The feasibility of numerical models in LNAPL related ground-water studies

English: Groundwater contamination as a result of Light Non Aqueous Phase Liquid (LNAPL) releases into the subsurface is a widespread occurrence across South Africa which threatens current and future water resources within the country. Groundwater contaminant fate and transport modelling are common elements of hydrogeological investigations and remedial design methodologies in many developed countries where the models are used as management and decision making tools. In South Africa this is not the case, with contaminant flow and transport modelling rarely being employed as part of LNAPL contamination investigations. Over the last three years, the Beaufort West study area has had extensive investigative work carried out with regards to the determination and delineation of LNAPL related groundwater contaminant plumes which are present underneath a significant portion of the town. As a result, an extensive data set has been generated with regards to aquifer geometry, fracture network distribution, aquifer parameters and contaminant plume concentrations and extent. The dataset should in theory provide an opportunity to construct a groundwater contaminant fate and transport model for the area as a remedial management tool. By means of collating previously existing data through a comprehensive desktop study, and supplementing this data with a toolkit of field investigation techniques such as diamond barrel core drilling, percussion drilling, electrical conductivity profiling, fluid electrical conductivity profiling, aquifer pump testing, and low flow inorganic and organic groundwater sampling, the conceptual model of the study area was updated and refined to a point where the feasibility of constructing a groundwater contaminant fate and transport model could be assessed. Based upon the conceptual understanding of the study area as defined in the conceptual model developed in the study, a groundwater contaminant fate and transport model is not considered feasible for the
Afrikaans: Grondwaterbesoedeling as ‘n gevolg van Ligte Nie-Waterige Fase Vloeistowwe (Light Non Aqeuous Phase Liquids - LNAPL) vrystelling in die ondergrond is 'n wydverspreide voorkoms regoor Suid-Afrika, wat huidige en toekomstige waterhulpbronne in die land bedreig. Grondwaterbesoedelling eindpunt- en vervoer modelle is algemene elemente van geohidrologiese ondersoeke en regstellende ontwerpsmetodes in baie ontwikkelde lande waar die modelle gebruik word as bestuurs- en besluitnemings middels. In Suid-Afrika is dit egter nie die geval nie, waar besoedelingsvloei- en vervoer modellering selde ingespan word as deel van LNAPL besoedeling ondersoeke. Oor die laaste drie jaar is daar uitgestrekte navorsing in die Beaufort-Wes studie area gedoen met ‘n klem op die bepaling en afbakening van LNAPL-verwante grondwater besoedelingspluime wat teenwoordig is onder 'n beduidende gedeelte van die dorp. As gevolg hiervan is 'n uitgebreide datastel beskibaar wat die geometrie, naatnetwerk verspreiding, akwifeer parameters en besoedelingspluim konsentrasies omvat. Die data bied in teorie die geleentheid om' n grondwaterbesoedeling eindpunt- en vervoer model vir die area op te stel as 'n remediërende bestuursmiddel. Die konseptuele model vir die studiegebied is opgedateer en verfyn tot ‘n punt waar die haalbaarheid van die model geassesseer kon word met behulp van die samestelling van bestaande data, 'n omvattende literatuurstudie, en aangevul deur veldondersoek tegnieke soos diamantkern boorweerk, druklug- boorwerk, elektriese geleidingsvermoë profilering, elektriese vloeistofgeleidingsvermoë profilering, akwifeer pomptoetse, en lae-vloei anorganiese en organiese grondwater monitering. Gebaseer op die konseptuele begrip van die studiegebied soos omskryf in die konseptuele model, is 'n grondwaterbesoelding eindpunt en vervoer model as onuitvoerbaar beskou met die data wat huidiglik beskikbaar is. Dit word hoofsaaklik toegeskryf aan die hoë vlake van ingewikkeldheid van die waarg