Mid-Kerry Water Supply Scheme – DB Contract

Project Summary

The Mid-Kerry Water Supply Scheme required the construction of a new Water Treatment Plant to treat surface water from Lough Callee and the Gaddagh River.

Coffey Construction Limited undertook the construction of this new 11,000m3/day treatment plant which included new process streams, chemical systems, electrical upgrades, ancillaries and upgrade of the sludge management stream together with the demolition of an obsolete part of the existing plant. The facility employs a direct filtration process, which involves first mixing a coagulation chemical into the raw water, allowing sufficient contact time with stirring to allow the suspended particles to bond together to form “flocs”, and then filtering out the suspended solids. Conventional filtration processes use sedimentation or flotation to remove these flocs prior to the filters.

CCL saw an opportunity at this site whereby careful design of the mixing, flocculation, and filtration stages, we could remove this sedimentation or flotation step, and allow the filters to be solely responsible for removing the suspended solids. This cost-effective solution provided savings to the client. The mixing and stirring of the coagulated water were achieved naturally without the need for energy and labour intensive paddle mixers.

CCL undertook the full design, supply, installation and commissioning of all process, mechanical and electrical equipment including electrically operated actuators, electromagnetic flow meters, pressure sensors, ultrasonic level sensors, telemetry outstations, local and remote control system, hand and automatic control systems, etc. The works also included the provision of a raw water pumping station (with pumps capable of achieving 308 l/s), a raw water storage tank, a new clear water storage tank and all associated raw and treated water pipelines. Along with all the MEICA and Civil works, CCL also undertook the associated site works and landscaping inclusive of the final road layout, kerbing and planting.

The water treatment plant was constructed on a remote, upland site, and the construction of the project was planned to be over the winter period, which turned out to be one of the coldest in many years. CCL looked for innovative ways of reducing the on-site construction time. The filter block is a large concrete structure. Conventionally, above-ground filters such as these are constructed by pouring concrete “in-situ” within a structural shutter and allowing the concrete to cure. CCL constructed the filters from a number of self-standing, pre-cast concrete sections that were manoeuvred into position, taking a precise measurement of levels and alignment. The sections were then “stitched” together with reinforcing steel bars and small, targeted in-situ concrete pours. In this way, the on-site construction time was significantly reduced.

CCL provided a SCADA and telemetry system to monitor real-time plant operation. As part of this system, the following signals were made available to the SCADA system: 4-20ma flow signal analog input, discrete input for reactor on/off control from remote location, 4-20ma UV dose analog output, 4-20ma UV intensity analog output, discrete output indicating critical alarm, discrete output indicating major alarm, discrete output indicating minor alarm, reactor status – healthy or tripped and UV transmittance. Continuous on-line monitoring with automatic instrumentation is required to monitor pH, corrosion rate, turbidity, dissolved oxygen, sodium, fouling, biological activity, and halogens.

Our success in the area of in-house process design and installation of new mechanical & electrical assets is demonstrated by the shortlisting of the Mid-Kerry WSS by the Building and Design Awards in 2011 for Water Project of the Year.

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