ARROZ

Until recently, mine water tracer tests were complicated and the results were sometimes unsatisfactory. Monitoring of flows within a flooded mine by tracer tests has therefore been uncommon. However, mine water tracer tests

Q M

c_t dt

t

=

∫

^∞0 × a predefined mass of tracer is suddenly poured into the water. Both methods

have their special field of application and Kimball et al. (2001; and other publications of that research team covering exactly the same subject) for ex-ample, showed how the “constant rate injection method” can be used to measure the flow of mine drainage into a mountainous stream. The “gulp method” has been used at the Gernrode/Germany fluorspar mine, for exam-ple, to measure small inflows into Steinbach Creek and to compare and cal-ibrate the results of current flow meter measurements (Fig. 48, Fig. 61).

Because the constant rate injection method requires a technically sophis-ticated installation, it is mostly used for scientific-based catchment investi-gations where different inflows have to be quantified. Either Mariott bottles or constant rate pumps are used to inject the tracer (Käß 1998). The flow cal-culation is comparably simple because the whole breakthrough curve does not have to be measured; instead, one only has to measure the plateau that de-velops after enough time, and the distance between the points of tracer in-jection and detection. The discharge can be calculated (U.S. Department of the Interior – Bureau of Reclamation 2001):

(60) with Q flow rate, m³ s^-1

q discharge of tracer into the stream, m³ s^-1 c₀ background concentration of tracer, g L^-1

Q q c c c c

= × −

−

1 2

2 0

9.2 Flow Measurements 169 168 Monitoring and Sampling

Fig. 61. Flow measurement with the salt dilution method in the turbulent Gern-rode/Harz/Germany Steinbach Creek. The salinity probe is hanging in the middle of the stream and the data logger records the electrical conductivity every second (pho-tographed by Andrea Berger).

to conduct laboratory experiments with the potential tracers. Successful tracer tests in mines need 2–8 weeks of time to make sure that as much of the tracer as possible is detected. After the tracer test, 1–2 months must be allowed to process the samples and to present the results. All together, 4–8 months are a realistic time for a well based tracer investigation in a mine.

Two different tracer injection apparatuses have been developed for tracer investigations in flooded underground mines. The first one, LydiA (Ly-copodium Apparatus), was invented for injecting a tracer into large diameter shafts. The other one, TinA (Tracer Injection Apparatus), can be used to in-ject a tracer through mine plugs or boreholes down to a diameter of 3″ (Fig.

63, Fig. 78). In conjunction with a special auto sampler (MeFiSTo: Multiple Filter Storage Tool), particle tracer tests can be conducted more reliably and more cheaply than in previous years (Wolkersdorfer et al. 1997a, 1997b).

Stable isotopes should be given special consideration as natural or artifi-cial tracers as they provide potentially powerful methods to deduce flow paths and residence times, and will help you to understand the results of your hydrochemical and hydrodynamic investigations. However, due to the com-have proven to be a valid decision-support tool for treatment or remediation

measures or diversions within a mine (for details, see chapter 10). Although tracer tests are site-specific tests, they can be used for catchment-based de-cisions where it is necessary to decrease the contaminant load in the entire catchment area.

Before a mine water tracer test is conducted, it is essential to monitor the hydrogeological regime of the mine. The overall flow situation must be known as precisely as possible because tracer tests will only be successful if the injection and sampling sites have been carefully chosen. Nothing is more frustrating than conducting an extensive and expensive tracer test without getting usable results!

Of the range of artificial (introduced) tracers used so far, microspheres (polystyrene beads of 0.2–100 µm diameter) seem to be one of the best op-tions (section 10.2.5.2). Most of the other artificial tracers are either not sta-ble in acid mine water (e.g. Na-fluorescein), are too expensive (e.g. bro-mides), their use is restricted (radioactive tracers), or the amount of tracer that has to be injected is too large (e.g. halide salts). Besides artificial trac-ers, natural (environmental) tractrac-ers, such as isotopes or rare earth elements have been used successfully to trace the surface and underground flow regimes of mines. Always, the background level of the tracers in the waters to be traced must be evaluated before the start of the test.

Before the tracer test starts, at least 2–4 months of work are necessary to investigate the hydrogeological situation, to get the necessary permits and

time t, s

0 100 200 300 400 500 600 700

concentration c, mg L-1

2.6 2.7 2.8 2.9 3.0 3.1 3.2

0

-1 0

-1 -1

1017.8g 64.9g s L 1017.8L s 15.7 L s

64.9

t

t

Q M c t M

c t Q

∞

∞

=

× Δ

=

× Δ = ⋅ ⋅

= ⋅ = ⋅

³

³

Fig. 62. Breakthrough curve and evaluation for a salt-dilution tracer test in the Ger-man Gernrode/Harz Steinbach creek. The distance between the tracer injection and the sampling site was 53 m and the complete mixing was tested in advance using a dye tracer.

Fig. 63. Tracer Injection Apparatus (TinA, left) and Lycopodium Appa-ratus (LydiA, right). The diameter of LydiA is 120 mm.

170 Monitoring and Sampling 9.2 Flow Measurements 171

istry or the instruments used are referred to the general literature (e.g.

Schwedt 1995; Kellner et al. 1998; Otto 2000) or the literature cited in the following paragraphs and sections.

The chemical composition of mine water discharges usually change over time (Fig. 64), except when it has been discharging for many decades. As discussed in section 5.4, the first flush occurs when water from a flooded abandoned mine reaches the surface; the concentrations of water constituents decrease thereafter. However, changes in mine water quality are not restricted to the time after the flooding of a mine; they also occur during the active working time or after the end of the first flush. In the case of the flooded Freiberg/Saxony underground mines, which are dewatered by the 50 km long drainage adit Rothschönberger Stollen, Fe_totwas about 2 mg L^-1during the active mining period, rose to 170 mg L^-1in 1969 (start of mine flooding), came down to about 20 mg L^-1in 1975 and has presently reached 1 mg L^-1. The flow, in 1997, ranged between 2 and 6 m³ min^-1(Merkel et al. 1997;

Baacke 2000). Therefore, both the mine water quality and flows must be measured for at least one hydrogeological year.

In the first set of samples for an unclassified mine water discharge, as many elements as possible should be analysed to identify potentially haz-ardous constituents. Because mine water usually does not contain large amounts of organic pollutants, it is normally adequate to measure only the in-organic parameters. Nevertheless, some mines discharge in-organic substances that pollute the receiving stream. If there is any concern or evidence to sug-gest that this might be the case, the sum parameter TOC (total organic car-bon) as well as other organic substances such as BTEX should be analysed.

Depending on the results of the analyses, further investigations may have to be considered.

At a minimum, the major ions (Na⁺, K⁺, Li⁺, Ca²⁺, Mg²⁺, NH₄⁺, Cl^-, SO₄^2-, HCO₃^-, NO₃^-) as well as ferric and ferrous iron, manganese, zinc, and alu-minium should be measured. Other analytes should be added based on the ge-ology and mineralogy of the mine site as well as any former use of the land property or mine (keep in mind potential underground waste disposal). As most modern laboratories have ICP-MS devices, it may be advantageous to have a screening of the full range of elements that can be measured using this method. The outcome of such desk and laboratory studies will be the basis for the future monitoring programme.

Anions like Cl^-, SO₄^2-, and NO₃^-are typically determined by ion chro-matography (IC). Cations can be also be analysed using this method, but it is recommended that you determine the cations by ICP-AES, Ca²⁺and Mg²⁺

by conventional titration, and Na⁺and K⁺with flame photometry. Although the major ions are (except Na⁺and Cl^-in salt mining) usually not considered as pollutants, those parameters are essential for thermodynamic modelling.

plexity of stable isotope studies they will not further discussed here (for de-tails see Clark & Fritz 1999); case studies can be found in: Allen and Voormeij (2002); Allen and Lepitre (2004); Davies et al. (2000); Helling et al. (1998); Jiries et al. (2004); Knöller et al. (2005); Melchiorre et al. (2005);

Pezdič (1998); Razowska (2001); Rees and Bowell (1999); Tröger et al.

(2005). But no tracer test is simple, and in fact, tracer tests should only be considered trustworthy if they are conducted by experienced consultants or research groups. Some examples of successful mine water tracer tests are described in chapter 12.

9.3 Physico-Chemical Measurements 9.3.1 Sampling Procedures

Sampling procedures for ground waters are described in detail in the litera-ture (e.g. Lloyd and Heathcote 1985; American Public Health Association et al. 1998), but the special prerequisites for mine water sampling are only rarely summarised in commonly available publications (e.g. Ficklin et al.

1999). We are still far away from regular process analyses (Kellner et al.

1998) and mine water diode or sensor arrays and mine water chips as are available for wastewater treatment (Bourgeois et al. 2003), are not even under development. Therefore, this chapter will highlight some of the necessities but will also describe standard procedures for collecting good quality mine water samples. Readers who are interested in the details of analytical

chem-9.3 Physico-Chemical Measurements 173

01.1992 07.1992 01.1993 07.1993 01.1994 07.1994 01.1995

U concentration, μg L-1

200 400 600 800 1000 1200 1400 1600

Fig. 64. Changing uranium concentrations at the measuring point m-107 of the aban-doned Niederschlema/Alberoda uranium mine (data from Wolkersdorfer 1996).

172 Monitoring and Sampling

Ranville and Schmiermund (1999) showed that the 0.45 µm filtration has consequences when conducting geochemical modelling with PHREEQE, as some phases are supersaturated in the < 0.45 µm filtrate and under saturated in the < 500 Dalton (approximately 0.005 µm) fraction (the latter can be seen as the true “dissolved” fraction of mine water). They conclude that geo-chemical modelling should be restricted to those constituents that are not sig-nificantly attenuated by the filtration process. Shiller (2003) compared re-sults of 0.02 µm filtrations with those of 0.4 µm and 0.45 µm filtrations. He used a field applicable filter tool for syringe filtration and noted some sig-nificant differences in the results based on the filter sizes he used. The dif-ferences were associated with both the different filtration techniques and the analysed element. Interestingly, the discrepancies between the 0.4 and 0.45 µm filtered results were sometimes larger than those between the 0.4 µm and 0.02 µm filter results.

After filtration, the sample that will be analysed for the trace elements must be acidified according to laboratory instructions or the QA/QC manual.

Acidification is necessary to prevent chemical reactions (precipitation or ad-sorption) during transportation and storage (Lloyd and Heathcote 1985). Usu-ally, 2–3 drops of HNO₃(ultra-pure!) per 50 mL of sample are used to sta-bilise the trace constituents by maintaining a pH < 2. For speciation analysis, or for analysis of Sb, Ru, and Sn, HCl (ultra-pure) has to be used instead (American Public Health Association et al. 1998). All containers (made of laboratory glass, PE, or PTFE) must be clean and pre-treated, labelled prop-erly with the place name, name of the sampling point, date, name of opera-tor, and treatment (e.g. filtered, acidified).

Mine water is usually monitored at its discharge point into the surface hydro- or anthroposphere. However, mine water quality does not only change over time, but also with depth. Many mines have stratified water columns, and incorrect treatment technologies have been constructed at some of these sites because this stratification was disregarded. This occurred, for example, at the Straßberg/Germany mine. Similarly to the physico-chemical properties, strat-ification can change significantly within very short times – even hours! Nut-tall et al. (2002) showed that the reasonably good mine water quality changed to a highly contaminated mine water during a pumping test (section 12.7).

Such observations can also be made in wells. Wells interfere with the aquifer or the shaft and disturb the natural situation with regard to the flow field and the chemical composition of the ground- or mine water. Further-more, wells show stratification similar to what is observed in mineshafts (Lloyd and Heathcote 1985). However, this stratification, though similar to that in a shaft, has a different physical background. It is affected by the length–diameter ratio in a well, which is comparatively large and causes wall roughness to play a more important role than in a shaft.

At least two water samples should be collected at every monitoring point:

one for the main ions and the other for the trace elements (often referred to as “heavy metals” – but this term is even more confusing than “trace ele-ments”, because many “heavy metals” are neither heavy nor are they metals at all; Duffus 2002). All water samples being analysed for trace elements should be filtered through a 0.2 µm filter, though most investigations and recommendations use a 0.45 µm filter. The reason for filtering the sample with 0.2 µm is twofold:

● Water contains particles, colloids, and solute constituents (Ranville and Schmiermund 1999). Usually colloids range in size from 0.001 to 1 µm; solute constituents have a defined diameter of less than 0.001 µm (Fig. 65). To separate solute constituents from non-solutes, a filtration with 0.001 µm pore size is required. Since this is very difficult in the field, 0.2 µm pore size is an operational measure (replacing the former 0.45 µm operational measure). However, a 0.1 µm filter is strongly rec-ommended if aluminium is to be determined, since aluminium tends to form colloids that are smaller than 0.2 µm in size.

● Water contains bacteria with an average size of 0.2 to 6 µm; by using 0.2 µm pore size filters, microbiological reactions are minimised in the filtered samples.

● However, not all samples should be filtered. Filtering samples that will be analysed for major cations and anions can change the concentra-tions of gases, of which CO₂is of particular concern since it affects the distribution of inorganic carbon species.

9.3 Physico-Chemical Measurements 175 174 Monitoring and Sampling

Fig. 65. Sizes of common water constituents and filtration techniques. The dotted lines gives the 0.02, 0.2, and 0.45 µm filter sizes used for filtrating water samples.

have a feeling for whether data is reasonable or unreasonable (for example, if pH in a carbonate aquifer is significantly deviating from near neutral to basic conditions). If one cannot count on an experienced hydrogeologist, sta-tistical methods should be used (e.g. Kellner et al. 1998); several procedures are available to compensate for any missing data (e.g. Lloyd and Heathcote 1985).

One of the standard methods to check the accuracy of a water analyses is a cation-anion balance calculation or a test of the electro neutrality of the analyses. Both methods are very similar and either can be used. Some authors use the expression “ionic balance,” which is simply twice the electro neu-trality and equivalent in meaning:

(62)

(63)

with cations and anions given in equivalents and the electro neutrality and ionic balance expressed in %.

If both anions and cations are missing in the same amount, this method will not detect the error in the analyses. Therefore, ion balancing should al-ways be accompanied by other statistical methods.

One of these other methods is comparing the electrical conductivity with the measured total dissolved solids (TDS). Depending on the water chem-istry, the following relations exists:

(64) with TDS total dissolved solids (calculated), mg L^-1

κ electrical conductivity, µS cm^-1

Some hand-held probes, such as the Ultrameter 6P (MYRON L Company, Karlsbad/USA), calculate the TDS depending on the temperature and the electrical conductivity. Such TDS values obviously cannot be used to eval-uate the accuracy of the electrical conductivity measurement.

Some chemical-thermodynamic codes calculate the electrical conductiv-ity based on the chemical analyses. Researchers very seldom use these results though they provide a very easy way to check the accuracy of a water analy-sis. Another mathematical method that even works for mine waters with com-plicated chemical compositions compares the ion mobility, u, and its

con-TDS= ×κ 0 6 0 725. ... . ionic balance cations

cations anions

= −

×

^∑ ( _∑ ^∑

+

_∑

^anions

)

^×

. %

0 5 100

electro neutrality cations anions cations anions

= −

+ ×

∑ ∑

∑ ∑

^100%

The usual procedure when sampling wells is to pump out three times the volume of the well before taking a water sample. Yet, it is more appropriate to pump until the on-site parameters remain constant. Those parameters are temperature, electrical conductivity, pH, or the oxygen content, which have to be measured in flow-through chambers. Also, if the well has a steel cas-ing, the mine water in the well may have been altered by a reaction with the steel. Samples taken in such a situation are not representative and must there-fore be avoided, as the steel-water reactions significantly change the physico-chemical parameters of the water (Lloyd and Heathcote 1985). Many aban-doned shafts are backfilled and equipped with cased wells. The sampling procedures required for wells also have to be applied to such shafts.

Samples taken must be representative of the water or sediment that has to be investigated, because treatment and remediation measures are based on the assumption that the results of any monitoring programme are representative for the catchment. To ensure representative samples, the geological, ecolog-ical, and hydrological situation in the catchment area must be known pre-cisely. During the implementation process of the EU Water Framework Di-rective, numerous European catchments were studied and so a lot of representative data is already available for researchers there. Besides the real sampling points in the catchment area, which represent the regional part cho-sen, there should also be blind sampling points for quality control purposes (see section 10.7).

Herbert and Sander (1989) explained that sampling highly saline mine wa-ters of salt mines (brines) requires the following precautions to ensure that the water sample is representative:

● avoid evaporation during sampling

● avoid contamination and an alteration of the sample by the mine air

● avoid particles in the sample

● samples should be stored at the same temperature and pressure condi-tions of the solucondi-tions in the rock matrix

During and after the Hope/Germany flooding experiment (section 12.14), Herbert and Sander (1989) developed a patented sampling tool that is able to take samples and determine on-site parameters under “real” in-situ condi-tions without altering the sample before or during the measurement.

For every dataset, it is important to record the name of the sampling point, dates and times of the sampling, the technicians or scientists who collected the samples, and the weather conditions. The brand of all meters, filters or any other tool should also be documented so that the cause of any potential mistakes can be identified. Finally, all chemical data should be tested for ac-curacy to reveal unreasonable values. Experienced hydrogeologists normally

9.3 Physico-Chemical Measurements 177 176 Monitoring and Sampling

oxygen content are always measured in the unfiltered sample, whereas fer-rous/ferric iron should be measured in both filtered and unfiltered samples.

For iron, it must be clear what the parameters “dissolved iron” and “total iron” mean. Authorities and even consultants often use the terms inter-changeably to mean the sum of the ferrous and ferric iron (that is, total iron).

Similarly, the expression “total metals” should be restricted to the sum of the species! The reason for the confusion is that the relevant regulations (DIN 38406-E1-1 May 1983; EN ISO 11885 November 1997; DIN 38406-32-1 May 2000) are unclear. Only EN ISO 11885 clearly – but unfortunately not precisely from a chemical and physical point of view – defines “dissolved”

metals: “The fraction of metals in a water sample that passes a 0.45 µm fil-ter”. Concerning aluminium, DIN ISO 10566 April 1999 clearly writes “fil-terable aluminium” instead of “dissolved” aluminium. Future version of

metals: “The fraction of metals in a water sample that passes a 0.45 µm fil-ter”. Concerning aluminium, DIN ISO 10566 April 1999 clearly writes “fil-terable aluminium” instead of “dissolved” aluminium. Future version of

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