Central Coast Drinking Water Source Documents for HSC Chemistry (Module 9.4: Chemical monitoring and management) 1. Introduction This PDF document, Central Coast Drinking Water , addresses the following statement on page 61 of the NSW HSC Chemistry Syllabus: “gather, process and present information on the features of the local town water supply in terms of - catchment area - possible sources of contamination in this catchment - chemical tests available to determine levels and types of contaminants - physical and chemical processes used to purify water - chemical additives in the water and the reasons for the presence of these additives ” (Source: NSW HSC Chemistry Syllabus, Section 9.4 Chemical Monitoring and Management). Its purpose is to complement the excellent teaching/learning module 'Water Quality: HSC Chemistry ' produced by the Sydney Catchment Authority (see SCA at http://hsc.sca.nsw.gov.au/chemistry/introduction ). Specifically, this document presents information for students and teachers on the Central Coast of NSW; information about the local water supply that will enable students to address the Chemistry Syllabus dot points in familiar terms and with relevant examples. This document does not attempt to deal with the broader issues of water testing purposes and methodology prescribed in the Syllabus. These issues are already well treated in the SCA module. Rather, the materials here are selected secondary sources that will assist Central Coast students to better understand the particular features of their Water Supply system and the regimes in place to monitor and ensure that high quality drinking water is available for all residents. These secondary sources should enable Central Coast students to complete the kind of assessment task suggested on the SCA webpage http://hsc.sca.nsw.gov.au/chemistry/drinking_water/report . 2. The structure of the current Central Coast water supply system Gosford City and Wyong Shire Councils share a joint water supply scheme administered by the Gosford/Wyong Council’s Water Authority. This is the third largest water supply system in NSW (see Figure 1). Figure 1: The Current Central Coast Water Supply System (Source: Gosford Wyong Councils’ Water Authority http://www.gwcwater.nsw.gov.au/index.php/our-system) Water is drawn from four streams (Mangrove and Mooney Creeks in Gosford and Wyong River and Ourimbah Creek in Wyong). The building of water storage infrastructure was begun 75 years ago, but most infrastructure in use today was completed during the past thirty years. Currently, the system incorporates three dams, three weirs, two treatment plants, 40 reservoirs, and 1900 km of pipelines. It has a total catchment area of about 700 square kilometres. Water is drawn from Mooney Dam and weir pools on Wyong River, Mangrove Creek and Ourimbah Creek. Wyong River and Ourimbah Creek extractions are stored in Mardi Dam. During dry periods, when the Coastal Mooney and Mardi Dams cannot meet the demand for water, supply can be released from Mangrove Creek Dam to provide adequate inflows at the weirs on Mangrove Creek and Wyong River. A key new element in WaterPlan 2050 (the long term water supply strategy for the Central Coast) is the Mardi-Mangrove Link Project. This will consist of a new 19 kilometre buried water pipeline from Mardi Dam to the existing Boomerang Creek tunnel at Mangrove Creek Dam together with supporting infrastructure. Construction of the pipeline will commence in early 2010 and will secure the region’s town water supply over the next four decades. Before being delivered to the community, the “raw” water is treated to produce a water quality that complies with the high standards of the NHMRC/ARMCANZ Australian Drinking Water Guidelines – 2004 . The JWSS has two water treatment plants, one located at Somersby in Gosford City and the other at Mardi, in Wyong Shire. Currently, approximately 60,000 properties in the Gosford local government area are supplied with a total of about 230 million litres of town water. About 290 million litres per week are consumed within Wyong Shire. 3. The Catchments A catchment is an area where water is collected by the natural landscape. In a catchment, rain will eventually flow to a dam, creek, river, lake or ocean, seep into the groundwater system, be used by vegetation and animals or evaporate. Each dam, river and creek has its own catchment. Together, the combined catchment areas of the Central Coast region’s drinking water system are about 727 square kilometres (Table 1). Table 1: Gosford-Wyong Councils’ Water Supply System (Source: Gosford Wyong Councils’ Water Authority http://www.gwcwater.nsw.gov.au/images/PDF/joint_water_supply_061103.pdf ) Catchment Year Catchment Maximum built area (km 2) capacity (ML) Mooney Mooney Dam 1961 39 4,600 Mardi Dam 1962 4 7,400 Lower Wyong River Weir 1968 355 300 Lower Mangrove Creek Weir 1975 140 300 Ourimbah Creek Weir 1978 88 100 Mangrove Creek Dam 1978-82 101 190,000 Totals 727 202, 700 Managing and protecting our catchments is a key process for ensuring good water quality. Gosford and Wyong Councils have catchment policies which identify specific activities which can be carried out within each catchment area (see Figure 2). Water supply extractions from weirs on the lower sections of Wyong River and Ourimbah Creek have no impact on the upper sections of the waterways but may reduce flushing in the lower saltwater sections during extended periods of low rainfall. In times of water shortage, water is released from Mangrove Dam into Wyong Creek to allow extractions to continue and to allow for environmental flows down stream. Possible impacts from this on Wyong Creek, such as unnaturally cool flows and introduction of new species of aquatic organisms, are monitored by the Water Supply Authority. The weirs also have the potential to block fish from swimming up and down stream, possibly affecting breeding. So, appropriate fish ladders have been put in place by the Water Supply Authority to overcome this. Figure 2: The Central Coast water supply catchments (Source: WaterPlan2050 ( http://www.gwcwater.nsw.gov.au/index.php/waterplan-2050 ) showing the planned Mardi-Mangrove Link (http://www.gwcwater.nsw.gov.au/index.php/mardi-mangrove-link ) 4. Possible Sources of Water Contamination Potential contamination of water supplies depends on the nature of the catchment areas from which the raw water is gathered. As examples of the kinds of contamination possible within the Central Coast catchment areas we consider the Mangrove Creek Dam, Lower Wyong River Weir, and Mardi Dam catchments. Mangrove Creek Dam Mangrove Creek Dam is the Central Coast’s major storage dam. It is located on Mangrove Creek and is the main storage that supplies the Coast during times of low rainfall. When there is insufficient storage in Mooney Mooney and Mardi Dams, or insufficient flows in Mangrove Creek, water is released from Mangrove Creek Dam. Water is drawn from the dam by a 50 metre high intake tower which transfers it under the dam wall and releases it into Mangrove Creek to supply Gosford City. Another, smaller intake tower draws water from the dam and pumps it through the Boomerang Creek Tunnel and into Wyong River to supply Wyong Shire. The catchment area of Mangrove Creek Dam is sandstone eucalypt bushland and is bounded by George Downes Drive to the east to the north and the Great North Road to the west. The land use in the catchment area as it was at the time of the dam’s construction is summarised in Table 2 and Figure 3. Table 2: Summary of land use in upper Mangrove Creek catchment as described in 1975 prior to the construction of the Mangrove Creek Dam ( Source: Where would you have put the dam? http://www.blueplanet.nsw.edu.au/SiteFiles/blueplanetnsweduau/Water%20History%20Case%20 Study.pdf ). Freehold or Leasehold McPherson Vacant Zones of impact for Stage 1 (hectares) State Forest Unreserved of the Mangrove Creek dam Agriculture Forest (hectares) Crown Land (hectares) Stored waters 140 690 340 0 Within 0.8 km of stored waters 0 370 3310 0 Within 0.8 km to 3.2 km of waters 90 720 3210 740 Remainder of Catchment area 120 50 100 160 (“Land Use Planning for the Catchment of the Proposed Mangrove Creek Dam” ‘Report on Investigations for Water Supply to the Gosford-Wyong Region’, Report No 2, Sept 1975, Department of Public Works N.S.W (page 11)) Figure 3: Original land use within the Mangrove Creek Dam catchment area. (Source: “Environmental Impact of the Proposed Dam“, Volume 2, “Mangrove Creek Dam – Environmental Impact Statement” 1977, Gosford-Wyong Water Supply, NSW Department of Public Works.) The Mangrove Creek Dam catchment is in excellent condition. • The land comprises extensive undeveloped, uninhabited land which helps to maintain a pristine catchment area. • The site has a rock foundation. Areas with a sandy base are not suitable for dam construction. • The naturally V-shaped valley is the ideal storage with a small surface area compared to volume – which means evaporation at the site is low. • The dam site is located relatively close to all other water catchments – which minimises the costs associated with transfer pipelines and pumping stations. One other catchment within the Central Coast supply with similar forested landscape Mangrove Creek Dam is the Mooney Mooney Creek Dam catchment (39 km 2). Lower Wyong River Weir Wyong River Weir has a catchment (355 km 2) three times the size of that of Mangrove Creek Dam (Figure 4). The weir’s catchment consists of significant areas of agricultural land in contrast to the mainly forest land of the storage dam. Agricultural enterprises include cattle grazing, small scale horticulture and orchard enterprises, and turf production. Other features within the Wyong River catchment include the F3 highway and feeder roads, and the small rural villages of Dooralong, Jilliby and Yarramalong.