Vadose Zone–Attenuated Artificial Recharge for Input to a Ground Water Model

Abstract

Accurate representation of artificial recharge is requisite to calibration of a ground water model of an unconfined aquifer for a semiarid or arid site with a vadose zone that imparts significant attenuation of liquid transmission and substantial anthropogenic liquid discharges. Under such circumstances, artificial recharge occurs in response to liquid disposal to the vadose zone in areas that are small relative to the ground water model domain. Natural recharge, in contrast, is spatially variable and occurs over the entire upper boundary of a typical unconfined ground water model. An improved technique for partitioning artificial recharge from simulated total recharge for inclusion in a ground water model is presented. The improved technique is applied using data from the semiarid Hanford Site. From 1944 until the late 1980s, when Hanford's mission was the production of nuclear materials, the quantities of liquid discharged from production facilities to the ground vastly exceeded natural recharge. Nearly all hydraulic head data available for use in calibrating a ground water model at this site were collected during this period or later, when the aquifer was under the diminishing influence of the massive water disposals. The vadose zone is typically 80 to 90 m thick at the Central Plateau where most production facilities were located at this semiarid site, and its attenuation of liquid transmission to the aquifer can be significant. The new technique is shown to improve the representation of artificial recharge and thereby contribute to improvement in the calibration of a site-wide ground water model.

Compendium of Data for the Hanford Site (Fiscal Years 2004 to 2008) Applicable to Estimation of Recharge Rates

“…The time required will depend on the thickness and hydraulic properties of the vadose zone and the deep drainage rate itself. Changes in the deep drainage rate, such as would result from changes in surface vegetative conditions that increase or decrease the evapotranspiration rate, can take many years to be reflected in the recharge rate for a thick vadose zone in arid conditions such as at the Hanford Site and can be an important consideration in characterizing recharge as well (Nichols et al 2007). …”

A coastal groundwater management model with Indian case study

“…Rao and Sreenivasulu (2004) studied the planning of groundwater development in coastal aquifers where seawater intrusion was controlled through a series of barrier extraction wells as a non-linear, nonconvex combinatorial model and was solved using a coupled simulation-optimisation approach. Nichols et al (2007) developed an improved technique for partitioning artificial recharge from simulated total recharge for inclusion in a groundwater model, thereby contributing to improvement in the calibration of a site-wide groundwater model. Mahesha (1996) carried out an analytical study on the transient effect of a battery of injection wells on seawater intrusion into coastal confined aquifers, analysed using a quasi-three-dimensional (3D) areal finite-element model derived based on the sharp interface approach.…”