Case Study – Goytre

AHU Refurbishment – MEICA Division

Area: Wales Client: Welsh Water, Goytre WWTW

Scope of work:

Design & construct additional biofilter capacity to ensure that extra flow from a new housing development did not impact the existing site performance.

Temporary Works Items

A temporary wetting system comprising of pump, pipework and valving was set up but not connected to be used in an emergency in case of flow issues to the filter beds throughout the works. The Ammonia levels were monitored throughout the scheme and the wetting system deployed if levels reached certain thresholds.

Temporary Works Items

Repairs to the existing defects in the biofilter walls. The filter walls were increased in size while the filters remained in operation. This was enabled by carrying out civil works to allow this increase in height on the embankment side of the filters
Increase the existing wall height of tank by approx 142 mm. Boards were placed over the outlet channels to stop any debris falling into the channels. Before the wall height was increased the handrailing was removed and the damaged corner sections carefully removed and rebuilt. Small areas of media were removed and supported by sandbags while the corner sections were rebuilt. Once complete new handrailing was installed on the section of the filter walls. Repointing of the wall was then carried out.
The operation of placing the 200mm of media over the filter was then undertaken over 1 working day, with the filter taken off line. The media was placed using an excavator reach from the extremities of the filter. Where the excavator could not reach a conveyor was used to move the media across the filter and spread manually.
Installation of the external supplementary support system to the biofilter walls. The works were programmed to allow the installation of these supports before the filters were loaded with the extra 200mm of required filter media. Full design and structural calculations were carried out.
Increase the biofilter's centre column wall height by approx. 142mm for distribution arms support, the centre brickwork was increased to the required height. The process of raising the distributor and brick work took no longer than 2 nr 8 hr shuts, alternating between filters as required.

Innovative Design / Construction Techniques / Value Engineering:

Careful planning of works ensured that when the filter walls were increased in height the filters were still kept online and running.

BIM technology was used to design the structural supports for the tank and give the client an early indication of how this would look. This also allowed the supplier of the structural steelwork to fabricate offsite knowing that the measurements would be exactly as required.

Programme Requirements / Risk Management

Monthly valuations were carried out onsite with the client to ensure a swift and issue free payment process.

A Microsoft Project programme was shared with the client via the Northavon Cloud which was updated and reviewed collaboratively.

A risk register was created by Northavon and shared with the client regularly, the main risk associated with the uninterrupted running of the tank whilst carrying out the rebuilding works. Also that the 2 nr shutdowns didn’t runover their allocated time periods. This was mitigated by allocating additional personnel and the use of BIM to ensure buildability within the minimum amount of time possible.

One of the key challenges of the programme was a hard end date of 21^st December to enable the tank to be back online and fully functioning before the Christmas period commenced. There was no allowance for any slippage beyond this date. This was achieved through strong programme and project management in collaboration with Welsh Water. BIM technology also ensured efficient onsite installation.

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