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Nonaqueous Phase Liquids (NAPLS)
Published in Stephen M. Testa, Geological Aspects of Hazardous Waste Management, 2020
The subsurface presence of LNAPL can occur under both perched and water-table conditions and under unconfined and occasionally confined conditions. LNAPL product in the subsurface is typically delineated and measured by the utilization of groundwater monitoring wells. While monitoring wells have provided some insight as to the extent and general geometry of the LNAPL pool, as well as the direction of groundwater flow, difficulties persist in determining the actual thickness and, therefore, the volume and ultimately the duration of recovery and remediation. One of the more difficult aspects in dealing with the subsurface presence of hydrocarbons is that accumulations measured in monitoring wells do not directly correspond to the actual thickness in the formation. The thickness of both LNAPL (and DNAPL) as measured in a monitoring well is thus an apparent thickness rather than an actual formation thickness (Figure 9-8). This relationship is schematically illustrated in Figure 9-9.
Contaminant transport mechanisms in karst terrains and implications on remediation
Published in Barry F. Beck, Felicity M. Pearson, Karst Geohazards, 2018
Wendell Barner, Kristine Uhlman
NAPLs include organic compounds such as chlorinated organic solvents (also known as volatile organic compounds, VOCs), cresols, creosote, some pesticides, and fuel hydrocarbons. NAPLs are immiscible with, and typically of dissimilar density than, water in their undiluted form. Although the less-dense Light NAPLs (such as gasoline) are prevalent contaminants, because they are lighter than and therefore float on top of the water table, they are more amenable to clean up. Where a water table exists in the soils above a karst aquifer, cones of depression centered on vertical cracks and other macropores hydraulically connected to solutionally enhanced conduits were found to be preferred transport routes of the separate phased as well as dissolved phase components of LNAPL hydrocarbons (Cooley, 1991). Some field investigators have found that LNAPL hydrocarbons can move in karst conduits as gross concentrations of free product at speeds of the order of kilometers per hour (Ewers, R.O. and others, 1991). A typical LNAPL remediation involves removal of source areas (excavation, vapor extraction, in-situ soil washing, and sparging coupled with ground water gradient control to induce the flow of LNAPLs downgradient towards collection wells or trenches (Recker, 1991).
Organic Chemistry Nomenclature
Published in Arthur W. Hounslow, Water Quality Data, 2018
Hydrocarbons are compounds made up of carbon and hydrogen atoms. They may be combined as chains or cyclic compounds, and may be saturated (containing single bonds only) or unsaturated (with double and/or triple bonds). A more complete classification is given in Table 7.1. Early chemists usually named a compound on the basis of its history, such as methane, which has one carbon atom. Methyl alcohol was originally obtained by the destructive distillation (distillation in the absence of oxygen) of wood, and therefore was named wood spirits, methic—wine; hule—wood. Acetic acid was named after Latin acetum, for vinegar. Ethane, or ethyl, was named after ether—from Latin aether or sky. Propane is from propionic acid (first of fatty acids) from Greek pion or fat. Butane is from butyric acid (hydrolysis product of butter—from Latin buterium or butter). Hydrocarbons with five or more carbon atoms are named after the number of carbon atoms in the molecule by using Latin numbers. One exception is that in the older literature pentane derivatives were also called amyl from amyl alcohol, which was first obtained from starch, Latin amylum. These compounds also include most of the petroleum compounds that are designated LNAPL—light nonaqueous-phase liquids that commonly occur as contaminants floating on groundwater.
Simulated groundwater dynamics and solute transport in a coastal phreatic aquifer subjected to different tides
Published in Marine Georesources & Geotechnology, 2021
Xiaohua Huang, Guodong Liu, Chengcheng Xia, Mengxi Yang
Increasing population, developing tourism, and industrial agglomeration are typical features of coastal areas that cause significant amounts of pollution around the coasts (Wang et al. 2018). Compared with the pollution of surface water and the atmosphere, which is visible and therefore easier to control, pollution in groundwater is hidden, persistent, and difficult to remediate (Zhang and Liang 2011). The characteristics of pollution in intertidal zones are complicated, as tides could cause significant disturbances to the dynamics of groundwater (Ansarifar et al. 2020). The spatial distribution of leaked pollutants discharging into the ocean is not only related to the local hydrogeological conditions, but also directly influenced by changes in the tides. With increased attention to environmental problems in groundwater, the interaction between seawater and groundwater and its importance in the management of pollutants has become a source of heated discussion in coastal hydrogeology (Li, Wan, and Jiao 2011). A complete investigation into the effect of different tides on the characteristics of solute transport is of great significance to the evaluation and remediation of groundwater in coastal areas. Particularly with regards to some of the light, non-aqueous phase liquids (LNAPLs) which spread over large areas (Geng, Boufadel, and Cui 2017; Lu et al. 1999). Therefore, the features of groundwater dynamics and the pollutants in intertidal zones subjected to different tidal conditions are worthy of an in-depth study.