CASE STUDY
Septic Tank Impact on Water Quality
Water testing for infectious agents and markers of human sewage contamination is an important tool for the management of urban and recreational waterways, including stormwater and septic infrastructure. These expensive and laborious operations can be more efficient when guided by spatially precise real-time tracking.
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THE PROBLEM
Differentiating sources of contamination
Derwent Estuary Program (DEP) partnered with Sorell Council (Tasmania) to assess water quality concerns at beach sites. Nearby septic tanks were suspected of contributing to contamination.
Enterococci and E. coli are both commonly used bacterial indicators of faecal contamination, but they are present in both the human and animal gut microbiome. To determine if high levels of these Faecal Indicator Bacteria (FIB) were due to human contamination, a different approach is needed.
THE SOLUTION
Source-tracking using the ZiP-Bactx-P2 test
A combination of marine water and groundwater seepage samples were collected from beach locations to determine whether high levels of Enterococci and E. Coli were actually coming from human waste. The ZiP-P2 platform was used to support this investigation as a rapid, field-deployable tool for the detection of Bacteroides dorei, a human-specific faecal pollution marker.
ZiP water tests are supplied as single-use packages that are suitable for room-temperature storage and transport. Tests were performed on the ZiP-P2 instrument. Screen-guided operation is easy and requires minimal training. The instrument has quality control systems that include self-tests and batch verification using external quality control materials.
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OUTCOMES
ZiP-P2 tests assist in tracking contamination sources
The ZiP-P2 platform provided valuable insight into likely contamination sources. Groundwater seepage showed clear signs of contamination by human faecal indicators. This strongly implicates septic systems near the beach contributing to poor water quality at the site. Some marine water samples showed high Enterococci and E coli levels but no matching human marker, indicating animal waste is likely the primary contributor. This is consistent with the expectation that human faecal matter may not always be the dominant source.
These results point to a mixed contamination profile, reflecting both human and animal contributions, and highlight the complexity of faecal pollution in coastal environments, where multiple sources can blur the picture. From a management perspective, this supports a combined approach - targeting septic system performance where human markers are present, while also addressing broader catchment pressures from animal sources.
This work provided Sorell Council with evidence-based confirmation that septic systems are contributing to local water quality issues. The ability to deliver rapid results enables more timely interventions, allowing councils to respond quickly to contamination events and better protect the community and recreational water users.
