Upscaling Point Velocity Measurements to Characterize a Glacial Outwash Aquifer

Abstract

Small-scale point velocity probe (PVP)-derived velocities were compared to conventional large-scale velocity estimates from Darcy calculations and tracer tests, and the possibility of upscaling PVP data to match the other velocity estimates was evaluated. Hydraulic conductivity was estimated from grain-size data derived from cores, and single-well response testing or slug tests of onsite wells. Horizontal hydraulic gradients were calculated using 3-point estimators from all of the wells within an extensive monitoring network, as well as by representing the water table as a single best fit plane through the entire network. Velocities determined from PVP testing were generally consistent in magnitude with those from depth specific data collected from multilevel monitoring locations in the tracer test, and similar in horizontal flow direction to the average hydraulic gradient. However, scaling up velocity estimates based on PVP measurements for comparison with site-wide Darcy-based velocities revealed issues that challenge the use of Darcy calculations as a generally applicable standard for comparison. The Darcy calculations were shown to underestimate the groundwater velocities determined both by the PVPs and large-scale tracer testing, in a depth-specific sense and as a site-wide average. Some of this discrepancy is attributable to the selective placement of the PVPs in the aquifer. Nevertheless, this result has important implications for the design of in situ treatment systems. It is concluded that Darcy estimations of velocity should be supplemented with independent assessments for these kinds of applications.

Contaminant mass discharge to streams: Comparing direct groundwater velocity measurements and multi-level groundwater sampling with an in-stream approach

“…The explanation for this is likely that the injection was conducted from a poorly orientated port, resulting in tracer transport away from the probe instead of around it. This is not a surprise, as groundwater flow directions can vary considerably at the point scale, as demonstrated by Labaky et al (2009) and Schillig et al (2016). In addition, PVP6 never produced any useable signals, possibly due to damage incurred during installation.…”

“…It also avoids the use of wells, which can introduce considerable uncertainty to groundwater velocity measurements. The PVP has been shown to be a promising tool for groundwater velocity measurements in several studies (Devlin et al, 2009;Kempf et al, 2013;Schillig et al, 2016Schillig et al, , 2011. Nevertheless, studies are still lacking in which PVPs are combined with multi-level groundwater sampling for the quantification of the contaminant mass discharging to streams.…”

Estimates of Horizontal Groundwater Flow Velocities in Boreholes

“…As an alternative to borehole observations, the Point Velocity Probe (PVP) (Labaky et al 2007;Devlin et al 2009) is a direct push method in which water velocity magnitude v ∞ and direction can be directly estimated from mini tracer tests performed around the measuring device without any assumption on the aquifer porosity. PVPs have been tested in several lab and field scale experiments with promising results (Labaky et al 2009;Devlin et al 2011;Schillig et al 2016;Gibson and Devlin 2017). Related to this technology, the newly developed In-Well Point Velocity Probe (IWPVP) (Osorno 2016;Osorno et al 2018) uses a similar principle based on mini tracer tests inside the observation borehole although in this case estimated velocities require further analyses to be transformed to regional Darcy flux q ∞ (or seepage velocity v ∞ ) as in all other in-hole methods.…”

An Inexpensive and Simple Experimental Approach for the Estimation of Solute Import into Groundwater and Subsequent Export Using Inflow/Outflow Data

“…The export in surface runoff from agricultural catchments to the GBR has been fairly well documented but that from the GW base flow discharge has received limited attention [12] [13]. The limitations are partially attributed to the complexities involved in characterizing and quantifying GW inflow/outflow from point measurement extrapolated to larger scale and over-time [3] [6] [7] [8] [9]. Coupling GW inflow/outflow with solute import/export spatiotemporally may help to at least partially resolve the issues mentioned above, however, to my knowledge, such coupling information is scarce.…”

“…[4] [6] [7][8] reported that extrapolations from point measurement (piezometer wells) of solute transport to catchment scale should take into consideration the issues of sorption in soil matrix and half-life of solutes along the transport path, including the aforementioned complexities. These workers have also indicated solutes with moderate sorption and long half-life are most susceptible to transport within an year of import.…”