Hazardous Waste Site Management Water Quality Issues (1988) / Chapter Skim
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8. USING MODELS TO SOLVE GROUND WATER QUALITY PROBLEMS
8. USING MODELS TO SOLVE GROUND WATER QUALITY PROBLEMS
Pages 139-151
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From page 139... ...
The use of mathematical models to simulate the behavior and movement of water and toxic chemicals in water-unsaturated and saturated porous media for ground water management is a controversial issue within the scientific community as well as among users of these models. Yet many of those responsible for ground water quality protection consider models to be the most pragmatic approach to a complex problem.
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From page 140... ...
Although major advances have been made in recent years in our understanding of the behavior of chemicals in water-unsaturated and saturated porous media, research in this area is still in its infancy. This is especially true for those cases in which water-miscible organic solvents may enhance the mobility of selected organic chemicals, in which immiscible solvents exist, and in which chemical movement occurs in fractured rock and well-structured soils.
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From page 141... ...
The contamination potential may be estimated from the chemodynamic properties of the chemicals of interest. Finally, toxicological potency may be deterrn~ned by comparing the action level set by the Office of Safe Drinking Water with that measured or predicted through the use of a model.
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From page 142... ...
Comprehensive mathematical models that include procedures for describing each process influencing the movement, sorption, degradation, and transformation of a specific chemical are more complex than ranking schemes. A primary question of concern in the use of complex simulation models is how chemical processes that occur at the interstitial level of porous media are represented on a field scale.
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From page 143... ...
Of all the processes responsible for organic chemical attenuation within the unsaturated and saturated zones, only biologically mediated transformations may lead to complete degradation of organic chemicals. Although the capacity for microbial degradation in surface soils has been studied extensively, the characterization of microbial activity in the vadose zone and in aquifers has received considerable attention only recently.
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From page 144... ...
(Adrion et al., 1982~. To evaluate ground water models in a systematic and consistent manner, some institutions have developed model review, verification, and validation procedures (Morgan and Mezga, 1982; van der HeijUe et al., 19853.
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From page 145... ...
Concerns of Those Using Water Quality Models In a recent report by van der HeijUe and Park (1986) , the folTowing concerns and needs were identified by national and regional EPA staff using water quality models: ~ a limited knowledge of what types of water quality models are available; .
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From page 146... ...
is currently using models to evaluate the following source types: sanitary landfi~Is; municipal, industrial, and mining surface impoundments; underground storage tanks; septic tanks; agricultural feedIots; road de-icing chemicals; hazardous waste landfi~Is; and hazardous waste surface impoundments. OWPE is also investigating the use of ground water modeling for fund-financed CERCLA actions, with an emphasis on using simple, desktop fate and transport calculations to predict leaching to ground water from residual soils at Superfund sites.
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From page 147... ...
A typical model application for a Superfund-financed or enforcement-related remedial response action includes both site investigation to assist in problem definition and system conceptualization to identify the contamination source and to predict future contamination and health risk. Models are also being used to develop and evaluate remedial alternatives during the remedial investigation/feasibility study stages and to analyze design specifications for remedial action alternatives.
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From page 148... ...
The extent to which such efforts are conducted will depend on the purpose of the model as well as the areal extent to which the model is expected to be representative. The alternative to modeling is one of reaction through an extensive soil and ground water monitoring program, a position that is not realistic if pristine ground water conditions are the anticipated goal.
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From page 149... ...
1980. Summary of selected groundwater quality impact assessment models.
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From page 150... ...
Models used to simulate ground water contamination for improperly disposed wastes will give a very different answer than when the same models are used to simulate ground water quality changes that result from a well-managed disposal facility. The issue is not one of using models or not using models but rather the accuracy, precision, and reliability of models.
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From page 151... ...
USING MODELS 151 are nothing more than mathematical descriptions used by those who know how to use them. These same models, however, are also available for use by those who do not quite know how to use them.
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