Modeling cross-hole slug tests in an unconfined aquifer

TL;DR

This paper applies a modified semi-analytical model to cross-hole slug test data in an unconfined aquifer, accounting for water-table and inertial effects, to estimate hydraulic parameters and validate against prior tests.

Contribution

It demonstrates the applicability of a semi-analytical model to multi-well pneumatic slug tests in unconfined aquifers, including water-table and inertial effects, and compares results with previous methods.

Findings

Hydraulic parameters estimated are consistent with prior tests.

Model effectively captures water-table and inertial effects.

Late-time data improves specific yield estimation but is limited by noise.

Abstract

A modified version of a published slug test model for unconfined aquifers is applied to cross-hole slug test data collected in field tests conducted at the Widen site in Switzerland. The model accounts for water-table effects using the linearised kinematic condition. The model also accounts for inertial effects in source and observation wells. The primary objective of this work is to demonstrate applicability of this semi-analytical model to multi-well and multi-level pneumatic slug tests. The pneumatic perturbation was applied at discrete intervals in a source well and monitored at discrete vertical intervals in observation wells. The source and observation well pairs were separated by distances of up to 4 m. The analysis yielded vertical profiles of hydraulic conductivity, specific storage, and specific yield at observation well locations. The hydraulic parameter estimates are compared to results from prior pumping and single-well slug tests conducted at the site, as well as to estimates from particle size analyses of sediment collected from boreholes during well installation. The results are in general agreement with results from prior tests and are indicative of a sand and gravel aquifer. Sensitivity analysis show that model identification of specific yield is strongest at late-time. However, the usefulness of late-time data is limited due to the low signal-to-noise ratios.