This grid is part of the regional hydrogeological mapping of the Calgary-Lethbridge Corridor (CLC) in southern Alberta. It represents the concentration of total dissolved solids (TDS) (in mg/L) in the Paskapoo / Porcupine Hills hydrostratigraphic unit (HSU) interpolated from wells in Alberta Environment and Parks' (AEP) Alberta Water Well Information Database (AWWID). The TDS concentration was mapped at a regional scale using many years of data, thus providing a good indication of regional water chemistry within the unit rather than site specific values.
This dataset supplements Alberta Geological Survey Report 91, which includes details on the data processing and interpolation in the CLC.
The following statistics describe the accuracy of the interpolated final clipped grid in relation to the input TDS point data:
Root mean square error = 189 mg/L
Mean error = -25 mg/L
Standard deviation = 190 mg/L
Maximum error = +314 mg/L / -862 mg/L
The methodology used to create this grid dataset is documented in AGS Report 91. The AWWID dataset (from which TDS values were sourced) was current up to April 2013.
Step 1 (Modelling the data): An ordinary kriging algorithm was used in the ArcMap Geostatistical Analyst extension to interpolate the TDS values and create a grid of the TDS concentrationin the Paskapoo / Porcupine Hills HSU. Wells in the AWWID are often only located to the middle of the quarter section (or sometimes section) and thus co-located data points exist. In these cases a mean of the TDS was used for the interpolation.
Selection criteria for AWWID chemical analyses used for interpolation of this grid are documented in AGS Report 91, and the final selection of wells in AGS DIG 2016-7273.
Method Report:
Method: Kriging
Type: Ordinary
Output type: Prediction
Trend type: None
Variogram: Semivariogram
Number of lags: 17
Lag size: 2295
Nugget: 0.048
Measurement error percentage: 100
Model type: Spherical
Range: 39015
Anisotropy: No
Partial sill: 0.095
Total points: 114
Cell Size: 200 m
Root mean square error (considering only the final clipped grid): 189 mg/L
Step 2 (Grid Alterations): Areas of the original extent of the grid results were clipped based on 1) the absence of the Paskapoo Formation (i.e., the eastern edge of the subcrop of the formation); and 2) the area being outside a buffer area, which consists of areas of contiguous 5000 m buffers around wells.