Water Journal : Water Journal December 2011
water resources technical features 58 DECEMBER 2011 water Study Overview Two scenarios were considered for the provision of water supply and wastewater services to urban communities in the Gold Coast region of SEQ. The infrastructure considered under each scenario was limited to those water supply and wastewater infrastructure types that are in use, or have been considered for use in the SEQ region. The 'Traditional infrastructure mix' was based on the water supply and wastewater infrastructure in operation at the Gold Coast during 2007/08. This 'Traditional' scenario is summarised in Figure 1 and included the following: • Dam-sourced mains water supply via two conventional Water Treatment Plants (WTP), supplemented by rainwater tanks on 15% of existing houses; and • Sewage collection and treatment (four STPs), utilising 20% of secondary treated effluent for non-residential (mostly irrigation) reuse, and 100% of biosolids for agricultural reuse. A 'Future infrastructure mix' was also defined, incorporating four alternative approaches to urban water supply in addition to the existing 'Traditional' infrastructure. The 'Future' scenario is summarised in Figure 2. The additional infrastructure included for the 'Future' scenario was: • The newly-constructed Tugun seawater desalination plant. • An indirect potable reuse (IPR) scheme delivering recycled water to the local water supply dam. This envisaged a hypothetical IPR scheme for the Gold Coast region similar to the Western Corridor scheme. The required Advanced Water Treatment Plant (AWTP) was assumed to be located at the largest sewage treatment plant (STP) in the Gold Coast region (Coombabah). Recycled water would be pumped to the local Hinze Dam. • A limited number of households (about 6% of total) being provided with Class A+ reticulated water for toilet and external uses, along with a 5000L rainwater tank to supply laundry demands. This encapsulated the newly constructed Pimpama- Coomera Waterfuture scheme. • All other (non-Pimpama) new households having a 5000L rainwater tank to supply toilet, laundry and external uses. This brought the overall coverage of households with rain tanks to 67% of total. • All other (non-Pimpama) new households serviced by new sewage and STP infrastructure equivalent to the conventional STP infrastructure of the 'Traditional' scenario. Methodology Scenario definition The scenarios were based on assumptions of average household water use generated from Gold Coast data for 2007/08. While high-level water restrictions were in place in the region Table 1. Water supply balance for infrastructure mix in each scenario. Traditional Future Urban Households 202,000 550,235 Peri-urban Households 20,000 20,000 Total Households 222,000 570,235 Water Use2 -- Total (ML/d) 140 377 Water Use2 -- Residential 98 262 Water Use2 -- Non-residential 42 115 Water Supply -- Total (ML/d) 140 377 Dam Supplies -- Environmental 137 141 Dam Supplies -- IPR -- 44 Seawater Desalination -- 125 Rainwater (Household Tanks) 3 64 Class A+ Residential -- 4 1. Connected to mains water supply & some with rainwater tanks; not connected to sewerage 2. Including allowance for mains distribution losses Figure 1. 'Traditional' scenario urban water system. Dam urban HH STP Ocean Biosolids to Farms Class B irrigation Non- residential tank WTP WTP sludge to sewer peri- urban HH tank outdoor use outdoor use Dam existing urban HH STP Ocean Biosolids to farms Class B irrigation Non- residential tank WTP STP SWRO Desalination plant Pimpama STP Pimpama RWP new HH toilet laundry tank new HH tank AWTP Product water to Dam ROC ROC existing periurban HH tank Ocean Ocean non-residential Class A+ reuse WTP sludge to sewer outdoor use outdoor use outdoor use outdoor use toilet laundry Figure 2. 'Future' scenario urban water system.
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Water Journal November 2011