Particular contaminants

At times, in situ chemical treahnents are used to remove particular contaminants. This is done by introducing... 

In conclusion, llic purpose of Ihe loxicily assessment is to weigh available evidence regarding the potential for particular contaminants to cause adverse effects in exposed individuals and to provide, where possible, an estimate of the relationship between the extent of exposure to a contaminant and the increased likelihood and/or severity of adverse effects. 

With regard to limiting the concentration of particular contaminants, these are generally referred to in terms of threshold limit values (TLV), expressed either in terms of a time-weighted average (TLV - TWA) which represents the average concentration for a normal working day over a 40-hour week to which nearly all workers may be exposed on a repeated basis or as a short-term exposure limit (TLV - STEL), which represents the maximum... 

Maintaining hydraulic fluid within allowable contamination limits for both water and particulate matter is cmcial to the care and protection of hydraulic equipment. Filters will provide adequate control of the particular contamination problem during all normal hydraulic system operations if the filtration system is installed properly and filter maintenance is performed properly. Filter maintenance includes changing elements at proper intervals. 

On a global scale, the atmosphere serves as the major pathway for the transport and deposition of contaminants from emission sources to terrestrial and aquatic ecosystem receptors (22, 27). Once a contaminant is airborne, the processes of atmospheric di sion, transport, transformation, and deposition act to determine its fate. These processes are complex and the degree to which they influence the fate of a particular contaminant is dependent on its physico-chemical characteristics, the properties and concentrations of coexisting substances, and the prevailing meteorological conditions, including wind, precipitation, humidity, temperature, clouds, fog, and solar irradiation. 

An isotherm test can determine whether or not a particular contaminant can be adsorbed effectively by activated carbon. In very dilute solutions, such as contaminated groundwater, a logarithmic isotherm plot usually yields a straight line represented by the Freundlich equation62 63 ... 

Avoid the gradual buildup of a particular contaminant with time... 

Vj-mm appears to increase with duct diameter, I). This trend has been recognized in many traditional pneumatic conveyors (Wypych and Reed, 1990 Zenz, 1964 Cabrejos andKlinzing, 1994), but also appears to be relevant for dust extraction (Cable, 1994 Miletich, 1994), which can be considered as a form of low-concentration pneumatic conveying (e.g., Vj= 10 m s 1 may be suitable for a particular contaminant in a duct size ofD = 100 mm but may cause deposition in D = 300 mm). Further evidence of this can be seen in the work of Zenz,... 

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. 

Information about construction materials used in the system may be contained within the plant records and can be useful in evaluating the fate and transport of a particular chemical contaminant through a system. For example, a particular contaminant may adsorb to the pipe material used in a utility s distribution system, and this type of information would be critical in evaluating remediation options following a chemical contamination incident. 

As for all petroleum products, considerations of safety in storage and transportation and, more particularly, contamination by more volatile products are required. This is usually accommodated by the Pensky-Martens flash point test (ASTM D93 IP 34). For the fuel oil, a minimum flash point of 55°C (131°F) or 66°C (150°F) is included in most specifications. 

Chelating polymers must be developed and evaluated according to the type of waste being treated. Because some contaminants may be present in relatively low concentrations with respect to other ions in waste solutions, polymers that have high binding and selectivity for the particular contaminant must be developed. 

Emission Standard A quantitative limit on the emission or discharge of a potentially toxic substance from a particular source. Tire simplest system is uniform emission standard where the same limit is placed on all emissions of a particular contaminant. 

Safe Drinking Water Act. (1974, 1986, 1996). Specifically applied to water supplied for humans consumption, this act requires the EPA to set maximum levels for contaminants in water delivered to users of public water systems. Two criteria are established for a particular contaminant the maximum containment level goal (MCGL) and the maximum contaminant level (MCL). The former, the MCLG, is the level at which no... 

Section 5.2 provides the thermodynamic basis for predicting whether or not a specific redox transformation can occur spontaneously in a given environment. The necessary redox halfreactions involving contaminants are usually well characterized because contaminants are the primary motivation for many studies of environmental systems. However, difficulties often arise in selecting the appropriate "environmental" half-reaction with which to balance the overall equation. When an environmental half-reaction cannot be identified, it is tempting to use traditional electrode potential measurements (127,128) as a generic measure of in situ redox conditions. These values (Emeas) then might be used as E°red or E°ox in Equation 14, to assess the thermodynamic potential of a particular contaminant transformation in a particular environment. However, a number of fundamental difficulties arise with this approach, so we do not recommend the procedure. 

The ability to define a reference population can be a substantial limitation. There may be insufficient information regarding the exposure history of the reference population to a particular contaminant of interest. It is important to know the range of values of a given biomarker in a normal population (NRC 1991), where normal is regarded as without occupational exposure or without observed or hypothetical environmental exposure. However, Schulte and Talaska (1995) point out that pristine populations are rare, so nonexposed populations generally have some exposure of widely varied extent. 

Classification system applies to any waste that contains radionuclides or hazardous chemicals. Waste classification system does not provide a substitute for site-specific risk assessments in developing waste acceptance criteria at particular disposal facilities or in developing criteria for remediation of particular contaminated sites. 

Because of the risk of environmental catastrophe due to the spilling of organic pollutants in water streams and increasing public concern, the establishment of limits on the suitable levels of particular contaminants in the environment exist. In this regard, adsorption methods are widely accepted as one of the successful processes to establish these limits. 

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