The Role of Sand /Shale Interfaces in Saturated Zone NAPL Trapping

Abstract

ABSTRACT• Spilled nonaqueous phase liquids (NAPLs) can be trapped by relatively small‐scale structures at sand/shale interfaces just as hydrocarbons are naturally trapped in larger scale structures in oil and gas fields. We measured microscale closure at the upper sand/shale interface for 62 locations at three sites for fluvial/alluvial and tidal flat depositional environments and found that closure volume ranged from 0.56 to 2.9 L/m2 and averaged 1.2 L/m2. The area of each measurement ranged between 1024 and 2090 cm2. We could not measure closure height for individual features, so we measured the topographic variation at each of the 62 locations. Topographic variation ranged up to a maximum of 3.3 cm, and site means ranged between 1.3 and 2.4 cm. We also conducted sand box experiments to see if microscale features have NAPL trapping potential. Our results suggest that for NAPL to be trapped at greater than residual saturation, the trap closure height must be greater than the capillary rise of water into the NAPL. A closure height of 4.0 cm effectively trapped Marvel Mystery Oil when the average grain size was 1.5 mm but failed to do so at smaller grain sizes. Our experimental results are reproduced adequately by Hobson’s Formula which states that the height of capillary rise is inversely proportional to grain size and is also a function of the physical properties of the NAPL. Further calculations using Hobson’s Formula suggest that traps containing coarse‐grained material are effective for some NAPLs at closure heights approaching 1 cm, whereas fine‐grained sands require minimum closure heights of slightly <1 to 5 m or more to trap NAPLs.

Landslide hazard zonation in high risk areas of Rethymno Prefecture, Crete Island, Greece

“…In nowadays, the development of GIS has enhanced the capabilities for the research of landslides susceptibility (Carrara et al 1995;Dikau et al 1996;Carrara et al 1999;Miles and Ho 1999;Miles and Keefer 1999;Luzi et al 2000;Fall 2000;Refice and Capolongo 2002;Fall et al 2006) while many studies have been carried out to overview the use of GIS for landslide susceptibility assessment (van Westen 1994;Carrara et al 1995;Aleotti and Chowdhury 1999;Dai et al 2002;Cevik and Topal 2003;Ayalew and Yamagishi 2005;Fall et al 2006). Moreover, remote sensing (RS) techniques are widely used in landslide susceptibility assessment in both the generation of landslide parameters thematic layers and the production of landslide inventory maps (Saha et al 2002;Park and Chi 2007).…”

Remediation of Trapped Free‐Phase LNAPL

“…The filled triangles represent a contact angle of 33 degrees and the unfilled triangles represent a contact angle of 50 degrees. See Whitworth and Hsu (1999) …”

“…For a trap to hold free-phase LNAPL at greater than residual saturation, the closure height must be greater than the height of capillary rise of water into the LNAPL body (Exhibit 3). In general, Exhibit 3 suggests that, unless the aquifer sands are very coarse, trap closure heights of about 1 to 1.5 meters must be exceeded before free-phase LNAPL can exist in the trap (see Whitworth and Hsu (1999) for further discussion of LNAPL capillarity). Love et al (1999) described the occurrence of potential LNAPL trapping features in the intermountain western United States.…”

“…Whitworth (1994), Vroblesky et al (1995), Whitworth and Hsu (1999), and Love et al (1999) have all pointed out that, just as free-phase oil and gas can be trapped in the deep subsurface, spilled LNAPLs can be trapped in smaller-scale stratigraphic and/or structural features in the subsurface. Only one instance of trapping of free-phase LNAPL below the water table has been reported in the peer-reviewed literature (Vroblesky et al, 1995); however, based on the geographic and geologic extents of subsurface features that might act as traps for free-phase LNAPL, we strongly suspect that many such occurrences may be either unrecognized or, if discovered and remediated, not made public.Therefore, our may be open to depths of meters to tens of meters or more.…”

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Free-phase light nonaqueous phase liquids (LNAPLs) may be trapped in certain stratigraphic and structural features near or at contaminated sites due to seasonal or other variations in the water

INTRODUCTIONThis article focuses on design considerations for remediation of free-phase light nonaqueous phase liquids (LNAPLs) trapped or pooled in the subsurface.Whitworth (1994), Vroblesky et al (1995), Hsu (1999), andLove et al (1999) have all pointed out that, just as free-phase oil and gas can be trapped in the deep subsurface, spilled LNAPLs can be trapped in smaller-scale stratigraphic and/or structural features in the subsurface. Only one instance of trapping of free-phase LNAPL below the water table has been reported in the peer-reviewed literature (Vroblesky et al, 1995); however, based on the geographic and geologic extents of subsurface features that might act as traps for free-phase LNAPL, we strongly suspect that many such occurrences may be either unrecognized or, if discovered and remediated, not made public.Therefore, our

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