This section provides information on groundwater salinity (represented by electrical conductivity or EC) and pH. In addition, it provides basic information on selected trace elements to highlight limitations of the available data, as only a limited number of groundwater samples have been analysed for most trace elements in the Richmond river basin. Further statistical analysis and interpretation conducted on the major ion chemistry of groundwater within the Clarence-Moreton bioregion will be provided in companion product 2.1-2.2 of the bioregional assessment , and additional information on water quality and the characteristics of major aquifers are presented in companion product 1.1 for the Clarence-Moreton bioregion .
Groundwater quality and chemistry data were compiled from the NSW groundwater bore database (Bureau of Meteorology, ). In this database, 501 bores within the Richmond River groundwater model boundary have records for electrical conductivity, and 502 records exist for pH, whereas only a fraction of groundwater bores have trace element chemistry records. Sampling dates range from 1971 to 2007. The time span of four decades over which samples have been collected has implications on data quality, this is attributed to significant changes to sampling protocols, database procedures and most importantly advances in analytical accuracy and precision (e.g. a significant reduction in methods’ detection limits has occurred).
There are 3934 bores from the National Groundwater Information System (NGIS) (Bureau of Meteorology, ) located within the Richmond River groundwater model domain, 3096 of which have construction information (e.g. screened interval depth) that is required to assign bores to aquifers. However, the majority of groundwater bores contained in the Bureau of Meteorology dataset for the Richmond river basin do not have any stratigraphic records. Without the assignment of the screened interval to a discrete stratigraphic unit, it would be impossible to report on the groundwater quality characteristics of different aquifers. Through data quality checks and interpretations of lithological logs, which are available for most bores, followed by integration of the lithological logs into a preliminary three-dimensional geological model for further checks in the spatial context, it has been possible to generate stratigraphic logs for most groundwater bores. This then allowed assignment of most bores to individual aquifers. The procedure is described in detail in companion product 2.1-2.2 of the Clarence-Moreton Bioregional Assessment . Results for EC and pH were only reported for bores where the hydrostratigraphic unit at the screened interval was determined with a high degree of confidence; bores screened across multiple aquifers were not considered.
To assess the potential hazards associated with using groundwater in the Richmond river basin, groundwater chemistry data were compared to national guidelines for water quality in which a number of possible water uses were considered. Water uses considered were: human drinking water, stock drinking water and water for long-term irrigation (defined as up to 100 years). For the assessment of potential adverse impacts associated with using groundwater in the Richmond river basin, groundwater quality parameters were compared to water quality national guidelines provided by the National Health and Medical Research Council and the Australian and New Zealand Environment and Conservation Council .
Electrical conductivity values that represent salinity for the Richmond river basin are presented in Table 14.
Values higher than the EC of seawater (approximately 50,000 µS/cm) were not considered in the assessment. It is possible in coastal catchments that seawater or estuarine water leaks into shallow aquifers. In the Richmond river basin, estuaries and tidal rivers extend far inland (up to Casino), and it is therefore possible that elevated salinities are related to leakage from estuaries or tidal rivers. However, this would still only explain EC’s less than that of seawater. Areas where elevated groundwater salinities are observed are located too far from the coast to be explained by seawater intrusion. In areas in Australia where hypersaline salt lakes are present, these can leak into underlying aquifers. However, as there are no hypersaline salt lakes within the Richmond river basin, values higher than seawater are considered incorrect, most probably resulting from either erroneous field measurements and/or database entries. Consequently, 57 measurements ranging from 70,000 to 4,850,000 µS/cm were excluded from calculations of the minimum, maximum and median values presented in Table 14. As only limited water quality records are available for most sedimentary bedrock formations in the Richmond river basin, bioregion-wide range of values (including the Queensland part of the Clarence-Moreton bioregion) are reported in Table 14 to give an indication of the possible range of values for different sedimentary bedrock aquifers, assuming basin-wide similar controls of water quality.
In total, 959 values were compared to Australian Drinking Water Guidelines (ADWG) trigger values for human consumption and the National Water Quality Management Strategy (NWQMS) for stock and irrigation water . As a full comprehensive analysis was not conducted for many sampling sites, EC is reported here in favour of total dissolved solids (TDS) concentration similar to other bioregions (e.g. Namoi subregion). The trigger values used for EC are given in Table 14 and are derived from the TDS concentrations in the guidelines, using an approximate conversion factor of 0.64, as recommended in the guidelines and as conducted in other bioregions (e.g. Namoi subregion). The range of EC values in the data is shown in Table 14 together with the proportion of samples in exceedance of the different guidelines.
Insufficient EC data exist for most aquifers, and thus, no spatial interpolation was conducted. Instead, maps showing EC ranges were generated for key aquifers within the Richmond river basin groundwater model domain. For less than 3% of the groundwater bores 10 or more EC measurements exist, and for more than 70% of the groundwater bores only one EC measurement is recorded in the database.
Richmond River alluvium
The EC of alluvial groundwater quality samples within the Richmond river basin ranges from 40 to 48,500 µS/cm, with a median of 885 µS/cm (based on 383 samples) (Table 14 and Figure 11). Approximately 35% of the samples collected from alluvial aquifers exceed the ADWG trigger of 1500 µS/cm, and approximately 10% and 9% exceed the trigger for irrigation and stock water, respectively. The ECs in the headwaters where the alluvial aquifers overlie the Lamington Volcanics and near the coast within the Richmond river basin are generally low. These low salinities indicate that recharge rates are generally high here. The low salinity of alluvial groundwaters within the extent of the Lamington Volcanics (Figure 11 and Figure 12) also confirms that there is a close hydraulic connection between the Richmond River alluvium and the underlying basalt in the headwaters, where the alluvium primarily consist of coarser sediments such as boulders, gravel and sand. In contrast, higher EC were reported for the central part of the Richmond river basin near Casino (Figure 11). Recharge rates here are likely to be lower due to presence of thick low permeability floodplain sediments at the top of the alluvium, which limit the downwards percolation of water and result in higher rates of evapotranspiration prior to recharge.
Basalt (Lamington Volcanics)
The EC of basalt groundwater samples within the Richmond river basin ranges from 50 to 9250 µS/cm, with a median of 499 µS/cm (based on 249 samples) (Table 14) (Figure 12). Only 13.7% of the samples collected from the basalts exceed the ADWG trigger of 1500 µS/cm, whereas 2.8% and 2.4% exceed the trigger for irrigation and stock water, respectively. This suggests that the basalts of the Lamington Volcanics contain the freshest groundwater within the Richmond river basin, and highlights the significance of the Lamington Volcanics as a major recharge area within the Clarence-Moreton bioregion. The role of the Lamington Volcanics as a source of high baseflow volumes was also discussed by Brodie et al. (2007) and in the companion product 1.1 for the Clarence-Moreton bioregion .
Grafton Formation undifferentiated
The EC of groundwater quality collected from the Grafton Formation (Piora and Rappville Members undifferentiated) within the Richmond river basin ranges from 80 to 10,100 µS/cm, with a median of 1250 µS/cm (based on 60 samples). Approximately 47% of all samples collected from the Grafton Formation exceed the ADWG trigger of 1500 µS/cm, whereas 3.3% of samples exceed the trigger for irrigation.
Orara Formation undifferentiated
No groundwater quality samples from the NSW groundwater database were assigned to the Orara Formation.
Walloon Coal Measures
Within the Richmond river basin, the EC of Walloon Coal Measures groundwater quality samples ranges from 400 to 4460 µS/cm, with a median of 1030 µS/cm (based on 16 samples). Of the samples, 25% exceed the ADWG trigger of 1500 µS/cm, whereas no samples exceed the ANZECC/ARMCANZ (2000) triggers for irrigation or stock water.
Within the entire Clarence-Moreton bioregion, the EC of the Walloon Coal Measures ranges from 86 to 26,500 µS/cm, with a median of 4095 µS/cm based on 92 samples. Approximately 75% of all Walloon Coal Measures groundwater quality samples within the Clarence-Moreton bioregion exceed the ADWG trigger of 1500 µS/cm, and a considerable proportion exceeds the ANZECC/ARMCANZ (2000) triggers for irrigation (approximately 25%) and stock water (approximately 7.6%). The considerable difference to the Walloon Coal Measures groundwater quality within the Richmond river basin probably suggests that the limited number of samples within the Richmond river basin does not provide a representative overview on the EC distribution or that the Walloon Coal Measures samples follow a different evolutionary pathway in the Richmond river basin.
No EC measurements exist within the Richmond river basin groundwater model boundary for bores screening the Koukandowie Formation. However, bioregion-wide, the EC of bores screening the Koukandowie Formation ranges from 765 to 20,000 µS/cm (median 4750 µS/cm based on 21 samples). Approximately 14.3% of all Koukandowie Formation groundwater quality samples within the Clarence-Moreton bioregion exceed the ADWG trigger of 1500 µS/cm, and a considerable proportion exceeds the ANZECC/ARMCANZ (2000) triggers for irrigation (approximately 24%) and stock water (approximately 5%).
No EC measurements exist within the Richmond river basin groundwater model boundary for bores screening the Gatton Sandstone. However, bioregion-wide, the EC of 218 groundwater quality samples collected from bores screening the Gatton Sandstone ranges from 92 to 39,000 µS/cm with a median of 5000 µS/cm. Most Gatton Sandstone groundwater samples (approximately 91%; Table 14) within the Clarence-Moreton bioregion exceed the ADWG trigger of 1500 µS/cm, and a considerable proportion exceeds the ANZECC/ARMCANZ (2000) triggers for irrigation (approximately 30%) and stock water (approximately 3%). This indicates that the Gatton Sandstone contains the most saline groundwater of all sedimentary bedrock formations within the Clarence-Moreton bioregion.
No EC measurements exist within the Richmond river basin groundwater model boundary for bores screening the Woogaroo Subgroup. However, throughout the Clarence-Moreton bioregion, the EC of 237 groundwater quality samples collected from bores screened within the Woogaroo Subgroup ranges from 65 to 20,000 µS/cm, with a median of 870 µS/cm (Table 14). Most samples (68.3%) have EC values below the ADWG trigger values, and only very few samples exceed the ANZECC/ARMCANZ (2000) triggers for irrigation and stock water, respectively. This indicates that the Woogaroo Subgroup contains the freshest groundwater of all sedimentary bedrock formations within the Clarence-Moreton bioregion.
Table 14 Electrical conductivity (EC) in Richmond river basin groundwater model domain compared to water guidelines
aBased on Australian Drinking Water Guidelines NHMRC and NRMMC (2011) and approximate conversion from TDS to EC. TDS >900mg/L is considered poor.
bBased on Table 4.2.5 in the National Water Quality Management Strategy ANZECC/ARMCANZ (2000).
cBased on National Water Quality Management Strategy ANZECC/ARMCANZ (2000) and approximate conversion from TDS to EC. TDS >13,000mg/L is the maximum concentration when a decline in health of stock would be expected .
One of the problems with pH measurements in the NSW and Queensland groundwater databases is that it is not always clear if the reported value represents the field measurement or the laboratory measurement, and particularly for samples that were collected decades ago, there is considerable uncertainty. In the Queensland Department of Natural Resources and Mines Groundwater Database (), most reported values appear to be laboratory measurements, whereas no information on whether the values represent field or laboratory measurements is provided for NSW.
The pH of groundwater samples in the Richmond river basin varies from 2.8 to 14.0 (Table 15). However, the median pH of most aquifers is within a narrow range from 7.1 to 7.5. The notable exceptions are the median pH of the Walloon Coal Measures (bioregion-wide), the Koukandowie Formation (bioregion-wide) and the Gatton Sandstone (bioregion-wide), which are higher and range from 7.9 to 8.2. While it is unusual for groundwater samples to have pH higher than approximately 9, selected bores within the Walloon Coal Measures and the Gatton Sandstone in the Clarence-Moreton bioregion have been visited during a previous study (Raiber, unpublished data), and these visits have confirmed that a high pH in a similar range as reported in the groundwater database occurs at these sites.
Table 15 Minimum, maximum and median pH for the aquifers in the Richmond river basin and Clarence-Moreton bioregion-wide for selected sedimentary bedrock aquifers
Only a very limited number of measurements are available for most trace elements, with the exception of aluminium, fluoride, iron and nitrate (Table 16). Exceedances for the trace elements available in the dataset were assessed using the ADWG for human consumption and NWQMS for stock watering and irrigation water (Table 16).
Due to the small number of measurements, the data presented in Table 16 do not provide a representative overview of the variability within the Richmond river basin and hence should be considered with caution. In addition, for some trace elements, difficulties can arise due to the absence of reported detection limits; as an example, this is evident for lead (Pb) where most samples are reported as 0.02 mg/L, and are therefore formally in exceedance of the AWDG trigger of 0.01 mg/L. However, it appears likely that most of these values represent the detection limit, and the actual value may therefore be smaller.
Table 16 Number of analyses and exceedances for trace elements in the Richmond river basin. Concentrations of metals are based on soluble form
dBelow detection limit
eAesthetic water quality trigger (not health related). NA = data not available
The coverage of bores with available groundwater quality data is limited for the deeper sedimentary bedrock hydrogeological units in the Richmond river basin. This likely reflects that these deeper units have to date not been extensively utilised as groundwater supply aquifers (most of the groundwater extraction occurred from the basalts and the alluvium, as also highlighted in Section 1.5.1 of this product).
The quality of the hydrochemistry data available for this assessment is difficult to determine. Analytical uncertainties or detection limits are not reported in the NSW groundwater quality dataset (Bureau of Meteorology, ). The dataset includes groundwater chemistry records that were collected from 1970 to 2007, and the different analytical techniques used during this long period of time involve different levels of accuracy and precision that result in inherent uncertainties. A lack of information on sampling protocols, particularly for trace elements, provides a further source of uncertainty.
The stratigraphic unit at the screened interval is unknown for many bores in the Richmond river basin. As this information is crucial to assess the differences of groundwater quality for different aquifers, one of the biggest challenges was to determine the stratigraphy of the bores, including the identification of the stratigraphic unit at the bore screen from the lithological logs. Following extensive initial data quality checks, this was achieved for a large number of bores by converting the lithological logs to stratigraphic logs and importing the data into a three-dimensional geological modelling software (followed by further substantial cross-checking), as discussed in detail in companion product 2.1-2.2 for the Clarence-Moreton bioregion .
Most trace elements have data available for only a few groundwater sampling sites. Where analyses have been performed, several elements have concentrations above ADWG or NWQMS triggers, but the current dataset is too sparse and the quality too uncertain to make conclusions about trigger value exceedances of these elements. Therefore, additional work is required to understand the range and distribution of trace element concentrations in the Richmond river basin.
ANZECC/ARMCANZ (2000) National Water Quality Management Strategy: Paper No 4 - Australian and New Zealand guidelines for fresh and marine water quality: Volume 1 - The Guidelines. Australian and New Zealand Environment and Conservation Council and the Agriculture and Resource Management Council of Australia and New Zealand, Commonwealth of Australia, Australia.
Brodie R, Sundaram B, Tottenham R, Hostetler S and Ransley T (2007) An overview of tools for assessing groundwater-surface water connectivity. Bureau of Rural Sciences, Canberra.
NHMRC and NRMMC (2011) Australian Drinking Water Guidelines Paper 6 National Water Quality Management Strategy. National Health and Medical Research Council, National Resource Management Ministerial Council, Commonwealth of Australia, Canberra.
Raiber M, Cui T, Pagendam D, Rassam D, Gilfedder M, Crossbie R, Marvanek S and Hartcher M (2015) Observations analysis, statistical analysis and interpolation for the Clarence-Moreton bioregion. Product 2.1-2.2 from the Clarence-Moreton Bioregional Assessment. Department of the Environment, Bureau of Meteorology, CSIRO and Geoscience Australia, Australia. Viewed 20 July 2015, http://data.bioregionalassessments.gov.au/product/CLM/CLM/2.1-2.2.
Rassam D, Raiber M, McJannet D, Janardhanan S, Murray J, Gilfedder M, Cui T, Matveev V, Doody T, Hodgen M and Ahmad ME (2014) Context statement for the Clarence-Moreton bioregion. Product 1.1 from the Clarence-Moreton Bioregional Assessment. Department of the Environment, Bureau of Meteorology, CSIRO and Geoscience Australia, Australia. Viewed 20 July 2015, http://data.bioregionalassessments.gov.au/product/CLM/CLM/1.1.
Dataset 1 Bureau of Meteorology (2014) NSW Office of Water – National Groundwater Information System. Bioregional Assessment Source Dataset. Viewed 23 March 2014, https://data.bioregionalassessments.gov.au/dataset/7ab9820e-1e43-4600-8875-a0834345fb6d.
Dataset 2 Queensland Department of Natural Resources and Mines (2014) Queensland groundwater bore data – update March 2014. Bioregional Assessment Source Dataset. Viewed 10 March 2014, (record pending).
Dataset 3 Bioregional Assessment Programme (2015) CLM - Richmond river alluvium Electrical Conductivity v01. Bioregional Assessment Derived Dataset. Viewed 19 October 2015, http://data.bioregionalassessments.gov.au/dataset/608d1699-2267-41db-bbfc-c89499fc0136.
Dataset 4 Bioregional Assessment Programme (2015) CLM - Richmond river basalt Electrical Conductivity v01. Bioregional Assessment Derived Dataset. Viewed 19 October 2015, http://data.bioregionalassessments.gov.au/dataset/e6457df0-71f9-4139-bd6e-d16558f3d3d7.