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CSIR RESEARCH REPORT 391
The isotopic, chemical and dissolved gas concentrations in groundwater near Venterstad, Cape Province
by
J.C. VOGEL, A.S. TALMA and T.H.E HEATON
Natural Isotopes Division
NATIONAL PHYSICAL RESEARCH LABORATORY Council for Scientific and Industrial Rostarch
CSIR Reaearch Report 391 UUC 556.314(687 8) ISBN 0 7988 2013 6 Pretoria, South Africa, 1980 1
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The isotonic, chemical and dissolved gas concentrations in groundwater near Venterstad, Cape Province
J.C. VOGEL, A.S. TALMA and THE. HEATON
Natural Isotopes Division
NATIONAL PHYSICAL RESEARCH LABORATORY Council for Sctentfffc and Industrial Rsstarch
CSIR Httr&i Report 391 HJDC W6 314(667 8) ISBN 0 7966 2013 Í PrrtOfia, South AtrK», 1360 L 1
CSJft ntninh R»port 381 UOC 556 314 PuM«hwJm1M0by»i« Natawl Ptíywc* naxwch L*borMor> o< t* Counci) lor ScianMc and Induttrwl RwMrcfi P09t*395 PRETORIA Printed by Grtphic An$. CSIR L ABSTRACT Groundwater was collected for a multi parameter in vestigation from 27 boreholes within a radius of 120 km from Venterstad (Cape Province). The samples were analysed for the isotopes carbon-14, carbon-13, oxygen-18, tritium and radon-222, for the dissolved gases nitrogen, oxygen, argon, methane and he3\u^i and for the major ionic species. These data, with those collected during previous investigations of the flooding of the Orange Fish tunnel, are used to discuss the geohydrology of the area. Three water types of different origin were delineated. This project was sponsored by the South African Water Research Commission under contract K5/28. KATURAL ISOTOPE STUDIES OF THE GROUMDVATBR IN THE VENTBRSTAD AREA. CONTENTS: I. INTRODUCTION 1 II. GENERAL CONCLUSIONS 3 III. METHODS 6 Sampling methods 6 Laboratory methods 7 IV. AGB DISTRIBUTION 8 Radiocarbon and tritium 8 Carbon-13 content 9 14 Initial nC concentration 9 Summary 11 V. CHEMISTRY AND OXYGBN-18 13 Chemical differentiation of water types 13 Oxygen-18 content of the water 14 Genetic relations between water types 15 A model for the formation of Venterstad groundwater 17 Chemistry and hydrology of the tunnel waters 18 Summary 20 VI. DISSOLVED GASES 22 Helium concentration vs age of water 22 Non-He migration model 24 Release of He from a fracture zone 25 He and CH, migration 26 Radon concentrations 27 Nitrogen and Argon 28 Methane stripping 29 Oxygen concentrations 29 Summary 30 ACKNOWLEDGEMENTS 32 REFERENCES 33 TABLES FIGURES LIST OF TABLES. 1. Borehole locations and sampling details. 2. Age determinations of sampled boreholes. 3. Analytical data of samples taken in 1970-72. 18 4. Major ion chemistry and 0 of samples. 5. Comparison of the three water types. 6. Quantities derived from chemical analyses. 18 7. 0 measurements from the area south of Venterstad. 8. Dissolved gas concentrations. LIST OP FIGURES. 1. Ar^a maps with sample points. 2. Radiocarbon and tritium relation. 3. Piper diagram of all samples. 18 4. 0 content as function of alkalinity percentage south of the Orange River. 18 5. 0 distribution south of Venterstad. 6. C as function of Na/Ca + Mg ratio. 7. Caf Mg and Ca + Mg as function of the alkalinity. 8. Relation between He and CH.. 9. Radon as a function of Helium. 14 ^ 10. Helium as a function of C and ^H ages. 11. Nitrogen and Argon concentrations. 12. Dissolved oxygen content as a function of tritium. 1. I. INTRODUCTION The Orange-Pish Tunnel diverts water from the Hendrik Verwoerd dam on the Orange river for 82 km southwards to the Great Pish and the Sundays rivers. In 1969, during con struction of the tunnel, a fracture zone was encountered approximately 15 km south of Venterr,tad (Pig. 1). The resulting inflow of groundwater,which caused extensive flooding of the tunnel, was calculated as 860 l/s. The geology and hydrology of the Venterstad area, with particular reference to this fracture zone, has been discussed by a number of authors (see Whittingham, 1970 and Olivier, 1972 for references). Country rocks in the Venterstad area are near- horizontal sandstones, siltstones and shales of the Katberg formation (part of the Beaufort group), intruded by a large number of dolerite dykes with a colluvial cover of several metres over a large part of the area (Pig. 1). The fracture zone consisted of a number of open fissures, dipping southwards at 75 . one of which was more than 7 cm wide at the tunnel level, 110 m below the surface. It has been postulated that the fracture zone may represent reactivation of an eastwards extension of the pre-Karoo Doornberg fault zone exposed near Prieska (Pig. 1), Thermal springs occur along the supposed line oi this fault extension, and include the Badsfountain spring which is only 2 km east of the tunnel. A total of 1,6 x 10 nr of water was pumped from the flooded tunnel and, after grout-sealing of the fractures, water levels in surrounding boreholes largely recovered within 7 months. This suggests the presence of a large, permeable and potentially important groundwater reservoir in the Venterstad area. 2. The task assigned to the Natural Isotope» Division of the NPRL in the framework of the overall project was to develop and evaluate isotope techniques as an aid to the determination of the water potential of groundwater bodies in South Africa. In ttie specific instance at hand the aim was to determine whether the groundwater associated with the fracture zone south of Venterstad could be identified and evaluated. The originally formulated five year research programme was subsequently reduced to a preliminary survey of one year's duration. Despite the limited extent of the operation, the insight into the ground water situation in the region could be substantially deepened and several significant conclusions could be drawn. The approach adopted was to analyse a large variety of parameters on the sane sample and to derive information on the history and dynamics of the underground waters by inter- | preting the observed interrelationships. More specifically, k the correlation of different measured quantities with the age * 14 of the groundwater as revealed by C end tritium analyses has been studied. The following parameters were measured: the isotopes i 14C, 5H, 222Rn, 226Ra, 4He, 1S0, 13C; the dissolved gases N2f Op, Ar, CH., HpS; the pH, the major element chemistry and, in more detail, the carbonate chemistry, pH and alkalinity were measured in the field to eliminate storage problems. Two field trips were undertaken in 1977 and 21 boreholes and springs were sampled in all. Three boreholes were sampled twice to check for variability. Initially USJ was made Of the chemical and geological survey of van der Linde ar.d Hodgson (1976, 1977) in the selection of sampling points in order to ensure that different types of water be collected. Additional information was available on samples previously dated by us, some of which have been published (Olivier 1972). II. GENERAL CONCLUSIONS. As stated in the introduction, the survey conducted in the Venterstad area was of lxaited extent and duration. Nevertheless, several important conclusions can be drawn from the results. 1. Host of tL» boreholes in the region tap groundwater, a | substantial portion of which is less than 20 years old (Ch. IV). This water is, therefore, superficial and of local origin. The » short residence time suggests that the reliability of this 9 source will be influenced by temporal variations of ) recharge. 2. In addition to this shallow calcium/magnesium bicarbonate I water (Type I), two further water types can be identified on I the basis of the major dissolved salts (Ch. V). These sodium bicarbonate (Type II) and sodium chloride (Type III) waters I range in age from 800 years to 7 500 years and are often warm, I indicating deep circulation. I By a consideration of the absolute concentrations of the dissolved ions as distinct from the relative composition, it is I shown that the three water types are genetically unrelated. • Final proof that Type III water has a different origin from I either of the other two types is brought by the stable isotope 18 composition [ 0 content) of the water (Ch. V). I This finding has practical implications. The older water * types II and III are at present only represented by a few > boreholes, but these have high yields. There are thus two deep seated water resources in the region which are virtually I untapped, but liave considerable potential for irrigation or 1 town supplies, if fully developed. Since these water bodies i are not directly related to the shallow phreatic aquifer, their utilization will have little effect on this water source. J 4. 3. Helium and radon have been used in other parts of the worla to locate active fractures. The survey of these two isotopes failed to reveal the presence of a localized anomaly in the vicinity of the assumed fracture zone south of Venterstad (Ch.VlX The radon contents of the samples were relatively uniform throughout and merely reflect the radioactivity of the rocks near the sampled boreholes. Unexpectedly high helium concentrations were encountered, but these were not restricted to one locality, although they may be associated with individual fissures in the host rock. The close correla tion with methane does suggest accumulation of gas derived from depth in those instances where high concentrations occur. 4. The helium data clearly separate into two groups (Ch.VI) Low helium concentrations are associated with the superficial groundwater which is less than 20 ye?rs old, while the older water types contain 2-3 orders of magnitude more helium. The fact that no intermediate values are observed, confirms the conclusion that the younger and older water types are not related. The large variation in helium content furnishes an extremely sensitive means of detecting mixing between different water types (e.g. mixing ir the borehole). Such mixing was observed in a few of the samples, 5. The recently recharged water is characterised by high oxygen concentrations, while the older water has little or no oxygen (Ch.VI). This observation provides a simple means of rapidly distinguishing recharge areas in broader field surveys where the hydrological conditions are unknown or unclear. It is suggested that analysis of nitrogen and argon in groundwater can provide information on the recharge conditions (e.g. recharge through the soil as distinct from recharge from a river-bed), although t:.e data did not lead to any hydrolo^ical conclusions in the present survey (Ch.VI). 5. 6. The combination of radiocarbon and tritium Measurements shows that the initial 14C content of the groundwater in the area lies between 80 and 90?* of that of the atmospheric carbon 13 dioxide. The C measurements and chemical composition, furthermore, show no evidence of carbonate exchange with the host rocks. The dates derived from C ar,> thus considered accurate estimates of the true residence times of the water samples underground (Ch.IV). 7. The practice of determining the pH and alkalinity direct ly in the field has been found to be most important, both in respect to the interpretation of the carbon isotope data, and to that of the major ion chemistry (Ch.V). Later analysis in the laboratory is not good enough if accurate data are required. 8. The water that flooded the Orange-Pish tunnel duri ^ excavation in 1969 originated from fissures in the sediments and was essentially of Type II. Water encountered along the dolerite dyke A (Pig. lc) and \ts intersection with the tunnel was of Type III (Ch. V,. The two types appear to be chemically unrelated. The lowering of the water level in the boreholes along the dyke during tunnel dewatering shows that a hydraulic connection exists between them. The fact that the chemical composition of the water withdrawn frooi the tunnel did not change during dewatering operations, shows that the contribution of water from the dyke must have been small. The nature of the obvious hydraulic connec tion is unknown at present. Summing up, it may be stated that the value of the multi parameter approach adopted in this investigation has been clearly demonstrated. Although further hydrological wovk in the area could be conducted with profit, it should probably concentrate on locating further occurrences of the two deep water bodies and optimizing their exploitation. In the course of the survey several novel techniques involving dissolved gases were developed and evaluated. Some of these have led to direct application in the study area, while several new possibilities of a more general nature are also indicated. It is therefore felt vhat, within the limits imposed, the assignment has been successfully accomplished. 6. in. METHODS Sampling: methods The boreholes selected for sampling can be divided into three groups (Fig. 1): a) Boreholes within the immediate vicinity (7 km) of the flooding point cf the Orange-Fish tunnel. These included samples from the only remaining accessible boreholes directly above the flooding point. b) Boreholes along a line from Venter*tad approximately 120 km NHW into the southern Orange Free State. This was an attempt to obtain water away from the fault zone on a larger distance scale. In the absence of chemical data the boreholes were selected to sample both sulphuretted and non- sulphuretted waters. 18 c) A set of samples solely for 0 analysis was collected from boreholes approximately 100 km to the east, south and west of Venter3tad (Pig. 5). Details of the sampled boreholes are given in Table 1. Existing pumps were used where available. The sampler di rectly above the tunnel flooding point (DB 12, 13 and l-i) ware obtained with a submersible pomp powered by a portable generator. The boreholes were thoroughly pumped before sampling in order to eliminate possible contamination effect?. Samples for dissolved gases were obtained by drawing water trom a bucket into ?. previously evacuated flask containing some phosphoric acid (to drive off C02) and mercuric chloride (to prevent oxygen consumption). pH was measured on the fresh water and alkalinity was titrated potentiometri~**lly (Tailing 1973). These latter two parameters were measured in the field because the laboratory determined value is not reliable. The pK values of the samples collected near Venterstad during the first sampling trip (DB 1 - 11) ranged from 7,1 to 8,5 an measured at the boreholes. The same samples stored in ?lass bottles and measured in the laboratory yielded pH values between 7,2 and 7,4. 7. Carbon dioxide for C analysis was extracted from 40 to 120 liters of water on the day of collection and concentrated in sodium hydroxide for further extraction in the laboratory (Vogel 1967). Other samples were taken for laboratory 18 analysis of 0, tritium and major ion chemistry. Laboratory methods Dissolved gases were extracted from the vacuum flasks with a Toepler pump and measured in a mass spectrometer (Heaton and Vogel 1979). C and total C02 content was measured on CO^ frozen out from this sample with liquid nitrogen. The yield of C02 and the alkalinity titrated I on the fresh sample provide a check on the field measured pH using Debye-Huckel theory (Stumm and Morgan 1970; Loewenthal and Marais 1976). The C and tritium measure- * ments were done using standard methods (Vogel and Marais > 1971; Vogel et al. 1974). Radon was transferred by C02 as carrier gas from a vacuum flask into a proportional counter (Heaton and Vogel 1979). Radium was neasured as accumulated * radon a month after sampling. Major ion chemistry was I analysed in the laboratories of the NIWR at Pretoria. H2S was measured at the Hydrological Research Institute at Roodeplaat near Pretoria. At a number of boreholes HpS could 1 be smelt but was in too low a concentration to be chemically ( detected (<0,2 mg/1 H2S), t i 8. IV. AGE DISTRIBUTION. Radiocarbon and tritium The measured C and tritium values are listed in Table 14 2. A large proportion of the samples (17 of 27) contain C and tritium produced by nuclear weapon tests since 1S54. In terms of C this means values greater than 90# and in the case of tritium it implies values greater than 2 T.U. These samples, therefore, represent superficial water that is rapidly recharged and of local origin. Most of them are in fact from shallow boreholes with relatively low yields which show seasonal va^ iability. 14 The samples with low C and tritium values invariably have an HpS odour (see Table 2). Some are also warm, indi cating deeper percolation. Ages calculated on the basis of an initial 14C content of 85$ (Vogei 1970) range up to 4 750 years and are consistent with a model of water percolating to a sufficient depth to acquire the higher temperatures observed (Bredenkamp 1971). There is no obvious correlation of age with locality. This is probably due to the highly fractured nature of the aquifer rock and the large number of dykes present. It is interesting to compare these results with measure ments on samples collected in 1970-1972 (Table 3). These were mainly samples of the water that flowed into the Orange- Fish tunnel during construction operations after the main flooding occurred near Shaft 2 in 1970. The majority of the tunnel samples have 4C contents similar to cche** waters in the Venterstad area (Tables 2 and 3). The temperatures of the waters encountered in the tunnel suggest penetration depths down to about 400 metres (Olivier, 1972). At the flooding point the tunnel was 120 metres below the surface. 9. I I Carbon-13 content. I The relative carbon-13 concentrations of the samples vary between -5,5 and -17,7#o PDB (Table 2). This seems t reasonable for water in which the dissolved inorganic carbon is derived from the reaction of soil COp (& ranging from -26 to-13?£o) with carbonate of marine origin (6 = 0#o) (Vogel 13 1967, Hendy 1971). Using the measured JQ values and the relative abundances of carbonate, bicarbonate and CO, in 13 the water one can calculate the C value of the gaseous COp in equilibrium with the water (Mook 1968, 1976, Hendy 1971). For the Venterstad samples these values range from -21 to -13#o (Table 6) and a single value of -25,5?So (DB 3). The former is in agreement with that which can be expected for this part of the country. Vogel et al. (1978) have shown tint more than 90$ of the grass species in the present study 13 area have C values near -12,5#o, The other plants (mainly shrubs) have 5 = -26#o. Soil C02 can therefore be expected to show 6 values between these two extremes (Rightmire and Hanshaw 1973). In fact, a single soil C0~ sample collected 13 close to D3 12 gave a VC value of -15,5#o which is within this range. The 6 value of DB 3 of -25,5#o (sampled twice) implies soil COp derived entirely from non-grass vegetation and is quite different from DB 1 which is only 700 m away and aimilar in other respects. No significant correlation of 13y Z with age or major ion chemistry is discernible. There is, therefore, no evidence of isotopic exchange with limestone in the host rock. The ages calculated from the C contents are thus probably not distorted to any major degree as a result of C loss. The initial C concentration In order to calculate the age of a water sample from its C content the initial 4C concentration must be known. The inorganically dissolved carbon (mainly HCOj") is derived in equal parts from soil COp, with a relative C content of 100$, and Ca(Mg)C0,, with little or no 14C. (Vogel and Ehhalt 1963, Hendy 1971). The total dissolved carbon thus 1 10. initially has a C content of at least 50<. Simultaneous isotopic exchange with soil C02, however, tends to increase this value until it nuy ultimately attain 100% that of modern carbon. On the basis of a limited number of samples an empxrical value of 80 - 90% of uhe atmospheric C concentration was originally suggested fo.* the initial 4C content of ground water (cf. Vogel and 3hhalt 1963). Since then several attempts have been made to calculate ti.is figure with greater accuracy from the 13C content and chemical composition of a sample (Pearson and White 1967, Mcok 1976, Wallick 1976). The validity of such calculations, in some cases involving elaborate computer programming can, however, not be readily assessed. The muin problem is to quantify the exóent of isotopic exchange between the gaseous and liquid phases in the unsaturated zone (Hook 1976). All these calculations rely heavily on the correct 13 assessment of the C content of soil CO- and can, therefore, not be applied in most of Southern Africa, since the isotopic composition of the plant cover has been shown to vary over too wide a range (Vogel et al. 1978). A reasonably accurate empirical estimate of the initial 4C content can, however, be made for the samples collected in the Venterstad area by making use of the simultaneous rise in the C level of atmospheric C02 (Vogel and Marais 1971) and the tritium level of rain (Vogel et al. 1974) caused by nucloar weapons. When assessing the C and tritium levels in iscent groundwater, however, the nature of samples collected from farm boreholes oust be born in mind: such boreholes generally penetrate the water-table to a dept'i of several meters and thus invariably produce water representing precipitation integrated over a number of years, if not decades. It is thus not surprising that none of the samples contains as much tritium as could be expected from the tritium content of the rain since 1962 (about 22 T.U., see Fig, 2). J 11. On the other hand any groundwater sample with more than 2 T.U. must at least partly be derived from precipitation that fell in the past 20 years. Similar considerations also apply to 14c From Fig. 2 it can be seen tuat those samples with more than 2 T.U. all contain more than 90$ C. This implies that the pre-1957 level must have lain below 90$. It is also evi dent that none of the samples with less than 80$ C contain measurable amounts of tritium (i.e.>2 T.U.) so that the pre-bomb C level could not have been much below this value. The relationship between C and tritium thus again suggests an initial 4C level of 80-90$. A further argument in support of this conclusion is that groundwater has not been found to contain more than 85$ of ' the highest G level that the atmosphere reached in 1962/3 > (160$). A lower Licit can be obtained from the maximum C content of 122$ (DB 6, 7 and 17) observed in this study, » viz : 122/160 = 76$. But even tnese samples do not contain ' enough tritium to be totally derived from 1962/3 rain. There is thus every justification for using a value of i (85+5)$ for the initial 4C content of groundwater in the area. Summary ' 1. The ages derived from the radiocarbon and tritium con- , tents of the analysed samples range from less than 20 years to 4 750 years. Ihe large group of samples containing atom bomb C and tritium which are thus less than 20 years old, ' represent the shallow phreatic water in the area, • The older waters are from deeper high-yielding boreholes , or springs. They show traces of HpS and thus reducing con ditions, and are often warm, indicating deep percolation and » rapid return to the surface through a high permeability path, 1 Some of the water collected in the Orange-Fish tunnel during construction in 1970-72 has. even greater ages, is warm and is definitely associated with fractures or dykes. 12. 2. The carbon-13 of the dissolved carbon is consistent with the mixed grass and shrub vegetation of the area and shows no evidence of isotopic exchange with limestone in the host rock, 14 lending credence to the C ages. 3. The C and tritium measurements suggest that the initial C content of the dissolved bicarbonate lies between 80 and 90?6 of that of atmospheric C02. A figure of 85jC is thus a satisfactory value to use for calculating the ages of ground water in the area. The observation that none of the samples contains the maximum expected 14C and tritium concentrations (13695 and 22 T.U.respectively) i^> explained by the fact that borehole samples of necessity integrate several years of recharge. 13. V. CHEMISTRY AND OXYGEN-18. Chemical differentiation of water types. The results of the analyses of the ma^or ion chemistry of the collected samples are shown in Table 4. Cation and anion analyses are given in milli-equivalents per liter to facilitate the discussion of exchange, solution and precipi tation processes. Some activity products have also been cal culated (Table 6) to aid the interpretation of the water chemistry. It can be seen that most of the waters are close to saturation with respect to calcite and that the caicite equilibrium is the limiting reaction as far as calcium and carbonate (and therefore pH and alkalinity as well, Hendy 1971) is concerned. The saturation towards dolomite is quite variable and while dolomite may have acted as a Mg source to the water its presence has no limiting effect on the Mg con centration. This can be expected since dolomites are only precipitated from highly concentrated brines (Hsu 1967, Millioan 1974). All the samples are highly undersaturated towards gypsum (CaSO.. 2H20) and no sulphate precipitation is therefore possible from these sample waters, not even at highe temperatures (Kharaka and Barnes 1973). A graphic presentation of the ion ratios in the- form of a Piper diagram (Figure 3) confirms the existence of three water types viz. water with predominantly Ca, Mg and HCO, (Type I), water containing virtually only NaHCO, (Type II) and waters with low alkalinity but containing mostly NaCl (Type III) (Olivier 1972, van der Linde and Hodgson 1976, 1977). Type I water was found throughout the sample area and originates from the Beaufort sandstone (van der Linde and Hodgson 1976). Type II water was found at Roodewal (DB 15) to the west of the tunnel area, and to the north of Venterstad (DB 22, 24 and 26). It is significant because it is very similar to the. waters found in the tunnel during excavation, and the water responsible for flooding of the tunnel (Olivier 1972 and Table 3). Type III water was sampled at Badsfontein (DB 1 and 3, 2 km east of the flooding point) and at a 14. windpump to the north (DB 11). Some of the other parameters measured in this study have values distinctly different in one or other of the water types found (Table 5) and are useful in evaluating the evolution of these waters. Oxygen-18 content of the water. The oxygen-18 values of the water samples are reported as the relative deviation of the 0/ °0 ratio froir SHOW (Table 4). Some samples taken in 1970 to 1972 were also measured (Table 3). These were mairly from water seeping in or flooding 18 the tunnel during its excavation. Because 0 does not change after infiltration, unless subject to evaporation, it can be useful in distinguishing waters of different origin, such as different altitude of recharge and temperature (Dansgaard 1964, Vogel and van Urk 1975). The measured values range from -6,1 to -3,95^0, and are typical of groundwater and rain on the South African inland plateau. In genral there is a tendency for lower values to be found towards the north of the sample area (DB 23, 24 and 26), but in the vicinity of the flooding point different values are found close together. The latter are related to the water types distinguished on the basi3 of th* major ion chemistry. Limiting oneself to the smaller area south of the Orange River where conditions are more uniform with regard to topography and vegetation, one finds a clear relation between 18 18 0 content and relative alkalinity (Figure 4). The lower 0 found in samples with low alkalinity implies a clear separation between Type I and II water (>-5,2#o) from Type III (<-5,4?'o). 16 The tunnel waters fit in with this separation. The lower '0 value of the Type III water ( -5,7#o as compared to -4,8 +G,4#o) suggests infiltration at about 300 m higher altitude (altitude effect*v0,3960/IOO m, Vogel et al 1975). 15. In order to assess the variability of 0 in the area a set of 19 more samples were collected to the E, S and V of Venterstad (Figure 5). The results (Table 7) show some more negative values near Teebus and Steynsburg. These are possibly associated with the higher altitude of the Suurberg mountains (2 000 m), nearby. The samples collected to the N of the 18 Orange river also show a slight decrease in 0 towards the north where the terrain rises gradually. Genetic relations between water types. The usual manner in treating the evolution of the major ion chemistry of groundwater is based on the ion ratios as represented in the Piper diagram (Piper 1944). Soil C02 dissolved in water leaches limestone in the soil or aquifer rock to form predominantly Ca and Mg bicarbonates, i.e. the Type I water found in this study area. Subsequent cation exchange with clays in the aquifer causes the Ca and Mg ions to be replaced by Na. This yields NaHCO, water similar to Type II. Further addition of NaCl decreases the relative contribution of bicarbonate to the total anions until a water of higher salinity with predominantly NaCl is formed (Chebotarev 1955, Johnson 1975). This evolution is represented as: Ca(Mg)HC0, —• NaHCO^ —» NaCl Variants on this scheme exist»taking into account sulphates and other chlorides. That Ca (Mg) HCO, solution is the initial stage of ground water evolution is amply confirmed in the Venterstad area: All the samples in the lefthand corner of the diamond field of the Piper diagram (Type I) are to a substantial part younger than 20 years old, while those to the bottom (Type II) and right (Type III) are all older (Figure 6). In order to judge whether the progression from Types I to II ~ Turning to some specific ions one can see that the ions to be removed when evolving from Type I to II, are CI, SO., HCO,, Ca and Mg. CI is the most soluble ion known and cannot precipitate, neither can SO. becaus MgSO. is very soluble and CaSO, is very unsaturated in these samples. (Table 6). The removal of SO. by reduction to E-.S by sulphur bacteria would result in HpS concentrations much higher than those actually ob&srved in Type II waters (Table 4). CaCO, precipi tation would require some mechanism to remove the C02 from the C02-HC0,-C0, system (Talma et al. 1974). Such removal of gas has not taken place in the samples of Type II. MgCO, is more soluble than CaCO, and will be less likely to precipitate. Even if CaCO, were to precipitate, Mg would thus remain in solution. There is, therefore, no obvious mechanism to explain the possible evolution of Type II from Type I water in the area under consideration and it must be concluded that these two water types developed independently. As for the hypothetical evolution of Typ^ III water from Type II water, it is noticed that there is no significant age difference between the two (Figure 6) making such a process unlikely. Table 5 shows that Type III water contains more NaCl, P and the gases CH. and H2S than Type II. These in creases could readily be explained, but the corresponding in crease in Ca and decrease in alkalinity could not be accounted for. The strongest argument for rejecting such an evolutionary 17. 18 development is, however, the more negative 0 values of Type III water. Type III -*ater could conceivably develop directly from Type I by addition of KaCl. However, here too substantial removal of HCO,, SO., Ca and Mg nould be required, which we have seen to be highly unlikely on chemic?1 grounds. In addition, such development is precluded by the IS0 contents of the two water types. It may also be pointed out that mixing of any two water types cannot produce the third for precisely the same reasons given in the discussion above. Mixtures between two water types can, of course, be distinguished in a few instances (e.g. DB 9, 21). The conclusion drawn from consideration of both the major ion chemistry and the environmental isotopes is that none of the three water types encountered in this area are genetically related. This is in contrast to the impression gained by con sidering only the ion ratios as represented by the Piper diagram. A model for the formation of Venterstad groundwater. Since it is concluded that the young Type I waters do not form the source water of the other two older water types, one must determine whether satisfactory alternatives are possible. The possible mode of origin of the three water types in the study area will be described. Type I: The high alkalinities of these samples (4 to 7 meq/1) indicate solution of Ca (Mg) CO, by high C02 concentrations in a fairly active soil zone (Vogel and Ehhalt 1963, Garrels and Christ 1965, Hendy 1971). This process would imply equality of the sum of Ca and Mg and alkalinity (Figure 7). Some cation exchange may have lowered the Ca and Mg content slightly. The virtual equality of Ca and Mg probably implies that the lime stone source is dolomite (Ca Mg (C0,)2). In addition some amounts of Na CI may dissolve in the water and 30, may be 18. formed by some pyrite oxidation or gypsum solution. ïhcee waters are mainly found in the sandstone aquifer at shallow depths. Type Hi This type of water with its lower alkalinity would have evolved from the solution of less limestone than Type I, by mors rapid infiltration. It would then have lost nearly all its Ca and Mg by ion exchange to end up with virtually pure NaHCO, in the water. This suggests infiltration in an outcrop area possibly directly into fractures with less soil influence to raise the CCL content (and thus the alkalinity). There is no addition of other salts (CI, SO., etc.) Most of the samples collected in the tunnel and associated with fractures, particularly those close to the 1969 flooding point, show a similar origin as do some deep boreholes close to this point (Figure lc). Type III; This water evolved from the solution of CaCO, at even lower C02 concentrations, thus resulting in high pH values (Hendy 1971). This is again typical of rapid infil tration in rocky outcrops virtually devoid of active soil and plant life. The equality of Ca and alkalinity implies that no cation exchange has taken place (Figure 7). Later addition of NaCl, F and other minor ions make up the entire ion chemistry of this water. Chemistry and hydrology of the tunnel waters. The available chemical and isotopic analyses of the water samples collected in or near the Orange-Fish tunnel during construction (1969-72) are given in Tables 3a and 3b. The ion ratios are plotted on a Piper diagram (Figure 3). These data provide information on the groundwater at greater depth which is no longer .accessible. It is seen that the three water types found in our larger survey are all present in this restricted area (Figure lc). 19. Young Ca and Mg bicarbonate water (Type I) was found in shallow boreholes. The water in the boreholes along dyke A, including the Badsfountain springs, and the water draining from this dyke into the tunnel is old, has NaCl as the main 18 constituent and a low 0 content (Type III). Water draining into the tunnel from dyke B was a mixture of these two types. The water flooding the tunnel from the main fissures (not associated with dolerite dykes) contained mainly NaHCO,, «ras less saline than other water in the area, and had a 14C content of less than 70# and 6 0 near -5,0?5o (Type II). A few boreholes close by (NL18 and 22) yielded the same type of water. During drilling of some of the boreholes (NL20, 22 and 25), Type I water was struck at shallow depths with a tendency for Type II water to be encountered at deaths greater than 70 m (Pig. 3). This Type II water was not encountered in the area during our survey since none of the deep boreholes are now accessible. It was only found at Roodewal (DB15, 20 km west) and across the Orange river, 100 km north of Venterstad (DB24 and 26). During dewatering of the fracture zone area it was found that the water levels in boreholes with Type ÏI water close to the inflow point were lowered rapidly by up to 12 meters, while boreholes with Type III water along the dyke wert> not affected as greatly (about 3 meters) indicating a hydraulic connection between them. The shallow boreholes in the vicinity containing Type I water were not affected by the dewatering at all (Olivier 1972). This shows that they can not be connected to the main fissure. It was furthermore observed that the chemical character of the water removed from the fissures remained practically the same I during the dewatering operation (Table 3a), This inplies that, while there is some hydraulic connection betwoen dyke A and the main fissures, there was very little mixing of ' the two water bodies: a 10$ contribution of Type III water ) to the water pumpeá from t,ho fissures would have shown up in the chemical analyses. The bulk of the main fissure water » 20. must, thereforeyderi.e from a different source to that of Badsfountain, a concl'ision which is in agreement with th* independent development of Type II and III water discussed in the previous section. These observations suggest the existence of a water body of lype II water, that can be tapped at depths in excess of 70 meters in this general area, and is not presently being utilised. Judging by the large inflow into the tunnel during its construction, this water body must be of considerable size. Prom the data presently available no conclusion about a possible connection of this water body with the waters sampled by us to the west and north can be made. Summary 1. The grouping of water samples according to their major ion ratios in the water shows the existence of three distinct water types viz. Type I: Ca and Mg bicarbonate water containing bomb radiocarbon and tritium; Type II: old KaHCO^water; and Type III: old NaCl water. Scne of the other parameters measured were found to group similarly, thereby confirming the classification into three types. An important conser vative tracer is oxygen-18 which in this case clearly pointed to a separation of Type III water from the other types. Calculations based in part on field measurements of pH and alkalinity showed the samples to be saturated only with respect to caicite and not to gypsum or dolomite. 2, The combination of major ion chemistry with environmental isotopes afforded a means of evaluating the relationship be tween different water types. It was shown that the three water types are unrelated in the sense that they cannot have evolved from each other. 21. The yotng Type I water is the only water to have infil trated through the soil cover in the sampling area. The other types must have infiltrated elsewhere under conditions of less soil activity. For Type III, in particular, the infiltration area is probably at greater altitude. One may have to consider the mountains to the east and south for possible source regions of this water. 3. The water found in the Orange-Pish tunnel during its excavation and flooding was predominantly of Type II and was unrelated to the local recharge 'percolating down through the soil cover. It was also foun1 in some exploration boreholes at depths greater than 70 meters and could be a useful water resource in this area. 22. VI. DISSOLVED EASES He concentrations range over three orders of mag . 'lude (Table 8), from 5xlO~5 ml STP/kg ELO, close to the value to be expected for air-equilibrated water, to as high as 10 ml STP/kg H20 in the thermal waters at Badsfontein (DB 1 and 3). CH. likewise shows a wide range in concentrations and has a marked positive correlation with He (Fig. 8). The He and CH^ rich waters are characterised by an HpS odour (Fig. 8). Rn concentrations are comparatively uniform, in the range 1 600 - 16 000 cpm/kg HpO, and show no apparent correlation with He concentrations (Fig. 9). Np and Ar concentrations are shown in Fig. 11. Whilst some of the waters have Np and Ar concentrations close to the values to be expected for air-equilibrated waters, most of the samples have higher concentrations. There is no apparent correlation between Np and Ar concentrations and He concen trations (Fig. 11). Op contents are generally lower than those for air-equilibrated waters, and there is a general tendency for He and CH, rich waters to have lower Op concen trations (Table 8). Helium concentration vs age of water The initial He concentration in groundwater, infiltrating as rain, must be expected to be about 3,8 x lO'^ml STP/kg H20. This is the He concentration for water in equilibrium with air at our ground surface conditions. A number of the waters analysed have concentrations close to this value. For samples with higher He concentrations, however, He produced as alpha particles by radioactive decay of uranium and thorium in the rocks must have been added to the water during its subsurface history. On the basis of their He concentrations the samples super ficially separate into ttfo groups: those with less than 4 5 x 10" ml He STP/kg H20 all contain more than 2 T.U. and/or over 90$ C, and are therefore of recent origin (<20 years J f old)} whilst those with more than 5 x 10 ml Ie 3TP/kg H20 23. contain less than 2 T.U. and less than 90?S C, and are therefore older than 20 years. An intermediate group (DB 8, 9, 12, 17) have relatively high He concentrations (3-9 4 x 10"'ml STP/«g H20) as well as elevated % and C contents, and apparently represent mixtures (Pig. 10). For the old, helium rich waters there is no clear distinction between the NaCl (DB 1, 3 and 11) and the sodium bicarbonate waters (DB 15, 24 and 26). The very high He concentration in the old waters has the effect that only a email addition of old water to recent water will substantially increase the He concentration of the recent water without significantly affecting its C or H concentration. The solid lines in Pig. 10 illustrate the effect of sujh mixing. The composition of sample 17, for example, can be adequately explained by the addition of about 2$ of water similar to sample 3 to water similar to sample 6. Such admixture of waters with different ages can easily occur in the borehole from which the sample is collected, especially if it penetrates the water-table to some depth. This is in agreement with conclusions drawn from the chemistry (in particular Ca, Mg and alkalinity) of the water. Those waters which have ages between 1 000 and 5 000 years 2 1 contain between 10" and 10" ml He STP/kg H90 (Pig. 10). On the average, therefore, about 3 x 10 ml He STP/kg Ho0 is 5 added per 2 000 years, or 1,5 x 10" ml 'le STP/kg H20 per year. The different mechanisms which could account for this are discussed below. 24. Non-He migration model This model assumes that the He removed by groundwater is derived only from the rocks through which the water passes (i.e. no migration of He to produce areas with anomalously high He concentrations). Then the He concentration in the water will depend on its age, i.e.: He = 3,8 x 10"5 • |. f.t, where: He = final He concentration in the groundwater (ml STP/kg) o = amount of He (ml STP) produced per year per kg rock p = amount of water (kg) per kg rock (a measure of porosity) f = amount of He removed by groundwater amount of He produced by rocks t = age of groundwater (years) The theoretical He concentration in groundwater as a function of its age for a non-He migration model is shown by the broken lines in Pig. 10. The rocks are assumed to have typical radioactivities of 2ppm U and 7ppm Th (Rogers and Adams, 1969); then a = 4,3 x 10 . Estimates oi the porosity of the rocks are difficult to make, but storage coefficients of Beaufort group sediments in other areas suggest effective porosities of the order of 0,1 to 0,01?S (Boehmer 1970; Leskiewicz, unpublished); then p = 3,7 x 10"4 to 3,7 x 10 . Whilst most rocks probably retain some of their He (ie. f The data in Fig. 10 suggest the following: (1) The He content of samples 11, 22, 24 and 26 could be accounted for with this model, if the very low porosities of 0,1 to 0,019C are "i-plicable and there is negligible reten tion of He in the rocks. (2) Samples 1, 3 and 15 would require even lower porosities, unless the rocks are anomalously radioactive. In general it may be stated that it is difficult, though not impossible, to explain the high He concentrations of the older waters by a non-He migration model. Release of He from a fracture zone High He concentrations could be accounted for if a small part of the sampled water had penetrated and dissolved He from rocks which had previously been accumulating He for several million years. Such a situation, where He is removed from rocks in which it had previously been retained, would be particularly favourable along an active fault zone. In such a zone rocks become fractured, exposing new surfaces to water, and mineral structures are stressed, favouring release of He. It has been suggested that the warm springs at Bads- fontein (DB 1, 3) and Roodewal (DB 15) may be related to an E-W extension of the fracture zone encountered during drilling of the Orange-Pish tunnel (Olivier 1972). If this fracture exists and is active, it could explain the high He concen trations in the waters at Badsfontein and Roodewal, and in DB 12 from above the fracture zone in the tunnel. Waters with high He concentrations, however, also occur up to 100 km away from this possible fracture zone (DB 17, 21, 24, 26). These are to the north of the Orange River where there is, to our knowledge, no evidence for a major fault. Therefore the thermal waters at Badsfontein, although they contain the highest measured He concentrations, are not markedly anomalous when compared with other waters away from 26. the fracture zone. In this respect the He data have not detected a localised anomaly in the vicinity of the tunnel fracture «one. It would appear that a more widespread pro cess is required to explain the high He concentrations throughout the sampling area. He and CH, migration The world's most abundant sources of He are CH. rich natural gas deposits, and the correlation between He and CH, concentrations in the groundwaters (Fig. 8) suggests that these gases are associated with one another in the sampling area. The high He concentrations in the groundwaters could result from the passage of water through rocks where He and CH. have accumulated through migration of gas from depth. CH./He ratios in the sampled waters vary from about 50 to 3 300, but the majority are in the range 200-600. Whilst the He concentrations in na-.aral gas are variable and gas solubilities have to be taken into account, s^ih ratios are reasonable for natural ga3 deposits. Zartman et al. (1961) calculated the mean He content of natural gas deposits to be 0,2$, which would suggest a mean CH./ He ratio of about 400-500. Pockets of CH, gas were encountered during oil/gas explo ration drilling in the Karoo sediments and during construction of the Orange-Fish tunnel (Rowsell and De Swardt 1976). The formation of this CH. during diagenesis of the sediments has been discussed by Rowsell and De Swardt (1976). CH- from the gas of DB 3b and lib was analysed for its JC/ C ratio and yielded 615C values of - 35,7 and - 32,2?6o (vs PDB standard) respectively. These values are within the range - 28,3 to - 41,3#o for CH- from a number of boreholes and warm springs in the Beaufort group (Vogel and Talma, unpublished), 27. Whilst such values are not totally unambiguous, CH- of biogenic origja, produced by low temperature decay of organic matter in anoxic waters, usually has lower C/ C ratios (< - 509(o). The carbon isotope ratios of DB 5b and lib are thus consistent with a thermal origin of the methane (Fuex 1977; Stahl 1977). This process of gas migration could be widespread and would account for the distribution of high He and CH. con centrations in groundwaters throughout the sampled area. The correlation between the He and CH. concentration of a sample and its age suggests that the older waters have either 1) penetrated to greater depths where higher He and CH. concentrations may be expected to occur; and/or 2) have had longer subsurface paths, thereby removing gas from a greater volume of rock. Radon concentrations The radium concentrations in the groundwater samples are low (Table 8) and can account for very little of the Rn in the water. Most of the Rn, therefore, jiust have been dissolved directly from the rocks. High Rn concentrations havo been reported from some natural gas deposits and may be associated with faulting (Zartman et al, 1961; Bulashevich et al. 1976). The Rn concentrations in the sampled groundwaters, however, are quite uniform and show no correlation with the large variations in He and CH. concentrations (Pig. 9). In addition the Rn concentrations are similar to those reported from other groundwater sampling areas (Tanner 1964; Dyck 1976). TK? data suggest that the Rn is not associated with a localised anomaly, such as a fault, and is not particularly associated with natural gas migration. The short half-life of Rn (3»82 days) suggests that Rn from deep sources would have to be communicated fairly rapidly to the surface for such sources to be detectable. In general the Rn concen- 28. trations in the groundwaters of the sampling area are con sistent with the Rn being derived essentially from the rocks through which the water passed during the last, near-borehole stage of its history. Nitrogen and Argon ihe Np and Ar concentrations in the sampled waters ar» shown in Fig. 11, and are compared with the concentrations for water in equilibrium with air at 10° to 30°C (solid line). Whilst some of the samples have N2 and Ar concentrations close to those for air-equilibrated waters (A.B.W.), most show a trend towards an excess of N~ and Ar above these concentra tions. This excess Np and Ar has a Np/Ar ratio similar to that of air; the effect of adding 10ml air STP/kg h*20 to air- equilibrated water is shown in Pig. 11. The data suggest, therefore, that excess air has been incorporated into the waters during some stage of their history. Air contamination during collection or leakage during storage of the samples is not suspected. Air bubbles may be incorporated in rainwater during its infiltration into the groundwater reservoir, a process some what analogous to air 'injection' into ocean waters (Craig and Weiss, 1971; Bieri, 1974). The entrapment of air beneath percolating water is a phenomenon well known to soil scientists and can play an important part in determining the rate of infiltration (Wilson and Luthin 1963; Dixon and Linden 1972; Vachaud et al. 1974). Rainfall in the sampling area occurs mainly as intermittent heavy downpours in the summer months October to May, and maximum seasonal water-level fluctuations of up to 9 m have been recorded (Olivier 1972). It is possible that rainwater, originally having Ng and Ar concentrations in equilibrium with air, may trap air occurring in the pore-space of the soil or subsoil. These air bubbles, if carried down to the water-table, could dissolve under the 29. increased hydrostatic pressure. Evidence for thi3 excess air is not restricted to waters in the Venterstad area, but is also found in the groundwater near Beaufort West and elsewhere (Heaton and Vogel, to be published). The amount of excess air trapped during infil tration may be expected to depend on the nature of the recharge and the structure of the unsaturated zone. Measurements of the amount nf excess air may, therefore, provide a means of distinguishing between waters recnarged under diffe.*ent conditions. Methane stripping Samples from DB 1, 3 and 11 have N2 and Ar concentrations distinct from those discussed above (Pig. 11). These three sites are all characterised by particularly high CH, concen trations (Table 8), and solubility data (Morrison and Billet 1952) suggest that the partial pressure of CH. in these waters exceeds atmospheric pressure. Under such conditions bubbles of CH. may form in the water and, if lost to the surface, they will remove Np and Ar in proportion to their solubilities. CH- 'stripping' may also have reduced the amount of He in CH.-rich waters. This mechanism can explain the Np and Ar concentrations at sites 3 and 11. Water from site 1, which is an open spring, may have a more complicated CH. stripping and atmospheric exchange history. Oxygen concentrations Op concentrations range from less than 0,01 ml STP/kg H20 up to 5,30 ml STP/kg H20, the latter value being close to the concentration for water in equilibrium with air. Within this range there is a qualitative correlation with the age of the water, 02 and tritium concentrations are shown in Fig. 12. Young waters with >2-3 T.U. have 02 concentrations >1 ml STP/kg H20, whilst the older waters with <2 T.U. have 02 concentrations <1 ml STP/kg H20, 50. Such a pattern, with 02 concentrations decreasing with the age of the water, aight be expected in a systea where 02 is progressively reaoTed by oxidation of organic matter in the water. The presence of organic aatter in soaa of the saaples to thich no HgCl^ and H,P0- had been added was suggested by the growth of a green sliae during storage. Suaaary 1. Low He and CH. concentrations are characteristic of recently recharged waters, and high He and CH. concentrations characteristic of older waters. The He concentration data appear to separate into two groups, with t gap in concen tration values between 5 x 10~* and 3 x 10~* ml STP/kg H20. This may indicate the presence of two water types (recently recharged and older groundwaters). The He concentration-age relationship of the saaples with intermediate He concentra tions is most easily explained in terms of mixtures of these two water types. 2. Recently recharged waters are also characterised by higher dissolved 02 concentrations (>0,9 ml STP/kg H20 for the samples reported here). Considering the ease with which 0o concentrations can be measured this may prove to be a useful technique for distinguishing between recent recharge and older groundwaters in broader field surveys. The presence of HpS might also be used in the Venterstad area as a field indicator of older groundwater, 3. He and Rn surveys in other parts of the world have been used to locate active fracture zones. In the Venterstad area the highest He concentrations were found in the thermal waters at Badsfontein, close to the site of the fracture zone in the Orange-Fish river tunnel. High He concentrations were also observed, however, in waters far to the north of this area, Rn concentrations were relatively uniform throughout the sampled area. The He and Rn data,therefore, did not indicate a localised active fracture zone south of Venterstad. 31. 4. The He concentrations of many of the waters are too high to be explained in terms of the groundwater age and a non-He migration model. He may have migrated upwards from greater depths. There is a marked positive correlation between He and CH4. The C/ C ratios of two methane samples suggest that they are of petrogenic, high temperature origin. He may have been carried upwards with the migration of natural gas methane. Higher H-S concentrations are characteristic of the older He and CH~ rich waters. Whilst SO. reduction may be the most obvious source for producing H-S, it can also be associated with ratural gas deposits. The uniformity of the Rn concentrations suggests that the uranium content, porosity and porosity distribution of the aquifer rocks close to the boreholes are fairly constant throughout the sampled area. 5. Np and Ar concentration data indicate that an excess component of air has been added to the water during some part of its history. It is suggested that under certain conditions air bubbles are trapped by the water during infiltration, carried dowi to below the water-table, and then dissolved under the increased hydrostatic press ore. Since the amount of excess air should depend on local infiltration conditions, studies on the N2 and Ar concentrations in groundwater may provide information on these conditions. 32. ACKNOWLEDGEMENTS. Ve gratefulLy acknowledge the Water Research Commission's financial support of this study. We also.wish to thank Prof. P.D.I. Hodgson and Mr. P.J. van der Linde for their assistance in the selection of samples, and Mr. L. Siebert (N.I.W.R., Pretoria) and Mr. L. Verhoef (Hydrological Research Institute, Roodeplaat) for their analyses of the major ion chemistry and H-S. Dr. D.B. Bredenkamp kindly made available unpublished chemical analyses of water samples collected during the excavation of the Orange-Pish tunnel. Finally we wish to thank the other members of the Natural Isotopee Division for their analytical services, and the farmers in the study area for their assistance in the collection of water samples. 33. REFERENCES. Bieri, R.H.t 1974. Dissolved conservative gases in seavater. In: The Sea j>, Ed. D. Goldberg, Wiley and sons, New York. Boehmer, W.K., 1971. Report on geohydrological investigations along the route of the Orange-Pish tunnel. Unpublished Interir Report, Geol.Surv. S. Afr. Bredenkamp, D.B., 1971. An investigation of the origin of groundwater and nature of the aquifer system in the vicinity of shaft no. 2 of the Orange-Fish tunnel. Unpublished Report, Hydro. 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Natural isotopes in surface and groundwater from Argentina. Hydrol. Sci. Bull., 20, 20?-221. Vogel, J.C., Fuls, A. and Ellis, R.P., 1978. The geographical distribution of Kranz grasses in South Africa, S. Afr. J. Sci., 74, 209-215. Wallick, E.I., 1976. Isotopic and chemical considerations in radiocarbon dating of groundwater within the semi-arid Tucson Basin, Arizona.Inrinterpretation of Environmental Isotope and hydrochemical data in groundwater hydrology IAEA, Vienna, 228 38. Whittingham, J.K., 1970. Report on geohydrological investi gations along the route of the Orange Fish tunnel, Cape Province. Technical Report Gh 1545, Geol. Surv. S. Afr. Wilson, L.G. and Luthin, J.N.t 1963. Bffect of air flow ahead of the wetting front on infiltration. Soil Sci., 96, 137-143. Zartoan, R.B., Vasserburg, G.J. and Reynolds, J.H., 1961. Helium, arg^i and carbon in some natural gases, J. Geophys. Res., 6o, 277-306. Table 1 Borehole Data 1 2 4 Saaple Par» Geographical Othar aaaple Puap Borehola * t..p. > Dolerite" Water ' no. position nuabera type dapth (a) Saapla data (»C.) dyke level(a) DB 1 Badefountain 30° 53.1* 3 25° 46,7'ii fciá(l) 72(2) Spring June 1977 27,1 X 0 2 Bad afoun tain 30° 52.6* 25» 46,5' HI3(1) 75(2) windaill 24,5 * 16 3a Badafountain 30° 53.2' 25» 46,5' AK2(1) 74(2) aubaera. « 27,0 z 3b Badafouatain Dee. 1977 4 Wilaebeeate nUt; 30° 48,7' 25» 46,2' 297(2) aubaora. 24,5 June 1977 16 X 3,0 5 Blaadafountain 30» 55,2' 25» 46,2« 118(2) aueaara. i. 16,2 6 aland efounta in 30° 54,3' 25» 46,2' m(l) 119(2) auaaera. * 15,8 7« Vaalekrena 30» 55,9' 25» 45.8- 326(2) windaill M 16 X 7b vaalekrana Dee. 1977 8 Bedafounttin 30» 50,9' 25» 45,6" 87(2) aubaore. June 1977 16 9 Wildebeeate valley 30° 49.4« 25» 46,9' 1(2) aubaera. m 18 X 10 Wildebeeate nUtj 30» 49.6' 25° 46.7' 67(2) aubaera. u 16,8 11* Badafountain 30° 50,5' 25° 46,0« 68(2) windaill n 17,8 Jib Badaf. untain Deo. 1977 12 Badafouatain 30° 53,3« 25° 45,3* ItL22(l) port.auba. >60 «• 19,9 15 13 Badafeuntain 75a on bearing 162»froa x>B12 port.auba. 54 B> 6 14 Badafountain 100a on bearing 175»froa DB12 N19U) port.auba. 38 H 19,4 6 15 Roodaval 30° 52.0« 25» 35.2' R¥2(l) spring II 30,2 X 0-3 16 Dlepíontein 30° 19.2' 26» 05,8' winaaill n 19,2 X n Beusing?ostein 30° 20.7" 26» 04.8« «indaill n 16,8 18 Uitkjk 30° 11,1' 26» 10,7' windaill « 17,2 X 19 Klipbankafontein 30° 35.5' 26° 02.8- windaill at 17,9 X 20 Kareefontein 30° 28,0« 26° 01.9' raoipr. 30 ft 19,0 21 Katfonteln 30» 28,4' 25» 05,1' windaill n 18,5 22 Taalbaak 30° 41,1- 25» 55.7* apring 27,5 * 20,2 0 23 Suiddeel 29° 53,1' 26° 18,1' windmill 24.5 N 16,8 24 Ileiabadfontein 30° 05.3' 26» 24,1* aprlng 36 m 18,2 X 25 Poortjie 30» 01.4' 26° 16,4' r windaill N 18,2 0 26 Da Bad 30° 06,4' 26» 12.8- windaill 27 n 16,7 X 1-3 27 Yaalkop 30» 44.8' 26» 53.5' raeipr. « 18,2 X 1. Faraera boraholea are uaually 20-30» deep. 2. Mean annual air teaperature at Oviaton over 6 year period 17-?0»C average 18,5»C (Olivier 1972) 3. x - Borehole close to, and probably taps water from, dolerit; dyke. Lack of evidenoe for a dyke doe* not prove ita absence. 4. Average water table depth is 7a in sampling area 1-14 (van der linde and Hodgson 1976) TABLE 1. Details of boreholes and springs sampled and their locations. References to other sample numbers are from 1. Whittingham (1970) and Boehmer (1971). 2. Van der Linde and Hodgson (197*, 1977) ard their hydrogeological map of the Venterstad area. TABLE 2. Results of age determinations and related quantities of samples collected in 1976/7. C is 14 reported as percentage of the atmospheric C content of the pre nuclear weapon era. Tritium {\) ±3 reported in tritium units (= 10 18T/H). Age is deduced from the presence of nuclear weapon 14C and T or from 4C decay with 85$ as initial 13 concentration. 0 is reported as the relative deviation of the 1'5C/ C ratio from P0B, Table 2 14C (Pta Ho) Tritiua Deduced Sample H S« Ko. (*) T.U. •*• (Jto PDB) 2 (yrs) DB1 70,8 + 0,5 (1953) ' 0,5 • 1,0 1 500 - 7.9 2 2 115.4 + 0,9 (1952) 0 + 1,0 <20 - 8,2 0 3a D 53.5 + 0.7 (1*94) 0 • i,o 3 750 - 17,7 2 4 111,2 + 0,9 (1954) 12,0 • 1,0 <20 - 9,4 0 5 117,7 + 0,9 (1999) 10,3 • 1,1 <20 - 10,8 0 6 122,2 + 0,6 (1998) 14.1 • 1,1 <20 - 11.4 0 7ab 122,6 + 0,6 (2000) 16.3 • 1,0 <20 - 11.1 0 8 105,2 + 0,8 (199?) 3.4 • 1,0 <20 - 8,0 0 9 95,1 + 0,8 (1958) 7,0 + 1,3 C20 - 7,6 1 10 110,8 • 0,9 (1997) 5.4 • 1,0 <20 - 10,2 0 llab 63,3 • 0,5 (19*0) 0,7 + 1,0 2 400 - 6,7 1 12 101,1 • 0,9 (2072) 3.7 • 1.0 <20 - 8,7 1 13 0 14 107,7 + 0,6 (2483) 4.7 + 1,0 <20 - 8,5 0 15 77,0 + 0,7 (2074) 2,0 + 1,0 800 - 9,3 2 16 5,8 + 1,0 <20 - 12,3 0 17 120,8 + 0,8 (2076) 7,2 + 1,1 <20 - 11,7 1 18 l * Presence of H2S is indicated as : 0 - no smell 1 - soell but <0.2ogS/l 2 - >0,2 mgS/1 TABLB 3a. Chemical and isotopic results of water samples collected in the Orange-Pish tunnel during its excavation in 1970/2. Chainage is the distance in feet from the mouth of the tunnel. The main Hooding occurred at chainage 72 425 on 26.8.69 and cewaterin,; of the tunnel continued up to December 1970 (Olivier 1972). The water types indicated were If deduced from the Piper diagram (Figure 3). Sources n of the chemical analyses are: CI a) Olivier 1972. ^ b) Unpublished analyses by Soils Research ^ Institute for the Department of Vater Affairs. ,J T-able "ja 1 Ca J M« Nu K Alk CI K * F Coinage Flov 14 19 Cond ••°i Tof»l Witer Jusple late C(!'t'») 0 -ouroe •:i/s (mü/sn1 (*o) iti*q/l ineq/1 Marts, of Inflow a rea i '.'Vie 26.10,70 36 340 l 44 1.5 0.4 3.0 2. '• 0 2,4 0 0,07 4.9 l/III i> ?i3aure faA3?^ 18.04,72 39 600 1.3 34.7~912> -5,6 55 0,65 0 5.0 - 0.6 0,38 4,8 0 • %7 in b • Fissure 29.10.70 39 625 2,5 -- 58 1.2 0,16 4.5 . 0,71 1.3 3.9 0 0,33 5.9 ni t Fisoure 7.11.70 40 933 15 _ . 32 0,31 0,08 3.1 - 1.6 0 2,0 0 0 3,6 b Fi3S ure Ir.04.71 44 245 1 -- 36 0,30 C •1.4 . 3.9 0,28 0,65 0 . 4,7 n/u1!i b Fiasure 12.05.72 50 355 0.1 _ - 42 0.76 1.4 3.3 - 3,3 0.33 1.4 0,31 - ' ,4 b Fissure 13.02.72 6 3 747 1.4 -- 45 0,2 0 5.1 - 3.4 0,14 1.9 0 - 5,3 n b Near Ir-Tlow area 2haft 2 *:orth (3A14) 6.10.70 79.1(418) 2yke 3 3.06.70 68 800 . . - 56 1.9 • 2~9 0,29 3,5 . 6,7 1/1:: b H 3T5 -y*e B 6.10.70 T.' -- 62 '.3 1.xT2? 3.3 - 3.4 0,40 3,6 S 0 0,07 7,4 1/111 Mb Dy ice A 3.06,70 69 600 2.5 -- 60 1.0 0,82 5.0 - 2.2 0,60 4.1 0 0,07 6.3 111 b liyke A (3A39) 6.10.70 t* 2.5 - -5,5 65 1.6 0,41 5,7 0,02 2,3 1.0 4.4 0 0,07 7.7 HI b Inclined shaft 2 12o 31.10,70 — - -4,2 60 2.1 3.5 2.0 - 5.3 0,39 1.9 0 0,02 7.3 1 b Tritiur 3,7 r; I.-.ol r,ei A-.jBkït 2 24a 31.10,71 • ------m . _ _ Tntiu* 3,3 VI Inol' i.ed shaft 2 ,161 31.10.71 • -- -574 . . . _ • - . . m • _ . - TriUus 0 TV i Knir. Fissure 10.03.70 12 nr*> -- 25 0,36 0,02 2.6 0,19 1,1 0,37 0,56 0 0,10 . 11 a I Mui:-. Fi3;-ure 11.03.70 ** -- 30 0,40 0,53 •',7 - -.3 0,4 9 0,79 0 0,1? 3,7 b H •>o n j Main Fissure 9.06.70 38 -- 30 0,50 0,25 2,7 - 2.5 0,20 0,70 0 0,06 3.4 11 ub [ M:ii:. Fissure 7.07.70 w 3t -- 30 0.60 0,03 3,1 . 2,9 0 0,90 0 . 3.9 11 b j Nair. Fissure 25,07,70 n --- 30 0.60 0,16 3.0 - 2.8 0 0,90 0 . 3.8 11 b 1 M-*ir> FiS3ure 6,oa,70 w 44 -- 31 0.55 0,16 3.1 - 2.9 0 0.90 0 - 3,8 TI b J Kui:. Fi3surt> 3.09,70 u 4 4 _ - 32 0,50 0,00 3,3 - 2.9 0 1.0 0 . 3.9 11 b Main Fissure 3.10.70 n 44 _ . 32 0,55 0,16 '3.1 . 2.9 0 1,0 0 . 3,9 II b Ma ir. Fissure 20,10.70 M --- 32 0,50 0.16 3.2 . 2,9 _ 1.0 0 _ 3.9 II b >!'ii.\ Fissure rsAi1 23,10,70 n 44 lb,4!330) -5.0 34 0,35 0,16 3.4 - 2.4 0.50 1,0 0 0,12 3.9 II ab Fissure 31.03,70 72 527 20 -- 35 0,20 0 4.0 - 2,9 0,43 0,8 0 . 4 ,2 II b Ficsure 1.06.71 73 022 11 -- 32 0,40 0,26 3.6 - 2. e 0,50 0,9 0 - 4,2 II b Fissure ' 3A26> Oet. 71 73 590 44 65,3'560) - - « - - - • . « ~ m - • - •A ,', b Fiss'ure (SA27) Oct. 71 73 321 '0 57,1(561) -5.0 30 C.26 0.1S - " ,'• 0.30 0,90 0 - 3.3 II | Fissure (SA23) Oct. 71 74 473 20+ 63,6(562) -4.5 40 0,56 0,04 i',<> - 4,5 0,26 0,56 0 . 5,3 II b [ Fissure (3A33) March 72 75 640 20 59.6(644) -4,4 - • . - • . . - . -- Fissure '3A3SÏ March 72 76 921 33 33,4(910) -5,0 43 0.15 0 5.3 - 4.4 0.31 0,70 0 - 5?4 II b Joutr. of Irjflow are* Fissure 6.01.71 111 476 0.2 45 0.25 0.1 5.1 4,0 0,05 0,9 0,1 « 5,5 11 b Fissure 17.06.71 113 753 2 3 . - 54 0,15 0.1 r.7 . 4,0 0,24 1.7 0 - ' .0 II b Fissure 14. Or. 72 153 245 0,4 . - 30 0,20 0 3.5 - 2.5 0 1.3 0 - 3.8 II b i Fissure 13.01.72 216 111 0,2 -- 24 0.35 0 2,3 - 0,90 0 1,3 0 - 2.7 III b Fi39..re 5.10.71 23? 193 1.9 -- 42 1.0 1.75 *~ » '' - > 6 1.4 1.4 0.1 - 5,3 I b F i? 3 ure It.03.71 233 901 0.76 _ - 32 0.6 0.17 5t- - 1.9 0.94 1.1 0,05 • - II/III b . Fissure ! •••A?4) March 72 2 33 920 104,3(645) -5,0 36 0,65 0 7.4 - 1.1 0,35 1.15 0 - 3,5 II/III b Fissure 10.05.71 236 162 10 -- 30 1.1 1.4 1.4 - l.J 1.1 0..-3 0.2V - 3.9 I v. Fis.- xxe 5.11.71 253 754 0,4 _ - 73 1.1 0,9 7.5 . 3.8 1,6 •1.1 0 - 9.5 II/III b ••'13J ;re 15.09.71 2 59 313 c.i • — 105 2.5 2,3 7.0 — •1.3 2.2 5.7 0 — 12,.; I/III b TABLE 3b. Chemical and isotopic results of water samples from boreholes sampled in 1970/2 in connection with the tunnel flooding investigation. The chemical water types indicated were deduced from the Piper diagram (Figure 3). Souices of the chemical analyses are: a) Olivier 1972. b) Unpublished analyses by Soils Research Institute for the Department of Water Affairs. Table 3b 14 18 Ca Na 30 CI N0 p Depth C (Pta) Mg K Allc 4 ? Total Borehole Date Yield 0 Cond Water Source (m) (1/s) (*) mS/m •eq/1 •oq/i type Boreholes and springs near tunnel flooding area Badsfountain NL 4 20.02.70 32 20 -- 74 1.4 0,08 6,3 . 1.1 0.29 6,4 0 0,26 7,9 III b Badsfountain NL 4 24.10.70 32 10 -- 80 1.4 0,42 6.4 . 1.1 0,49 6,6 0 - 8,2 III b Badsfountain NL 4 (SA41) 26.09.72 -- 54,8( 909) -5.8 Badsfountain NL 5 20.02.70 32 10 -- 78 1.4 0,42 6,6 ~ 1.0 1,0 5,2 0,15 0,29 8,0 III b Nest to DB1 Badsfountain NL 5/A 9.06.70 _ 2.5 — — 87 1.7 0,33 7.2 0,03 C,66 0,49 8,0 C 0,32 9,3 III ab Badsfountain NL 5/B (SA 3) 24.10.70 32 25 51,0( 382) -5,6 88 1,6 0,4 7.0 0,50 0,50 8,0 0 0,33 9,2 III ab Badsfountain AK1 16.03.70 38? 13 - — 85 2,0 0,16 8,8 - 0,25 0,49 8,0 0 0,29 10,0 III b Near DB3 Badafountain AK1 20.10.70 28? 25 — - 90 1,8 0,33 7,9 - 0,90 0,90 8,2 0 0,35 10,2 III b Badsfountain AKI (SA40) 25.09.72 -- 60,5(2498) -5,4 Bad3fountain KL18 5.09.70 79 23 _ - 34 0,60 0,17 3,0 _ 2,9 0 0,90 0 - 3.8 II b Badsfountain NL19 10.09.70 17 0,37 — — 45 2.3 1,5 1.7 - 5,0 0,21 0,31 0 - 5,5 I b Badsfountain NL20/A 11.09.70 37 0,04 -- 39 1.0 1,5 2,2 - 4,2 0,21 0,31 0 0,02 4,7 I b Badsfountain NL20/B 12.09.70 79 4 -- 43 1.2 0,82 3.2 - 4.6 0 0,59 0 0,03 5,2 I/II b Baisfountain NL22/A 15.09.70 17 0,076 -- 42 1,8 1.8 1,6 - 4.5 0,29 0,39 0 0,02 5,2 I b DB12 Badsfountain NL22/B 16.09.70 76 13 — • 34 0,65 0,25 2,9 « 3.0 0 0,79 0 0,05 3,8 II b Badsfountain NL23/A 23.09.70 70 0,1 -- 42 1.6 0,41 3,3 - 4.2 0,50 0,51 0 0,02 5,2 I/II ab Badsfountain NL23/C 24.09.70 70 7,6 -- 34 0,6 0,16 3,4 - 2.9 0,40 0,90 0 0,06 4,2 II ab Badsfountair NL24 26.09.70 95 — - 43 0,6 0,16 4.1 - 4.1 0 0,08 0 0.03 4,5 II b Badsfountain S3 24.10.70 98 15 -- 42 1.2 0,41 3.4 - 4,4 0 0,51 0 0,03 5,0 II ab Badsfountair. AS13 27.10.70 32 1 -- 54 1.2 2.1 3.4 - 5.1 0,60 0,51 0,31 0,04 6,6 I ab Boreholes and springs away froa flooding area Badsfountain KL14/A (Dyke D) 9.06.7C 59 11 58 3.3 1.8 2.0 5,1 0,60 1.0 0,40 0,33 7,2 I b Badsfountain NL14/B '<*« C1 TO.10.70 59 11 91,2? 384) -572 54 2.8 1.4 2.6 0.12 5.1 0,60 0,9 0.31 0,24 7.0 I ab Kleinvlei JW1 19.02.70 10 19 -- 68 2.8 4,4 1.4 - 7.0 0,50 1,0 0 0,02 8,6 I b Kleinvlei JV13 27.10.70 122 3 -- 29 0,33 0,40 2,8 - 1,7 0,21 0,7y 0 0,04 3,5 II b Roodewal Rfl. (SA 4) 29.10.70 - 40 69.4( 383) -5,0 31 0,50 0.33 2.9 - 3.0 0 0.71 0 0 3.7 II ab Roodeval RW2 (SA42) 1972 -- 67.1( 90<-> Roodeval RV4 (SA43) 15.07.72 -- 95,51, 905) -3.8 50 0.15 0,08 4,6 - 3.5 0,54 0,76 Ö - 4,8 II b Roodewal (A Regers) 25.02.70 - 20 -- 30 1.5 o.oe 2,2 - 3.0 0 0.79 0 0,15 3,8 I/II b Raodeval (J Lategan) 25.02.70 _ 13 — — 30 0,60 0,58 2.3 - 1.9 0,69 0.79 0 0,15 3.5 II b Aliwal North Spring 31.01.70 — - - — - 4,2 0,40 15,3 • 0,70 1.2 18,4 0 - 20,1 III ab Aliwal North Spring (SA24/5) 14.07.71 -- 38,9(549) -6.2 TABLE t. Results of major ion chemical and 0 analyses of collected samples. Duplicate samples are given for comparison. Results are reported in meq/l unless otherwise indicated. il -°8; !,l,,--!990;.'°.0»<> $^s:;x:sí:x:sáx«Aí3ss::sss!::s: fï ooooooooooooooooooooooeooooo'o hi ooooooooo ooooooooooooooooo »'2S8Xï!S2338333SS8331§o'StlS85;gS £ oooooooooooo«.o'o«roooooooooooo<> •-• o O0O«O0xa««O0<«Oa'«0O«0»>O0«>«0X>0MM« £ ooooo»«ooowoooooooooo«>eoaooooo «4**<*0**>'*'**«t>'"«W«*k*»'***>'*'*'*M'**>S***J« * 3 ac S3S3S833S8Sd333Í8 33S3333S3 33 3 OOOOOOOOOOOOOOOOOOOOOOOOOOOOO _ ^ **»<»^ • • t» •» o fc E3 t s 9 <•• «•««<•• • <« • • o • » • 8 :h3 8he«NHinn:xtist«i^sss^s08. i iTiiTTTnTiiTT-iiTTTTVUTtTiT: OO 0«t»*OOi**000«>00*00«tOOOO«»«»0«>0 H Ê S 1 S S » 6 8 3 S S C fí 5 8 S X* 5 S X R 5 S 5 X 8 5 £ £ % CÊax&sxsssssssRxssasaíixsxsïP:; f * TABLE 5. Summary of the properties of the three chemical water types in the study area as exem plified by the samples collected in 1976/7. Obvious mixtures between these types (DB 9, 21, 22) have been excluded. TYPE I T!TPE II TTPB III UNITS Samples 2,4-8,10,12-14, 15,24,26 1.3,11 16-20,23,25,27 14C >100 47-77 53-71 Jt recent Tritium >3 <2 <1 T.U. He 6-900 850-1900 570-10000 10~5ml/kg »2 12-18 15-17 6-16 ml/kg °2 1) 1-5 0,1-0,7 0,3 cl/kg Ai 0,29-0,39 0,32-0,36 0,16-0,28 ml/kg CH4 0,002-2 2-5 26-43 ml/kg Rn 1600-15COO 5000-11000 2000-8000 cpm/k ? 18 0 -6,1 to -3,9 -5,8 to -5,2 -5,9to -5,7 fo SMOW 180 south 2) -5,2 to -3,9 -5,2 -5,9to -5,7 fo SMOW Ca 1,3-5 0,1-0,4 0,6-1,4 meq/1 Wg 0,4-4,5 <0,08 <0,26 meq/1 Na 0,8-4 3-3,5 5-7 meq/1 Alkalinity 4-7 2,6-3,2 0,6-1,6 meq/1 so4 0,5-1,2 <0,1£ 0,14-0,6 meq/1 CI 0-2,5 0,6 5-7 meq/1 N05 0,02-0,7 H2S 0 0,1-1 1,7-6 mgS/1 Total meq. , 5-11 3-4 7-9 1) Oxygen was only measured on samples 3b, 7b, lib and 12-27. 2) Excludes samples north of the Orange river. TABLE 6. Listing of quantities derived from the chemical analyses and useful for the interpretation of the genesis of the water. 13 6PCO2 is the C value of the gaseous CO- in equi librium with the groundwater. (Deines et al. 1974) S.I. (= saturation index) is the logarithm of the activity product divided by the solubility product of the species concerned. S.I. = 0 iuplies saturation and +0,3 (= log 2) implies 2x oversatu- ration. In the case of carbonate minerals this will precipitate about 10?£ of the available alka linity when reaching saturation, in other cases it will be 40$. Total milliequivalents equals the sum of cation plus anion concentrations divided by two. Tabla 6 ChaaAcal d«rlwj quantities CO,''" HCO," COjdiss. »pC02 Saapla TDS Sat.Ind.» Sat.Ind.» 3at.Ind.» Total •g/l swq/l •tq/1 *> CalCitt Doloaita Oypiua ••VI DB 1 41? 0,023 1,26 0,019 -V.6 •0,0 -0,8 -2.5 6.9 2 543 0,044 6,41 0,23 -16.8 +0.1 +1,6 -1.8 9.6 3a 535 0,022 0,845 0,0089 -25,5 -2.0 8.9 3b 463 0,023 0,573 0,0037 -25.0 -0.2 -0,9 -2.8 7.8 4 434 0,015 5,84 0,52 -17.4 -0,1 +0,6 -1.7 7.6 5 f 02 0,0088 6,81 1,07 -18,0 -1.1 10,8 6 560 0,020 8,32 0.94 -19.2 +0,1 +1,0 -1.5 10.3 7a 439 0,028 6,18 0.35 -19.5 +0,2 •1.3 -1.5 7,8 7b 0,017 5.71 0,47 -19,8 +0,0 •0,9 8 409 0.014 5,31 0,45 -16,1 -0,1 •0,4 -1.7 7,1 9 625 0,044 5,82 0,20 -16,0 +0,1 •1.2 -1.3 10,9 10 435 0,011 5,76 0,76 -17,8 -0,2 +0,3 -1.5 7,7 11a 389 0,029 1,38 0,016 -15.3 -0,3 -0.3 -2.3 7,2 11b 417 0,080 1,47 0,0060 -16,7 -2,8 7,3 12 300 0,012 4.04 0,34 -16,5 -2.0 5,2 13 319 0,018 4.81 0,31 - -0,1 •0,6 _i 5,9 14 239 0,016 4.83 0,37 -16,3 —*, 6,1 15 224 0,032 3.15 0,080 -16,5 -0,3 -1.0 -3.0 3,9 16 242 0,0086 3.92 0,45 -21,2 -2.0 4,3 17 383 0,0094 6,28 1.03 -18,9 -0,3 •0,3 -1,6 7.2 18 366 0.018 S65 0,43 -15,5 -0,2 •0,6 -l,o 6,2 19 366 0,010 6,40 0,96 -18,2 -0,1 •0,3 -1,7 6,9 20 290 0,0062 4,51 0,79 -19,6 -0,6 -0.3 -1.9 5,4 21 385 0,016 3.12 0,15 -18,2 -0,4 -0,2 -2,1 S.7 22 286 0,017 2.73 0,11 -17.1 -0,7 -0.9 -3.0 5,0 23 35C C.OU 4,77 0,52 -13,4 -0,4 -0,0 -1.9 6,1 24 190 0,26 2.35 0,0047 -18,6 -0,2 •0.3 -4 i.O 25 307 0,012 4.89 0.41) -14,2 -0.3 +0,2 -2,1 5,6 2f 196 0,146 2.63 0,011 -18,1 -0.2 -0.2 -3,5 3.4 327 0,0072 4.88 0,83 -1É.C -0.5 -0,2 -1.7 5.9 " * Solubility products of calcite and gypsum are frotc Kharaka and Barnaa (1973); that of doloaite was taken as 10 (Rau 1967). LI I «I •9 10 TABLE 7. Samples taken for 0 analysis only on a circular route to the east, south and west of Venterstad. The altitudes were estimated from topographic maps. L Table 7 Saaple Fare Altitude lO0(1h> SHOW) a 1727 Blydskop 1310 -0.9* 1728 Van Vyks Fontein 1320 - 4,5 1729 Benzaaaheid 1370 - 5.5 1730 Buffelsvalley 1390 - 4.3 1731 Diapers Application 1*13 - 4,8 1732 Rietfontein 1453 - 5,0 1733 Palsefontein 1510 - 5,6 1734 Bdendale 14 90 - 4,9 1735 Sherborne 1350 - 6,7 1736 Leewfontein Vlakte 1270 - 6,8 1737 Bloubosstasie 1260 - 5,1 1738 Vriesfontein 1180 - 4,7 1739 Teebu8Stasie 127C - 6,0 1740 Zeekoei 6at 1480 - 7,2 1741 Groote Vallei 154C - 2,9* 1742 Blesbok 1*40 - 4,3 1743 Leeufontein 157C + 0,5* 1744 Helvetia 145C - 4,5 1745 Tweefontein 1460 - 4,7 1746 Rosendal 1610 - 5,4 1747 Lekkerdraai 14 3C - 5,1 * irobably subject to evaporation. TABLE 8. Dissolved gases in water samples. COp is the sum of all the COp liberated by addition of acid(=C02 + HCO, + CO,) L J Table 3 a B e Ar CH4 co 1 N2 °2 2 Sample 1 1 Rn Corrected So. cpr./k*; H20 *«• (yre) ml 3Tf/l.•« H20 1 5.68 T XO"2 16.f 2 0,28 33,74 29,57 3 Of 1 475 2 3.93 * NT4 12,20 0.29 0,02 148,74 1 621 <20 3 9.88 * 10"2 9,51 0,22 42,80 20.27 2 246 3 730 3b 7.73 x 10~2 8.4C 0,32 0,20 43,00 13,26 6 614 4 1.10 x 10"4 20,83 0,46 0,10 141,34 8 665 «0 5 1,97 x WT4 23,67 0,53 n.d. 169,57 5 892 «20 « 8.91 x 10"5 17,62 0,39 0,04 211,90 3 320 «20 7 5,0 X 10'5 14,61 0,34 n.d. 147,35 3 047 <20 7b 7.69 x 10"5 15.00 0,67 0,54 0,002 140,00 8 7.54 x 10~3 15,10 0,30 1,10 127.OS 11 524 420 9 4,37 x 10~' 17,59 0,34 1.35 135,52 6 675 <20 U 8,52 x 10"' 7.73 0,24 32.54 30,91 5 574 2 375 lib 5,70 x 10~3 5,19 0,54 0,16 26,17 32,26 7 943 12 8,98 x 10~3 13.37 2.46 0,30 1,82 102.14 10 211 <20 14 7,57 x 10"5 11,65 5,30 0,29 n.d. 122,08 5 139 <20 15 1,90 x 10~2 14,81 0,73 0.32 4,82 74,14 3 936 800 16 2,02 x 10"4 14.14 1.53 0,33 0.11 105,50 8 903 <20 17 3,34 x 10"' 16,67 0,91 0,37 0,30 163,30 9 099 <20 18 4,68 x 10"4 13.27 3,63 0,32 n.d. 134,18 7 167 «20 19 8,04 x 10"5 12.39 2.73 0,30 n.d. 163,07 3 211 <20 20 7,15 x 10"5 13.91 2.61 0,33 n.d. 118.94 15 4*1 420 21 3,45 x 10~2 11.25 0,23 0,26 15,08 71,(8 15 472 <20 22 3,55 x XO-2 10,70 a saeplea 1-11 did not contain HgCl2; soa* 02 My have been organically cor.su»»!. 3aaples 3b, 7b, lib and 12-27 contained HcCl. 0 15 r..d. * not detestable. N places lower detection limit of «U,002al 3H4/kg H20. 0 Jorrectej to tice of' collection, ?i?ures include aimnte^ratiuns of to »nu i-o, DiviJe oy ~ 'i for J .f ,a. " Rn, J ;*a (cp»/ic« H..C) : Sample 1 = 1,7? *0,3 ; 7 - 3.08 +C.3 ; * * l,f«! «0,1 ! 9 - 1.95 «0,1 , 3ee r.ote -'. FIGURE la. Locations of sampled boreholes and springs. Solid squares represent pre 1954 infiltration (i.e. they do not contain % or *C from nuclear weapon contamination). The inset shows the position of the study area in relation to the main divisions of the Karoo supergroup: the Dwyka formation, Bcca group and Beaufort group; Stormberg = the Molteno, Elliot, Clarens formations and the Drakemberg group. . J ; +REDDERSBURG D23 OZS 124 lOKai Ol6 Ol7 HEDBRK \€RWOERD OAM Q27 AUWAL NORTH 115 PIGURB lb. Locations of samples DB 1-14 in relation to the geology of the Venterstad area (from the Geohydrological Map of the Venterstad Area, Institute for Groundwater Studies, Bloemfontein, 1979). i ft ft ft I I I I I I I J FIGURE lc. Map of the area near the Orange-Pish tunnel flooding area (Vhittingham 1970) showing the tunnel, dolerite dykes and road. Numbers * (68-77) indicate chainage in the tunnel in 11 thousand feet. H Symbols indicate: H 0 Type I water H • Type II water A Type III water § Mixture of I and II water • Type I water shallow, changing to type II when deeper water was struck. Letters with samples indicate: DB : boreholes sampled in present survey, 1977. NL, AS, AK, S : boreholes sampled in 1970/2 (Table 3b) IS : water sanples from inclined shaft 2 (Table 3a) Unnumbered samples were taken in the tunnel (Table 3a) L •J FIGURE 2. Comparison of ^C and tritium values. The solid lines indicate the expected relation in groundwater from different years: based on the assumption that the C content of the groundwater is 85$ of that of atmospheric C02 and that it reaches the water table one year earlier than the water. Numbers represent sample numbers (DB). Error bars are one standard de viation. (ni) wninyi L FI3URE 3. Piper diagram of all samples collected in the present study (•) as well as those sampled in 1970/2 close to the tunnel flooding point (0). The extent of the three water types is shown. The arrows show the change of water chemistry from shallow to deep water. Sample numbers signify: e.g. ED . Borehole DB21 Q • Borehole NL5 0,® • tunnel water from dyke A or B ® : tunnel water from inclined shaft (S) tunnel water from main fissure © • tunnel water from minor fissures I CltNOjtF L •J FISURE 4. Relation between 0 and # alkalinity of samples south of the Orange river. Numbered points are DB samples collected in 1977. Lettered points are samples collected in 1970/2: M : Main fissure in tunnel P : Minor fissures in tunnel IS : Inclined shaft 2 A : Water from dyke A crossing the tunnel Symbols are: 0 Type I chemistry § Type II chemistry A Type III chemistry 2 o L J FIGURE 5. Distribution of 0 values south of Venterstad. The dotted areas indicate altitudes exceeding 1890 meter (= 6000 ft). Doubtful samples have been omitted (Table 7). srs 3P30S 25«E 25#3tfE 26«E PIGURB 6» The relation between C content and the Ha-t-K: Ca+Mg ratio. Solid circles indicate chloride water, open circles bicarbonate water and half circles mixtures. Tunnel waters have been included. The extent of the three water types (If II and III) is shown. O BCMBONATE WATER • NoCI WATER KX>- % 1 0.1 0,2 Ofi 2 K) 20 90 No+K Co+Mg FIGURE 7. Plots of Caf Mg and their sum as a function of alkalinity. The dotted line in the lover figure shows the relation expected for simple carbonate solution. Points below this line indicate Ca and Mg loss and its replacement by another cation. Solid circles are old samples, open circles are younger than 20 years, crosses indicate tunnel waters collected in 1970/2. The extent of the three water types (I, II and III) is shown. r 1 CALOUM 4- % %o o o o MAGNESIUM o 9» O <%0 • s° Jl lt s Co+Mg 4 6 L ALKAUNITY (MEQ/L) t FIGURE 8. Helium and methane concentrations, showing waters with higher H^S concentrations. L^^^^^^^^^ i i i i i i i 11 i i i ii i i 11 iM i i 11 i i i i iii J «fa turns T") **o L :1 FIGURE 9. Helium and radon concentrations, L 1 X) ro ro - O CVJ CM evil in CM I o CVJ™^ • 0>l q. a. m I- CO CM Q> ro CM I m I <0I I <0 I I 8 o I 13 m oi •a. % % (iTH&VUJdo) uy FIGURE 10. Helium concentrations in the sampled waters compared with their C concentrations and calculated ages. The solid lines show the compositions of mixtures of samples 6 and 3, and 4 and 26, with the % component of the older water; calculated on the basis that the older waters contain aDout 2,5 ti-es less dissolved carbon dioxide than the younger waters (Table 8). The broken lines show the theoretical maximum helium concentration in water as a function of its age for a non helium migration model (see text), where the rocks contain 2 ppm. U, 7 ppm. Th and have porosities of 1, 0,1 and 0,01$. 1 (SJA) 960 pepejjoo CSI b <*, 'e fc o X 'o K> 8 8 S 8 § 15 (wepouKfc)^ L FIGURE 11. Dissolved nitrogen and argon concen trations and the relative helium concentrations in the sampled waters. N2 and Ar concentrations are compared with the N~ and Ar concentrations for water in equilibrium with air (A.E.W.) at 660 mm Hg, 10 - 30°C. The composition of A.B.V. to which 10 ml STP/kg HpO of extra air has been added is also shown. 1 1 1 1 1 1 ! _ *v N^ N Vv \ X v \ X \ \ \ \ \ % *« \ \8" \ s» « \ \ \ s \ ^ • \ J «I z _ i| í* \ -io s. 1: 1* tí V t K a V 1 3 £ Q 2 " * ~ A V w < -» « • < • 1 1 1 1— i i S g 8 8 $ 8 c> c» o , o o o o II II I 1 FIGURE 12. Oxygen and tritium concentrations L I I I < 4 4 9H (Tritium Units) .& 00 I» L U