Sandy Flat Mine remediation

Several studies have been done at the Sandy Flat Mine site.

These include all of the below.

Completed works

Groundwater investigation - a hydrogeological drilling program including the installation of extra groundwater wells to investigate the:
- groundwater conditions at the site
- mechanisms for contaminant transport.
Site telemetry installation - including weather station and groundwater monitoring equipment.

Hazardous material survey - to identify any hazardous materials including asbestos that need to be managed during any remediation activities.

Site fencing - installation of a stock fence to restrict stock access to potentially contaminated materials.
Bathymetric survey - a detailed survey of the flooded pit to collect accurate high-resolution data, including calculating the volume of the pit.

Fish survey - instigated by concerns from the Traditional Owners about potential impacts to human health from eating fish downstream from the site.

Independent review and gap analysis - consolidation of existing information and identification of knowledge gaps.
- This also proposed a work plan to address the identified gaps to develop an appropriate remediation plan.
Mine waste characterisation and material assessment - an understanding of the waste material at the site, including the primary source of contamination and the associated volumes had been identified as a key knowledge gap.
- This assessment was designed to address this and inform future remediation planning through a better understanding of the waste at the site.
Lidar survey - to develop an accurate 3D model of the site.
- This provides critical information about material volumes and is an input for any future engineering design work.
Wet season site inspection - the site is not easily accessible during the wet season.
- A wet season inspection was undertaken via a helicopter in early 2020 to:
  - measure the groundwater levels
  - measure the stream flow rates
  - inspect seepage from the site.
- This added valuable information to our understanding of site conditions.

Site telemetry review and maintenance - review and maintenance of the site telemetry including:
- weather station equipment
- groundwater monitoring equipment.
Additional mine waste characterisation - some areas of further work were identified from the waste characterisation work.
- This was to further delineate the waste at the site.
Conceptual remediation plan - this plan was developed to facilitate discussion about potential remediation options.

Cultural heritage - an assessment will be used to identify areas of cultural heritage that much be avoided or managed during remediation.

Conceptual hydrogeological model and water load balance model - the model represents the current conditions at the site and how contaminants are moving to the receiving environment.
- An understanding of where the contamination is coming from and how it is moving is critical to developing a robust remediation plan.
Aquatic biota and sediment assessment - a tender for aquatic biota and sediment assessment has been awarded and the fieldwork is proposed to be undertaken when site access is possible after the wet season.
- This assessment will provide a baseline condition of the downstream environment and this information will be used to demonstrate improvements post-remediation.
Drilling program - a program of drilling to finalise the waster characterisation and install more groundwater wells is proposed for the 2022 dry season.
- Procurement for this has commenced.

Development of a transient flow and transport model - this model will be used to simulate current conditions, conditions during remediation and post-remediation conditions.
- This package of works will be used to model the expected improvements to the receiving environment based on the proposed remediation approach.
Remediation options assessment - to assess the potential remediation options and the benefits and risks associated with different options.
- This is a critical piece of work in justifying the selection of a remediation approach and next work to develop detailed plans.
Geotechnical assessment of the pit - an assessment of the geotechnical stability of the pit will be required before assessing the feasibility of backfilling the pit.
Engineering design - once a preferred remediation option is determined, detailed engineering design can begin.
Water treatment assessment - an assessment of the potential options for water treatment will be required, including consideration of feasibility trials.

For more information, email lmu.ditt@nt.gov.au.