businesses and, in particular, to demonstrate that any odours created posed no risk to human health. Planning permission was granted by Limerick City and County Council (LCCC) in 2013 after assurances were provided in relation to the significant amount of environmental monitoring which would be undertaken during the works including air quality, noise, dust, groundwater monitoring, vibration and odours in addition to the safeguarding of Protected Structures of significant architectural value on site. An application for an Industrial Emissions Licence (IEL) was successfully granted by the EPA (W0281-01) in 2014; the first such licence to be granted in Ireland for a remediation project under the new Industrial EmissionsLicensing Regulations, 2013. The works had to be undertaken in accordance with a comprehensive set of conditions which covered all aspects of the remediation works. An Appropriate Assessment Screening Report also had to be prepared to assess ecological implications as part of the Habitats Directive as the adjacent Lower RiverShannon is a Special Area of Conservation (SAC) and a Natura 2000 site.