All borehole data and synthetic data were sampled to the AltaLIS 15 m provincial digital elevation model (DEM; resampled to 200 m grid cell resolution ) to provide a borehole top elevation (m asl) from which to correlate the bedrock strata between boreholes and to create the bedrock topography grid. This process was necessary as the elevation of AWWID water wells, in many cases, was not available/recorded or verified, and if reported, was estimated from a topographic map, field investigation or handheld Global Positional System (GPS) device. GPS devices have accuracies reported by the AWWID of ~1–30 m, but are of varying device quality and cannot be assessed for accuracy between devices. Elevation values of moderate- and high-quality data were also checked with the DEM to verify elevation accuracy and modified to match the DEM, if necessary.

Original elevation information for subsurface information that was not sourced from the AWWID (i.e., AGS boreholes and field data, and geophysical logs), was deemed high quality; comparisons were made between the elevation information and the DEM to ensure the correctness of the original elevation information. If the original elevation data from a borehole or field site was approximately the same as the DEM the original elevation information was used. Where original elevation information deviated from the DEM, the DEM value was used at that location.

The vertical accuracy of the 12 m DEM is stated as 5 m @ 90% where derived from 1:60 000 aerial photographs using photogrammetric methods.

Modelling software used to create grid: ESRI® ArcMap™ 10.6.1 (grid interpolation) and Viewlog™ (deterministic alterations)

Number of data points available: 33188

Data sources: A variety of low- to high-quality multisource data were used including borehole and field data, geospatial datasets in GIS format, and interpreted point data. Borehole data consist of lithologs submitted by water well contractors and compiled in the Alberta Water Well Information Database (AWWID), downhole geophysical logs collected from water wells, AGS drillholes and field data, as well as industry information.

Interpreted point data include sediment veneers overlying bedrock, and synthetic control points. Synthetic points were created to constrain the bedrock topography where data was sparse or the complexity of the bedrock topography required further control points to influence the geometry of the modelled surface. Interpreted point data were evaluated and compared on cross-section with available borehole data.

Cross-sections of these data sources were plotted in Viewlog™ to generate stratigraphic picks of the bedrock topography.

Cell Size: 200 m

The Geostatistical Analyst ArcMap extension was used to interpolate the elevation value for the Edmonton–Wabamun area bedrock topography gridded data. A second-order regional trend surface was modelled from the bedrock topography data points and removed prior to interpolation. A simple kriging algorithm was then used in the ArcMap Geostatistical Analyst extension to interpolate the residual elevation values and create a grid of the structure top of the bedrock surface.

The following Method Report and Prediction Errors provide information about the parameters used to create the grid, and any errors associated with the gridding process.

Method Report:

Method: Kriging

Type: Simple

Output type: Prediction

Variogram: Semivariogram

Number of lags: 12

Lag size: 3894.1

Nugget: 0.10

Measurement error percentage: 100

Model type: exponential

Range: 46729.69

Anisotropy: No

Partial sill: 1.00

Prediction Errors:

Mean: 0.016

Root mean square error: 9.90

Mean standardized: 0.001

Root mean square error, standardized: 0.66

Average standard error: 14.91

Error exclusion: 0

Number of points excluded: 0

Percent error exclusion: 0

Deterministic Grid Alteration Information:

The regional trend was added back to the residuals to create the final geostatistical layer. The layer file was then extrapolated to cover the full extent of the Edmonton–Wabamun study area and then converted into an ArcGIS ASCII grid file. The grid file was truncated where it contacted the DEM (resampled to a 200 m grid cell size).