2.3 Baseline information
Collection of data on the current hydrogeology, water quality and ecological status of any streams that may receive mine drainage discharge is a critical first step in being able to determine the potential impact of that discharge. This information may subsequently be used in models to predict downstream water chemistry at a specific site. In addition, baseline information might form the basis for consent application details where consent conditions are related to maintaining previous water quality.
Charge-balanced analyses, which sum up all major cations and anions, can provide a check that all major components have been analysed (Standards New Zealand 1998a, b). This analysis provides a useful tool for interpreting water chemistry but is not essential at all sites.
2.3.1 Site hydrogeology
Surface water hydrogeological data, including detailed knowledge of stream channels and measurements of flow volume, are required for characterisation of catchment conditions. Ultimately, a hydrogeological model is required of the catchment to be disturbed by mining. In particular, hydrogeological models that include calculation of the amount of rainfall that contributes to surface flows, compared with groundwater, are required to calculate the flow volumes from mining disturbances. These models are best completed by a suitably qualified specialist.
Collection of flow data
A suite of average-stream-flow measurements is required to predict the effects of mixing mine drainage with other catchment water. Stream flow measurements are required for all tributaries that contribute more than 5% of surface flow volumes or 5% of any dissolved components to the main stream of interest.
The frequency and duration of sampling will be dependent on the variability of the background flow conditions. At a minimum, flow should be measured concurrently with the collection of water quality samples (see below), although continuous flow measurements from at least one site in each catchment will provide additional robustness.
Additional information on flow rates and their variability with season, rainfall, and drought is useful for detailed planning of water management strategies at mine sites. This information can be coupled with water chemistry to assist in the design, optimisation and implementation of water management or treatment strategies.
At some mines, e.g. underground mines or possibly deep opencast mines, groundwater flow will be more important than surface water flow. At these sites three-dimensional hydrogeological models will be required and the influence of groundwater flow into rivers should be compared with measured surface runoff. Groundwater data collection and modelling is a specialist field and is best completed by an experienced or suitably qualified hydrogeologist. Background data are used to characterise the environment prior to mining and some of the data collected can be used to predict the impact of mining downstream should consent applications proceed.
2.3.2 Baseline chemical water quality
The chemistry of the receiving environment can have a significant impact on water quality downstream. For example, if the background water has sufficient alkalinity, addition of small volumes of AMD might have minimal downstream effect. Or where streams contain naturally elevated concentrations of trace elements, additions of small volumes of neutral mine drainage with higher trace elements (contaminated neutral drainage, CND) might cause only a very small change to overall water quality. In contrast, streams with low alkalinity or low trace elements could be severely impacted by small volumes of AMD or CND.
On the West Coast, water quality from streams draining different geological formations can be highly variable. For example, water draining from Greenland Group rocks often has neutral pH, elevated alkalinity and naturally elevated As concentrations, whereas water draining from Brunner Coal Measures often has low pH (down to <4) as well as elevated Al and trace elements (Pope et al. 2006, in press). Therefore it is essential that baseline water quality data are collected prior to mining so that the likely level of environmental impact can be estimated.
There are several key chemical factors to consider in an assessment of baseline water quality. These include:
- Natural sources and concentrations of alkalinity;
- Natural sources of acid rock drainage (ARD);
- Background or baseline physiochemical properties (pH, electrical conductivity (EC), dissolved oxygen, etc.) and concentrations of sulphate, dissolved Fe and Al, and other dissolved trace elements such As and Zn; and
- Existing sources of mine drainage.
Collection of baseline water quality data
A representative suite of samples collected from the entire catchment of a proposed mine site during typical flow conditions will generally be sufficient for characterisation of background water quality. If the rock geochemistry is characterised (Chapter 3), these water samples are also important for prediction of downstream water chemistry, should mining proceed). As a rule of thumb, this suite of water samples should include samples collected at a sufficient number of locations to capture all inputs that contain greater than 5% of flow volume or 5% of any dissolved component to the most downstream site. Samples should be collected concurrently with any biological monitoring being undertaken.
The characterisation of background site chemistry requires dissolved concentrations of all relevant components and samples should be collected according to standard methods (e.g. Standards New Zealand 1998a, b). The minimum analysis should include:
- Physiochemical properties pH, electrical conductivity (EC), total suspended solids (TSS), dissolved oxygen (DO);
- Major chemical components including bicarbonate (HCO3-), sulphate (SO42-), Ca, Mg, Na, K, Fe, Al; and
- Trace elements
Selection of analyses of trace elements such as Zn, As, antinomy (Sb), Ni, or Mn may be relevant for certain systems and in some cases non-filtered samples might be required to identify the mode of transport for some trace elements. The importance of different trace elements at different types of proposed mines can be established by analysis of data from other similar operations. Where a new type of mine is proposed, a cautious approach to trace element analyses is recommended.
Other parameters such as oxidation/reduction potential (Eh), salinity, or Fe speciation can be used to refine water quality assessments and predictions. More detailed analytical procedures such as repeat sampling, data-logging and monitoring of chemistry throughout rainfall events can all be used to improve and strengthen water quality predictions.
The sampling strategy and analyses required to characterise a site prior to mining are site specific and experienced water quality scientists should be consulted to determine the location and number of samples and types of analyses.
Drainage from historical mining activities
Sites that are impacted by historical mine drainage should have a baseline chemical and hydrological survey completed. This survey should include chemistry and quantity of the historical mine drainage in addition to inputs from unimpacted streams. Assessment of historical mine drainage chemistry has predictive value for future operations and provides a baseline from which change due to new operations can be measured.
2.3.3 Baseline biological monitoring
Biological monitoring involves the assessment of stream communities in order to determine their current health or condition. It is essential to conduct baseline monitoring prior to any mining as these data provide the background for any future comparisons of impacts or recovery. The same general techniques are used for monitoring after mining operations commence (Chapter 8).
Because stream organisms live most of their lives under the water, stream communities reflect an integrated record of water quality over an organism’s lifetime. Fungi, bacteria, meiofauna (e.g. plankton and mites), algae, macroinvertebrates and fish are all important in natural stream communities and each is vulnerable to mining impacts. In this document we focus on using macroinvertebrates (Figure 5) as biomonitoring agents, largely because they are relatively easy to identify, sampling procedures are simple and well developed, and there is considerable knowledge of their ecology including how they respond to mine drainage (see Appendix D for further discussion). In addition, most regional councils in New Zealand conduct annual biomonitoring of macroinvertebrates as part of their State of the Environment reporting, so there are numerous organisations experienced in using macroinvertebrates for biomonitoring.
Figure 5 Examples of macroinvertebrates that commonly live in streams and rivers throughout New Zealand. Top left: the spiral-cased caddisfly Helicopsyche. Top right: the stonefly Zelandoperla. Bottom left: ubiquitous mayfly, Deleatidium. Bottom right: the common stonefly Zelandobius.
Macroinvertebrates can be sampled at differing levels of intensity:
- Qualitatively, where the presence or absence of a species is recorded at a site;
- Semi-quantitatively, where the relative abundance of each species is determined; and
- Quantitatively, where the abundance of each species is determined in a sample of known streambed area. Abundance is usually expressed as a number of animals per square metre of streambed.
New Zealand has standard protocols for each of these sampling methods, and they are detailed in Stark et al. (2001) and paraphrased in Appendix D.6.
Of the three levels of data intensity, qualitative data are the fastest and cheapest to collect, and a number of measures (metrics) can be calculated using the presence or absence of species (Appendix D.6). However, qualitative data do not detect changes in the relative abundance of key species, and therefore overlook a potentially significant component of change in stream communities. Results can also be influenced by the sampling effort as greater sampling effort collecting the samples will capture more species. By contrast, semi-quantitative data can detect changes in relative abundance and require no additional sampling effort and only a minor increase in laboratory effort. Thus, the majority of stream monitoring should obtain at least semi-quantitative data. The third method, quantitative sampling, provides higher resolution data that can detect subtle changes in community structure. Quantitative sampling provides the strongest data for any assessment. However, the increased number of samples (or replicates) and greater laboratory processing time mean that this sampling will be more expensive.
In addition to biological sampling, assessing the physical and water chemistry properties of sites is strongly recommended. These assessments should occur at the same time as biological monitoring. Physical habitat conditions can also be incorporated into analyses to increase the ability to detect subtle changes in stream condition. Standard protocols for physical stream habitat assessment are outlined in Harding et al. (2009).
Collection of baseline biological data
A baseline biological survey should be completed prior to any mining and will usually be a requirement as part of any assessment of environment effects (AEE). Sampling should include both ‘control’ and potentially impacted sites to enable the subsequent detection and quantification of mining-induced change. A control site is a site that represents a typical non-mine-impacted site in the region. It is absolutely essential that control sites are included in any baseline survey as data from these sites provide the ability to detect any changes that might occur independently from mining activities, e.g. changes caused by large floods, droughts, vegetation regeneration or other factors. A critical aspect of designing a biological monitoring programme is selecting the location and number of sampling sites, as they directly influence the ability to detect and monitor change. The most important considerations are:
- The location of potentially impacted and control sites; and
- Replication of both impact and control sites.
To enable both temporal and spatial reference comparisons, sites used for future monitoring and consents should be selected from those sampled during the initial baseline survey.
Analyses should involve before-after-control-impact comparisons (BACI designs), which are widely accepted as the standard method to detect and quantify ecological impacts (see Figure 6 for an example of the sample design and Appendix D.6 for more detail).
Figure 6 Before-after-control-impact (BACI) sampling designs for assessing the environmental effects of human impacts on stream ecosystems. Each circle represents a sampling site. A rigorous BACI design includes multiple sampling sites in impacted reaches, and upstream and additional stream controls, both before and after an impact.
Baseline biological sampling for AEE occurs before access or resource consent proceedings and generally only needs to be done once (although multiple surveys will always provide stronger data). During a survey, all sites should be sampled within a few days of each other to minimise the likelihood of events such as floods or stream-drying influencing differences among sites. Furthermore, as invertebrate communities can be in a state of recovery after flooding events, a general rule of thumb is to sample at least 5 days after any major flood that has moved large bed material. Smaller floods can probably be sampled after 23 days.
Although stream invertebrates can be sampled at any time of the year in New Zealand they are often larger (and easier to identify) during late winter to early summer (August-January). So it is preferable to conduct surveys during these months.
Baseline biological surveys often focus on biodiversity, thus the emphasis is often placed on collecting qualitative or semi-quantitative data across multiple sites, rather than quantitative data over fewer sites. Although this framework focuses on macroinvertebrates, baseline assessments would also normally qualitatively sample fish communities. Currently no standard protocols exist for sampling freshwater fish in New Zealand. These surveys should be conducted by an experienced freshwater scientist.
In summary, baseline sampling should include:
- An absolute minimum of three control sites (ideally 5 or more) including sites both upstream of the impact zone and preferably also unaffected catchments;
- Sites in all potentially impacted tributaries and sites arranged longitudinally downstream on the mainstream river; and
- Sampling should include extensive semi-quantitative or quantitative data.