Barwon Water will conduct further testing at its Anglesea borefield to determine the long-term sustainability of the groundwater resource.
Test pumping over nine months will generate additional data for a detailed review of the operating licence.
Barwon Water will ramp up environmental and water quality monitoring during testing, with the results also forming an important part of the August, 2013, review.
Barwon Water was granted the bulk entitlement in June, 2009, to extract an average seven gigalitres a year from the area. Pumping began in October, 2009.
The borefield, with six of seven planned bores constructed, has been operating at a reduced rate because the triggers were approached more quickly than expected and water levels in greater Geelong's storages recovered following significant rain.
Geelong's storages are currently at 87 per cent capacity, the highest since 2001.
At Barwon Water's request, Water Minister Peter Walsh has granted a minor amendment to the original bulk entitlement to allow further test pumping as part of the information-gathering exercise.
He also has agreed to an extension of the review, from December, 2012, to August 31, 2013, to allow a better informed assessment of the aquifer's sustainable yield.
Barwon Water Managing Director Michael Malouf said the additional data was crucial to ensuring the long-term operation of the borefield.
"It will not only tell us the sustainable level of extraction, but it will assist in protecting the area's environmental values and the health of groundwater dependent ecosystems.
"In short, it will give us a thorough understanding of how the resource can be best managed."
Mr Malouf said pumping would be conducted within trigger levels re-set for the term of the test that determined the amount of water that could be taken.
Water level and environmental monitoring will also be increased during the test phase. The amendment includes a three month rest period with no pumping, so the borefield recovery can be monitored.
Barwon Water has requested these amendments following consultation with key stakeholders, including the EPA, DSE, Surf Coast Shire, Corangamite CMA, Parks Victoria and Southern Rural Water, on the pumping and monitoring program.