technical features
common planning assumptions and baselines. Future demands were projected based on population projections for TCC and customer shires. T he impact of longer term demand reductions arising from water conservation measures and the instaJlarion of rainwater tanks under current TCC policy were also included in planning assumptions. Included in rhe review was a preliminary investigation using a Level of Service (LOS) approach based on the work undertaken for the SEQRWSS. Existing supply side options were reviewed based upon the latest analys is of yield for surface water storage systems and long-term ava ilable supply from groundwater systems. Figu re 1 provides a summary of demand and supply source assumptions used as the context for this review. Figure 2 is a map of T oowoomba and its surrounds, involved in the study.
Detailed Review of the Options
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Option 1 This option was proposed by T CC and was named the Water Furures Toowoomba initiative. This initiative involved a number of measures bur principally indi rect potab le reuse (IPR) of water from T oowoomba's Weta lla Sewage Treatment Plane by co nstruction of an advanced water treatment plane that would treat efflu ent to a suitable level for pumping in to the storage reservoir, Cooby Dam. Implementation of this option will have rhe benefit of recycling a total of 6,500 ML/a comprised as fo llows: • 5,000 ML/a of IPR fed into Cooby Dam from the advanced water treatment plant • 1,000 ML/a of recycled water sent to local Hampton lrrigators and replaced with 1,000 ML/a of bore water (extracted from Geham bore) • the remaining 500 ML/a will be subsrirured by dual reticulation use at a green field development at the High fields estate Key issues associated with chis option include: • ga ini ng public support for rhe scheme • esrablishing the sustainabil ity of the scheme with its added diversity, renewabi licy . and independence from climatic variab ility • managing public health risks (real and perceived).
Option 2 T his option involves sourcing water from bore licence holders in the Oakey Creek Grou ndwater Management area (O CGMA) which is approximately 40km west of Toowoomba, in rerurn fo r treated effluent from the Weralla Sewage Treatment Plant.
The expectation is char up to 6,500 ML/a is available from this source. An extraction of 8,528 ML/a from OCG MA raw bore water would be req ui red to provide 6,5 00 ML/a of potable water based on a 75% recovery rare from the water treatment process. An estimated 22 bores would be required to service this demand. Key issues associated with ch is option incl ude: • high capital cost of this option • Ii mi red avai lability of the water resource • difficulties in removal/transfer of existing water entitlements • potential sustainabi lity of rhe proposed scheme.
Option 3a Th is op tion involves partial sourci ng of future demands (6,500 ML/a) from bore licence holders in the Condamine G roundwater Manage ment Area (CGMA), which is some 70km south west of Toowoomba, in return for treated effluent from Wetalla Sewage Treatment Plant. Ir is expected char an extraction of 7,871 ML/a of bore water wou ld be requi red to provide 6,500 ML/a of drinking water allowing for an 80% recovery rare from rhe water treatment process. Ir is anticipated that approximately 11 bores wou ld be required to service rhe needs of this option. Key issues associated with chis option include: • high capital cost • limited ava ilability of rhe water resource given the over-allocated nature of the existing groundwater area
• difficu lties in removal/transfer of existing water entitlements • potential sustain abili ty of rhe proposed scheme.
Option 3b This option involves sourcing considerably more water fro m bore licence holders in the CGMA in return for created effluent from Weralla Sewage Treatment Plane boosted by supply from the proposed Brisbane to Darling Downs effluent pipeline. The estimated long-te rm extraction from the CG MA is 23,100 ML/a including an existing 3,661 ML/a urban entitlement. Therefore the remaining volu me of water char can be sustainably extracted from the CGMA for supply to Toowoomba is assumed to be I 9,439 ML/a. Allowing fo r losses during the treatment process, 16,053 ML/a of water can be retu rned to Mount Kynoch Water T reatmenc Plant fo r drin king water purposes. Key issues associa ted with this option incl ude: • high cap ital cost (note: th is analysis assumes no capi ta l conrribucion to the proposed Brisbane to Daring Downs effluent pipeli ne) • dependence on rhe Brisbane to Darling Downs effluent pipeline project proceeding • difficulties in removal/transfer of existi ng water entitlements.
Option 4 This option is to import rhe by-product water extracted during coal seam gas production from rhe gas fields southwest of Chinch illa, approximately 190km from T oowoomba. Ir has been claimed char up to
Journal of the Australian Water Association
Water
SEPTEMBER 2006 65