Executive SummaryThe majority of Mount Gambier’s urban stormwater is discharged directly via drainage wells or sink holes into the unconfined, karstic Gambier Limestone aquifer. This aquifer is the dominant source of water for Blue Lake, from which Mount Gambier’s drinking water supply is drawn. In addition to its value as a drinking water supply, the Blue Lake is of high environmental value to the region as a tourist attraction due to its annual colour change process and vibrant blue colour in summer.The scope of this risk management plan covers harvesting of urban stormwater generated within the City of Mount Gambier, the processes for intentional recharge of this stormwater, the consequent groundwater quality in the Gambier Limestone aquifer and use of this groundwater via the Blue Lake for the raw water for the Mount Gambier drinking water supply. This plan also covers use of groundwater potentially affected by stormwater recharge in the City of Mount Gambier for non-potable domestic and irrigation use. Drinking water supply providers are required to develop and adopt an appropriate risk management plan under the Safe Drinking Water Act 2011. SA Water has an approved Water Safety Plan under the Safe Drinking Water Act 2011.This report documents the application of each of the twelve elements of the National Water Quality Management Strategy risk management framework. When implemented this will assist in protection of public health and the environment in compliance with the National Guidelines for Managed Aquifer Recharge and for Augmentation of Drinking Water Supplies.The South Australian Department of Environment, Water and Natural Resources; Environment Protection Authority, South Australia; South Australian Water Corporation; City of Mount Gambier; and District Council of Grant were consulted in preparation of ‘A risk-based management plan for Mount Gambier stormwater recharge system’. At the time of writing, consultation with these key agencies was undertaken through their representation on the Blue Lake Management Committee. Since completion of this plan, the Blue Lake Management Committee has been disbanded. Nonetheless, the agencies consulted remain as the key stakeholders for management of the stormwater recharge system and protection of Blue Lake and its groundwater system. While the Blue Lake Management Committee can no longer oversee this plan, the recommendations made for management of the stormwater recharge system remain relevant.With the shared responsibility of stakeholders in mind, proposed actions for various stakeholders are suggested to support this risk-based management plan. Appendix A presents a proposed Activities Schedule for implementation of this plan, with possible suggestions for the agency that would take responsibility for implementation of recommended actions. Measures suggested include new programs for monitoring the quality of stormwater recharge and groundwater to complement the existing water quality monitoring in Blue Lake; catchment hazard assessment and protection; regular inspection of non-licensed risk activities; improvement of existing pre-treatment of recharge; documentation and review of incident and emergency response actions; and review of training procedures for employees and contractors involved with the recharge system.
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