Possible impact of shallow interfluve traps on groundwater remediation

Whitworth, Thomas M.

doi:10.1007/bf00773136

Cited by 3 publications

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“…Love et al (1999) described the occurrence of potential LNAPL trapping features in the intermountain western United States. Whitworth (1994) described the traps of the LMRV. Since more data is available for the LMRV traps, this article will focus on these.…”

Section: Northeastern Arkansasmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 97%

“…Potential traps of free-phase LNAPL, such as those in the LMRV, typically have smaller vertical closures (Whitworth, 1994).Therefore, an important question to address is how much vertical closure height is necessary to trap free-phase LNAPLs?…”

Section: Introductionmentioning

confidence: 99%

“…Residual LNAPL saturation is defined as the saturation at which the LNAPL phase becomes discontinuous in water-wet porous media; in the saturated zone, this usually ranges between 5 and 30 percent of total pore volume (EPA, 1992). Whitworth (1994) suggested that spilled LNAPLs in the LMRV might reach the underlying confined aquifer under the following conditions:• If construction, such as tank installation, breaches the clay layer.• Through cracks or fractures in the clay.• Through biologic structures such as root traces. Palmer (1992) The capillary barrier is a fine-grained sediment, usually clay.…”

mentioning

confidence: 98%

“…If released in sufficient volumes into a confined aquifer, they can rise to the top of the aquifer and can be pooled or trapped by local stratigraphic and structural features with closure heights (the vertical distance from the highest point in the trap to the lowest closed contour) greater than a few centimeters, and horizontal extents of meters to hundreds of meters or even kilometers (Love et al, 1999;Whitworth, 1994).…”

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Remediation of Trapped Free‐Phase LNAPL

Whitworth

Elmore

2002

Remediation Journal

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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 T. M. Whitworth Andrew Curtis ElmoreRemediation of Trapped Free-Phase LNAPL purpose in writing this article is to present these concepts for consideration by the professional community.Spilled free-phase LNAPLs are less dense than water and thus are buoyant. If released in sufficient volumes into a confined aquifer, they can rise to the top of the aquifer and can be pooled or trapped by local stratigraphic and structural features with closure heights (the vertical distance from the highest point in the trap to the lowest closed contour) greater than a few centimeters, and horizontal extents of meters to hundreds of meters or even kilometers (Love et al, 1999;Whitworth, 1994).A free-phase LNAPL trap must, in addition to closed contours, have an upper boundary with pores small enough so that the nonaqueous phase liquid (NAPL) will not enter them (Exhibit 1).This boundary usually consists of clay-rich sediments. For example, the Lower Mississippi River Valley (LMRV), located in parts of Missouri, Arkansas, Louisiana, and Mississippi, has thousands of these potential near-surface LNAPL traps located beneath the geomorphic surfaces mapped as outwash or braided stream (Exhibit 2; see Whitworth, 1994).Free-phase LNAPL is sufficiently saturated so that it will flow as a body in the subsurface. LNAPLs can also be trapped in pore-scale features as residual saturation (Cohen & Mercer, 1993). Residual LNAPL saturation is defined as the saturation at which the LNAPL phase becomes discontinuous in water-wet porous media; in the saturated zone, this usually ranges between 5 and 30 percent of total pore volume (EPA, 1992). Whitworth (1994) suggested that spilled LNAPLs in the LMRV might reach the underlying confined aquifer under the following conditions:• If construction, such as tank installation, breaches the clay layer.• Through cracks or fractures in the clay.• Through biologic structures such as root traces. Palmer (1992) The capillary barrier is a fine-grained sediment, usually clay. The cap...

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Section: Northeastern Arkansasmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 98%

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confidence: 98%

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Remediation of Trapped Free‐Phase LNAPL

Whitworth

Elmore

2002

Remediation Journal

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

Whitworth

Hsu

1999

Environ Geosci

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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.

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Site characterization considerations for LNAPL spills on the buried valley train surfaces of the lower Mississippi River Valley

Whitworth¹,

Ghazifard²

2009

Environ. Geosci.

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A large number of potential light nonaqueous-phase liquid (LNAPL) traps exist in poorly sorted sands underlying the buried valley train surfaces in the lower Mississippi River Valley (LMRV). These traps should be considered during site characterization and remediation activities related to spilled nonaqueous-phase liquids and leaking underground storage tanks on the valley train surfaces of the LMRV. These traps have apparent average dimensions of 0.84 by 0.21 km (0.52 by 0.13 mi), with an average closure height of 2.7 m (8.85 ft). The maximum apparent lateral dimensions are 4.19 by 0.69 km (2.6 by 0.42 mi) and the minimum observed lateral dimensions are 0.06 by 0.02 km (0.03 by 0.01 mi). Apparent closure heights range from less than 1 m (3 ft) to an apparent maximum of 7.6 m (24.93 ft). A depth of about 4.3 m (14.1 ft) is assumed to be a maximum likely excavation depth for underground storage tank installations in the LMRV. The top stratum thickness in 47 of the 100 borings used to construct cross sections in this study was less than 4.3 m (14.1 ft).Thus, it is likely that underground storage tank installations, for example, have or will breach the top stratum at many sites on the valley train surfaces. In order for spilled LNAPLs from underground storage tank sites to migrate into one of these traps, it is probably necessary that the original excavation breach the low-permeability top stratum and that the water table seasonally fluctuates from below the base of the top stratum to above the base of the top stratum.

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Possible impact of shallow interfluve traps on groundwater remediation

Cited by 3 publications

References 2 publications

Remediation of Trapped Free‐Phase LNAPL

Remediation of Trapped Free‐Phase LNAPL

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

Site characterization considerations for LNAPL spills on the buried valley train surfaces of the lower Mississippi River Valley

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