Castletroy Wastewater Treatment Plant


The works to be constructed include:

  • Construction of a new 3,750 m³ stormwater storage tank
  • Installation of new primary treatment filters and lifting pump
  • Construction of a new primary sludge holding tank
  • Upgrade of the existing secondary treatment tanks to provide additional capacity
  • Upgrade of the plant’s sludge treatment facilities

The plant is currently operating at capacity of 45,000 population equivalent (PE), which is appropriate to cater for existing wastewater loads. However, the demands of population growth and industrial development will cause Castletroy WWTP to become overloaded in the coming years. The proposed upgrade project will increase its capacity to treat wastewater for the calculated 10-year growth projections of 77,500 population equivalent (PE).

Moreover, there is currently no provision for stormwater storage at Castletroy WWTP which means that occasionally during heavy storm and rainfall events excess stormwater is discharged untreated into the Lower River Shannon. This proposed project upgrade will include the construction of a  3,750 m³ stormwater storage  tank in order to store excess stormwater until the main plant can accept and treat the excess flow.

The Lower River Shannon is an area of environmental conservation under the Habitats Directive 92/43/EEC (Commission of the European Communities, 2007) and must be protected from any potentially harmful wastewater emissions.

The proposed upgrade at Castletroy WWTP will bring many benefits including:

  • Modernise and improve the performance of the existing wastewater treatment plant
  • Improve the health and integrity of the environment
  • Protect the water quality in Lower River Shannon and conservation habitats
  • Provide sufficient capacity to facilitate future population and industrial growth
  • Protect recreational waters for fishing and boating activities
  • Ensure compliance with Irish and EU legislation now and into the future

The application for planning permission, which will include all relevant environmental and consultation documents, will be submitted in November 2022.

The application may be viewed/downloaded at www.water.ie/castletroy.

Subject to the outcome of the planning application, works are expected to start in 2024 and continue into 2026.

We all create wastewater in our everyday lives. At home, we access water with ease; we turn the tap, we flush the toilet and we hit the button on the washing machine. Industry, hospitals, schools and offices also create wastewater.

Wastewater can contain a wide range of contaminants, some of which can be broken down in the environment easily while others not so easily and must therefore be treated to ensure that it is not a threat to public health or the environment when discharged to the receiving environment. Wastewater is collected and transported via underground sewers / pipelines to be treated at a wastewater treatment plant (WwTP).

Untreated wastewater poses a threat to public health and the environment. Treatment is therefore carried out in order to produce an environmentally safe liquid that is suitable for disposal to our aquatic environment, such as rivers, lakes and seas.

Proper wastewater treatment systems are essential for sustaining modern living and contributing to development as householders, businesses, industries, schools and hospitals all rely on a robust wastewater treatment system to maintain their daily activities.

The sewerage system transports wastewater via underground sewers / pipelines to a wastewater treatment plant where it is treated to strict standards under EPA licence and in compliance with EU and national water quality legislation, to a standard that is safe to be discharged to the environment.

At the treatment plant, contaminants are removed including fats, oils and greases along with biological matter such as bacteria and faecal matter.

For more information on the wastewater treatment, check out our section From Drain to Sea.

Wastewater will be transported from homes and businesses to the wastewater treatment plant (WwTP) through an underground drainage network.

The sewer system in Limerick was built in the 1900s and, as was typical at the time, it carries both wastewater from homes and businesses and water that is drained off roads and pavements. When more rain and wastewater arrives at the plant than it can process, the excess is discharged directly to the Lower River Shannon as untreated effluent. This is to prevent the sewer network from backing up and causing the flooding of roads and properties.

When more rain and wastewater than the plant can process arrives, the excess is directed to a stormwater holding tank. When the rain has passed and the incoming flow returns to more normal levels, the stormwater in the tank is returned to the plant for full treatment. 

The proposed upgrade of Castletroy WWTP means that the plant’s capacity will be increased and a stormwater tank installed. Therefore, stormwater overflow incidents will be significantly reduced.

Irish Water notifies Local Authorities and the EPA of any incidents or overflows that occur at the plant that could impact the receiving waters.

During the works a traffic management plan, agreed with Limerick City and County Council will be in place. To minimise traffic disruption, construction vehicle movements will only take place outside of peak morning and evening traffic times.

All potential impacts resulting from construction works were subject to Environmental Impact Assessment by An Bord Pleanála. All mitigation measures contained in the assessment will be strictly complied with.

To minimise disruption heavy construction equipment/machinery will only be operated during the following hours:

  • Monday to Friday 7.00am to 7.00pm
  • Saturday 7.00am to 2.00pm
  • No operation on Sundays or Bank Holidays
  • Note that these limits exclude the tunnelling machine and directly associated activities which are low noise emitting activities

In order to minimise the generation of dust, the team will undertake the following:

  • Spraying of exposed earthworks activities and site haul roads during dry weather with water
  • Provision of wheel washes at site exit points
  • Control of vehicle speeds, speed restrictions and vehicle access
  • Sweeping of hard surface roads
  • Provision of a 2.4 metre hoarding around the site

In order to minimise the generation of noise the team will ensure the following measures are in place:

  • Provision of hoarding around the construction works
  • Continuous noise monitoring will be undertaken to ensure it does not exceed limits
  • Continuous vibration monitoring will be undertaken to ensure it does not exceed limits

An Environmental Impact Assessment (EIA) is the process of identifying, predicting, evaluating and mitigating the possible effects on the environment of a project before a decision is made whether or not to proceed with that project. The steps in the EIA process are set out in national and EU legislation. Most large-scale infrastructure projects are subject to EIA as part of their planning consent process.

When a project proposer submits its application for consent to An Bord Pleanála it must include an Environmental Impact Assessment Report (EIAR) describing the project and its anticipated effects on the environment. A period of statutory public consultation then follows, during which the public and any interested body may make comments and observations to An Bord Pleanála on the project and its environmental effects. An Bord Pleanála must then undertake an environmental impact assessment of the project before making its determination on the application.

An Environmental Impact Assessment Report (EIAR) is an analysis of the likely effects (positive and negative), that a proposed development may have on the environment. This includes any likely effects on people, flora, fauna, soil, water, air, landscape and cultural heritage.

The Birds and Habitats Directives of the EU sets out various procedures and obligations including the establishment of Special Protection Areas (SPAs) and Special Area of Conservation (SACs) for the protection of specific habitats and species. Collectively, the SPAs and SACs established throughout the EU comprise a network known as Natura 2000.

The Habitats Directive imposes a duty on EU Member States to consider the possible nature conservation implications of any project on the Natura 2000 site network before any decision is made to allow that project to proceed. This assessment procedure is known as Appropriate Assessment (AA) and is quite similar to the EIA procedure. It is normally undertaken by the project team at the planning consent stage with An Bord Pleanála.

Like the EIA procedure, a document is prepared by the project proposer and submitted with its application for project consent. This document is known as a Natura Impact Statement (NIS). While there is significant overlap between the EIA and AA processes, it should be noted that the NIS and AA only consider and assess impacts on the Natura 2000 network and that AA is a separate legal consent process distinct from EIA.