A £200,000 increase in capital funding is required for the Causeway Hospital car park extension after invasive Mare’s Tail was discovered across the proposed works area immediately before construction was due to begin.
The addendum would raise the scheme’s business case from £624,377.33 to £824,377.33. Detailed estimates put the additional cost at £195,218.04.
The plant’s invasive nature and deep root system mean the original construction design could have allowed it to grow through the completed car park surface and kerbing. Such regrowth could damage and break down the new surfaces.
Following consideration of treatment options, the project team agreed that the most expedient approach was to revise the construction design. The amended plans include protective root barriers and adjusted site levels intended to reduce excavation and the off-site disposal of affected material.
The largest additional expense is £99,860.86 for a contractor-designed Mare’s Tail-proof membrane beneath the car park. The system will require specialist detailing around kerbs, manholes and drainage runs.
Revised earthworks are expected to cost £22,233.38, while imported fill, a blinding layer and compaction for the raised car park levels are estimated at £24,507.79. Some excavated material will be retained on site and used to create embankments along two sides of the car park.
Surplus material containing Mare’s Tail is classed as controlled waste under Northern Ireland regulations and must be transported and disposed of appropriately. The estimated disposal cost is £12,112.80 for 412 cubic metres, of which 246 cubic metres remains provisional.
Further costs include £7,694.50 for contamination testing and £9,456.33 for additional topsoil stripping, grass reinstatement and seeding. Contractor preliminaries associated with the extra time on site are estimated at £4,712.95.
Above-inflation price increases caused by the delayed start are expected to add £11,265.92. The additional works total £191,844.53 before £14,849.34 in omitted original work is deducted, producing a net addition of £176,995.19.
General inflation on the original contract adds a further £18,222.85, bringing the estimated overall increase to £195,218.04. The business case addendum provides for a £200,000 uplift to meet the revised capital requirement.