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Carrigans Wastewater Network Upgrade


Carrigans in Co. Donegal is located a short distance from the River Foyle on the R236, approximately 1.5km west of the border between the Republic of Ireland and Northern Ireland. The Carrigans Wastewater Treatment Plant (WwTP) is located to the south of Carrigans village and adjacent to the Carrigans River. The 2016 Census recorded the population for Carrigans as approximately 330.

Existing wastewater treatment

The Carrigans WwTP currently provides primary treatment only. The plant is a twin-cell horizontal flow septic tank, with a design capacity of 280 Population Equivalent (PE). It is estimated that the current wastewater load being received at Carrigans WwTP is around 330 PE.

Carrigans Wastewater Treatment Plant currently discharges via an outfall pipeline directly to the lower reaches of the Carrigans River, which is part of the River Finn Special Area of Conservation.

There are currently no storm water holding facilities at Carrigans WwTP and excess flows overflow to the outlet chamber and discharge via the discharge pipe to the Carrigans River.

Need for upgrade

The wastewater treatment plant in Carrigans is overloaded and needs to be upgraded to meet the needs of the village and to protect the environment.

We need to improve the wastewater treatment so that the receiving waters are not impacted. We therefore need to upgrade the size of the wastewater treatment plant as well as the level of treatment.

The current discharge from Carrigans WwTP is to the Carrigans River, rather than the main channel of the River Foyle, where significantly greater dilutions are available.

Carrigans Location


  • Upgrading the treatment for Carrigans will bring benefits to the village by meeting the current needs of the area and allowing for future growth.
  • The project will reduce impact of storm water overflows.
  • We will help improve water quality in Lough Foyle and nearby coastal areas.
  • Ensure wastewater is treated and discharged in compliance with EU regulations.

What the upgrade will involve

In order to overcome these deficiencies it is proposed to pump the untreated wastewater to St. Johnston WwTP. The upgrade at Carrigans Wastewater Treatment Plant will involve:

  • Decommissioning of the existing Carrigans WwTP septic tank, convert this to a storm tank and construct a new pumping station at the site.
  • Construction of a new rising main over a distance of 3,500m to transfer the full Carrigans load to St. Johnston WwTP.
Lough Foyle

When will the work take place?

The Swell Project Waves

We are currently at the design phase of the project. It is expected that construction will start in Q3 2020 with works complete by the end of 2021.

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