Toowoomba's GAB bores - the experience to date ...

Toowoomba Water Supply Emergency GAB Bores Project - Status Report

AUTHOR - Manager, Water Project Services (Greg Dinsey) - 27 February 2009

PURPOSE OF REPORT

To provide Council with an update on the status of the Toowoomba Water Supply Emergency GAB Bores Project.

ISSUES AND RESPONSES

1. Project Funding

In September 2007, Toowoomba City Council was advised of approved subsidy of up to $11,841,300 under the Urban Drought Water Program (UDWP) for the construction of emergency water supply bores into the Helidon Sandstone aquifer of the Great Artesian Basin as follows:

Eligible cost under UDWP $17,166,561
Less Council's contribution (10% TCC water revenue) $ 1,378,160
$15,788,401
State contribution under UDWP (75%) $11,842,300
Council funding under UDWP (25%) $ 3,947,101
Total Council funding required $ 5,325,261

This approval is subject to the establishment of test bores to confirm quantity and quality availability prior to drilling permanent infrastructure, as well as a requirement to work closely with Department of Natural Resources and Water (NR&W) Officers.

Following several meetings with NR&W Officers a strategy for the development of "Test Production Boreholes" was agreed.

2. Emergency GAB Bores - Hydrogeological Modelling

Australasian Groundwater and Environmental Pty Ltd (AGE) undertook numerical modelling of the impacts of sourcing 5,000ML per annum of GAB water from the Cooby Dam/Meringandan area. Their final report dated November 2007 concluded that the modelling results show no significant additional long term impacts on the Helidon Sandstone aquifer. The modelling showed that, during periods of extraction, some impacts can be expected in nearby areas to the borefield, however due to the elastic nature of the aquifer once the extraction is over, the water levels rapidly recover to a level just under the predicted level had the extraction not occurred. To minimise capital costs as well as operational and maintenance costs, the modelling investigation ended with a concentration of bores in the vicinity of Cooby Dam.

3. Bore Construction

Through a Services Agreement with Department of Natural Resources and Water (DNR&W), DNR&W acted as a contractor to Council for the construction of the first two "test production bores". These arrangements negated the need for Council to prepare documentation for the drilling and casing of test holes and production bores and the potentially time consuming tender/contract process. DNR&W's bore drilling, casing and cementing sub-contractor was Queensland Drilling Services Pty Ltd. The bores were constructed at the Leahy Road and Loveday Cove (East) sites in the period November 2007 to February 2008.

In May 2008, it was decided to proceed with the construction of up to an additional three bores. Council invited public tenders for this work in June 2008 and a contract was subsequently awarded to Queensland Drilling Services Pty Ltd mid-August 2008. Construction of the Loveday Cove (West) bore was commenced and completed in November 2008, the construction of the Pipeline Road bore was commenced in December 2008 and completed in January 2009. Due to a combination of factors including low dam levels, unpredictable rainfall patterns, contractor and materials availability, it was decided to proceed with the construction of the fifth bore. The Paton Road bore was commenced late January 2009 and completed late February 2009.

All five bores are of similar construction comprising 323mm cemented steel casing to the top of the Helidon Sandstone aquifer with 219mm slotted steel casing within the aquifer. Depths to the top of the aquifer (415m - 490m below ground level) and the thickness of the aquifer (75m - 90m) were in close agreement with the predictions of AGE Consultants hydrogeological modelling.

4. Test Pumping

A requirement of the UDWP subsidy funding was the confirmation of water quantity and quality. Following construction of the bores, the drilling contractor undertook air purging and air lifting of water from the bores to clean out and partially develop the bores. Water samples were taken during this operation with favourable water quality test results.

Test pumping of the first two bores (Leahy Road and Loveday Cove (East)) was arranged using the services of a local experienced contractor Australian Groundwater Services Pty Ltd. Test pumping was undertaken at the then anticipated production flow rate of 35L/s. A test pump (35L/s versus 420m head, 1,000 Volt 230 kW motor), suitable for later use as a production pump, was purchased from Tyco Pumping Systems (Southern Cross). A 100 hour pump test and recovery was undertaken at each bore as well as water sample testing for water quality and monitoring of water level drawdown at GAB bores adjacent to the test pumped bore.

Test pumping was undertaken in the period September to December 2008.

Test pumping results were analysed and reported on by AGE Consultants. The analysis confirmed the earlier numerical modelling of the borefield and enabled further modelling with parameters established from the test results. The analysis confirmed that pumping of the emergency GAB bores has the potential to adversely impact on the Reushle Road bore in the long term, with the recommendation of regular drawdown monitoring during times of production pumping. It is noted that modelling, and experience during the test pumping, indicates that the water levels rapidly recover following cessation of pumping.

It is planned to test pump either the Pipeline Road bore or Paton Road bore to confirm both water quantity and water quality (as a consequence of further development of the bore during the test pump). Air purging and air lifting of water from these bores following their construction indicates potentially different drawdown characteristics to the other bores.

5. Production Pumping

The test pump was left in the Loveday Cove (East) bore following the test pump of the bore with the intention of putting the bore into production using a diesel fuelled generator for power supply. Production pumping from the bore commenced early January 2009 and has continued uninterrupted, except for regular servicing of the generator, at a flow rate of 40L/s (3.45ML/day). Over 200ML has been pumped to date. The generator and fuel tank have been hired for an initial three month hire term.

Due to the high lift (at the Loveday Cove (East) site the static lift is over 340 metres), the power requirements are significant. Fuel consumption is in the order of 1,350 litres/day. The base cost, excluding monitoring and the transport of hired equipment, of pumping from the bore is $2,145 per day (or $15,000 per week). This equates to approximately $0.60 per KL of water pumped. Advice has been received from DNR&W and DLGP&R that these operational costs are subsidisable under the Urban Drought Water Program.

Ergon Energy has been requested to supply quotations for the provision of permanent power to each of the bore sites. Indicative Council contributions for power to the Pipeline Road site and Paton Road site are $170,000 and $185,000 respectively if both are done together, or $390,000 if one site only is done.

Because of the high cost of pumping and increasing confidence in the timely availability of water from Wivenhoe Dam to Cressbrook Dam, it is intended to review the current temporary pumping regime in consultation with DNR&W officers in the near future.

6. Water Quality

Testing of water samples taken during the drilling contractor's air purging and air lifting, and more importantly during the 100 hour test pumping, revealed that the water quality is similar from each bore and similar to the Reushle Road bore water which has been in production for some time. Typically the water has iron (2.80 - 4.0 mg/L), manganese (0.07 - 4.07 mg/L) and total dissolved solids (560 - 670 mg/L) which exceed the aesthetic guideline values of the Australian Drinking Water Guidelines.

7. Scheme Details

As the Toowoomba Water Supply Emergency GAB Bores Project has progressed, the ultimate scheme, should completion of the project be realised, has developed to the following components:

• continued pumping of the Reushle Road GAB bore water into the Leahy Road storage lagoons

• pumping of Leahy Road GAB bore water into the Leahy Road storage lagoons

• pumping of GAB bore water from the Leahy Road storage lagoons via a new pipeline that parallels the Cooby Pipeline to a location near the Pipeline Road GAB bore for discharge into a waterway that discharges to Cooby Dam

• pumping of Loveday Cove (East) GAB bore water via a short length of new pipeline directly into Cooby Dam via a rock riffle to aerate the water

• pumping of Loveday Cove (West) GAB bore water via a short length of new pipeline directly into Cooby Dam via a rock riffle to aerate the water

• pumping of Pipeline Road GAB bore water via a short length of new pipeline directly into Cooby Dam via a rock riffle to aerate the water

• pumping of Paton Road GAB bore water via a short length of new pipeline directly into Cooby Dam via a rock riffle to aerate the water

The above scheme results in all the GAB bore water being piped to Cooby Dam where natural processes within the lake will aid in the treatment of the water. The existing Cooby Dam pump installation has the capacity to deliver all the GAB bore water to the Mt Kynoch Water Treatment Plant.

Based on the results of the numerical modelling and the test pumping results to date, it is intended that extraction of 1,250ML/annum from each of the GAB bores will be targeted. This provides 5,000ML/annum production with four of the five bores operating on average throughout the year.

8. Project Expenditure

Project costs to date are:

Leahy Road bore - $1,404,725
Loveday Cove(East) bore - $1,108,416
Loveday Cove (West) bore  - $1,098,331
Pipeline Road bore - $1,326,495
Paton Road bore - $1,184,924
Other (test pumping, reports, etc) - $443,501
Total - $6,566,392

At this stage, only one test (production) pump and ancillary equipment (including switchboard /transformer, power and control/monitoring cables, riserless packer system) have been procured. As indicated above, permanent power to each of the sites (with upgrade of existing power to the Leahy Road site only envisaged) is likely to afford a better long-term financial benefit to Council than the use of diesel fuelled generators.

Forecast project costs are in the order of $7.0 million should the project not proceed to the next phase (refer Next Steps section below).

9. Next Steps

In January 2009, DNR&W and Council officers concluded that the decision to proceed with equipping the bores and bringing them into production could be deferred until May 2009. This conclusion was based on a number of contributory factors including the promise of the Wivenhoe - Cressbrook Pipeline being completed and commissioned by early 2010, the reasonably good outlook for increased useable dam storage levels from summer/autumn rainfall events and the fact that useable storage levels were similar to the storage levels at the same time in January 2008 as a result of the good rainfall experienced in December 2008.

Equipping the bores and bringing them into production could be achieved progressively within 4-5 months of a May 2009 decision to proceed.

With the completion of the construction of the bores, project activities and timelines are:

Test pumping of Pipeline Road and/or Paton Road bore - April 2009
Civil, electrical, mechanical design/documentation - April 2009
and subject to a decision to proceed to the next phase of the project (in May 2009):
Civil, electrical, mechanical design/documentation - September 2009
Power supplies - October 2009
Commissioning completion - October 2009
...

COMMITTEE RECOMMENDATION

That Council note the status of the Toowoomba Water Supply Emergency GAB Bores Project as detailed in the report of the Manager, Project Services dated 27 February 2009 and, that decisions in relation to the progression of the project to bring the bores into full production mode will be made in consultation with the officers of the Department of Natural Resources and Water in accordance with the terms of the Urban Drought Water Program subsidy approval.

See - Toowoomba Regional Council - Committee Meeting - 10 and 11 March 2009.