Jean van Niekerk and Eelco Lukas COMMON INACCURACIES TO AVOID IN THE FIELD: A FOCUS ON THE SADC REGION Institute for Groundwater Studies

INTRODUCTION The recognition of mistakes can be useful in all disciplines of life. Every discipline of groundwater encounters inaccuracies, and the gathering of field data is no exception. Due to the complexity of this science it is necessary to integrate a variety of specialist skills The success of sustainable groundwater management is influenced by data quality, identifying problems and the associated cause of each problem.

INTRODUCTION Issues relating to groundwater management will be covered including: Geographic Positioning Systems Geophysical surveys Borehole construction and maintenance Water level measurements Groundwater sampling Groundwater modelling

GROUNDWATER MONITORING Geographic Positioning System A GPS is an important tool for geohydrology. Most GPS receivers are capable of an accuracy ranging from 1 to 10 meters - suitable for location but poor for elevation. Datums and coordinate systems. Fixed reference points.

GROUNDWATER MONITORING Geophysical Investigations Significant differences of subsurface geology in the field may result in very small differences in measured readings. Lack of experience Minimise Errors: Effective planning Time management Guidance from more experienced geohydrologists

GROUNDWATER MONITORING Borehole Construction and Maintenance Monitoring boreholes Borehole development Borehole casing/ screen Gravel packs

GROUNDWATER MONITORING Water Level Measurements The foundation of a groundwater dataset Borehole inspection Methods: Dipmeters Pressure Transducers

GROUNDWATER MONITORING Groundwater Sampling Specific causes of error at various steps in groundwater sampling are shown in the Table below: Step: Sources of error: Establishing a sampling location Improper well construction and material selection Field measurements Instrument malfunction, operator error Sample collection Sampling mechanism bias, operator error, contamination Sample transfer Sample exposure; de-gassing, oxygenation Field blanks/ standards Operator error, matrix interferences Field determinations Instrument malfunctions, operator error Preservation/ storage Matrix interferences, handling/ labeling errors Transportation Delay, sample loss

GROUNDWATER MODELLING Garbage in – Garbage out principle Lack of experience Set realistic objectives

CONCLUSION Realising the importance of accurate field data Time management Planning Experience

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