Zasiooh-^ Per-143
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-TTW- ZASIOOH-^ PER-143 Augustus 1986 A SUMMARY OF THE GEOTECHNICAL AND ENVIRONMENTAL INVESTIGATIONS PERTAINING TO THE VAALPUTS NATIONAL RADIOACTIVE WASTE DISPOSAL FACILITY Principal Investigators B B HamMeton-Jonas N J B Andarsen M Levin HJBrynard F A G M CamísanJ-Calzolarí JNFaurie N Niamand F. Raubanhatmar MAGAndreoH SJPosn* Dapartmantal Managars P D Toant and D van As ATOMIC ENERGY CORPORATION OF SOUTH AFRICA LIMITED PRETORIA THIS DOCUMENT MAY NOT BE COPIED IN ANY WAY WHATSOEVER PEF-143 ATOMIC ENERGY CORPORATION OF SOUTH AFRICA LIMITED A SUMMARY OF THE QEOTECHNICAL AND ENVIRONMENTAL INVESTIGATIONS PERTAINING TO THE VAALPUTS NATIONAL RADIOACTIVE WASTE DISPOSAL FACILITY Principal Investigators: B B Hambleton-Jones* N J B Andersen* M Levin* H J Brynard* F A G M Camisani-Calzolari J N Faurie* N Niemand* E Raubenheimer* MAG Andreoli* S J Posnik0 Departmental Managers: P D Toens* D van As0 POSTAL ADDRESS: "Department of Geotechnology "Department of Isotopes and Radiation P.O. Box 582 PELINDABA PRETORIA August 1986 0001 ISBN 0 88960 826 6 CONTENTS Page SAHEVATTING 1v EXECUTIVE SUMMRY vl 1. INTRODUCTION 1 1.1 Structure of the Radioactive Waste Disposal Project 1 1.2 Soclo-Economlc Considerations OurTng the Screening and Site Selection Phases 2 1.3 6eo1og1ca1 Considerations During the Screening and Site Selection Phases 3 2. GE06RAPHY AND DEN06RAPHY 5 2.1 Site Location 5 2.2 Site Description 7 2.2.1 Mineral rights 7 2.2.2 Physiography 7 2.2.3 Population distribution 1? 2.2.4 Uses of adjacent land and waters 16 3. ECOLOGY 20 3.1 Introduction 20 3.2 Zoological Studies 21 3.2.1 A survey of the distribution and habits of mammals 21 3.2.2 Detection of environmental mutagens 23 3.2.3 A survey of the distribution and habits of termites and ants 24 3.3 Botanical Studies 28 3.3.1 Geobotanlcal studies 28 3.3.2 Revegetation of denuded areas 29 NETE0R0L06Y 1 Regional Meteorology 2 Vaalputs Meteorology 6E0L06Y 1 Geomorphology 2 General Geology 5.2.1 Introduction 5.2.2 Basement rocks 5.2.3 Surflclal deposits 3 Se1sm1c1ty GEOHYOROL06Y 1 Surface Hater 2 Unsaturated Zone 6.2.1 Evapotransplration and percolation 6.2.2 Hydraulic velocity/conductivity 6.2.3 Volumetric moisture content 6.2.4 01spers1v1ty 6.2.5 Natural Isotopes In the soil moisture 6.2.6 Distribution coefficients 6.2.7 Soil chemistry 3 Saturated Zone 6.3.1 Nature of the aquifers 6.3.2 Depth to the p1ezometr1c surface 6.3.3 Elevation of the p1ezometr1c surface relatl to sea level 6.3.4 Hydrogeochemlstry 6.3.5 Natural Isotopes 6.3.6 Permeability and storage characteristics 4 Ground Water Modelling 6.4.1 Description of the model 6.4.2 Discussion of results PER-143 - iii - Page 7. ENVIRONMENTAL RADIATION 128 7.1 Environmental Monitoring 128 7.2 Background Radiological Characteristics 130 7.3 Critical Pathways of Exposure and Derived Concentrations 1n Ground Water 133 8. REFERENCES 135 PER-143 - iv - SMtEVATTING Hlerdle vers lag beskryf die geologlese en omgew1nusonderso>>ke wat gelel het tot die keurlng en finale evaluasle van die Vaalputs Naslonale Fas1l1te1t vlr die Uegdoenlng van Radloaktlewe Afval wat In Namakwaland geleê 1s. Flslografles Is Vaalputs sowat 100 m bo seevlak geleë en beslaan die water skeldlng op die rand van die Groot Eskarpemert. Ten ooste van die waterskeldlng Is die dulneveld van die Boesmanland Plato waarln die wegdoenlngsterreln geleë 1s en wes daarvan die heuwelagtlge eskarp. Die ekologlese studies het hoofsaakllk ondersoeke oor die gewoontes en verspreldlng van soogdere, termlete, mlere en plantspesles 1nges1u1t. Voorloplge data het die onderllnge afhank11khe1d van belde die dlerkundlge en plantkundlge lewe óangetoon wat 'n belangrlke langtermyn Inpak op die wegdoenlngslerreln kan he. Wearkundlge mon1ter1ng het aangedul dat die gemlddelde reënval 74 am per jaar 1s met die grootste deel hlervan as hewlge donderbule. Geologlese karterlng, geoflslese opnames en boorwerk 1s gebrulk om die geologlese ontwikkeling van Vaalputs en sy omgewlng te ontrafel. Die vloergesteentes slult 1n gesteenies van die Namakwaland Metamorfe Kompleks van Proterosolese ouderdom, Karoogesteentes van Permo-Tr1ass1ese ouderdom asook klmberllet en verwante 1ntrus1es van Terslfire ouderdom. Hlerdle vloergesteentes word oordek denr oppervlakafsettlngs van die Dasdap en Vaalputs Formasles 1n die omgewlng van die wegdoenlngsterreln waar dlktes van tot 35 m voorkom. 'n Probabllistless selsmlese r1s1ko-anal1st het aangetoon dat die makslmum grondversnelllngsresultaat van 'n aardbewlng met 'n 1ntens1te1t VII en IX wat kan voorkom op die terreln, sal van die orde van 8,6 % g y4r 'n opererende basis aardbewlng en "5,6 % g v1r 'n veH1ge-afslu1t1ng- aarbewlng wees. Geohldrologlese ondersoeke Is ultgevoer op belde die versadlgde en PER-H3 - v - onversadlgde sones. Die data word as Invoer gebrulk In 'n model om die potenslële migrasle van radlonukllede te voorspel In die geologlese omgewlng en die ultelndellke roetes na die blologlese slklus via boorgatwater. voorloplge modellelng het aangetoon dat oor 'n perlode van 75 jaar daar slegs gerlnge beweglng sal wees en radlonukllede sal feltllk beperk wees tot die sloot omgewlng. PER-143 - vi - EXECUTIVE SUMMARY Geography and Demography Vaalputs Is located In the north-western Cape, 90 km south-east of Springbok, between 30*05' and 30*10' south and 18*25' and 18*37' east. It 1s situated In the District of Namaqualand on adjoining portions of the farms Vaalputs (portion 1, Geelpan and portion 2, Garlng) and Bokseputs (portion 1, Stofkloof). The mineral rights on the three portions above, with respect to gold, silver and precious stones, are reserved to the State. Physlographkally Vaalputs straddles the watershed on the edge of the Great Escarpment with the dune-covered Bushmanland Plateau In the east on which the disposal site 1s situated, and the mountainous escarpment area on the west. The disposal site 1s at an altitude of approximately 1 000 m above mean sea level and 1s topographically elevated above the surrounding plateau. Rainwater will therefore flow away from Vaalputs which will Inhibit a potential flood situation although minor ponding may occur within pans 1n the Interdune troughs. The population within a 20 km radius of Vaalputs (Including 38 AEC personnel) amounts to 102 persons, some of whom are seasonal migrants, with the majority being concentrated to the south and west of Vaalputs. It appears unlikely that the demography of the region will change significantly over the next 50 years as the climate Is arid and there 1s a lack of mineral resources. Approximately 66 % of the agriculture In the region consists of sheep farming with the remainder ie1ng restricted to other livestock and crop farming primarily for domestic use. Ecology Preliminary data from the ecological studies have demonstrated the Interdependence of the zoology and botany at Vaalputs, both of which could have an Impact on the radioactive waste disposal site 1n the long term. PER-143 - vii - The Karoo rat, spring hare, honey badger and aardvark are the burrowing manna Is that are most likely to pose a potential threat to the disposal site. Although the mole rat, which 1s an avid burrower, has not been Identified 1n the Immediate vicinity of the site, 1t has been noted on the eastern boundary of Vaalputs about 3 km away from the disposal site. The baseline mutagen studies 1n small mammals have Indicated an extremely low level of spontaneous chromosome damage. From <1x arthropod species studied, the common harvester termite poses the greatest potential Impact on the disposal trenches. It has the ability to excavate to depths In excess of 9 m, which Is well below the floor of the proposed trench. The termites' activity 1s most severe In denuded areas typical of the trench caps and as their diet consists primarily of dry grass they could adversely affect the revegetatlon program. Revegetatlon experiments of denuded areas have shown that 1t 1s Important to transplant the correct grass 1n Its peculiar environment. Irrigation 1s necessary for the establishment of the root system but over a long period It causes a build up of toxic salt concentrations. The geobotanlcal studies are assisting 1n developing a predictive knowledge of the structure and functioning of the plants, their associates and their habitat which Is essential for managing the plant cover at Vaalputs and restoring It after disturbance. Meteorology The regional meteorology of the north-western Cape can be described as desert and poor steppe with a maximum annual precipitation of 200 X of the norm. The rainfall 1s unreliable and an average of 74 mm pa can be taken for the Vaalputs area. The bulk of the precipitation occurs 1n single, episodic showers. Using data from Springbok 1t was calculated that 123 mm could precipitate every 100 years over seven days of rainfall. However, runoff and the high evaporation rate reduces the available water for percolation into the trench. Temperatures are extreme, with a diurnal variation of 15*C being common. Strong, PER-143 - viii - northerly winds occur frequently 1n April and July and gusts of up to 36,6 m.s~ have been recorded at Uplngton. Geology 6eomorpho1og1ca11y Vaalputs and Its environment, through the last 25 Ha, has a record of aggradatlonal and degradatlonal cycles. The sedimentary accumulations, which constitute the disposal site, are of mid- 3rt1ary age which reflect the long-term geomorphologleal stability of the region. Currently Vaalputs Is 1n a degradatlonal cycle which consists essentially of the redistribution of material by sheet erosion with very little being removed. The basement rocks of the Vaalputs area Include the Namaqualand Netamorphlc Complex of Proterozolc age consisting mainly of pre-tecton1c supracustal and syntectonlc Intrusive units, the Karoo Sequence of Permo-Trlasslc age and k1mber11te and related Intrusions of Tertiary age.