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 Gaugush (1993) developed sampling design software specifically for water quality sampling in
reservoirs and tailwaters and the software and user's manual are included with this manual. One of the
applications of this software includes a trade off analysis based on sample size (or allocation of
constituents) versus available budget and the change in certainty associated with redistribution or
reduction of sample allocation and size. This software and an example application are provided in
Appendix 2.1B.
2.1.7 WATER QUALITY MODELS
Numerous water quality models exist for assessing rivers and reservoirs. These models provide
1, 2, and 3 dimensional descriptions of water quality processes including hydrodynamics, thermal
attenuation, chemical cycling, and biological interactions and dynamics. A partial list of models and a
brief description is provided in Table 2.1.1.
2.1.8 FATE AND TRANSPORT MODELING FOR CONTAMINANTS
The movement of contaminants in an aquatic system may occur through biological, chemical, or
physical processes. Models such as WASP4 (Ambrose et al. 1988) and CE models such as
RECOVERY and ICM/TOXI (described below) may be used to simulate transport and fate of toxic
pollutants in aquatic systems such as lakes, reservoirs, and estuaries.
The RECOVERY model is time-varying with a well-mixed, zero-dimensional water column
underlain by a vertically stratified, one-dimensional (1D) sediment column (Boyer et al. 1994).
RECOVERY contaminant fate processes include: water column and sediment sorption and decay;
water column volatilization; sediment burial and resuspension; water column settling; sediment and pore
water advection; and pore water diffusion among sediment layers and across the sediment-water
interface. RECOVERY assumes a steady-state solids balance for one class of solids where the user
specifies the suspended solids concentration and two of the three rates for burial, settling, and
resuspension, and the model computes the third rate. Sediment porosity can vary over depth but is
constant over time. RECOVERY uses an Eulerian framework with a fixed number of layers. Thus,
burial and resuspension result in vertical advection of sediment-bound and pore water contaminant
relative to the fixed surficial sediment reference. The 1D, total contaminant concentration equation for
the sediment bed is solved with a Crank-Nicholson finite difference representation.
ICM/TOXI was developed from the 3D eutrophication model, CE-QUAL-ICM (Cerco and
Cole 1995), which was originally developed during a study of Chesapeake Bay (Cerco and Cole
1993) and was modified (Wang et al. 1997) for application to trace contaminants. The contaminant
version is referred to as CE-QUAL-ICM/TOXI, or simply ICM/TOXI. The chemical kinetic
algorithms included in ICM/TOXI were based on those of the Water Quality Analysis Program,
WASP, (Ambrose, Wool and Martin 1993).
2.1-14
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