ORGANIZATIONAL AND METHODOLOGIC PROBLEMS IN THE GEOCHEMICAL STUDIES

ON SURFACE WATERS

Mario DALL'AGLIO (*)

Mobile Laboratories for Chemical Analysis of the Waters-Data Storage and Statistical Processing

ABSTRACT

During the last years the searchers of the Geological and Mining Laboratory of C.N.E.N, have devised, and widely adopted in Italy a new method of geochemical prospecting for uranium. Such method, named as "regional geochemical prospecting", is based on the sampling and analysis of surface waters adopting a sampling net of about 5 km on the hydrographie net-work, which corresponds to a density of about 1 sample every 20 square kilometers. Such method of prospecting involves the investigation of wide areas (1.000 to 10.000 square kilometers) for every field survey.

The hydrogeochemical features are generally very heterogeneous, also in a single survey, cause of the varying geolithological, hydrogeological, climatic and seasonal conditions.

It resulted convenient to analyse all the main solved elements in the examined waters in order to exactly classify from a geochemical point of view the water samples.

For this reason it was necessary to resolve technical, organization and interpretation problems: a) Appropriate portable and carborne analytical equipments were projected and

settled up ; several instruments were projected just for such a work. b) All the geochemical data collected in these surveys have been enabled to use the

modern computers for the statistical retrieval of the data in elaborating the results. In this paper the results hitherto acquired in both the above mentioned arguments

are reported.

RÉSUMÉ

Au cours des dernières années les chercheurs du laboratoire géologique et minier du CNEN ont mis au point et largement adopté en Italie, une nouvelle méthode de prospection géochimique de l'Uranium. Cette méthode connue sous le nom de « prospection régionale géochimique » est basée sur l'échantillonnage et l'analyse des eaux de surface en adoptant un réseau d'échantillonnage de 5 km de côté environ, ce qui correspond à une densité de 1 échantillon par 20 km2. Chaque campagne de recherche permet ainsi l'étude de 1000 à 10000 km2.

Les conditions hydrogéologiques sont souvent très hétérogènes, même dans une seule campagne, à cause des conditions lithologiques, hydrogéologiques, climatiques et saisonnières très variables.

Nous avons préféré analyser tous les principaux composants dissous dans les eaux examinées afin de classifier exactement les échantillons au point de vue géochimique. Il a été nécessaire pour cette raison de résoudre de nombreux problèmes techniques et d'interprétation au suject des laboratoires mobiles que nous avons mis au point et au suject de la mise sur l'ordinateur et du traitement-automatique des données géochimiques.

Cette étude présente les résultats obtenus.

1. FOREWORD

Over the last few years, the researchers of CNEN's Geology and Mining Laboratory have devised, developed and extensively applied on the national territory a new method of geochemical prospecting for uranium ore deposits. This method, called regional-

(*) Geochemical Section, Laboratorio Geominerario del C.N.E.N. Centro Studi Nucleari délia Casaccia, S. Maria di Galeria, Roma.

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scale geochemical prospecting, is based on the sampling and analysing of surface waters, samples being collected at intervals of about 5 km (3 miles) on the hydrographie grid, corresponding to a density of about 1 sample per 20 sq. km (7 sq.mi). Surveys of this type involve very large areas (from 1,000 to 20,000 sq. km) (400 to 7,000 sq.mi) for each prospecting survey.

In such case the heterogeneousness of the hydrogeochemical conditions is generally very marked, even within the same survey, due to the changes in geolithologic, hydro-geologic, climatic and seasonal conditions.

In order to obtain an accurate geochemical classification of all water samples, it was found useful to analyse for all major constituents dissolved in the waters examined. The scope of this research has made it necessary to solve technical, organizational and data-processing problems, in order to ensure an integrated and rational approach to the surveys to be conducted.

1. Special analytical laboratories, mobile and truck-mounted, have been designed and built. Several instruments used in these laboratories were specially designed for this kind of work (Brondi et ai, 1966);

2. AU geochemical information collected in the course of the campaigns was stored in punched cards or magnetic memories. This has made it possible to use the modern computers for the statistical processing of the data and for the elaboration of the results (Dall'Aglio, Tonani, 1960 and 1965);

3. Finally, there was collected and processed a large number of data on the geo­chemistry of the major and minor constituents dissolved in some 5,000 water samples.

In view of the considerable mass of information and experience acquired in the field of the geochemistry of surface waters, it was deemed appropriate to report on the results obtained in two separate papers. This paper sets forth the results achieved in the field of the organisation of the analytical work, in the development of methods particularly suitable for geochemical surveys and in the statistical processing of information. Another paper reports on the knowledge acquired concerning the geo­chemistry of the major and minor inorganic constituents in Italy's surface waters.

2. THE ANALYSIS OF NATURAL WATERS

II. 1. Towards a correct geochemical interpretation of the analytic results collected, two conditions in particular should be met, and namely:

a) The analytical work should be dimensioned to suit the intended result. In the case of geochemical studies this involves, on the one hand, the solving of technical and organizational problems, such as the determination of certain compounds dissolved in waters at the time when the sample is taken ; and on the other, a correct choice of the analytical methods and equipment to be used with a view to obtaining the largest number of quality information at the lowest possible cost;

b) The most complete possible knowledge should be obtained of the physico-chemical balances and of the environmental conditions which most markedly affect the dissolution or precipitation of the elements present in the natural waters. For instance,' the mere knowledge of the Ca, Fe, Mn or U contents in ground waters does not supply complete information concerning the processes acting in a given context. The additional determination of the pH, Eh, pCÛ2 values and of the basic ion composition, instead, makes it possible to determine whether precipitation processes are in progress, or whether certain compounds have reached, or are far from, concentrations close to precipitation.

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II. 2. SPECIFICATIONS FOR ANALYTICAL METHODS AND EQUIPMENT

The range of the contents of compounds dissolved in natural waters is very broad. The concentrations of major and minor constituents can vary by several decimal orders, depending on the variations in geochemical and environmental con­ditions.

If, in addition to this broad variability in contents, we also take into account the general requirement, in hydrogeochemical surveys, for a large number of analytical data on a great many samples, we find that the analytical methods and equipment should meet the following requirements:

a) The methods and equipment should be simple and useable with satisfactory results also by personnel lacking a high degree of skill ;

b) Certain determinations have to be carried out at the time when the sample is collected, or immediately thereafter. This means that portable and self-contained equipment is necessary ;

c) In hydrogeochemical surveys, analytical methods ensuring a very high degree of accuracy are not required. For major constituents; a 5% error is generally accept­able; for minor constituents, a 10-20% error is largely acceptable, both because it is extremely hard to obtain better results with samples of diverse composition, and because a higher accuracy is rarely needed ;

d) It is convenient, and at times necessary, to use highly specific methods, for in natural-water samples presence of elements capable of interfering with the determi­nations to be carried out cannot always be ruled out;

e) The methods and equipment should be able to cover a broad range of concen­trations without changes having to be introduced therein. Furthermore, the relative error in the determinations should remain roughly constant over the entire range of concentrations encountered.

II. 3. PRESERVABILITY OF WATER SAMPLES

One particular problem, to which adequate attention is not always paid, is that of the preservability of water samples. This problem is of importance in view of the execution of chemical analyses in laboratories located at a distance from samples collection site. In practice, it is evident from the scientific literature that almost always a long time elapses between samples collection and laboratory analyses.

a) Determination of Physico-Chemical Parameters

The determinations of pH and Eh values, if they are to be significant, must be carried out on site. Even when appropriate precautions are taken, during the shipment of samples to the laboratory, pH values, for instance, may rise by as much as 1 to 1.5 units, due to the heating of the sample with the resulting shift in the bicarbonate-carbonate balance and escape of CO2 from the solution. Even substantial changes in the value of the oxidoreduction potential may occur during shipment, due to the oxygen in the air and/or to the development of biologic activity. Also the determination of electrical conductance, or equivalent measurements, are best carried out in the field, since precipitation processes may alter the significance of laboratory measurements.

b) Determination of Compounds or Combination States Unstable under Storage Con­ditions

As typical examples we can mention the determination of the concentration of hydrogen sulphide and ferrous iron. The former is readily oxidized by the oxygen in the air to sulphur, sulphates, etc., and the latter is oxidized to ferric iron. It is readily

68

evident that determinations of such products, if carried out days or weeks later in distant laboratories, are almost worthless.

c) Determination of Major Constituents Dissolved in the Waters

As regards the major constituents dissolved in the waters, i.e. Ca+2, Mg+2, Na+ 1 , K+ 1 , HCO3""1, SO4 - 2 and CI - 1 , there may occur during shipment a precipitation chiefly of calcium carbonate, since the other constituents are readily soluble and, in most cases, far from the saturation limits.

d) Determination of Minor Constituents

We regards as minor constituents of the waters those that are present in very small quantities, down to contents in the order of gamma/liter(*). In principle, it is desirable that the determination of a minor constituent be carried out in the field or at least in laboratories located near the sampling site, and above all without delay. Generally speaking, no reliance can be placed on the preservability of the concentrations of these elements in water samples, for the following reasons:

— the container used to receive water samples can take up, even in fairly short periods of time, appreciable or even quite high percentages of the element to be determined (for instance Hg and Heavy Metals) ;

— conversely, the containers can irrepairably contaminate the samples. It is very difficult, for instance, to obtain containers free from the presence of quantities of Pb, Zn or Cu capable of substantially altering the initial contents of these metals in the natural waters;

— the biological activity continues to develop even after the samples are collected. Not only can the biologically active constituents be released or consumed, but the organic substances of themselves can take up preferentially certain elements, such as for instance uranium;

— precipitation or co-precipitation phenomena can remove certain elements from the solutions. Thus, for instance, in waters with calcium and fluorine contents exceeding the values corresponding to the product of solubility of ftuorite (CaF2), the determi­nation of fluorine cannot be too long delayed without risking the precipitation of fluorite.

The conclusion to be drawn from the above considerations on the preservability of water samples therefore practically leads to the necessity of carrying out the chemical analyses involved on the spot or immediately after the sample is taken.

It should also be noted that the possibility of carrying out certain determinations on the spot can provide valuable indications for the operational decisions to be adopted For instance, in the study of a group of contiguous springs, even the knowledge of pH, temperature and electric conductance values only will give valuable help in selecting the samples to be subjected to subsequent analytic investigations.

II. 4. MOBILE LABORATORIES FOR WATER ANALYSES

It appears from the foregoing that the analytical methods and equipment to be used in hydrogeochemical surveys should meet very special requirements. As regards the analytical methods to be used, the major progress made by analytical chemistry, particu­larly over the last decade, make available to the researcher increasingly sensitive and specific methods. The latter, with suitable adaptations, are generally capable of meeting the requirements of geochemical analyses on both major and trace constituents.

(*) 1 gamma (7) = 10~6 grams; 1 y/lt = 1 part per billion (ppb).

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It is impossible, instead, to obtain " off the shelf" the analytic equipment required for hydrogeochemical surveys, which will meet all specifications set forth above, particularly as regards the attainment of a fair compromise between specificity and sensitivity on the one hand, and simplicity and independent operation on the other.

Among the instruments specially designed and built by us for this purpose we shall mention chiefly a two-channel flame photometer for the simultaneous and separate determination of Na and K, a battery-powered conductance meter and all instruments contained in the analytic kit shown in figure 2.

For this reason, the Gecchemical Section of CNEN has conducted a complex effort to design and build ex novo certain instruments particularly suited for geoch-emical surveys, and to assemble in the most rational manner commercial and special instruments fcr the most efficient conduct of the analytical work.

Of particular interest are above all the mobile and truckmounted laboratories which our organization has been using and continuously improving for several years.

Fig. 1 — House-trailer mounted laboratory. The instruments installed include: an analytical scale, a titration bench, a spectrophotometer, a flame photometer, a fluorimeter, a pH-meter and conductancemeter battery powered.

Apart from the "Central Laboratory", which possesses the standard geochemical-laboratory instrumentations, such as for instance optical emission spectrography, X-ray fluorescence, spectrophotometers, etc., mobile laboratories have been developed to meet the requirements set forth above, and specifically:

a) House-trailer mounted laboratory. This is a reduced-scale but complete chemical laboratory, incorporating also specially designed and built analytical equipment. It functions as a mobile field laboratory, but it generally operates with the support of local facilities (power supply, etc.) (fig. 1). The instruments installed include:

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an analytical scale, a titration bench, a spectrophotometer, a flame photometer and a fluorimeter, plus the normal laboratory equipment (glassware, reagents, etc.). In this laboratory it is possible to carry out practically all chemical analyses not requiring the use of large instruments, such as the high-dispersion optical spectro­graph and the X-ray fluorescence spectrometer. The analytic work currently done on water samples includes the determination of Ca+2, Mg4 2 , Na+ 1 , K+1 , HCOs - 1 , S 0 4 - a , CI-1, F - i , SiOa, P 2 0 5 , boron, Heavy Metals.

The work speed achieved in this laboratory is satisfactory; also thanks to a careful organisation of the analytical operations, two persons can carry out in one work week all the determinations listed above on about 80 water samples.

b) Portable laboratories for on-the-spot analyses. These laboratories comprise the instruments required for analyses to be done on the site where samples are col­lected (fig. 2). A more complex and better equipped type is mounted on a van, while smaller units are housed in special containers, which can be carried on cars or even on man's back.

Fig. 2 — Portable laboratory for analyses "in loco". By means of this miniature scale laboratory it is possible to carry out the determination of Ca+2, Mg+2, Carbonate-bicarbonate-carbon dioxide and SO--3.

4

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The latest type of these smaller units was specially designed and built with all of its components. In a package weighing 5 kilos (11 pounds) and measuring a compact 3 2 x 1 3 x 2 2 cm (12Vi"xS"x81/£'1') j s contained a real miniature-scale laboratory for the determination of water-dissolved Ca, Mg, bicarbonates-carbonates-carbon dioxide and SO4.

Mobile laboratories are also equipped with a battery-powered pH meter and conductance meter. The latter was designed and built in our laboratory, since an instrument meeting our technical and operational requirements was not commercially available.

The mobile portable water-analysis laboratories developed by CNEN researchers can provide an example of how a correct approach to applied basic research can lead to the development of certain by-products which, because of their applicability to similar fields, cease to be such and become important of themselves.

Thus, in our case, the need for solving technical and organisational problems connected with the development of a new geochemical prospection method has resulted in the development of certain mobile and portable water-analysis laboratories.

The design work on these laboratories, and the planning of the analytic work done in them, have always been conducted in the light of geochemical requirements, and above all of the requirements to be met by analytical work in order to provide the fullest information on hydrogeochemical phenomena.

Because of the increasing importance of water analyses, laboratories of this kind can make an effective contribution to the solution of all hydrogeochemical, hydrologie and natural-water quality and pollution measurements problems, which require the exe­cution of mass chemical analyses of water samples.

III. STORAGE, RETRIEVAL AND STATISTICAL PROCESSING OF HYDROGEOCHEMICAL DATA

III. 1. INTRODUCTION

Hydrogeochemistry is concerned with the distribution and circulation of chemical elements in natural waters. Like all other sectors of geochemistry, its progress is strictly connected also with a statistical, and therefore probabilistic, description of the various natural phenomena. For this reason, it is indispensable to be able to utilise fully all information contained in the great many data collected in various types of work: from hydrologie surveys to hydrogeochemical prospection campaigns.

The full utilisation of the data collected presupposes, in the first place, a "rational" data storage system. By "rational" we mean a method making it possible to locate and retrieve, as easily, promptly and inexpensively as possible, all information that may be needed, even a long time after the data were collected.

Beginning in 1958, the researchers of CNEN's Geochemical Section have been conducting a series of tests and studies with a view to developing a punched-card data storage system which would meet the following requirements:

1. Availability of a simple method of data representation, useable in routine work also by personnel not possessing a high degree of skill;

2. Possibility of storing all data obtained in the progress of work, without excluding the information not used immediately, and this with a view to prevent any loss of data collected ;

3. Availability of a simple method allowing the ready retrieval, without undue expenditures of time and effort, of all data or samples required;

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4. Possibility of using directly the stored material to carry out statistical computing wotk, such as data tabulating and charting, histograms, correlation calculations, etc., without having to go through complicated intermediate conversions.

Over the last few years the teams of CNEN's Geochemical Group have collected over 1,000 samples of surface waters a year. For all such samples the teams have determined the temperature, pH, electric conductance, the contents of Ca, Mg, Na, K, HCO3, SO4, CI, Si02 and P2O5, as well as the contents of the elements with which geochemical prospecting is specifically concerned, such as U, F, B, Heavy Metals, etc.

Because of the quantity and complexity of the hydrogeochemical data collected, the storage of all information obtained constitutes the first necessary step towards their full utilisation.

III. 2. DATA STORAGE

After thorough testing, it was possible to adopt on a routine basis in 1960 a storage system based on the punched-card recording of the hydrogeochemical data collected (Dall'Aglio, Tonani, 1960).

Some changes were subsequently introduced in this procedure, but the overall scheme remained the same as originally proposed.

111.2.1. Analytical Data Storage

All data relating to the concentration of the elements contained in the waters are expressed in equivalents per liter or their multiples. These values, as well as conductance and flow values, are expressed by three digits with a floating-point-system.

The value is expressed by two digits, involving a relative indétermination varying from 5% (fig. 10) to 0.5% (fig. 99). The third digit represents an exponent of 10, i.e. the position of the decimal point. Thus, 435 = 43.10~5, or 0.00043 equivalents per liter.

It is of interest to observe that this kind of notation proved easy to learn even for personnel lacking a high degree of skill. In actual use, errors were very infrequent.

The adoption of the floating-point system proved of extreme importance for the direct use of computation programs on modern electronic data processing machines.

111.2.2. Descriptive Information Storage

The punched-card storage of all descriptive data presents problems that are far more arduous than those involved in storing analytical data. Theproblem admits of no simple and univocal solution, for it would be necessary to satisfy two conflicting re­quirements. On the one hand, the use of numerical codes would simplify the work involved in selecting.and processing the data required, and would also constitute a first step towards an attempt at expressing natural phenomena in a quantitative manner. On the other hand, a very extensive letter code would make the stored data more readily understandable also to those who are unfamiliar with the codes used. On this problem several tests have been carried out, but the results achieved cannot be regarded as definitive. Close cooperation even among persons of widely different professional backgrounds will be needed to achieve some truly tangible results.

Tests have been conducted by our organisation, chiefly with the use of numerical codes.

Figure 3 shows the field form for the recording of the analytical and descriptive data on each water sample; figure 4 shows the final form. These forms have turned over to the mechanical recording services which transfer them into puched cards.

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II.3. DATA RETRIEVAL

When all data have been recorded on puched cards or magnetic tapes, it is very easy to select the samples or data desired. The selection can be done on the basis of the values of one or more stored parameters. We may wish, for instance, to retrieve all samples collected in a given watershed, or only the data for a given region, or all samples with a given content of one or more elements.

I1I.4. DATA PROCESSING WITH PARTICULAR REGARD TO STATISTICAL CALCULATIONS

The ease with which statistical calculations can be done increases substantially the true value of the available data, for the final interpretation can be based on objective probabilistic values.

Any type of statistical calculation can be readily done by using electronic computers. In this paper we shall discuss briefly only the statistical calculations in common use.

a) Through a first program, the value of the arythmetic average, standard deviation and variation coefficient of each parameter considered (temperature in °C, pH, conductance, Ca, Mg, etc.) are computed. The second part of this first program involves the computing of the simple linear corelation coefficient among all possible parameter pairs. It was necessary to develop special calculation programs, for the existing ones also consider zero values. According to the notation adopted by us, the symbol 000 means "not determined", while for determinations which yielded results below the limit of sensitivity of the method a very low conventional value is used, say 10' 10 - 8 or 10-10~~9 (respectively 108 and 109). In the programs devel­oped by us for each variable, all parameters of zero value are selected and eliminated from the calculation;

b) A second program carries out directly the plotting of the histograms of the various stored parameters. Figure 5 shows a histogram obtained in this manner;

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76

c) Often it is useful to check visually the pattern of corelation of two parameters. A calculation program "draws" corelation diagrams between any two parameters. Figure 6 shows one example of these diagrams;

d) One calculation process which has proved highly useful to evidence the functional ties existing between the various geochemical parameters consists in plotting the variations in the contents of one or more elements as a function of another con­stituent dissolved in the waters. In an initial stage, all samples considered are arranged by increasing values of the variable chosen as independent (say, conduc­tance). The samples are then divided into equinumerical classes (of 20 or 100 terms according to the cases), and for each of these classes the averages, standard devi­ations and variation coefficients for all parameters stored are then computed. Examples of statistical processing according to this procedure are supplied in the report on the geochemistry of surface waters presented at this Symposium (Dall'Aglio, 1967);

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77

e) It is often useful to study the statistical ties existing among more than two geo-chemical parameters. The regression analysis has often been carried out by digital calculation, using IBM's No. 60.003 program, which proved highly satisfactory.

III.5. On conclusion of the description of the method of geochemical data storage and statistical processing, and after years of practical experience in this field, we deem it appropriate to stress the following aspects: 1. The system adopted should have been fully tried out in its many aspects, and 2. The systems used should be simple in all working stages.

The most urgent problem, with a view to preventing a large mass of information from remaining practically unused and lost, lies in the necessity of making an early start on the systematical storage of all hydrogeochemical data collected by the various organisations operating in the different countries. The experience has taught us that, once, the information is stored on puched cards and like systems, the modern computers can easily resolve the problems connected with the conversion into codes even different from the original, and therefore carry out the most appropriate statistical processing.

IV. CONCLUSIONS

The méthodologie and organisational work, connected with the geochemical surveys and studies conducted over the last few years by the researchers of the Geo­chemical Group, has developed along different lines:

a) The most appropriate analytical methods have been chosen in view of their appli­cations to geochemical studies and surveys (DalPAglio, Tonani 1960). It was often necessary to carry out special development studies and to modify the existing procedures, or even to devise and use entirely novel procedures (Dall'Aglio, Gragnani, 1966);

b) The rational organisation of work, and the desirability of obtaining the largest number of quality results of the lowest possible cost, have made it advisable to design ex novo and build instruments and analytical laboratories;

c) In order to ensure the complete utilisation of the data collected, and even more to prevent their practical loss, we have developed and systematically applied a punched-card and magnetic-tape data storage system. This has made it possible to carry out the most appropriate statistical calculations using modern electronic computers. The most important aspect to be stressed lies in the fact that méthodologie research

towards obtaining the most valuable and least expensive information for the solution of geochemical problems was conducted in an integrated manner. Thus, for instance, the accuracy of the analytical methods adopted was determined in relation to the degree of accuracy actually required in hydrogeochemical studies. The indétermination of the procedure of punched-card storage, besides, is in the same order as the errors com­mitted in the determinations, and commensurate to the degree of discrimination re­quired for the solution of hydrogeochemical problems.

REFERENCES

BRONDI, M., DALL'AGLIO, M., TONANI, F. e VISIBELLI, D., (1966), Laboratori mobili per l'analisi delle acque naturali, L'Industria Mineraria. Gennaio 1966.

DALL'AGLIO, M. e TONANI, F., (1960), Archiviazione e trattamento dei dati idrogeo-chemici. Studi e ricerche del/a Divisione Geomineraria. Vol. I l l , C.N.R.N. , Roma.

DALL'AGLIO, M. e TONANI, F., (1965), Storage and retrieval of geochemical data. C.N.E.N., RT/GEO(65)l, Roma, febbraio.

DALL'AGLIO, M. e GRAGNANI, R., (1966), Determinazione del mercurio nelle acque naturali. Atti Società Toscana Scienze Naturali. Série A.

DALL'AGLIO, M., (1967), Geochemistry of major and minor constituents of surface waters. This Symposium.

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