This data release is a compilation of hydraulic head data used to create potentiometric surfaces for the Calgary-Lethbridge Corridor (CLC) project. Source datasets include hydraulic information from Alberta Environment and Parks' Alberta Water Well Information Database (AWWID), and drill stem test (DST) data from oil and gas well data holdings at the Alberta Geological Survey. Data have been processed, relevant records selected, and outliers removed to compile this dataset.
This dataset supplements Alberta Geological Survey Report 91, which includes details on the data processing and potentiometric surface interpolation in the CLC.
Any errors in the original data were carried into this dataset and no systematic checking of attributes from original data sources was undertaken. Some obvious errors in the AWWID were corrected. For example, we fixed the records that had the top and bottom of the screened/perforated interval reversed in the original database.
Water well locations from the AWWID may be up to 800 metres from their correct locations where the well is located to the centre of a section. As the well elevation is derived from the provincial 25 m DEM based on surface location, elevation accuracy is affected by the variability of the local topography and the potential locational inaccuracy. Any error in elevation may influence the allocation of the well into the modelled hydrostratigraphic unit (HSU) as well as the hydraulic head values, as the land surface elevation was used to calculate the mid-screen elevation and corresponding hydraulic head from measured “depth to” values. This is especially true where there are large changes in elevation within a quarter section, such as along the banks of rivers or in the Porcupine Hills and Okotoks Uplands. Additionally, most wells have a casing above the land surface from which measurements of water level are usually recorded. The calculation of hydraulic head does not take into account the elevation difference between the top of the casing and the land surface because this number was not always recorded in the AWWID. These sources of error are not unique to the CLC and are encountered in any hydrogeological study that uses the AWWID, unless further refinement of well locations is undertaken.
The allocation of well data to HSUs is based on the modelled 3D gridded surfaces and the elevation of the middle of the screen, rather than the lithology at the screen interval in a particular well. While there is generally good agreement between the lithology of the borehole at the mid-screen elevation in the well, and the HSU allocation, there are cases where the allocated HSU does not match the lithology of the associated interval in the well. In spot checks, this appeared to be more common in areas where there were sparse data for modelling the hydrostratigraphic surfaces, and in areas of variable elevation in the modelled surfaces (e.g., slope breaks in the bedrock topography). Errors in allocation will also be greater where the HSUs are thin (e.g., Battle HSU, HSU S1, at subcrop edges), or where the middle of the screen is located close to the boundary between two HSUs, where the well screen may straddle multiple HSUs.
Data are compiled from different sources (i.e., Alberta Water Well Information Database, IHS, AGS well database) and have been collected over decades, by different parties, and using different methods.
There is only one record for each "AWWID_ID", although geographic coordinates (lat/long) may be the same for different wells, often because the AWWID wells have been located as being in the middle of a quarter section or section.
There may be more than one "DST_well_ID" for the DST data, although they will have different DST numbers ("DST_NO") or HSU allocations.
Null values were assigned where attributes were not present for the AWWID and DST data types. For AWWID data there is no "DST_well_ID", "DST_NO", or "KB_elev". For the DST data there is no "GIC_Well_ID", "DEM_elev", or "SWL_depth".
The potential for up to 400 m (sometimes 800 m) of horizontal accuracy error may also introduce errors in the surface elevation, which is determined by taking the land surface elevation from the 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 (e.g., Porcupine Hills, hills south of Calgary, along river valleys).
Additionally, most wells have a casing which sticks up above the land surface from which measurements of water level are usually recorded. The calculation of hydraulic head does not take into account the elevation difference between the top of the casing and the land surface because this number is not always recorded in the AWWID.
AWWID data, current up to March, 2013 (records ranging in time from 1912-2013), provided hydraulic information in the upper approximately 200 m of the subsurface. Data in feet were converted to metres.
Selection criteria for AWWID wells were as follows.
First, wells were selected that had only one well record, a single screened interval, a single static water level, and that were not under flowing artesian conditions.
Second, outliers were manually removed during the interpolation of potentiometric surfaces where:
1) the mid-screen depth was much deeper (or shallower) than surrounding wells;
2) the static water level was significantly different from surrounding wells and these differences could not be rectified;
3) the water well was interpreted to be incorrectly located (e.g., on an upland versus a valley bottom in areas of slope breaks, due to well placement at the middle of the ATS quarter section) and caused significant discrepancies in hydraulic data measured from the land surface; and,
4) the water well was located in the middle of the ATS quarter section where other adjacent wells had more accurate location co-ordinates (e.g., wells located within a Legal Subdivision (LSD), or a GPS was used to document location co-ordinates, especially for wells in the Scollard / Willow Creek formations and Paskapoo / Porcupine Hills formations).
This dataset includes only those wells that were used in the production of final potentiometric surfaces.
DST data, current up to 2014 (test dates ranging from 1960-2005), were used to provide hydraulic information for the deeper groundwater system.
Selection of the DST records was done as follows.
First, DST records with no interval or pressure data were discarded. Then, the remaining records were culled based on a number of parameters including: interval length, intervals which straddle HSUs, quality code, qualitative permeability, qualitative hydro factor, flow and shut-in times, and recovery and blow description. A method called the Cumulative Interference Index was also used to examine the influence of production and injection on the pressure recorded during the DST. AGS Report 91 contains more details on the selection method, including references.
Recorded pressure (in kilopascals, KPa) from the DST was converted to a freshwater pressure head (in metres) using the following formula: psi=P/(rho*g) where psi= pressure head [m], P= recorded DST pressure [Pa], rho= density of water [1000 kg/m3], and g= gravitational acceleration [9.8 m/s2]. Total hydraulic head was calculated by summing the calculated pressure head and the elevation of the mid-point of the interval tested (i.e., the elevation head).