This grid represents the distribution of total dissolved solids (TDS) in the Paskapoo hydrostratigraphic unit (HSU). It is a result of a geostatistical model which was constructed using publicly available water chemistry data from the following sources:
1. The Alberta Government's Alberta Water Well Information Database (AWWID)
2. A previous Alberta Geological Survey water sampling project reported in AGS Special Report 81
The TDS surface 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.
The following statistics describe the accuracy of the geostatistical layer used to create the final grid.
Samples:
Mean error: -0.631 mg/L
Root mean square error: 333.0 mg/L
Mean standardized error: 0.006
Root mean square standardized: 0.96
Average standard error: 336.8
The potential for up to approximately 566 m (sometimes approximately 1131 m) of horizontal accuracy error for water wells may also introduce errors in the surface elevation, which is derived from the provincial 25 m DEM, based on the location of the well. This error is likely on the order of plus/minus 5 m, but may be 10's of metres in areas where there are large changes in elevation. Any error in elevation may influence the allocation of the well as well as sampling location. These sources of error are not unique to this study and are encountered in any hydrogeological study that uses the AWWID, unless further refinement of well locations is undertaken.
The mid-point of the sampled interval is a calculated value and its accuracy is dependent on the accuracy of the measured depths and elevations provided in the well header. These values are somewhat inconsistent for the water wells because many of them are not surveyed.
Step 1 (Modelling the surface): Empirical Bayesian kriging was used in the ArcMap 10.8.1 Geostatistical Analyst extension to interpolate the total dissolved solids values and create a grid of the total dissolved solids surface of the Paskapoo HSU.
Method Report:
Output surface type: Prediction
Power: 1
Neighbourhood type: Standard
Maximum neighbours: 15
Minimum neighbours: 10
Sector type: 1 sector
Samples: 12 679
Cell size: 500 m
Step 2 (Grid Alterations): The final grid was clipped based on the extent of the Paskapoo HSU, and spatial distribution of data.