This exploration survey used the cross-hole resistivity method to detect if there was industrial waste water leakage from an industrial waste water process pond. Chemical analyses concluded that this specific waste water has a much lower resistivity than normal water.
The figure below shows that the area above 45m is a relatively high resistive zone made of limestone. Below this depth is a middle resistive zone with some low resistivity spots or bands visible; they are the source of possible leaks or fracture zones.
A borehole between ZK7 and ZK8 was drilled to test one of these low-resistivity locations. Polluted water was found at a depth of 52m. The figure below shows that a consistency among joints exists between each adjacent cross-hole. Detailed geological information can thus be obtained from this kind of resistivity survey.
Oil spill pollution detection
The primary ive of this project is to determine flow pathways of groundwater contamination from the source of release, in this case, being an adjacent refinery. The survey aims to identify areas of greater groundwater permeability / flow pathways within the basalt aquifer. The aquifer is suspected to be fractured, hence groundwater flow may be following preferential fracture-flow pathways, as well as more discrete inter-granular / inter-fracture flow pathways.
Fracture porosity is considered likely to be the main mechanism for groundwater flow through the bedrock. It is likely that major fracture zones are associated with increased weathering around the fractures, resulting in the formation of clay minerals. Given that basalt weathers to form clay minerals with low resistivity, the fracture zones should be of a similarly low resistivity. The direction of groundwater flow is from west to east (right to left in the figures beow).
The resistivity inversion image from Line 8 shows low resistivity between 120-140m at depth 0-10m, which correlates with the EM survey result (Max sensistivity at 8m depth, 20m separation vertical dipole mode).
ZZ Resistivity Imaging Pty. Ltd.
sales@zzgeo.com
Address：Unit 3 / 239 Magill Rd， Maylands 5069 Adelaide, South Australia
Copyright: May 2021
https://www.linkedin.com/in/zz-geo-2b794a169/
https://www.youtube.com/channel/UCIvYShsZNr0w_Nm3r3td06Q
