An operational model for managing the effect of land treatment of wastewater on groundwater quality
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Date
2001-12
Type
Conference Contribution - published
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Abstract
Some land uses, such as land treatment of wastewater, could be operated for protection of the
underlying groundwater if appropriate monitoring information were available. It is suggested that leachate
quality in the vadose zone be monitored for operational management, by means of lysimetry, in preference to
observations of groundwater quality with transport lag of months or years. Leachate data comprise values of
solute concentration and associated increments of soil drainage flux, often collected at irregular time
intervals, which are highly variable in space and time. These characteristics pose a data processing problem
for operational management analogous to the requirement for the techniques of statistical process control in
the manufacturing industries. For credible management of potential environmental effects, it is desirable that
the quality assurance technique is based on concepts of physical processes which can be openly debated in
terms of assumptions and model parameter values. This paper describes a data processing method based on
one-dimensional solute transport through the vadose zone to the groundwater surface and subsequently by
streamtubes in the groundwater to the designated target region. Smoothing of the leachate data. for real-time
comparison wilh maximum allowable values, is governed only by longitudinal dispersion within the vadose
zone and streamtubes, The concept of stream tubes without transverse dispersion addresses issues of
equitable use of allowable aquifer contamination by land use managers. The computational algorithm for
continual updating of management information is derived from the mixing cell concept for simulating dispersion. A demonstration example is presented using data on nitrate-N concentration and drainage flux of leachate
from land treatment of meat processing wastewater, for feasible values of dispersivity in the vadose
zone, and underlying aquifer.
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