Applications of Environmental Aquatic Chemistry: A Practical Guide - Chapter 7 ppt

7 Behavior of Dense Nonaqueous Phase Liquids in the Subsurface 7.1 DNAPL PROPERTIES Dense nona queous phase liquids (DNAP Ls) are liquids that are only sligh tly solub le in wate r and there fore exist in the subsur face as a separate fluid ph ase immis cible with both wat er and air.* The densi ty of DNA PLs is greater than water (DNA PL density > 1g=cm 3 at 48 C) and their mobili ty in the subsur face is governe d more by gravity and the proper ties of the DN APL and surro unding soil than it is by g round- water movement . Unlike ligh t nonaqueo us phase liquids (LNAPL s) such as gasol ine, diese l fuel, and h eating oil (which are less dense than water), DNAPLs relea sed into soil s can sink b elow the water table where thei r more -sol uble co mponents can slowly diss olve into flowi ng groundwat er, giving rise to diss olved contam inant plum es. A relea se o f DNAP L at the ground surface can therefore lead to long-term contamina tion of both the vadose and saturated zones a t a site. DNA PLs such as wood preser vatives like creoso te, transform er, and insulating oils contain ing polych lorinated biphen yls (PC Bs), coal tar, and a varie ty of chlor in- ated solve nts such as trichlor oethene (TCE) and tetrachlo roeth ene (PC E) have been widely used in industry since the beginn ing of the twentieth c entury. However , their importan ce as soil a nd groundw ater contam inants was not recogniz ed unti l the 1980s, mainly beca use of the limit ations of early analytical met hods. As a resul t, chemical material safety data sheet s (MSD S) distributed as late as early 1970 sometim es recom mended that waste chlor inated solve nts be disca rded by spread ing them onto dry ground and allowing them to evapora te. These early MSD Ss acknow - ledged the volat ile nature of many DNA PL chemicals , but d id not recogni ze their ability to in filtrate rapidly into the subsur face, causing soil and groundw ater pollu- tion. It is not surpr ising that DNA PLs are the contamina nts of greatest concern at many Su perfund and other hazardous waste sites. Table 7.1 lists many of the DNA PLs commonl y found at Superfu nd sites, along with their chemi cal form ulas, some alternative names, and common abbreviations. * See Chapter 6 to review the properties of nonaqueous phase liquids (NAPLs) in general and light nonaqueous phase liquids (LNAPLs). ß 2007 by Taylor & Francis Group, LLC. TABLE 7.1 DNAPL Contaminants of Concern at Many Hazardous Waste Sites Chemical Abstracts Service (CAS) Name Abbreviation CAS Number Other Names Molecular Formula Structural Formula Chloromethane Artic; R40 74-87-3 Methyl chloride; monochloromethane CH 3 Cl CH 3 Cl Dichloromethane Methylene chloride; MC 75-09-2 Methylene dichloride CH 2 Cl 2 CH 2 Cl 2 Trichloromethane CF 67-66-3 Chloroform; methane trichloride CHCl 3 CHCl 3 Tetrachloromethane CT 56-23-5 Carbon tetrachloride CCl 4 CCl 4 Chloroethane CA 75-00-3 Ethyl chloride C 2 H 5 Cl Cl 3 CÀÀCH 3 1,1-Dichloroethane 1,1-DCA 75-34-3 Ethylidene dichloride C 2 H 4 Cl 2 Cl 3 CÀÀCH 3 1,2-Dichloroethane 1,2-DCA, EDC 107-06-02 Ethylene dichloride C 2 H 4 Cl 2 Cl 3 CÀÀCH 3 1,1,1-Trichloroethane 1,1,1-TCA 71-55-6 Methyl chloroform, chlorothene, methyltrichloromethane C 2 H 3 Cl 3 Cl 3 CÀÀCH 3 1,1,2-Trichloroethane 1,1,2-TCA 79-00-5 Vinyl trichloride b-trichloroethane C 2 H 3 Cl 3 Cl 2 HCÀÀCH 3 Chloroethene VC 75-01-4 Vinyl chloride; chloroethylene C 2 H 3 Cl ClHC¼¼CH 2 1,1-Dichloroethene 1,1-DCE 75-35-4 1,1-Dichloroethylene; vinylidine chloride C 2 H 2 Cl 2 Cl 2 C¼¼CH 2 ß 2007 by Taylor & Francis Group, LLC. (E)-1,2-Dichloroethene trans -1,2-DCE 156-60-5 trans-1,2-Dichloroethene; trans-1,2-dichloroethylene; acetylene dichloride C 2 H 2 Cl 2 t-ClHC¼¼CHCl (Z)-1,2-Dichloroethene cis -1,2-DCE 156-59-2 cis-1,2-Dichloroethene; cis-1,2-dichloroethylene; acetylene dichloride C 2 H 2 Cl 2 c -ClHC ¼¼ CHCl Trichloroethene TCE 79-01-6 Trichloroethylene C 2 HCl 3 Cl 2 C¼¼CHCl Tetrachloroethene PCE 127-18-4 Perchloroethylene; tetrachloroethylene C 2 Cl 4 Cl 2 C¼¼CCl 2 Chlorobenzene CB 108-90-7 Monochlorobenzene, benzene chloride, phenyl chloride C 6 H 5 Cl C 6 H 5 Cl 1,2-Dichlorobenzene 1,2-DCB 95-50-1 o-Dichlorobenzene C 6 H 4 Cl 2 C 6 H 4 Cl 2 1,3-Dichlorobenzene 1,3-DCB 541-73-1 m-Dichlorobenzene C 6 H 4 Cl 2 C 6 H 4 Cl 2 1,4-Dichlorobenzene 1,4-DCB 106-46-7 p-Dichlorobenzene C 6 H 4 Cl 2 C 6 H 4 Cl 2 1,2,3-Trichlorobenzene 1,2,3-TCB 87-61-6 vic-Trichlorobenzene C 6 H 3 Cl 3 C 6 H 3 Cl 3 1,2,4-Trichlorobenzene 1,2,4-TCB 120-82-1 Trichlorobenzol C 6 H 3 Cl 3 C 6 H 3 Cl 3 1,3,5-Trichlorobenzene 1,3,5-TCB 108-70-3 sym-Trichlorobenzene C 6 H 3 Cl 3 C 6 H 3 Cl 3 1,2,3,5-Tetrachlorobenzene 1,2,3,5-TECB 634-90-2 1,2,3,5-TCB C 6 H 2 Cl 4 C 6 H 2 Cl 4 1,2,4,5-Tetrachlorobenzene 1,2,4,5-TECB 95-94-3 s-Tetrachlorobenzene, sym-tetrachlorobenzene C 6 H 2 Cl 4 C 6 H 2 Cl 4 Hexachlorobenzene HCB 118-74-1 Perchlorobenzene C 6 Cl 6 C 6 Cl 6 1,2-Dibromoethane EDB 106-93-4 Ethylene dibromide; dibromoethane C 2 H 4 Br 2 C 2 H 4 Br 2 Polychlorinated biphenyls PCBs — Aroclor; Phenoclor; Pyralene; Clophen; Kaneclor — See Section 7.4 ß 2007 by Taylor & Francis Group, LLC. Pro perties of DN APL liqu ids and surro unding soils that are useful for predic ting DN APL mobility are describe d in Tab le 7.2. So me imp ortant DNA PL compo unds and thei r proper ties found at these sites are inclu ded in Table 7.3. 7.2 DNAPL FREE PRODUCT MOBILITY In a DNAPL release, the free product sinks vertically downward through the vadose zone under gravitational forces, spreading laterally under capillary forces and leaving behind a trail of residual soil-sorbed DNAPL. In the vadose zone, DNAPL behaves similarly to LNAPL, moving downward while spreading laterally and leaving a trail of soil-sorbed and immobile liquid NAPL in the form of disconnected blobs and ganglia of free product that remain behind the trailing end of the downward-moving DNAPL body. 7.2.1 DNAPL IN THE VADOSE Z ONE Lik e LNAP L, DNA PL in the vadose zone will partition into soli d, liqu id, and vapor phases so that different portions are present as free product, pore space vapor, diss olved in wat er, and sorbed to soil (see Figure 6.3 ). Bec ause of con tinual losses to other phases, the downward-moving free product is continuall y diminished in mass and volume. It also undergoes changes in composition as the more volatile and soluble components preferentially leave the free product mix ture. A point may be reached at which the remaining DNAPL free product no longer holds together as a continuous phase, but rather is present as immobile isolated globules and ganglia, held in place by capillary forces. Only DNAPL present as a continuous, immiscible, liquid phase is mobile. If sufficient DNAPL was originally present, liquid free product will eventually reach the water table interface between the vadose and saturated zones. The fraction of liquid hydrocarbon that is retained by sorption and capillary forces in the pores of soils is referred to as residual saturation and is relatively immobile.* Percent residual saturation (%RS) is defined by Equation 7.1. %RS ¼ 100  volume of NAPL trapped in subsurface pore spaces total volume of pore spaces  (7:1) The amount of residual DNAPL retained in a typical soil such as silt, sand, or gravel is generally between 5% and 20% of the soil pore space. In the vadose zone, only DNAPL in the vapor, dissolved, and liquid free product phases has significant mobility; DNAPL sorbed to soil surfaces or trapped in pores is immobile unless it partitions again into one of the three mobile phases. DNAPL in the vapor phase is generally denser than air and tends to sink. However, it spreads laterally wherever the subsurface is least permeable, often moving far beyond the region of resi dual saturation, where the vapors can contaminate soils and ground- water distant from the region of the spill. * A common operational definition of NAPL mobility is that mobile NAPL can drain under gravity into a monitoring well, while immobile NAPL (residual saturation) cannot. ß 2007 by Taylor & Francis Group, LLC. TABLE 7.2 DNAPL Properties Important for Predicting Mobility in Environment Properties of DNAPL=Soil De finition=Typical Units Comments Density (d ) d ¼ mass=volume d ¼ gÁcm À3 ;lbÁft À3 Density distinguishes between LNAPLs (d DNAPL < d water ) and DNAPLs (d DNAPL < d water ). It depends on temperature, pressure, molecular weights of components, intermolecular forces, and bulk liquid structure. Dynamic viscosity ( m) m ¼fluid internal resistance to flow or shear. The CGS unit is poise (P); SI unit is NÁsÁm À2 . 1P¼ 100 centipoise ¼ 1g=cmÁs ¼ 0.1 PaÁs Dynamic viscosity is a measure of the force required to move a liquid at a constant velocity. The common unit of m is the centipoise (cP) because water at 20.28 C has a convenient viscosity of 1.000 cP. Viscosity decreases with increasing temperature (note water in Table 7.2). Intermolecular attractions are the main cause of viscosity. The lower the viscosity, the more fluid the liquid and the more easily it will flow through soils. The reciprocal of dynamic viscosity is called fluidity. Kinematic viscosity ( n) n ¼ dynamic viscosity=density The CGS unit is stokes (St) or centistokes (cSt); SI units are m 2 Ás À1 ; stokes ¼ poises=density 1St¼ 100 cSt ¼ 10 À4 m 2 Ás À1 When the force causing a liquid to move is only due to gravity, as in NAPL movement in the environment, the fluid density, as well as the dynamic viscosity, affects the rate of movement. Using kinematic viscosity includes density in its defi nition and eliminates the force term (N or Pa). Kinematic viscosity is convenient for calculating hydraulic conductivity, which is inversely proportional to n . Since the density of water at 20.28C is 0.998 g=cm 3 , the kinematic viscosity of water at 20.28 C is, for most practical purposes, equal to 1.0 cSt. Solubility in water (S) S ¼ mass of dissolved substance per unit volume of water, in equilibrium with the undissolved substance. For environmental pollutants in water, the common units are mg=Lor m g=L. Solubility measures a compound’s tendency to partition from the bulk compound into water. For a single-component NAPL, the solubility is the concentration of dissolved component in equilibrium with the NAPL. For NAPLs that are mixtures, each component of the mixture has its own characteristic solubility, which is generally lower than the solubility of the pure component (see Section 6.3.8). Thus, the overall solubility of an NAPL mixture is variable, depending on its composition, and changes with time as the more-soluble components leave the NAPL by partitioning into the water. Solubility can vary with temperature, pH, TDS, and the presence of cosolvents (e.g., detergents, EDTA, etc.). In general, the greater the molecular weight (high polarizability) and symmetry (low polarity) and the fewer hydrogen-bonding atoms, the lower the solubility, see Section 2.9. (Continued) ß 2007 by Taylor & Francis Group, LLC. TABLE 7.2 (Continued ) DNAPL Properties Important for Predicting Mobility in Environmen t Properties of DNAPL=Soil Definition=Typical Units Comments Vapor pressure (P v ) P v ¼ pressure exerted by a vapor in equilibrium with the liquid or solid phase of the same substance. There are many different units for pressure. The more common units are millimeters of mercury (mm Hg), torr, and atmosphere (atm). The SI unit is pascal (Pa). 1mmHg¼ 1 torr ¼ 760 À1 atm ¼ 1.333 mbar ¼ 133.3 Pa ¼ 1.934310 À2 psi 1 Pa ¼ 1N=m 2 ¼ 10 À5 bar ¼ 7.50310 À3 torr ¼ 1.450310 À4 psi Vapor pressure indicates an NAPL’s volatility, or tendency to vaporize, at a given temperature. It depends only on the temperature and increases exponentially with increasing temperature. On a molecular level, vapor pressure is an indication of the strength of intermolecular attractive forces, see Section 2.8.6. The vapor pressure of DNAPLs ranges from very high to very low; for example, compare 1,1-dichloroethylene and chrysene in Table 7.2. Henry’s law volatility The Henry’s law volatility of a compound is a measure of the transfer of the compound from being dissolved in the aqueous phase to being a vapor in the gaseous phase. The transfer process from water to the gaseous phase in the atmosphere is dependent on the chemical and physical properties of the compound, the presence of other compounds, and the physical properties (velocity, turbulence, depth) of the water body and atmosphere above it. The factors that control volatilization are the solubility, molecular weight, vapor pressure, and the nature of the air–water interface through which it must pass. The Henry’s constant is a valuable parameter that can be used to help evaluate the propensity of an organic compound to volatilize from the water. The Henry’s law constant is defined as the vapor pressure divided by the aqueous solubility. Therefore, the greater the Henry’s law constant, the greater the tendency to volatilize from the aqueous phase, refer to Table 7.1. ß 2007 by Taylor & Francis Group, LLC. TABLE 7.3 Values for Important Properties of DNAPL Contaminants Commonly Found at U.S. Superfund Sites Chemical Compound Density (g=cm 3 ) Water Solubility (mg=L) Vapor Pressure (torr) Henry’s Law Constant (atm m 3 =mol) Dynamic Viscosity a (centipoise) Kinematic Viscosity a (centistokes) Water 0.9991 (158C) — 12.8 (158C) — 1.145 (158C) 1.146 (158C) (for comparison) 0.9982 (208C) 17.5 (208C) 1.009 (208C) 1.011 (208C) Halogenated semivolatiles Aroclor b 1242 1.3850 0.45 4.06 3 10 À4 3.4 3 10 À4 Aroclor b 1254 1.5380 0.012 7.71 3 10 À5 2.8 3 10 À4 Aroclor b 1260 1.4400 0.0027 4.05 3 10 À5 3.4 3 10 À4 Chlordane 1.6 0.056 1 3 10 À5 2.2 3 10 À4 1.104 0.69 1,4-Dichlorobenzene 1.2475 80 0.6 1.58 3 10 À3 1.258 1.008 1,2-Dichlorobenzene 1.3060 100 0.96 1.88 3 10 À3 1.302 0.997 Dieldrin 1.7500 0.186 1.78 3 10 À7 9.7 3 10 À6 Pentachlorophenol 1.9780 14 1.1 3 10 À4 2.8 3 10 À6 2,3,4,6-Tetrachlorophenol 1.8390 1,000 Halogenated volatiles Carbon tetrachloride 1.5947 790 91.3 0.020 0.965 0.605 Chlorobenzene 1.1060 490 8.8 3.46 3 10 À3 0.756 0.683 Chloroform (trichloromethane) 1.4850 7,920 160 3.75 3 10 À3 0.563 0.379 1,1-Dichloroethane 1.1750 5,500 182 5.45 3 10 À4 0.377 0.321 1,2-Dichloroethane 1.2530 8,690 63.7 1.1 3 10 À3 0.840 0.67 cis-1,2-Dichloroethylene 1.2480 3,500 200 7.5 3 10 À3 0.467 0.364 (Continued) ß 2007 by Taylor & Francis Group, LLC. TABLE 7.3 (Continued) Values for Important Properties of DNAPL Contaminants Commonly Found at U.S. Superfund Sites Chemical Compound Density (g=cm 3 ) Water Solubility (mg=L) Vapor Pressure (torr) Henry’s Law Constant (atm m 3 =mol) Dynamic Viscosity a (centipoise) Kinematic Viscosity a (centistokes) trans-1,2-Dichloroethylene 1.2570 6,300 265 5.32 3 10 À3 0.404 0.321 1,1-Dichloroethylene 1.2140 400 500 1.49 3 10 À3 0.330 0.27 1,2-Dichloropropane 1.1580 2,700 39.5 3.6 3 10 À3 0.840 0.72 Ethylene dibromide 2.1720 3,400 11 3.18 3 10 À4 1.676 0.79 Methylene chloride 1.3250 13,200 350 2.57310 À3 0.430 0.324 1,1,2,2-Tetrachloroethane 1.6 2,900 4.9 5. 0 3 10 À4 1.770 1.10 1,1,2-Trichloroethane 1.4436 4,500 0.188 1.17 3 10 À3 0.119 0.824 1,1,1-Trichloroethane 1.3250 950 100 4.08 3 10 À3 0.858 0.647 Tetrachloroethylene (PCE) 1.620 200 14 0.0227 0.890 0.54 Trichloroethylene (TCE) 1.460 1,100 58.7 8.92 3 10 À3 0.570 0.390 Trichloromethane (chloroform) 1.4850 7,920 160 3.75 3 10 À3 0.563 0.379 Nonhalogenated semivolatiles 2-Methyl naphthalene 1.0058 25.4 0.0680 0.0506 o-Cresol 1.0273 31,000 2.45310 À1 4.7 3 10 À5 p-Cresol 1.0347 24,000 1.08310 À1 3.5 3 10 À4 2,4-Dimethylphenol 1.0360 6,200 0.098 2.5 3 10 À6 m-Cresol 1.0380 23,500 1.53310 À1 3.8 3 10 À5 21.0 20 Phenol 1.0576 84,000 5.293 3 10 À1 7.8 3 10 À7 3.87 Naphthalene 1.1620 31 2.336 3 10 À1 1.27 3 10 À3 ß 2007 by Taylor & Francis Group, LLC. Benzo(a)Anthracene 1.1740 0.014 1.16 3 10 À9 4.5 3 10 À6 Fluorene 1.2030 1.9 6.67 3 10 À4 7.65 3 10 À5 Acenaphthene 1.2250 3.88 0.0231 1.2 3 10 À3 Anthracene 1.2500 0.075 1.08 3 10 À5 3.38 3 10 À5 Dibenzo(a,h)anthracene 1.2520 2.5 3 10 À3 1 3 10 À10 7.33 3 10 À8 Fluoranthene 1.252 0.27 7.2 3 10 À5 11 3 10 À6 Pyrene 1.2710 0.148 6.67 3 10 À6 1.2 3 10 À5 Chrysene 1.2740 6.0 3 10 À3 6.3 3 10 À9 1.05 3 10 À6 2,4-Dinitrophenol 1.6800 6.0 3 10 À3 1.49 3 10 À5 6.45 3 10 À10 Miscellaneous Coal tar (458 F) 1.028 18.98 Creosote 1.05 ~1.08 (158 C) Source: Adapted from USEPA, Dense Nonaqueous Liquids, S.G. Huling and J.W. Weaver, Ground Water Issue, Office of Research and Development, Office of Solid Waste and Emergency Response, Washington, DC, EPA=540=4-91-002, March 1991. a Dynamic viscosity measures a liquid ’s resistance to flow. Kinematic viscosity is the ratio of dynamic viscosity to density, see Table 7.2. b Aroclor is the trade name for polychlorinated biphenyls (PCBs) manufactured by Monsanto. See Section 7.3.4. ß 2007 by Taylor & Francis Group, LLC. Because the v apor pressu re of many DNA PL compo unds is relativel y high, the lif espan of residual DNAPL in the unsat urated zone, where vaporizati on oc curs, can be much less than the lifespan of residual DNA PL below the water tabl e, wher e vap orization cannot occur. The vapori zation proces s can deplet e resi dual DNA PLs hav ing high vapor press ures, such as the solve nts TCE and PCE, wi thin 5–10 years in relat ively war m and dry c limates. This will not elimin ate the presence of vapor ph ase, adsorbed phase, and aqueous phase contam ination in the unsat urate d zone, bu t it can lead to an absence of the DNA PL phase. The absence of DN APL in the un saturated zone at a site does not necess arily imp ly that no DNA PL was ever relea sed at that sit e in the pa st, or that past releases of DNA PL have failed to reach the water table. Water percolati ng down ward throu gh the vadose zone wi ll prefer entially leach the more -soluble compo nents of DNAP L from the free product and resi dual satur- atio n that it contac ts; eventu ally c arrying diss olved DN APL to the satur ated zone, con taminating groundw ater there . Partitio ning of residua l satur ation into the d is- solve d phase is facilitated further by the rise and fall of the wat er tabl e. 7.2.2 DNAPL AT THE W ATER TABLE At the water table inte rface, DNAP L behaves very diff erently from LNAPL . Being den ser than wat er, it does not float a bove the water tabl e but tends to conti nue do wnward throu gh the capil lary zone of the water tabl e into the satur ated zone, wher e partitio ning into the diss olved phase is maximi zed. To continue movi ng downward in the saturated zone, DNA PL must displace water held in the soil pore spaces by capillary forces. Consequently, at the water table interface, downward movement slows while DNAPL piles up and spreads laterally. If sufficient weight of DNAPL accumulates, it presses down ward through the capillary zone and continues do wn through the saturated zone, see Figure 7.1. Bec ause soil surfa ces in the saturated zone are already wetted by water, DNAPL movement below the water table does not leave a trail of soil-sorbed DNAPL, although some DNAPL can become trapped as residual saturation where water is not readily displaced. 7.2.3 DNAPL IN THE SATURATED ZONE In the saturated zone, DNAPL can exist only in three phases: the continuous liquid free product, dissolved, and residual saturati on phases. The vapor phase is absent. In the saturated zone, residual saturation DNAPL is in continual contact with water and, therefore, continually partitions its more-soluble components into the dissolved phase. Thus, the properties of the DNAPL change progressively, gene rally toward greater density and higher viscosity. In most soils, hydraulic gradients large enough to mobilize horizontal movements of residual DNAPL are unrealistic. Therefore, investigation and remediation activities involving intensive well pumping are not likely to draw residual DNAPL into wells. If the initial release was large enough, DNAPL will continue downward through the saturated zone to the bottom of the aquifer. Only an impermeable obstruction, such as bedrock, or complete depletion of mobile free product by sorption and capillary retention within the soil, stops the downward movement of DNAPL mobile ß 2007 by Taylor & Francis Group, LLC. [...]... and 20% of the soil pore space 5 DNAPLs with high vapor pressure can totally evaporate from the DNAPL phase in the vadose zone in a relatively short time Therefore, the absence of DNAPL in the unsaturated zone at a site does not necessarily imply that no DNAPL was ever released at that site in the past, or that past releases of DNAPL have failed to reach the water table Vapor phase, sorbed phase, and... stratigraphic units of low permeability, such as a clay lens or bedrock, it spreads out until it can enter a preferential pathway of greater permeability that allows it to continue downward DNAPL entering fractured rock systems may follow a complex pattern of preferential pathways free product A decrease in soil permeability, such as a clay layer,* whether in the unsaturated or saturated zone, affects... recover * Also called a clay lens or low permeability lens ß 20 07 by Taylor & Francis Group, LLC all of the trapped residual DNAPL DNAPL that remains trapped in the soil=aquifer matrix acts as a continuing source of groundwater contamination DNAPLs with low viscosity (e.g., methylene chloride, perchloroethylene, 1,1,1-TCA, TCE) can infiltrate into soil faster than water The relative values of DNAPL viscosity... sample EXAMPLE 1 USING GROUNDWATER CONCENTRATIONS SINGLE-COMPONENT DNAPL TO ESTIMATE THE PROXIMITY OF RESIDUAL Analysis of a water sample from a monitoring well indicated 6.4 mg=L of tetrachloroethene (PERC) Tetrachloroethene was a target contaminant because a dry cleaning establishment had once been on the site near the well Is residual tetrachloroethene DNAPL likely to be in the subsurface upgradient... isomers) PCBs have many desirable properties for commercial applications: very high chemical, thermal, and biological stability; low water solubility; low vapor pressure; high dielectric constant; and high flame resistance It is not surprising that PCBs found wide application as coolant and insulation fluids in transformers and capacitors, and as flame retardants, plasticizers, solvent extenders, organic diluents,... operation is called fluff, and consists of shredded solid plastics, foamed plastic, rubber, glass, wood, etc The fluff was oily, having absorbed much of the residual oil remaining in the original metal components Fluff was disposed off by transport to a landfill Acceptance by the landfill operators was conditional on a chemical analysis that showed the fluff did not contain excessive levels of toxic materials... mix of shredded materials had changed significantly, the laboratory analyses were suddenly showing greater than 50 mg=kg of PCBs Were these results accurate or not? Because PCB mass spectra overlapped the motor-oil GC=MS spectral range, it was possible that oil compounds were being mistaken for PCBs Arrangements were made with a knowledgeable laboratory director to be especially careful in sample cleanup... THE INITIAL COMPOSITION IS KNOWN A remediation project was being planned for a site that had contained a metal degreasing facility The degreaser solution that was used consisted of 70 wt% trichloromethane, 15 wt% trichloroethylene, and 15 wt% tetrachloroethylene A matrix of monitoring wells was drilled to try to locate subsurface source zones of DNAPL releases A water sample from well SW-4 contained 88... calculated from Equation 7: 3: Csoil (a) ¼ Since the sum of the estimated mole fractions, was present in the soil sample P a Cmeas (a) , min Csoil (a) Seff (a)  ðKd db þ pw Þ db is greater than unity, DNAPL 7. 4 POLYCHLORINATED BIPHENYLS 7. 4.1 BACKGROUND Polychlorinated biphenyls (PCBs) are a family of stable man-made organic compounds produced commercially by direct chlorination of biphenyl PCBs were manufactured... mg=L, of component a in a DNAPL mixture ¼ mole fraction of compound a in the mixture Xa Spure (a) ¼ pure-phase solubility of compound a, in mg=L 7. 3.1 CONTAMINANT CONCENTRATIONS IN GROUNDWATER AND SOIL THAT INDICATE THE PROXIMITY OF DNAPL If any of the following conditions exist in groundwater, there is a high probability that DNAPL free product is near the sampling location Groundwater concentrations . Contaminants of Concern at Many Hazardous Waste Sites Chemical Abstracts Service (CAS) Name Abbreviation CAS Number Other Names Molecular Formula Structural Formula Chloromethane Artic; R40 7 4-8 7- 3 . no DNA PL was ever released at that site in the past, or that past releases of DNAPL have failed to reach the water table. Vapor phase, sorbed phase, and dissolved phase contamination may still. mainly beca use of the limit ations of early analytical met hods. As a resul t, chemical material safety data sheet s (MSD S) distributed as late as early 1 970 sometim es recom mended that waste chlor