Tetra Tech engineered the upgrade of the regional water-supply scheme at Lough Talt (County Sligo), securing a first-ever imperative reasons of overriding public interest (IROPI) permission under the Habitats Directive.
From February 2018 to January 2019 over 13,000 residents within Lough Talt’s catchment area were under a boil water notice due to contamination. The water treated from Lough Talt used chlorination, which did not protect against cryptosporidium, trihalomethanes and falls short of EU drinking water standards.
In May 2019, in a landmark ruling, Sligo County Council granted planning permission for the upgrade of the existing Water Treatment Plant at Lough Talt, Co Sligo. This was the first project in Ireland to gain permission using the Habitats Directive IROPI process. Working closely with Irish Water, Sligo County Council and the National Parks and Wildlife Service, our engineering and environmental team delivered this landmark approval.
Challenge
We began the preparation of a Water Abstraction Order for Lough Talt in 2010 to regularise the abstraction ongoing for over 70 years. Lough Talt is designated as part of the Lough Hoe Bog Special Area of Conservation (SAC) and the River Moy SAC. Due to environmental sensitivities, we carried out detailed hydrological and geological investigations between 2012–2016 to assess the potential impact of the existing abstraction on the integrity of the European sites’ conservation objectives. We found that during periods of extended dry weather the lake level drops because of the abstraction operation, which impacts the Lough Hoe Bog SAC, potentially endangering the protected Geyer’s whorl snail.
Solution
To avoid the impact the abstraction needed to reduce by approximately 50% during a significant portion of the year (approximately 95 days). This would not be adequate to supply the existing population requiring a supplementary water supply. Based on the studies and reporting prepared by Tetra Tech, Sligo County Council completed the Appropriate Assessment. An assessment of solutions showed no available alternative options to supply safe drinking water in the short to medium term. Consent was granted for IROPI to address the ongoing contamination and public health risk.
Based on the documents prepared by Tetra Tech, including IROPI and compensatory measures, a statement of case was prepared for consideration by the government. The compensatory measures including the reintroduction of the whorl snail were accepted by the Minister for Housing, Planning and Local Government and Minister for Culture, Heritage and the Gaeltacht as being sufficient to safeguard the protected site.
We then provided detailed design services to Sligo County Council for the water treatment plant (WTP) upgrade.
Project timeline
- 2010: Preparation of water abstraction order
- 2012: Hydrological and geological investigations commence
- 2016: Investigations submitted
- 2019: Application for IROPI approved, WTP construction work commences
Benefits
- 13,000 homes affected
- 12.5MI/d abstraction order required
- 12,500m³ water treatment plant
At a glance
Client
Sligo County Council and the National Parks and Wildlife Service
Location
Sligo, Ireland
Services
AA Screening / NIS—Stages 1–4 of the Appropriate Assessment process was completed, architecture, assigned and design certifier, civil & structural engineering, contract administration, contract documents, detailed design / specimen design, employer’s representative, mechanical and electrical engineering, optioneering / feasibility including site / route selection report, planning applications for the WTP upgrade, project management, quantity surveying, tender assessment
The project featured in this article was undertaken by RPS, A Tetra Tech Company and originally published on RPSgroup.com. In March 2026 RPS rebranded to Tetra Tech.