Groundwater Modelling for Tea Gardens Aquifer

Summary and scope

Please refer to the Specification document for further information. This project has been established to improve Council’s understanding of the Tea Gardens aquifer through predictive groundwater modelling and the compilation of a groundwater modelling technical report that documents the capacity/capabilities of the Tea Gardens borefield during drought conditions. The scope of this project is as follows: Review of existing groundwater model to determine adequacy to be utilised for proposed predictive modelling. a. Model review should include: i. Model layers (thickness, lithological layering, bedrock depth) ii. Aquifer hydraulic conductivity data, heterogeneity and isotropy iii. Water levels and flow patterns iv. Recharge and discharge mechanisms b. If the existing groundwater model does not accurately simulate actual groundwater trends over recent 3-5 years. The margin for error and impact on predictive accuracy is to be discussed with Council. Council may require recalibration of groundwater model to improve the reliability of the results. The cost and work involved to recalibrate the groundwater model should not be considered in the tendering stage, recalibration shall be considered as a variation, with scope to be defined when/if required. Undertake predictive modelling to on a drought scenario, similar to the 2019 drought period. a. Predictive modelling to extend drought period (rainfall patterns etc.) by an additional 3 months b. Borefield demand (as supplied by Council) to include the supply of both Tea Gardens and Gloucester townships for the duration of the modelling period. c. Modelled demand to be forecast 10 years from existing demand. i. Demand figures to be provided to successful tenderer. Produce an aquifer modelling report that shall: a. Determines the environmental impact of groundwater extraction under extended drought conditions, specifically: i. Impact of extraction on the hydraulic gradeline throughout the aquifer; ii. Impact of extraction on groundwater dependent ecosystems and environmentally sensitive areas (SEPP (Resilience and Hazards) 2021 wetlands); iii. Maintenance of positive head pressure at the aquifer boundary with the Myall River b. Assess the sustainable yield (maximum yearly extraction potential ML/yr)) of the aquifer considering the environmental constraints above and a dry year scenario (600mm rainfall). c. Identify the requirement for additional production bores to meet forecast demand. i. If additional production bores are required, propose the optimum location of these bores for both yield and environmental impact.