GEO-STABILITY DESKTOP STUDY FOR A PROPOSED FILLING STATION AT ROODEKRANS MOGALE CITY, GAUTENG

Transcription

1 GEO-STABILITY DESKTOP STUDY FOR A PROPOSED FILLING STATION AT ROODEKRANS MOGALE CITY, GAUTENG Page 1 of 11

2 GEO-STABILITY DESKTOP STUDY FOR A PROPOSED FILLING STATION AT ROODEKRANS MOGALE CITY, GAUTENG Prepared for FRIEDCORP 344 CC Prepared by Author: K. Gounden First Floor, North Block, 181 Arkansas Way, Berario, Tel: (011) , Fax: (086) , kahmani@ecopartners.co.za Page 2 of 11

3 TABLE OF CONTENTS DISCLAIMER INTRODUCTION METHODOLOGY STUDY RESULTS Geology Hydrogeology Dolomitic Land Slope CONCLUSION ABBREVIATIONS & GLOSSARY Abbreviations Glossary REFERENCES LIST OF FIGURES Figure 1: Satellite Image of the Proposed Site of the Filling Station... 5 Figure 2: Geology of the Area of the Filling Station... 7 Figure 3: Dolomitic Outcrops in Relation to the Study Site... 9 Page 3 of 11

4 DISCLAIMER The opinions expressed in this report are based on the information supplied to EcoPartners by Robb Dubbini. EcoPartners has exercised due care in reviewing the relevant information. Whilst EcoPartners compared and reviewed data from existing data sources, the accuracy of the results and conclusions from the review are entirely reliant on the accuracy and completeness of the existing data. EcoPartners does not accept responsibility for any errors or omissions in the supplied information and does not except any consequential liability arising from commercial decisions or actions resulting from them. Opinions presented in this report, are based on only a desktop study, reviewing the relevant literature and maps available on the locality. These opinions do not necessarily apply to conditions and features that may arise after the date of this report, which EcoPartners had no prior knowledge nor had the opportunity to evaluate. Page 4 of 11

5 1. INTRODUCTION Robb Dubbini of Friedcorp 344 cc, appointed EcoPartners to conduct an Environmental Impact Assessment for the establishment of a new fuel station, in Roodekrans in the West Rand District of Gauteng. As part of the Environmental Impact Assessment, a geological stability study was required. The geological stability of an area refers to the particular interaction of soil, underlying rock, groundwater and slope and stability of any site. The site this geological stability desktop study focused on was located, on the corner of Hendrik Pogieter and Furrow Road (in the West Rand District, Gauteng )(Figure 1). Figure 1: Satellite Image of the Proposed Site of the Filling Station Page 5 of 11

6 2. METHODOLOGY In order to determine the geological stability of the site at a desktop level, the following criteria were analysed: Geology of the area Hydrogeology Presence of soluble rock types The slope of the area It was important that the area be within stable rock types, not be underlain by limestone. The slope of the area affects the stability as an area with a steep slope would be prone to erosion and landslides and therefore not be seen as stable. The hydrogeology gives an indication of the strata below the surface as well as the closeness of an aquifer and therefore the potential impact of the filling station on this could be determined. The study was conducted using the 1: Geology Map of the West Rand, the 1: Hydrogeology Map of Johannesburg and data and maps from the Department of Water Affairs (DWA) as well as other sources. Page 6 of 11

7 3. STUDY RESULTS 3.1. Geology The proposed site for the filling station is located on the farm Roodekrans 183 IQ, in the West Rand Area. The geology of the area is predominantly the rocks of the Roodekrans Complex, which are inliers of greenstone remnants in the Johannesburg Dome. The Johannesburg Dome is formed by a series of magamatic events, during the Archaean and is now composed of various gneisses, and granodiorites. The rocks of the Roodekrans Complex in particular are mafic, granodiorite intrusions that are dated to be around 3114Ma. Overlying the Roodekrans Complex are the sedimentary formations of iron rich shales and quartzites of the West Rand Group of the Witwatersrand Supergroup which are dated at ~2 900Ma (Anhaeusser, 2006). Figure 2, shows the location of the proposed site in relation to the surrounding geology. The site of the filling station is within the rocks of the Roodekrans Complex denoted as Zh and Zm and the rocks of the West Rand Group denoted Rh and Ro on the map. It can also be seen that there are no major faults as well as soluble carbonitic rock types of limestone and dolomite. Figure 2: Geology of the Area of the Filling Station Page 7 of 11

8 3.2. Hydrogeology According to Barnard, 2000; there are four aquifer types that are catergorised according to the water bearing properties of the rock formation: Class A: Intergranular (Unconsolidated material, sand and gravel) Class B: Fractured (Hard rock, with fractures and fissures) Class C: Karst (Limestone and dolomite areas) Class D: Intergranular and Fractured (Weathered and hard rock) The study site is associated with two of the above aquifer types, Class B and Class C. The Roodekrans Complex is classified as a Class D aquifer this type of aquifer consist of unconsolidated weathered rock in which water is stored in the intergranular spaces overlying a more sturdy hard rock of which water is transported through fractures in the rock. The groundwater yield potential in this rock types is on average between 2l/s to 5l/s. The depth to the groundwater differs from 5m below surface in some areas to 30m in other areas. The West Rand Group, is characterised as having a Class B aquifer, a hard rock aquifer, in which the water is stored and transported in fractures and fissures. The average borehole yield in this rock formation is less than 2l/s, with a groundwater depth about 10-25m below the surface Dolomitic Land The area of the proposed filling station is not located in an immediate area of dolomitic land. The dolomite outcrops in the West Rand Area occur at approximately 10-15km to the west of the proposed site. Page 8 of 11

9 Figure 3: Dolomitic Outcrops in Relation to the Study Site 3.4. Slope The slope of the area has an effect on the rate of erosion of the soil and rock surfaces, therefore affecting the stability of the land surface. In an area of high slope the rate or erosion is much greater than are area of shallow slope. The study is an areas of a shallow slope, the area of the proposed filling station, slopes at an average of 0.04 to the north east. This slope is characteristic of level to nearly level land. 4. CONCLUSION Based on the results of the study, the following can be concluded: The rock type found on the site is stable, and does not contain soluble rocks and there are no major faults on the site. There are no boreholes located on the site There are no groundwater boreholes within 1km of the site The depth to the groundwater in the immediate area is unknown, but on a regional level is stated to be 5-30m below the surface. The groundwater potential is moderate to good between 2l/s to just over 2 l/s According to the Hydrogeological Map of Johannesburg, there is no large scale groundwater abstraction in the area. Page 9 of 11

10 The Crocodile River is approximately 3.5km east of the site The geology of the site appears to be stable on a regional level. There is no extraction of groundwater in the immediate area, however due to the fractured nature of the rocks, there will be an interaction of groundwater and the overlying rocks. If the storage tank or the underground fuel supply lines had to leak, this could pose a threat to the groundwater in the area. This is normally detected by monitoring boreholes in the vicinity. Page 10 of 11

11 5. ABBREVIATIONS & GLOSSARY 5.1. Abbreviations Degrees km l/s Ma kilometers Litres per second Million years ago 5.2. Glossary Soluble Rock Types Gneiss Granodiorites Carbonate rocks, primarily limestone and dolomites that dissolve over time, creating karsts in the landscape A metamorphic rock with distinct banding Granular, high quartz content, similar to granite 6. REFERENCES Anhaeusser, C.R. (2006). Ultramafic and Mafic Intrusions of the Kaapvaal Craton. In: Johnson, M. R., Anhaeusser, C. R. and Thomas, R. J. (Eds), The Geology of South Africa Barnard, H. C. (2000). An Explanation of the 1: General Hydrogeological Map: Johannesburg Department of Water Affairs. Page 11 of 11