Water sampling

Introduction

Kaisa Turunen (GTK), Geological Survey of Finland, P.O. Box 1237, FI-70211 FINLAND, kaisa.turunen(at)gtk.fi

The potential influence of mining operations on surface and ground waters can be monitored through water analysis, determination of biological indicators, such as plankton and benthic fauna, measuring chemical and physical parameters of the water and/or by studying aquatic sediments (Heikkinen et al 2008). The purpose of this water sampling section of Closedure is to describe procedures for environmental quality assessment of waters, whereas the characterization of sediments is dealt with in detail in soil and sediment sampling section.

Monitoring of the potential effects of the mining on downstream waters is usually evaluated before environmental permit application and the mine closure. In addition, a reference background data is often obtained during baseline studies or environmental assessment phase of mining (Heikkinen et al. 2008). However, in the case of abandoned mines and mines operated and closed before comprehensive environmental permit procedures, this kind of a data is not usually available. This means that the background concentrations for surface and ground water are further defined by sampling one or more locations upstream with respect of ground and surface water flow patterns. While soil and bedrock sampling campaign is usually performed only once, water sampling campaign needs to be executed several times, due to the seasonal variations in water quality. In addition, it is advisable to collect several water samples when assessing a comprehensive hydrogeochemistry and contaminant migration at the site. (Younger et al. 2002, Heikkinen et al. 2008).

The critical contaminants are usually deriving from a mine site through water as solutes. Thus, in order to determine the contaminant fluxes, both the hydrological and water quality parameters of the site have to be determined. The discharge flow rates are combined with chemical information and physical parameters of water in order to assess the source and extent of possible contamination as well as the rates of processes that generate or at best attenuate the contamination. In addition, the results can be used in deciding the most appropriate closure strategies and determining the need for further follow-up studies or remedial actions. (Younger et al. 2002, Heikkinen et al. 2008).

Water quality is determined from a combination of field measurements and laboratory analysis. The laboratory and field methods are used as tracers for weathering processes that generate contaminant fluxes in real environment. For instance, sulphate resembles the weathering of pyrites. (Younger et al. 2002, Heikkinen et al. 2008). However, for comprehensive evaluation of contaminant loads and recommendations for mine closure, hydrological and hydrochemical modeling is often needed. Different types of modeling methods are described in more detail in Water management section.

The selection of the sampling and monitoring sites is based on hydrogeological and sedimentological characters of the site to estimate the pathways of the contaminants. During mine closure, the routine monitoring should include measures at least from outflow and discharge sites in downstream. However, since the mine closure may change the hydrological flowpaths in the vicinity of the mine site, it is advisable to study the water quality inside the mine site as well as in the backgound. Water quality is affected by variousl of parameters, and for comprehensive knowledge of chemical reactions in water, the total chemical composition of waters, including cations and anions as well as organic contaminants should be characterised. Total chemical composition of water allows detecting the small changes in water chemistry related to mining activities. The sampling campaign should be more frequent for the first few years of the closure and after awhile, providing that the water quality and flow stays constant, sampling campaign may be performed less frequently and the parameters to be decreased. A constant online monitoring system enables detecting the changes in physical characteristics in water quality and an immediate geochemical sampling and analysis can be overtaken and possible intervention procedures started to prevent adverse effects. (Heikkinen et al. 2008).

Surface and ground water sampling techiques

Kaisa Turunen (GTK), Geological Survey of Finland, P.O. Box 1237, FI-70211 FINLAND, kaisa.turunen(at)gtk.fi

The water sample is taken by immersing the bottle by hands covered with disposable glovesto 5-10 cm of depth (Photo 1) or with a sampler such as Limnos water sampler (Photo.2) Water volumes in groundwater wells are replaced by pumping prior to sampling and the groundwater samples are taken from existing wells by a sampler such as tube bailer. During sampling, the underlying layers should not be disturbed, to prevent the release of particles from the bottom and mixing with the water. To avoid mixing of the sediments in shallow sampling locations, sample can be collected with syringe. Each container will be rinsed 2-3 times with the sample water before collecting the actual sample. The water chemistry changes according to time, depth and current. Thus, the chemical differences must be taken into account when sampling. For instance, when taking water samples from a lake it is advisable to take samples from various depths to assess the water quality troughout the waterbody. Measuring the physico-chemical parameters also pinpoints the most problematic locations according to water pollution derived from mining activities. (Kauppila et al. 2013 and Räisänen 2013)

 
 

Figure 1. a) Taking surface water sample into a bottle. b) Taking a lakewater sample with a Water Limnos Sampler. c) Taking a seepage water sample with a fringe. d) Taking a groundwater sample with a pump. e) Taking a pore water sample with a Rhizon sampler. f) Taking a groundwater sample with a tube bailer sampler. Photos © (a and b) Kaisa Turunen, (c) Teemu Karlsson, (d and e) Tommi Kauppila, (f) GTK.

An example of a sampling gear for water sampling (modified from Räisänen 2013):

  • Coolers for transporting and storing the samples
  • Sample containers:
    • plastic (HPDE or LPDE) bottles of varied volumes (1l, 0.5l, 100ml, 50ml) for water samples
  • Disposable contamination-free plastic gloves
  • Disposable unpowdered nitrile gloves
  • Disposable syringes
  • Filters, such as:
    • Three layered PVDF 0.45 µm GD/XP-filters, which include 20 µm and 5 µm pre-filtering (Figure 2a)
    • Vacuum filters with 0.2 µm filter, that filters also colloidal Fe and Al (0.2 µm filtration technique in Closedure R&D) (Figure 2b)
  • Ionised water
  • Disposable pipettes for conservation
  • Laboratory paper
  • Acids for conservation of the water samples
  • Samplers, such as:
    • Water Limnos sampler (Figure1b).
    • Tube bailer (Figure 1d)
  • Multi-detector equipment for measuring of physico-chemical parameters in conjunction with sampling

Figure 2. a) Filtering water samples at field by a three layered PVDF 0.45 µm GD/XP-filters, b) Filtering water samples at field by a vacuum filters with 0.2 µm filter, c) Preserving the water samples at field with acids. Photos © (a) Anna Tornivaara, (b) Kaisa Turunen and (c) GTK.

General instructions of handling the water samples properly

Kaisa Turunen (GTK), Geological Survey of Finland, P.O. Box 1237, FI-70211 FINLAND, kaisa.turunen(at)gtk.fi

Because mine waters are reactive and sample quality may change during the transport to laboratory, preserving water samples in low temperatures hinders the chemical transformation during transportation. For instance, the pH generally decreases and redox potential increases after sampling, which results in precipitation of iron and/or aluminium through oxidation. This in other hand may enhance the co-precipitation of other elements, which skews the distribution of total and dissolved concentrations of elements in water. This is crucial especially in case of elements such as Cd or As of which even small concentrations pose a risk to human health and the environment. For the same reason, reactive water samples should be pre-treated by filtration and acid conservation immediately on field. Through conserving of water samples the chemical reactions are hindered and the precipitation and/or dissolution of particles prevented. For the evaluation of dissolved concentrations, the suspended solids are removed through filtering. Needed volumes and pre-treatments for different water analysis are described in Table 1. (Heikkinen et al. 2008 and Räisänen 2013)

The water sample is usually taken into larger containers, from which it is divided into smaller subsamples. Each container will be rinsed 2-3 times with the samples prior sampling and sample division. This means, that the bottles for unfiltered samples are rinsed with unfiltered water and bottles for filtered samples are rinsed with filtered water. The rinsing of the bottle is undertaken with a lid and shaking heavily, after which the rinsing water is thrown away. For each sampling point, the filter and syringe will be replaced. (Kauppila et al. 2013 and Räisänen 2013)

Prior to the collection of a sample, consideration must be given to the type of sample containers, sampling equipment and acids needed for conserving the samples. Choosing the proper composition of sample containers, adequate sampling equipment and pre-treating methods will help to ensure that the quality control of sampling is maintained. For instance, glass is often the recommended container type because it is chemically inert to most substances, whereas in plastic containers hazard substances may potentially leach plastics into the sample. However, some metals species will also adhere to the sides of glass containers in solutes. The analytical method requirements, sample matrix and contaminants determine the required sample container type and needed pre-treatment methods. Collecting samples will be undertaken with new sampler at each sampling point. However, if the sampling will be performed regularly, the same sampler can be used again at same sampling location, providing it is stored properly without any possible contamination between samplings. (Heikkinen et al. 2008 and Räisänen 2013)

Due to the uncertainty of the sampling procedure, all monitoring and sampling should be undertaken through quality assurance measures and coupled with a statistically based sampling plan to maintain quality in all aspects of the research. This will improve sample collection while maintaining the integrity of the samples prior to analysis. As in any chemical analysis, blanks should be measured parallel with the actual samples and duplicate samples taken for every fifth samples to ensure environmental monitoring data is of known quality and to attain the quality-control of the measure procedure. Quality control determines the validity of specific sampling and analytical procedures and determines the overall precision and accuracy of your data. Blanks are taken to demonstrate the accuracy and for identifying of possible contamination during and/or due to sampling and analyse procedures. Blanks are deionised water which is treated as the actual samples. The duplicate samples reflect the precision and repeatability of the sampling procedure and are taken at the same place, in conjunction with actual sampling. The sample is usually split into subsamples called as lab replicates at the laboratory, which are analyzed and the results compared. Lab replicates are like duplicates, analysed to test the precision of the laboratory measurements. In addition, accredited labs undertake also calibration blank samples to zero the measuring instrument. The calibration blank is determined to check the measuring instrument periodically for “drift” and can also be compared to the field blank to pinpoint where contamination might have occurred. (Heikkinen et al. 2008, Kauppila et al. 2013 and Räisänen 2013)

Water analysis in laboratory

Kaisa Turunen (GTK), Geological Survey of Finland, P.O. Box 1237, FI-70211 FINLAND, kaisa.turunen(at)gtk.fi

The water samples are analysed at least for total and soluble metal and metalloid concentrations and anions. In addition, dissolved organic carbon (DOC), total organic carbon (TOC) and ferrous iron (Fe2+) can be significant for estimation of water quality. The dissolved and total concentrations of cations in water can be measured by using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), Inductively Coupled Plasma Mass Spectrometry (ICP-MS) or Atomic Adsorption Spectrometry (AAS), whereas anions are determined using ion chromatography. Organic contaminants are generally determined with gas- or liquid chromatographic methods, carbon through CHN-analyser and phosphate and Fe2+ by spectrometric methods. (Heikkinen et al. 2008 and Kauppinen et al. 2013)

Table 1. Analysis methods, sample volumes and pre-treatments for water samples to determine concentrations, speciation and related chemistry (modified from Kauppila et al. 2013 and Räisänen 2013).

Analysis Volume of the sample Pre-treatment
Multielement, ICP-OES/MS-ICP 100 ml filtering with 0.45 µm GD/XP-filter or 0.2 µm vacuum filter, conserving with suprapur® HNO3, 0.5 ml/100 ml
Multielement (acid-soluble), ICP-OES/MS-ICP 100 ml conserving with suprapur® HNO3, 0.5 ml/100 ml
Fe2+, spectrophotometric 100 ml filtering with 0.45 µm GD/XP-filter or 0.2 µm vacuum filter, conserving with HCl 4 ml/100 ml
TOC, CHN-analyser 100 ml conserving with H3PO4 1 ml/100 ml
DOC, CHN-analyser (142L) 100 ml filtering with 0.45 µm GD/XP-filter or 0.2 µm vacuum filter, conserving with H3PO4 1 ml/100 ml
tot-N, ammonium 100 ml no pretreatment
     
Ion-chromatographic analysis of anions (SO4, Cl, F), suspended solids, pH, spectrophotometric analysis of phosphate, alkalinity, NO3, NO4 1 liter no pretreatment

Ecotoxicity

(SFS‐EN ISO 6341)

 2 x 1 liter filtering or no pretreatment

 

References

Heikkinen, P.M., Noras, P. and Salminen, R., (eds). 2008. Mine closure handbook, Environmental techniques for the extractive industries. 169 pages.

Kauppila, T., Komulainen, H., Makkonen, S. and Tuomisto, J., (eds). 2013. Improving Environmental Risk Assessments for Metal Mines: Final Report of the MINERA Project. Report of Investigation 199, Geological Survey of Finland, 223 pages. (in Finnish)

Räisänen, M. L. 2013. Guide for surface water sampling. Geological Survey of Finland. Unpublished guide.

Younger, P.L., Banwart, S. A. & Hedin, R. S. 2002. Mine water – Hydrology, Pollution, Remediation. Environmental pollution. Volume 5. Kluwer Academic Publisher, The Netherlands.464 p.