GIS-based TOOL FOR REGIONAL GROUNDWATER RISK ASSESSMENT IN POORLY PRODUCTIVE AQUIFERS Janmaizatulriah JANI, David N LERNER, Steve WISE Catchment Science Centre University of Sheffield, UK GroPro - Groundwater Protection Plans and Implementation in a North European Perspective Korsør, Denmark September 2008

Research Background GIS based modelling GIS use for surface hydrology Groundwater hydrology only consider vertical pathways Horizontal outputs; Change location of risky area as pollutant transported Pollutant concentration decrease Vertical outputs; More local risk High pollutant concentration Groundwater risk assessment

Research aim and objectives General Aim To extend GIS based groundwater risk assessment by including the analysis of horizontal pathways of pollutant Overall objectives To develop a GIS-based geological model To utilise geological model for groundwater hydrology analysis To analyse risk of groundwater

Initial modelling: GIS based geological modelling Objective To represent subsurface geology using GIS tools Tests Reconstruction of geological map Reconstruction of subsurface contours map and cross section

Conceptual diagram of GIS based geological representation One unit of geology Top of geological unit Stack of planes Outcrops ∆d 1 t ∆d –displacement t - thickness ∆d 3 ∆d 2 Fault line

Reconstruction of geological map: Dove valley of the Don catchment, UK Geology of Dove; Carboniferous rock – Middle Coal Measures, Lower Coal Measures Geology beds – steady North Easterly, Varies in thickness and dip direction Numerous faults – dip about 5° Don catchment, UK Dove valley e.g. Stratigraphy units Middle Coal Measures M.R O.R W.E.R Coal © Environment Agency

Modelling assumptions Re-categorise of rock groups; –Sandstone rock –Mudstone/Siltstone rocks Geological beds are planar Constant dip angle - 4 ° Constant strike Uniform thickness Vertical faults displacement Simplified version of geology map Mudstone/siltstone rocks Sandstone rocks Derived from 1:50000 scale BGS Digital Data under Licence 2008/08 British Geological Survey© NERC

Model outcrops Original geology mapModel 2 Mudstone/siltstone sandstone All Faults Model Faults

Predicted total area of sandstone rocks ItemStrikeThicknessSandstone rock Area (km 2 ) True values30 °- 70 °Varies47 Model 155°Uniform32 (68%) Model 245 °Uniform36(76.5%) Model 360 °Uniform26(55%)

Matched outcrops: model 2 matched mudstone/siltstone Actual mudstone not predicted Actual sandstone not predicted matched sandstone

% matched outcrops Model Rock type Matched (km 2 ) Unmatched (km 2 ) % Matched Model 1 Sandstone Mudstone/siltstone 2515 Model 2 Sandstone Mudstone/siltstone 2416 Model 3 Sandstone Mudstone/siltstone 2713

Geological view – Cross section of Silkstone Coal Fault lines

Conclusions The best model prediction - model 2 Less accuracy of model prediction are due to; –Insufficient geological inputs –Simplification and assumptions –Model do not replicate real geology Application of methodologies; Potential of using GIS for geological modelling Capability to model; –Limited subsurface information –Important of details geological description Provide extra geological views

Next Future works Can GIS model groundwater flow? Groundwater hydrology analysis Identification of groundwater catchment, flow directions and groundwater discharge points. Analyse groundwater risk

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