Terms of reference for IPART to undertake a targeted assessment of the construction costs for six priority stormwater detention basins and associated soil disposal costs in Blacktown City Council's (Council's) Contribution Plans No. 20 Riverstone and Alex Avenue (CP20) and undertake a targeted assessment of the construction costs of one priority stormwater detention basin and associated soil disposal costs in No. 21 - Marsden Park (CP21 ).