Draft Status Quo Report for the Pixley Ka Seme ... - SRK Consulting

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SRK Consulting in association with BKS Pixley Ka Seme Local Municipality EMF – Draft Status Quo Report Page 25 dioxide, released on combustion of fossil fuels, can give rise to sulphuric acid in rainwater (acid-rain) and as such, this results in the return of sulphate to surface waters in the environment. Calcium sulphate is naturally released from the weathering of rocks such as Gypsum; • The concentration of heavy metals is generally low, with the exception of manganese identified at the monitoring station adjacent to Maquasa West Mine; • Nutrient levels are slightly elevated in the Skulpspruit, while the stream next to Maquasa West Mine, the Klip River and the Rietspruit at N11 Tapfontein bridge between Ermelo and Amersfoort can be classified as eutrophic, indicating high nutrient loads from pollutants. The final effluent discharge from Amersfoort WWTW, Volksrust Sewage Treatment Works and Volksrust- Vukuzakhe WWTW to the Mahawane Buffels River, is considered hypertrophic. Electrical conductivity Monitoring stations at WWTWs at Amersfoort, Volksrust canal and Vukuzakhe have electrical conductivity (EC) values exceeding the guideline value for domestic use. The high variability of the water quality data at the WWTW indicates highly variability in the quality of the inflowing water. Stations not associated with urban areas have an EC value within the target range for domestic use. EC concentrations between 70-150 mS/m results in water having a salty taste, but no health effects are likely. Groundwater quantity Aquifer lithologies The regional hydrogeological zones in PKSLM are broadly defined by the underlying geology in the area comprising sedimentary rocks of the Karoo Sequence intruded by dolerite sills and dykes. The groundwater potential of the Karoo formations is generally limited in their pristine state due to low permeability and storage capacity. Secondary processes, alteration due to contact metamorphism with the intrusive dolerite, are recognised to enhance the groundwater potential of these lithological units (SRK, 2010). Aquifer zones identified within these lithologies generally include: • Intergranular upper weathered aquifer within in the weathering zone (5-12 m) below surface which is typically low yielding (1-10 m 3 /d) due to the shallow thickness and usually provides storage to the underlying fractured rock aquifers. Groundwater flow is generally along the fractured transition zone between weathered and fresh bedrock contact. The aquifers are likely to be semiconfined with a low to medium development potential as permeability, transmissivity and storage capacity may be limited especially in the shales, sandstones and siltstones of the Karoo formations; • Fractured rock aquifers of variable yield and occurrence with yields varying from 0.1-2.0 L/s. Fractured fault zones (such as in the southern area), especially if related to tensional stresses, are potentially rich targets for groundwater development; • Saline deep-seated aquifers occurring below the coal seams. Contacts between different rock lithologies, including coal seams, and bedding planes within the sediments, coal and adjacent strata (no fissures) have lower hydraulic conductivities of
SRK Consulting in association with BKS Pixley Ka Seme Local Municipality EMF – Draft Status Quo Report Page 26 Map 14 (after GRAII: Department of Water Affairs and Forestry (DWAF), 2005) and Vegter, 1995) represents the regional hydrogeology, which comprises: • The Estcourt Formation (Karoo Supergroup), extending from the south western to the western boundary of PKSLM (including the towns of Perdekop and Volksrust). This is characterised by arenaceous rocks made of mudstone subordinate sandstone and is locally intruded by dolerite dykes and sills. Yields vary from 0.5-2 L/s with a generally lower occurrence (0.0-0.1 L/s) in the area of Volksrust; • The Volksrust Formation (Karoo Supergroup) underlying the centre of PKSLM consists of mudstones and shale subordinate silstones. Dolerite sills and dykes intrude the area. Yields vary from 0.1 to 0.5 L/s increasing in the southern area to between 0.5 – 2.0 L/s; and • The Vryheid Formation mainly on the eastern side of the PKSLM and comprises sandstone, shale with coal seams and intrusions of dolerite dykes and sills. Those rocks are characterised by massive, low porosity rocks with a few widely spaced joints and the yields vary between 0.5-2.0 L/s. The sandstone has very little storage capacity for water and transmits water slowly, mostly through fractures and faults. Groundwater recharge mbgl, and increases from west to east across the study area. Surface water and groundwater interaction occurs along the river and stream courses, where groundwater levels are likely to be not more than a few meters below surface. Fountains (springs or seeps) have been mapped (regionally) along the contacts of the Karoo Vryheid Formation sediments and intrusive dolerite sills. Aquifer classification The aquifer is classified as a minor aquifer on a regional scale. The aquifer is neither classified as a sole source aquifer nor a special aquifer (South African Aquifer System Management Classification of South Africa, R. Parsons, 1995). Groundwater supply and use At a provincial scale, 65% of water resources available in Mpumalanga come from surface water resources. Water transfers into the Province provide 19% of total water availability, while groundwater accounts for 6% of available water (Mpumalanga State of Environment Report (SOER), 2003). Data for groundwater supply and use are limited and according to DWA WARMs database, there is one registered water supply borehole located in the northern part of the PKSLM, with a yield of 0.041 million m 3 /a. No other boreholes were listed and it is therefore difficult to determine the current groundwater use. The upper weathered aquifer is recharged by rainfall with the annual groundwater recharge expected to be in the order of 22 to 180 mm/a (GRAII, 2006), and increases from west to east across PKSLM. The mean annual groundwater recharge is presented, after Vegter (1995) and GRAII (2006), in Map 8. The recharge rate in weathered sediments could be highly variable depending on the hydraulic conductivity of the overlying soils (clays would for example limit the ingress of rainwater) and variable surface topography. Groundwater flow Groundwater levels would be expected to mimic surface topography in the catchment due the semiconfined nature of the aquifers. According to the GRAII database, the depth to groundwater ranges between 6-16 The groundwater potential of the Karoo formations located in the study area is limited in their pristine state due to low permeability and storage capacity. Secondary processes, alteration due to contact metamorphism with the intrusive dolerite, are recognised to enhance the groundwater potential of these lithological units. Minor faults are localised in the southern area and may increase the groundwater occurrence. The annual groundwater recharge is expected to be of the order of 22 to > 180 mm/a, and increases from west to east across PKSLM (Vegter, 1995 and GRAII, 2005). Groundwater levels would be expected to mimic surface topography in the catchment due the semiconfined nature of the aquifers. According to the GRAII database (DWAF, 2005), the depth to groundwater KILI/BEAT G:\404946_PIXLEY EMF\7REPORTS\Status Quo report\Draft report\Draft status quo report, July 2010.docx July 2010
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