Toxicity monitoring - Ranger Mine
In this form of monitoring, effects of runoff water from the Ranger uranium minesite on receiving waters are evaluated using responses of aquatic animals exposed to creek water. More information about the research originally conducted to develop these tests can be found in the Supervising Scientist Annual Report 2000–2001 (pp 49–50) section 3.1.4.
From the 1991-92 through to the 2005-06 wet seasons, the freshwater snail (Amerianna cumingi) and the larvae of black-banded rainbowfish (Melanotaenia nigrans) were used for toxicity monitoring. The endpoints of the tests were reproductive output (egg production) and larval survival, respectively. However, the fish test was not only much less sensitive than the snail reproduction test to uranium and magnesium in Ranger minesite water, but the fish larvae also suffered much higher (natural) mortality rates at the upstream control site, compared with the downstream 'exposed' site. For these reasons, routine testing using the fish larvae was discontinued in the 2006/07 wet season, with resources directed towards developing improved toxicity monitoring techniques (such as in situ methods, discussed below) and continuous water quality monitoring (see Supervising Scientist Annual Report 2007–2008 (pp 52–60), section 3.2).
Toxicity monitoring is conducted in Magela Creek upstream of the mine (control site) and at an ‘exposed’ site located approximately 400 m downstream of the gauging station GS8210009, some 5 km downstream of a point directly adjacent to the mine (see map). The sites are the same as those at which the SSD collects water chemistry samples and associated information (grab samples and continuous data).
The creekside technique (Figure 1A) provided the primary means for toxicity monitoring from 1991–92 through to the 2007–08 wet season. Creekside monitoring used water pumped from the creek to header tanks located on the bank. The water stored in the header tanks provided continuous water flow to chambers (aquaria) containing the test organisms.
At the end of each four-day test, the mean number of eggs per snail pair (and previously, mean number of fish surviving per replicate), are noted and compared between the upstream and downstream sites. Specifically, when data from the downstream site are subtracted from those at the upstream site, a set of 'difference' values are derived. These difference values may be compared statistically for different parts of the time-series. For example, 'difference' data for the current wet season may be compared with those from previous years. If a significant difference is detected, using an ANalysis Of VAriance (ANOVA) test, it may indicate a mine-related change - with more detailed investigative work triggered. Technical details of the statistical design and data analysis procedures may be found in Humphrey et al (1995), in Appendix 4, volume 2 of ANZECC and ARMCANZ (2000), and in the paper ‘Toxicity monitoring in Magela Creek’ located in the eriss research summary 2007–2008.
Following three years of development, which included two years comparative testing, the creekside monitoring technique was replaced by an in situ monitoring (Figure 1B) method. In situ monitoring uses floating test chambers tethered in the creek, requiring greatly reduced test infrastructure and staff resources while providing improved water flow-through and contact conditions for the test organisms. This technique is also portable and potentially, may be readily deployed at new testing locations.
Figure 1A eriss staff conducting toxicity monitoring of freshwater snails and fish fry at a creekside station on Magela Creek (2004)
Figure 1B Toxicity monitoring using in situ floating test containers (2007)
The results of the comparative testing conducted during the 2006–07 and 2007–08 wet seasons showed that the upstream-downstream ‘difference’ values between in situ monitoring and creekside monitoring were directly comparable (no significant difference between the ‘difference’ data). Most importantly, the results demonstrated that results from the in situ technique would be comparable with the time series of data collected since the 1991–92 wet season using the creekside method. The in situ method using freshwater snails replaced the creekside method from the commencement of the 2008–09 wet season. For further details of the comparative study, see ‘Development of in situ toxicity monitoring methods for Magela Creek’ in the eriss research summary 2007–2008.
Some limited additional evaluation of the fish larvae method was done during the 2006-07 and 2007-08 wet seasons. Testing was confined to the upstream site to determine if the high mortality rate observed at this site during earlier years was specifically attributable to features of the creekside methodology, and whether survival could be increased. Comparison of the results from creekside and in situ deployment showed that there was no improvement in the larval fish survival when using the in situ monitoring technique. Because the in situ monitoring technique did not resolve the high upstream mortality in larval rainbowfish and because the fish larvae are not nearly as sensitive as snails to Ranger mine waters, this test is no longer conducted as part of the Ranger mine toxicity monitoring program.
Currently the response of one test species is employed, namely, reproductive output (egg production) of the freshwater snail, Amerianna cumingi, measured over test periods each of four days using the in situ deployment method.
In recognition of the increasing importance of Gulungul Creek in the context of runoff from the recently lifted tailings dam walls and the prospect of future mine-site infrastructure that may be constructed in the catchment due to proposed expansion of mining and milling at Ranger, SSD has increased its environmental monitoring effort in this creek. In addition to upgrades of the continuous monitoring equipment in the creek, biological (toxicity) monitoring also commenced in the 2009–10 wet season with the trial in situ deployment of the freshwater snail reproduction technique. This method of biological monitoring has been routinely deployed in Magela Creek over many years (since 1992). As with toxicity monitoring in Magela Creek (results presented above), it is intended that in situ biological monitoring will be used in Gulungul Creek as an early detection method for identifying changes in water quality.
The trial deployment was conducted firstly to establish the logistics of reliably conducting toxicity monitoring procedures in the creek and secondly to start acquiring biological response data to develop a baseline prior to any significant future disturbance in the catchment. The test design was the same as that used for the routine monitoring of Magela Creek with upstream ‘control’ and downstream ‘exposed’ sites co-located with water quality monitoring. While the control and exposed sites in Magela Creek are accessible by boat throughout the wet season, the upstream control site on Gulungul Creek is not accessible by boat at any time, nor by road for the majority of the wet season. Hence it is necessary to access this site by helicopter.