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Soil parameters controlling vapor flow in the subsurface are necessary to design soil vapor extraction (SVE) cleanup systems. Previous work assumes a confined flow model, with concrete and asphalt surface covers providing the confining layer and preventing air leakage into the zone of vapor transmission. SVE field tests conducted as part of this investigation, however, exhibited responses that are inconsistent with a confined flow model; it appears that the real world leaks. This paper develops a transient soil vapor extraction (SVE) testing method that considers the effects of vertical leakage. Analytic methodologies are developed that allow use of commonly available ground‐water flow type curves to evaluate SVE test data. The key implications of leaky compared to confined flow are (1) smaller values of derived vapor permeability, and (2) decreased radial cleanup efficacy, both with time and distance.

Light nonaqueous phase liquid (LNAPL) saturation and movement in the subsurface are controlled by soil capillary characteristics, permeability, and fluid properties. Where free-product occurs in monitoring wells, LNAPL saturations in the formation vary significantly as a function of the observed thickness in the monitoring well and soil type. Fine-grained soils generally exhibit lower LNAPL saturations than coarse-grained material for the same observed thickness in a monitoring well. MAGNAS3 [MAGNAS3. HydroGeoLogic, Inc., Herndon, VA, 1992; Huyakorn, P. S.; Panday, S.; Wu, Y. S. J. Contam. Hydrol. 1994, 16, 190−130], a three-dimensional, finite-element model that can simulate movement of three active phases (air, water, and LNAPL), was used to investigate LNAPL recovery in three different soil types and using several recovery designs to examine the effect of these factors on LNAPL recovery. The results of this analysis show that, because the relative mobility of LNAPL decreases with decreasing saturation and because the intrinsic permeability of fine-grained soil is less than that of coarse-grained soil, free-product pumping or skimming has less likelihood of success in fine-grained soil. Recovery in fine-grained soils was minimal, with significant reductions in LNAPL saturation occurring only within about 10−15 ft of the well. Recovery of LNAPL in coarse-grained soils was simulated to be much more successful, with ap proximately 95% of the original hydrocarbon recovered through fluid pumping. The results of the modeling further shows that, for any soil type, recovery decreases LNAPL saturation and mobility near the well with the effect diminishing with distance. Therefore, a zone of decreased LNAPL permeability is formed near recovery wells that acts to impede additional recovery from greater distances. Increases in the hydraulic recovery rate (i.e., not considering volatilization) can be realized in all of the soils studied through vacuum enhanced free-product recovery.

No abstract

Non‐aqueous phase liquids (NAPLs) represent direct and indirect sources of potential risk. NAPL can be a long‐lived source of groundwater and vapor impacts because a small volume of NAPL phase can feed very large daughter plumes. For many years, the general environmental industry has built a database of limited remediation success, particularly in terms of mitigating source NAPLs. Any method of cleanup, no matter how fundamentally suited, will likely fail if the zones of NAPL impacts are not effectively targeted. This is analogous to enhanced oil recovery in the petroleum field; recovery enhancements occur only when targeting the zones containing oil. Although cleanup to pristine conditions is usually not viable, cleanups can do a far better job at reducing potential risks when NAPL factors are considered. This said, cleanup technologies also have specific limitations, and success must be defined in terms of the risk–benefit of the applied actions. Full treatment of the NAPL zones may be difficult, but it is usually possible to mitigate risk through remediation and management. This paper provides a few field examples of cleanup failure and documents the specific reasons why the failures occurred. In none of the cases was the failure attributable to geologic complexity or the “tailing” effect of fine‐grained layers. In a last example, cleanup design shortfalls were mitigated by proactively considering the NAPL target zones. Cleanup occurred in less than <6 months using simple technologies.