Dense non-aqueous phase liquids DNAPLs

Villaume, J.F., Investigations at sites contaminated with dense non-aqueous phase liquids (DNAPLs),... 

Conner, J. A., Newell, C. J., and Wilson, D. K., 1989, Assessment, Field Testing and Conceptual Design for Managing Dense Non-Aqueous Phase Liquids (DNAPL) at a Superfund Site In Proceedings of the National Water Well Association and American Petroleum Institute Conference on Petroleum Hydrocarbons and Organic Chemicals in Groundwater Prevention, Detection, and Restoration, November, pp. 519-533. 

The Ferox process offers several potential advantages over conventional permeable barrier walls. For example, Ferox injection parameters may be modified to reflect the contaminant concentration heterogeneities present at most dense non-aqueous-phase liquid (DNAPL) sites. Unlike permeable walls, Ferox is not limited to the treatment of dissolved-phase contaminants and may be applied under structures. In addition, Ferox is not limited by depth and does not require the use of excessive quantities of iron powder. 

In situ chemical oxidation using potassium permanganate was also demonstrated to treat dense, non-aqueous-phase liquid (DNAPL) at the Canadian Forces Base Borden in Ontario, Canada, between 1996 and 1997. This application used a series of six injection and five oxidant recovery weUs. The total cost of the project was approximately 45,000 (D18766A, p.l3). 

Waterflood oil recovery is a commercially available, in situ techuology for the treatment of groundwater contaminated with dense non-aqueous-phase liquids (DNAPLs) such as oil. Water-flood oil recovery is tailored to specific site conditions and is generally used in conjunction with barrier technologies. All information is from the vendor and has not been independently verified. 

CESAR was developed to address the problem of locating, characterizing, and removing dense non-aqueous-phase liquids (DNAPLs) from contaminated aquifer systems. The process is particularly suited to remediating groundwater contaminated with chlorinated solvents, such as trichloroethylene (TCE), tetrachloroethene (PCE), trichloroethane (TCE), and carbon tetrachloride (CCE). According to the vendor, CESAR can also be applied to sites contaminated with creosote, polychlorinated biphenyls (PCBs), Freon 113, volatile organic compounds (VOCs),... 

The process of anaerobic biotransformation with steam injection is a technology for the in situ remediation of soils and groundwater contaminated with dense non-aqueous-phase liquids (DNAPLs). Using this approach for remediation, steam is injected into the soil to volatilize and remove DNAPLs, with the simultaneous introduction of nutrients. The resulting subsurface conditions are suitable for biotransformation of the dissolved phase, into compounds that are more easily removed by vapor and groundwater extraction. 

Reclaim is commercially available and suitable for the recovery of VOCs, vinyl chloride, trichloroethylene, carbon tetrachloride, dense non-aqueous-phase liquid (DNAPL) compounds, and, in particular, petroleum hydrocarbons. The vendor states this technology has been used in a wide variety of industrial applications, such as the remediation of groundwater at service stations, dry cleaners, herbicide production facilities, and municipal and industrial landfills, among others. 

ISOTEC was chosen to treat soils contaminated with dense non-aqueous-phase liquids (DNAPLs) at a Superfund site in Florida. With a projected cost of 340,000, ISOTEC was cheaper than the alternative technologies considered. The estimated cost for implementing six-phase heating at the site was 535,000, and the estimated cost for excavation and ex situ treatment was 835,000 (D21478I, pp. 10, 11). 

The vendor states that tetrachloroethane (PCE), trichloroethene (TCE), and other volatile compounds are difficult to remove from saturated soils because they are relatively insoluble. The vendor states that the technology is especially applicable to sites contaminated with dense non-aqueous-phase liquids (DNAPLs). Using the ISSZT technology creates an unsaturated zone from which these contaminants can be readily air stripped. Other contaminants such as polychlorinated biphenyls (PCBs) or metals can be isolated from groundwater and contained within barriers preventing the spread of contamination. 

During the field demonstration in 1997 at the Department of Defense s (DOD s) Operable Unit 2, Hill Air Force Base in Utah, approximately 908 gal of dense, non-aqueous-phase liquids (DNAPLs) were removed from contaminated soils. The cost of the demonstration was 230/yd of soil treated and 165/gal of DNAPL removed. These costs included the purchase of all the equipment and an extensive monitoring network. It is estimated that future applications at the site would require roughly half as many wells and the boiler rental would be restricted to a much shorter period. These conditions would lower the direct treatment costs to 103/yd of treated soil and 74/gal DNAPL removed (D18518W, p. 216). 

Terra Vac s dense non-aqueous-phase liquid (DNAPL) vaporization involves heating the subsurface, including both groundwater and soil, to vaporize the DNAPL. According to the vendor, this technology is appropriate for medium and large sites with separate pools of dense chlorinated solvents, such as chloroform, dichloroethane, dichloroethene, Freons, methylene chloride, and vinyl chloride. This technology is commercially available. 

The technology has been applied primarily at sites contaminated with petroleum hydrocarbons. The Vacu-Polnt technology can remove hydrocarbons and chlorinated solvents from contaminated groundwater and soil. The developer asserts that the technology can treat VOCs, and all phases of non-aqueous-phase liquids (NAPLS) and dense non-aqueous-phase liquids (DNAPLS). 

In Illustrative Example 19.4, the dissolution of a non-aqueous-phase liquid (NAPL) into groundwater was discussed. Here we consider a similar (although somewhat hypothetical) case. Assume that a mixture of chlorinated solvents totally covers the flat bottom of a small pond (maximum depth zmax = 4 m, surface area Asurface = 104 m2) forming a dense non-aqueous-phase liquid (DNAPL). The DNAPL is contaminated by benzene which dissolves into the water column and is vertically transported by turbulent diffusion. The pond is horizontally well mixed. The vertical turbulent diffusion coefficient is , = 0.1 cm2s l and approximately constant over the whole water column. 

Electric fields use in soil restoration has been focused on contaminant extraction by their transport under electroosmosis and ionic migration. Contaminant extraction by electric fields is a successful technique for removal of ionic or mobile contaminants in the subsurface. However, this technique might not be effective in treatment of soils contaminated with immobile and/or trapped organics, such as dense non aqueous phase liquids (DNAPLs). For such organics, it is possible to use electric fields to stimulate in situ biodegradation under either aerobic or anaerobic conditions. It is necessary to evaluate the impact of dc electric fields on the biogeochemical interactions prior to application of the technique. It is not clear yet how dc electric fields will impact microbial adhesion and transport in the subsurface. Further, the effect of dc fields on the activity of microorganisms in a soil matrix is not yet well understood. 

NAPL) Any liquid other than water. In environmental fields this term commonly refers to petroleum hydrocarbons less dense than water (light non-aqueous phase liquid, LNAPL), or oils such as chlorinated hydrocarbons that are more dense than water (dense non-aqueous phase liquid, DNAPL). 

Figure 10.1 Sources and plumes of light non-aqueous phase liquids (LNAPL) and dense non-aqueous phase liquids (DNAPL) in an aquifer. DNAPL can penetrate the ground water table.

J. A. Cherry, S. Feenstra and D. M. Mackay, Concepts for the Remediation of Sites Contaminated with Dense Non-Aqueous Phase Liquids (DNAPLs), in Dense Chlorinated Solvents and other DNAPLs in Groundwater, eds. J. F. Pankow and J. A. Cherry, Waterloo Press, Guelph, Canada,... 

A possible remedy for CHC dense non-aqueous phase liquid (DNAPL) is to install an in-creased-efficieney pump-and-treat system based on introducing surfactants into the aquifer to increase the solubility of CHC and the rate at which it transfers into the water phase. In this type of system, groundwater is extracted, DNAPL is separated (if present), dissolved CHC is air-stripped or steam-stripped from the water, surfactant is added to the groundwater, and the surfactant-rich water is re-injected into the aquifer up-gradient of the suspected DNAPL deposit. As the surfactant-laden groundwater passes across the DNAPL zone it is capable of reaching a CHC saturation level that is many times the natural CHC solubility, thus removing DNAPL more efficiently. 

One of the best-known classes of groundwater contaminants includes chemicals known as chlorinated solvents one example of this class of compounds is dry cleaning fluid, also known as perchloroethylene (PCE). As a general mle, the chlorine present in chlorinated solvents makes them more toxic than the respective non-chlorinated organic molecules. Unlike petroleum-based fuels, solvents are usually heavier than water and thus tend to sink to the bottoms of aquifers, forming the so-called dense non-aqueous phase liquid (DNAPL) DNAPLs usually represent a long-term secondary source of pollution. This makes solvent-contaminated aquifers much more difficult to clean up. 

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