Hazardous Materials in the Hydrologic Environment The Role of Research by the U.S. Geological Survey (1996) / Chapter Skim
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3 Characterization: Processes and Methods for Improving Understanding
3 Characterization: Processes and Methods for Improving Understanding
Pages 23-36
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From page 23... ...
Since the industrial revolution, human activities have served to introduce both anthropogenic and natural materials to the environment in unnatural ways. For example, certain mining operations have produced widespread contamination of surface waters and stream sediments with elevated levels of metals.
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From page 24... ...
reported elevated activities of radium and radon in ground waters of the Piedmont Plateau and the Blue Ridge Mountains. Other toxic substances known to occur naturally at levels exceeding drinking water standards include arsenic, fluoride, lead, strontium, and selenium (Hem, 1992~.
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From page 25... ...
The geology and hydrology define the transport characteristics of the system. Dissolved anions and cations, mineral surfaces, and natural organic matter all represent chemical "reagents" that react in distinctive ways with hazardous waste chemicals.
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From page 26... ...
Indeed, a remediation strategy involving no additional active measures is being considered for some contaminated sites where the processes of natural attenuation and biodegradation are acting to remediate the site. This new approach to cleanup of hazardous waste sites is highly dependent on a good characterization of the environment and a sufficient understanding of these processes.
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From page 27... ...
In particular, more has been learned about depositional models, diagenetic processes Hat alter geologic materials, subsurface heterogeneities, and the hydrology of ground waters that flow through complex subsurface matrices. Additional advances are needed to achieve a better understanding of the heterogeneous nature of the subsurface, however.
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From page 28... ...
True multiphase capabilities incorporating complex patterns of gas flow and mass removal have been developed to support theoretical investigation of remedial approaches such as gas sparging or soil venting. Mass transfer between NAPEs and water and between aqueous and gas phases is being studied to improve the knowledge of contaminant migration through the subsurface (Anderson et al, 1992; Miller et al., 1990; Whelan et al., 1994~.
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From page 29... ...
has extended the discrete modeling approach to accommodate complex fracture matrix coupling in both flow and contaminant transport. Most field and laboratory studies related to fractured rock problems continue to be motivated by the need to assess the implication of fracturing in relation to waste storage and contaminant transport.
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From page 30... ...
Energy production, manufacturing, agricultural production, mining, and waste treatment all are performed in close proximity to surface waters, and all represent potential sources of contamination. In addition, surface waters receive both ground water and atmospheric inputs of contaminants.
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From page 31... ...
Indirect information about the subsurface geology also can be obtained using both surface and downhole geophysical tools. Existing methods for character~zing the hydrology of a site include the installation of wells and piezometers from which aquifer tests and tracer tests can be performed.
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From page 32... ...
Other innovative drilling technologies include sonic drilling, which minimizes hazardous waste materials extracted during drilling while maintaining the quality of He core that can be obtained from the subsurface (Barrow, 1994~. Horizontal drilling has been modified for drilling at hazardous waste sites, enhancing access to the subsurface and promoting characterization and remediation of sites otherwise inaccessible, such as under large buildings or under landfills (Kaback et al., 1989~.
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From page 33... ...
can be used to resolve anthropogenic inputs from those derived from natural sources. Characterization of natural organic matter is needed to evaluate its ability to form complexes with toxic metals, form covalent compounds wig pesticides, participate in dissolution/precipitation reactions of minerals, serve as a carbon source for bacteria, and form chlorination byproducts during drinking water chlorination (Aiken and Cotsaris, 1995~.
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From page 34... ...
methods to obtain fundamental information regarding natural organic matter functional groups are currently under development Thorn et al., 1992~. Capillary electrophoresis, which separates organic molecules according to molecular charge and hydrodynamic radius, has been shown to resolve natural organic matter sub-fractions (Garrison et al., 1995~.
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From page 35... ...
A major research need with respect to characterizing biological processes in the subsurface is to improve the fundamental understanding of microbial populations in context with the heterogeneous physical and chemical conditions of the subsurface. Questions remain as to how microbial populations develop and are maintained in aquifers through periods of environmental stress caused by insufficient substrates, nutrients, moisture, or other undesirable conditions.
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From page 36... ...
· Sediment-water interactions, such as contaminant entrainment in sediments by particle settling, resuspension by storms, and release caused by chemical and biological processes within the sediment. · Direct photolysis of contaminants in surface waters, and the reaction of contaminants wig reactive species generated through He photolysis of organic maker and other natural solutes.
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