Geostatistics of the Borden Aquifer: High‐Resolution Characterization Using Direct Groundwater Velocity Measurements

Abstract

In 1986, a seminal data set from the Canadian Forces Base (C.F.B.) Borden aquifer, Ontario, Canada, was published, illustrating, in unprecedented detail, the spatial distribution of hydraulic conductivity (K). Among many contributions attached to that data set was a geostatistical examination of field‐based data for comparison with theoretical predictions of macro‐dispersivity. However, that work treated K as a static parameter and the sole source of flow variability. Here, point velocity probes (PVPs) are used to extend the earlier work by collecting a novel high‐resolution data set of groundwater velocity (v) measurements in the C.F.B. Borden aquifer. Velocity is a dynamic parameter of fundamental importance, closely tied to solute dispersion. Over 400 velocity measurements were collected along a transect perpendicular to flow, analyzed geostatistically, and compared with the analysis of the B‐B′ cross‐section of K reported by Sudicky (1986), https://doi.org/10.1029/wr022i013p02069. The PVP measurements exhibited geostatistics similar to those previously estimated by Sudicky (1986), https://doi.org/10.1029/wr022i013p02069. This finding suggests, as implicitly assumed in the previous work, the distribution of v is primarily controlled by K. PVPs also provided a novel, high‐resolution data set of groundwater flow directions. Since the ultimate objective of aquifer characterization includes the definition of velocity fields, this work not only extends the 1986 work, but also demonstrates a viable alternative for characterizing flow patterns in aquifers—with the advantage that direct v measurements reflect variability in porosity and hydraulic gradient, as well as K. This could ultimately be advantageous at sites with greater heterogeneity or other dynamic hydrogeological variabilities more pronounced than those at the Borden site.

WellSTIC: A Cost‐Effective Sensor for Performing Point Dilution Tests to Measure Groundwater Velocity in Shallow Aquifers

“…Across all tests, the magnitude of groundwater velocity calculated from point dilution tests ranged from 0.07 to 1.7 m/d. This range is a reasonable amount of variability for a single field site (Osorno et al., 2022; Sudicky, 1986), especially mountainous floodplains, which exhibit highly heterogeneous flow networks (Hauer et al., 2016; Poole et al., 2006; Woessner, 2000). To gauge the reproducibility of this technique, two point dilution tests were performed on back‐to‐back days in the same piezometer; velocities from the two tests (0.73 ± 0.01 m/d and 0.70 ± 0.01 m/d) are in close agreement, suggesting the results from an individual dilution test can be replicated.…”

“…Narrow piezometers (<2 cm) can be installed by hand in coarse sediments to depths of 10 m using a post pounder (e.g., Solinst Drive‐Point Piezometers, Solinst Canada Ltd.), but larger wells (>5 cm diameter) require mechanized drilling equipment for installation in coarse sediment or to deeper depths. Drilling equipment adds expense to a project—which can be significant given the number of measurement points required to characterize a heterogeneous velocity field (e.g., Mackay et al., 1986; Osorno et al., 2022; Sudicky, 1986)—and may be impossible for remote field sites with limited road access.…”