Executive Summary:

An assessment completed at the former Coochiemudlo Island landfill to characterise the environmental risk posed by this facility by GHD in September 2018 (Coochiemudlo Island Former Landfill – Monitoring and Environmental Risk Review Report (GHD, 2018)). Primarily this assessment was competed to assess risk to the adjacent Melaleuca Wetland, although a broader review of potential receptors was incorporated.

Additional surface water and groundwater monitoring was completed in November 2018 to confirm the findings of the Risk Review, with results presented in the current report. Three rounds of surface water and groundwater monitoring have been completed in 2018 to inform environmental risk characterisation. Laboratory results identified several parameters at concentrations in excess of the adopted assessment criteria, however typically results in down gradient / down stream locations were consistent or less than background locations, indicating the landfill represents a low risk to the identified receptors for most parameters assessed.

Ammonia in groundwater and electrical conductivity in surface water were identified at concentrations in excess of the adopted assessment criteria and at concentrations that were elevated in comparison to background conditions. These results were sporadic in nature and are not representative of the general downstream /  down gradient dataset, and a review of the monitoring results does not indicate gross landfill impact. Ammonia results provide further support to this conclusion as ammonia is a typical indicator of landfill impact. Ammonia is readily detected in areas of landfill impact due to its typically high concentration in landfill leachate and its mobility in groundwater. Although ammonia was marginally elevated in downstream monitoring location GW3, the results do not support landfill impact.

CISW2 and CISW3 were dry during the November 2018 monitoring round and data was not available to indicate the water quality of the potential wallum frog habitat. However, during previous monitoring events, it was determined that the water quality is outside the optimal ranges for wallum frog species, however this is not attributable to the former landfill. Based on the findings of this assessment the former landfill is considered to present a low risk to down gradient receptors and remedial works at the landfill are not considered to be required.

While this assessment has characterised the risk posed by the landfill to identified receptors to be low, it is noted that limited monitoring (three complete events) has been completed and further monitoring is recommended to validate the findings of this assessment and enable characterisation of potential risks over differing climatic and seasonal conditions.

The full report is available through the following link –

21 December 2018 – Redland City Council Coochiemudlo Island Former Landfill Surface Water and Groundwater Monitoring Report