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Highlights
- Full hydrogeological characterisation supported by drilling
investigations
- Characterisation of contaminants present in underlying
groundwater
- Recommendations for containment and monitoring.
Background
A waste management facility at Orange has been managed as
an ongoing operation by Orange City Council. In addition,
an extension to the south of the existing landfill was being
sought. Terrasciences Ltd engaged C. M. Jewell & Associates
Pty Ltd to undertake profiling of the geology, depth to
groundwater, hydraulic gradient, distribution of hydraulic
conductivity and groundwater chemistry.
Hydrogeological Environment
The landfill area is underlain by volcanogenic basement
rocks of Ordivician age. The rocks comprise tuffs, shales,
chert, breccia and dolerite. The basement's fabric is steeply
dipping north-west trending foliation pattern. Zones of
fractures and deformation, with distinct joint sets are
observed in exposures. Overlying the basement a residium/colluvium
or regolith of up to 8 metres thickness is found. Variable
depths of saturation are observed in the voids and fractures
within the basement rocks. The water table follows the topographic
profile, albeit in a subdued manner.
Objectives and Scope
An initial desktop assessment was made employing data available
from the Department of Land and Water Conservation. Subsequently,
a drilling program placing six boreholes was initiated on
the margins of the active landfill. Each borehole was characterised
as follows:
- geological logging of chips and core
- geophysical downhole logging
- installation of a piezometer and correction of water
level to common datum
- permeability testing (rising head)
- groundwater sampling for characterisation of water quality
The resulting data was analysed to provide information
on the impact of the landfill activity on surrounding groundwater.
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Projects