Mass transport and scale-dependent hydraulic tests in a heterogeneous glacial till–sandy aquifer system

Nilsson, Bertel; Sidle, Roy C.; Klint, Knud Erik S.; Bøggild, Carl Egede; Broholm, Kim

doi:10.1016/s0022-1694(00)00416-9

Cited by 69 publications

(40 citation statements)

References 27 publications

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“…Transmissivity (and for that matter hydraulic conductivity) is one of many aquifer parameters that vary with the scale of measurement. This issue is well documented in the literature (Sánchez-Vila et al, 1996;Nilsson et al, 2001). An in-depth analysis of this topic is well beyond the scope of this work.…”

Section: Hydraulic Conductivitymentioning

confidence: 72%

Conceptual and numerical modeling approach of the Guarani Aquifer System

Rodríguez

Vives

Gómez

2013

Hydrol. Earth Syst. Sci.

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Abstract. In large aquifers, relevant for their considerable size, regional groundwater modeling remains challenging given geologic complexity and data scarcity in space and time. Yet, it may be conjectured that regional scale groundwater flow models can help in understanding the flow system functioning and the relative magnitude of water budget components, which are important for aquifer management. The Guaraní Aquifer System is the largest transboundary aquifer in South America. It contains an enormous volume of water; however, it is not well known, being difficult to assess the impact of exploitation currently used to supply over 25 million inhabitants. This is a sensitive issue because the aquifer is shared by four countries. Moreover, an integrated groundwater model, and therefore a global water balance, were not available. In this work, a transient regional scale model for the entire aquifer based upon five simplified, equally plausible conceptual models represented by different hydraulic conductivity parametrizations is used to analyze the flow system and water balance components. Combining an increasing number of hydraulic conductivity zones and an appropriate set of boundary conditions, the hypothesis of a continuous sedimentary unit yielded errors within the calibration target in a regional sense. The magnitude of the water budget terms resulted very similar for all parametrizations. Recharge and stream/aquifer fluxes were the dominant components representing, on average, 84.2 % of total inflows and 61.4 % of total outflows, respectively. However, leakage was small compared to stream discharges of main rivers. For instance, the simulated average leakage for the Uruguay River was 8 m 3 s −1 while the observed absolute minimum discharge was 382 m 3 s −1 . Streams located in heavily pumped regions switched from a gaining condition in early years to a losing condition over time. Water is discharged through the aquifer boundaries, except at the eastern boundary. On average, pumping represented 16.2 % of inflows while aquifer storage experienced a small overall increment. The model water balance indicates that the current rate of groundwater withdrawals does not exceed the rate of recharge in a regional sense.

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Section: Hydraulic Conductivitymentioning

confidence: 72%

Conceptual and numerical modeling approach of the Guarani Aquifer System

Rodríguez

Vives

Gómez

2013

Hydrol. Earth Syst. Sci.

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“…The intercalated and discontinuous coarser lenses create a complex, shallow, unconfined aquifer system where water tables occur at depths ranging from 0.45 to 7.82 m. Similar aquifer systems in coarser layers and lens in glacial till are reported by Nilsson et al (2001), Broster and Pupek (2001) and Meriano and Eyles (2003). The water levels in GA6 and GA10 are about 0.8 m lower than GA11, GA12 and GA13, which may indicate that GA6 and GA10 penetrate a different lens.…”

Section: Hydrogeologymentioning

confidence: 80%

Fate and transport of volatile organic compounds in glacial till and groundwater at an industrial site in Northern Ireland

Phillips

Thomas

Forde³

et al. 2006

Environ Geol

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Volatile organic compound (VOC) contamination of subsurface geological material and groundwater was discovered on the Nortel Monkstown industrial site, Belfast, Northern Ireland. The objectives of this study were to (1) investigate the characteristics of the geological material and its influences on contaminated groundwater flow across the site using borehole logs and hydrological evaluations, and (2) identify the contaminants and examine their distribution in the subsurface geological material and groundwater using chemical analysis. This report focuses on the eastern car park (ECP) which was a former storage area associated with trichloroethene (TCE) degreasing operations. This is where the greatest amount of volatile organic compounds (VOCs), particularly TCE, were detected. The study site is on a complex deposit of clayey glacial till with discontinuous coarser grained lenses, mainly silts, sands and gravel, which occur at 0.45-7.82 m below ground level (bgl). The lenses overall form an elongated formation that acts as a small unconfined shallow aquifer. There is a continuous low permeable stiff clayey till layer beneath the lenses that performs as an aquitard to the groundwater. Highest concentrations of VOCs, mainly TCE, in the geological material and groundwater are in these coarser lenses at~4.5-7 m bgl. Highest TCE measurements at 390,000 lgL -1 for groundwater and at 39,000 lgk g -1 at 5.7 m for geological material were in borehole GA19 in the coarse lens zone. It is assumed that TCE gained entrance to the subsurface near this borehole where the clayey till was thin to absent above coarse lenses which provided little retardation to the vertical migration of this dense nonaqueous phase liquid (DNAPL) into the groundwater. However, TCE is present in low concentrations in the geological material overlying the coarse lens zone. Additionally, VOCs appear to be associated with poorly drained layers and in peat <3.0 m bgl in the ECP. Some indication of natural attenuation as VOCs degradation products vinyl chloride (VC) and dichloromethane (DCM) also occur on the site.

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“…Based on field investigations (Nilsson et al, 1997;Murdoch et al, 1999;Fredericia, 1990Fredericia, , 1991, the hydraulic conductivity for the uppermost 1 -5 m below ground surface of the clayey till is evaluated to be significantly higher than for the deeper sequences of the clayey till. This is due to fractures.…”

Section: Geologymentioning

confidence: 99%