Purpose:
Environmental monitoring should be carried out in order to:
- Assess potential impacts from aquaculture containment structures on the environment or nearby groundwater users. This can include contamination of groundwater, waterlogging or salinisation of surrounding soils or accelerating discharge of existing poor-quality groundwater to environmentally sensitive areas.
- Assess the potential for shallow groundwater or seepage to affect embankment stability. As embankments and foundations become wet they can weaken. Where groundwater levels rise above the base of lined containment structures, the liner may rupture when structures are drained for maintenance.
- Assess the potential for surrounding groundwater quality to affect containment water quality. Containment structures built in areas of shallow, poor-quality groundwater can become contaminated by groundwater in?ow when water levels drop below groundwater levels.
- Identify, prior to construction, any groundwater issues, including nutrient contamination, shallow watertables, acidity or salinity that might otherwise be attributed to aquaculture operations if detected in the future.
Visual inspections:
Problems with containment structures may be discovered via the following visual indications:
- waterlogging
- salinisation e.g. salt scalds
- vegetation dieback or changes in vegetation characteristics e.g. to more salt or water logging tolerant species
- evidence of exposure of acid sulfate soil (e.g. iron stains)
- embankment failure, slumpage or bulging
- overtopping
- erosion.
It is strongly recommended that routine inspections are carried out, and permanent photographic monitoring points are established. This will provide a record of visual changes in surrounding environments and at representative points at the perimeter of the containment structures.
Particular emphasis should be placed on sensitive environments and the property boundary adjacent to sensitive land uses. Photographs should be taken at least annually at the same time of year as a permanent record of visual changes.
Groundwater monitoring:
Purpose:
Groundwater monitoring helps to identify any significant problems with containment structures. Experience has shown that installing groundwater monitoring bores and commencing groundwater monitoring should be undertaken as soon as possible in the life of the project.
In the event of allegations of environmental impacts, baseline monitoring data will provide valuable information for those investigating and assessing the allegations. It is likely to be cost effective to install the monitoring bores at the same time as the geotechnical and acid sulfate soil investigations are undertaken.
Both tasks should be carried out by skilled and competent people. While leakage from synthetic lined ponds (concrete, HDPE lined) is not expected, it is recommended that monitoring bores be installed to account for potential impacts from hydrostatic mounding or liner damage.
Location and number of monitoring bores:
The initial bores installed to collect baseline data should be located outside the proposed construction area but must be suitably positioned so they can be used for future monitoring.
This will minimise any risk of damage during construction and will enable the same monitoring bores to be used for baseline and post-construction data acquisition, providing a clear comparison of pre- and post-construction data.
Groundwater monitoring bores should be located so that baseline conditions, including seasonal and tidal variation in water quality and potentiometric levels are defined.
This will enable early detection of any impacts from aquaculture farm construction or operation, and identify the difference between impacts from farm operations from those due to other sources.
Before choosing the locations of monitoring bores at the site, the following conditions should be considered:
- likely direction and velocity of the groundwater flow
- potential off-site contaminant sources
- geology of the site and the region
- location and proximity of the site to surface water resources
- location and proximity of the site to groundwater bores used for extraction of potable water
- surface topography of the site and likely underlying topography of any aquifer.
The number and location of monitoring bores will depend on geological assessment and the characteristics of the aquifers, depth to groundwater, direction and rate of flow, hydraulic gradient and distance to sensitive receptors. The number and location should allow for monitoring of both spatial and temporal trends.
It is recommended that at least two bores are placed between the containments structures and sensitive receptors or neighbouring properties to identify changes in depth and quality of any groundwater over time.
These may need to be nested bores depending on the aquifers. If trends are recognised, other bores may need to be installed to gain a better understanding; this may require a bore within the containment area. Trend information is important in assessing seepage problems.
Control bores:
Where practical, it is strongly recommended that a control bore or bores be installed at a location distant to the development area (e.g. >250m) to provide a reference against which to evaluate the magnitude of any impacts detected in the monitoring bores. For example, a control bore should be installed in an adjacent property to monitor the same groundwater aquifer as the impact monitoring bores (permission should be sought when installing bores on other properties).
Depth of monitoring bores:
The shallowest aquifer is the most critical to monitor, as it will be the most sensitive to any problems with the containment structures. Groundwater monitoring bores should be installed so they can take samples across the full depth of the aquifer. The ultimate depth of each bore will depend on the depth to the watertable as well as the saturated thickness of the aquifer.
At sites with multiple aquifers it may be necessary to install nested bores, comprising a separate bore screened in each aquifer. Under no circumstances should bores be constructed with screens, filter packs or permeable backfill extending across multiple aquifers.
Monitoring bore construction standards:
All monitoring bores must be drilled and constructed by a licensed water bore driller, with copies of bore logs submitted to the Department of Natural Resources and Water, as required by the Water Act 2000.
The monitoring bores should be constructed in accordance with the Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ) Minimum construction requirements for water bores in Australia. A suitably qualified engineer or hydrogeologist should collect soil samples and log the lithology on-site.
For security, bores should have lockable, heavily-galvanised, steel bore shields or standpipes. The standpipe should protrude above potential flood or tidal inundation, or at least 0.5 m above the ground surface, and be bedded in concrete to a depth of approximately 0.3 m.
The annulus between the PVC casing and the standpipe should be backfilled with filter pack material or grout to minimise the risk of fire damage to the casing. The standpipe should be painted in a high-visibility colour, with the well ID (e.g. BH01) marked on the top of the standpipe.
In cases where vegetation may obscure the bore headworks, a star picket, painted in a high-visibility colour, should be installed, extending above the expected height of the vegetation where feasible.
The location, natural surface level and casing level of the monitoring bores should be accurately surveyed (location to ±0.1m and height to ±0.005m). The location and natural dry season surface level of nearby surface water bodies should also be surveyed where applicable.
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