Comparison Between Protection Zones in Secondary and Primary Aquifers, a South Africa Case Study

COMPARISON BETWEEN PROTECTION ZONES IN SECONDARY AND PRIMARY AQUIFERS, A SOUTH AFRICA CASE STUDY

 Adolf October¹, Lihle Mqayi², Jaco Nel³

 ^{1. University of the Western Cape, Department of Earth Science, Private Bag X17, Bellville, 7535, Email: 2451121@uwc.ac.za
2.  University of the Western Cape, Department of Earth Science, Private Bag X17, Bellville, 7535, Email: 2502701@uwc.ac.za
3.  University of the Western Cape, Department of Earth Science, Private Bag X17, Bellville, 7535, Email: jmnel@uwc.ac.za}

 Key words: Protection zones, tracer tests, effective porosity, flow velocities, modeling

 ABSTRACT

 

Characterization of groundwater resources will enable us to mange and protect aquifers better. This study focuses on protection zone delineation of both primary and secondary aquifers found on the University of the Western Cape campus research site. At the research site a Quaternary sand aquifer of about 40m thickness overlies a fractured late Precambrian shale bedrock aquifer. The investigated site is situated in an urban area and is neighbored by both industrial and residential areas.

Rhodamine WT and NaCl salt are used in the tracer tests to compute effective porosity and flow velocities. Both single well and radial convergent tracer test were conducted for both aquifers. The data for the tracer tests is interpreted by comparison with analytical breakthrough curves. Flow velocities and effective porosities display an order of magnitude difference in values for the primary and secondary aquifers. Groundwater velocities for the secondary aquifer display significant higher values than that of the primary aquifer.

The data would be integrated into a model and used as a case study for the new South African Protection Zoning policy. Separate 2D protection zones for the individual aquifers are expected for comparison. The importance of tracer tests in determining flow velocities for fractured rock aquifers to determine protection zones are highlighted in this approach.