SIGNIFICANCE OF VERTICAL LEAKAGE FOR AN MAR SCHEME IN A CARBONACEOUS AQUIFER: GEELONG, AUSTRALIA

Stephen Parsons1, Gwyn Hatton2

1. Sinclair Knight Merz, sparsons@skm.com.au
2. Barwon Region Water Corporation, Gwyn.Hatton@barwonwater.vic.gov.au

Abstract

Barwon Water Authority supplies around 270,000 people in the Greater Geelong area (60km south west of Melbourne, Australia) with water and sewerage services.  During the current prolonged dry period, groundwater  comprises up to 50% of the Greater Geelong water supply. Managed aquifer recharge is therefore a logical non-conventional technology for investigation.  Barwon Water is currently pursuing three investigation areas in the region – this paper presents the results to date of a 20 month investigation program in one of these areas, the Upper Eastern View Formation (UEVF) in the Jan Juc Syncline.

The UEVF Aquifer consists of interbedded sands/gravels, clay and coal seams.  Within the study area the aquifer is confined by a 60-100m aquitard, with a potentiometric level 40-70m below ground level.  Groundwater salinity ranges from less than 1,000 mg/L TDS to 4,000 mg/L TDS.  Organic carbon levels in the groundwater (TOC/DOC  up to 10 and 6 mg/L respectively) are indicative of the impact of carbonaceous materials adjacent to the target sand layers.

This paper describes the results of the first two stages of the investigation program: Stage 1 involving drilling and hydraulic testing of six observation bores and water quality sampling; and Stage 2 involving a long term pumping test and hydraulic modelling to determine various MAR options.  The modelling explores a range of options including ASR and ASTR, with each fulfilling different scheme objectives.  A possible source water for the scheme is high quality recycled water – under this scenario, obtaining minimum residence times as an additional barrier is an important objective.  A nearby borefield in the Lower EVF has potential implications for induced vertical leakage and subsequent impacts on recovery efficiency.

Design of the remaining stages of the program are discussed, including geochemical modelling, solute transport modelling and the injection trial.  Particular challenges for MAR at the site are likely to be around water quality issues associated with the carbonaceous nature of the aquifer and vertical leakage impacts.
Keywords:  ASR, MAR , vertical leakage, Geelong, Australia.