Northern Ireland: Dorisland WTW, GAC Filter Building

DAWSON-WAM Ltd were appointed by Northern Ireland Water to design and construct a new Granulated Activated Carbon (GAC) filter plant within the existing Dorisland Water Treatment Works, Carrickfergus.  The scheme was necessary to ensure the drinking water provided to Carrickfergus and the surrounding areas is of the highest standard and will continue to comply with EU drinking water quality standards well into the future.

The filter building comprises of 8no. GAC tanks complete with plenum filter floors, 1.2million litre capacity clean backwash tank, 2no. dirty washwater tanks,  plant room, a mezzanine floor housing the motor control center and an upper filter gallery 8meters above the lower filter gallery.

Overhead gantry cranes were installed within the plant room and the lower filter gallery to assist with future maintenance requirements. 2no. split level crane set down areas / loading floors were constructed to aid with plant movements.

All cladding and structural steel work were designed and constructed to a high humidity specification to deal with the onerous conditions experienced within the treatment building.  Cladding was selected to match the existing site buildings and parapet wall cladding was erected to provide continuity with the remaining industrial units within the plant.

The excavation for the GAC building involved the removal of approx 7,000m3 of material; the reinforced concrete structure required over 2,500m3 of concrete and 240T of steel reinforcing.

External to the building an extensive ducting network was installed to allow the new GAC plant to be fully integrated within the existing plant.  Gravity pipework ranging from 150mm dia to 900mm dia was installed, along with pumping mains ranging from 125mm PE pipe to 800mm ductile iron pipe.

Access roads/ hardstanding and heavy duty tanker loading bays capable of withstanding GAC tanker weights of 80T were constructed around the building.

Up to 7m depth of fill material was then landscaped around the GAC building to lessen its impact on the skyline above Carrickfergus.  Gabion baskets were employed to construct a 6m high retaining wall along the south side of the site adjacent to NIE infrastructure. Easy care planting was completed on the sloping banks to provide shielding and a low cost easily maintained area for the client.

Due to the strategic importance of the plant enhanced security measures were installed around and within the industrial building to the government’s strict Centre for the Protection of National Infrastructure (CPNI) criteria.

During design careful consideration was required to limit the visual impact of the enhanced security measures on the final building aesthetics, with security mesh being incorporated within the building’s brick skin to hide from view and special high strength engineering brick produced and used to minimize final wall thickness.

In addition to the physical building protection, an extension of the enhanced security fencing / CCTV network and Perimeter Intruder Detection System (PIDS) was undertaken.

Careful planning and coordination with the client during construction was necessary to both maintain full site security at all times while managing the interface of a busy construction site and operational water treatment plant.

The deadline to provide a safe and compliant water supply was the driving force behind a compact construction programme with efficiency in delivering each individual phase programmed to eliminate lag. Zoned working areas were utilized to ensure high levels of health and safety between individual disciplines while working together on site.

This scheme ensured the client, Northern Ireland Water, could deliver on their commitment to providing a safe and sustainable water supply to the greater Carrickfergus area.