Plumes, contaminant, determination

Determine exposure via groundwater define contaminant plume for evaluation of interception methods... 

Electromagnetic (EM) Conductivity Measures the electrical conductivity of materials in microohms over a range of depths determined by the spacing and orientation of the transmitter and receiver coils, and the nature of the earth materials. Delineates areas of soil and groundwater contamination and the depth to bedrock or buried objects. Surveys to depths of SO to 100 ft are possible. Power lines, underground cables, transformers and other electrical sources severely distort the measurements. Low resistivities of surficial materials makes interpretation difficult. The top layers act as a shunt to the introduction of energy info lower layers. Capabilities for defining the variation of resistivity with depth are limited. In cases where the desired result is to map a contaminated plume in a sand layer beneath a surficial clayey soil in an area of cultural interference, or where chemicals have been spilled on the surface, or where clay soils are present it is probably not worth the effort to conduct the survey. 

The use of degradation rates to determine the age of a contaminant plume assumes a contaminant from a single, slug-type release, which degrades to a more recalcitrant chemical compound (i.e., trichloroethene degrading to 1,2-dichloroethene), will enter the water table or aquifer at a point in time when none of the daughter product is present in the aquifer ... 

Hydrolysis can explain the attenuation of contaminant plumes in aquifers where the ratio of rate constant to flow rate is sufficiently high. Thus 1,1,1-trichloroethane (TCA) has been observed to disappear from a mixed halocarbon plume over time, while trichlo-roethene and its biodegradation product 1,2-dichloroethene persist. The hydrolytic loss of organophosphate pesticides in sea water, as determined from both laboratory and field studies, suggests that these compounds will not be long-term contaminants despite runoff into streams and, eventually, the sea (Cotham and Bidleman, 1989). The oceans also can provide a major sink for atmospheric species ranging from carbon tetrachloride to methyl bromide. Loss of methyl bromide in the oceans by a combination of hydrolysis... 

The results are compared with solutions determined using fixed-length management periods. The hypothetical homogeneous, isotropic, confined aquifer is comprised of 60 finite elements and 77 nodes, with dimensions 1500 m by 900 m (Culver and Shenk, 1998). The initial contaminant plume, which has a maximum toluene concentration of 40 mg/L, is shown in Figure 1. An easterly steady flow was maintained with a constant hydraulic head of 12.0 m and contaminant concentration of 0.0 mg/L on the left side, a constant hydraulic head of 0.0 m and contaminant concentration of 0.0 mg/L on the right side, and no flow at the top and bottom boundaries. In this example, the sorbed phase is assumed to remain in equilibrium with the... 

In late April 1994, one additional monitor well (MW-9) was installed in an attempt to define the southern boundary of the contaminant plume. The consultant also conducted a pilot test to determine the design parameters for an SVE system (INTERA/BAI 1994b). The pilot test was done using 50 inches water column (we) vacuum, resulting in a well flow rate of 3 cubic feet per minute (cfm) and extracted vapor concentrations of less than 1,000 parts per million volume (ppmv). The radius of influence (ROI) suggested by the test results ranged from about 6.8 to 8.6 feet, which would result in an extraction well spacing of 10 to 15 feet. 

Another inverse analytical technique was developed by Ala and Domenico [1] to determine parameters such as the source strength and size, and the advective position of the contaminant front for the instantaneous contaminant plumes at Otis Air Force Base (AFB), Massachusetts. The contaminant plumes contained chloride, biodegradable and nonbiodegradable detergents, trichloro-ethene, and tetrachloroethene. To obtain the uniquely determined parameters, Ala and Domenico structured the analytical technique to solve several equations simultaneously. By assuming a uniform vertical contaminant distribution, the steady state analytical solution becomes... 

Determination of the presence of contaminant plumes and their flow direction and movement rate is commonly required at hazardous waste sites. The first determination is whether leakage from the hazardous waste site is occurring. If the existence of a plume is confirmed, its direction and extent should be established and identified. A preliminary geophysical survey can aid in better defining the contaminant plume, leading to more effective monitoring with a smaller number of monitoring wells. 

In the stratification strategy with a replacing air distribution in the lower zone, the height of the boundary layer between the lower and upper zones can be determined with the criteria of the contaminant interfacial level.This level, where the air mass flow in the plumes is equal to the air mass flow of the supply air, IS presented in Fig. 8,4. In this ideal case the wait and air temperatures are equal on the interfacial level. In practical cases they are not usually equal and the buoyancy flows on the walls will raise the level and decrease the gradient. 

H-labeled substrates have been used to determine the dissipation and degradation of aromatic hydrocarbons in a contaminated aquifer plume (Thierrin et al. 1995). Its application was particularly appropriate since the site was already contaminated with the substrates. With suitable precautions, this procedure seems capable of extension to determining the presence—though not the complete structure—of metabolites, provided that the possibility of exchange reactions were taken into account. 

Defining the plume of the contamination was straightforward by using existing domestic wells and a few monitoring wells. However, determining the nature of the problem beneath the potliner pile and its vicinity was much more difficult. 

Typically, application of science involves prediction of function such as determining at what rate a well must be pumped to create a suitable capture zone. What period of time will be required to biodegrade a mass of contaminant within a plume How much activated carbon will be required to treat the discharged vapor What will be the cost of electricity to power the remediation system Engineers are more likely capable of designing a balanced remediation system that has flow rates matched to reaction times or water-air contact rates. Tank sizes, power consumption, and similar rate-time-related calculations also fall within the specialty of the engineer. 

In place of distance measurements, concentration can be used to determine the age of a plume. Assuming that the plume is derived from a single slug-type release of a contaminant which is only partially soluble in groundwater, and not present as an NAPL, then the date upon which the contaminant enters the water table or aquifer is equivalent to that point in time when the concentration of the contaminant approaches its solubility limit ... 

This method is best solved graphically by plotting the maximum concentration measured at the center of the plume on different dates, then extrapolating to determine the date on which the concentrations of the contaminant in question approaches its solubility limit. The solubility limit, corrected for the temperature of the aquifer, for a particular contaminant can be obtained from the literature. 

Petroleum group analyses are conducted to determine amounts of the petroleum compound classes (e.g., saturates, aromatics, and polars/resins) present in petroleum-contaminated samples. This type of measurement is sometimes used to identify fuel type or to track plumes. It may be particularly useful for higher-boiling products such as asphalt. Group-type test methods include multidimensional gas chromatography (not often used for environmental samples), high-performance... 

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