_REVISION - M1977208 ‎(3)‎

• Permit No: M1977208
• IBM Index Class Name: Revision
• Doc Name: RESULTS OF SOUTHDOWN INC LYONS PLANT INVESTIGATION INTO ON SITE STORAGE OF CEMENT KILN DUST
• Type & Sequence: TR1
• Media Type: D
• Archive: No

DG°i~
~I~
5~
~ Sorption is treated as linear equilibrium partitioning between aqueous and
solid phases;
• Transport of a single solute species for a given simulation is adequate.
Interactions between species are not considered.
7.3.3 Data Sources
• MYGRT only simulates groundwater flow and solute transport in the
saturated zone; unsaturated (vadose) zone transport is not considered;
• The groundwater seepage velocity remains constant over the distance of
a given simulation;
• Dispersion is represented by Fick's Law. The coefficients remain constant
for a given simulation;
The shortest distance to the property line was chosen as a conservative
~~ ~(~ assumption. The geologic units between the C-Pit and the hypothetical receptor
~u ~ ,(Gr" ~ wells were assumed to be saturated and to exhibit uniform porous medium
.S ,characteristics.
The aquifer parameters used in MYGRT are summarized in Table 7.2. Solute
transport simulations to the alluvium were conducted using a hydraulic
conductivity value of 2,000 feet per year for the weathered Niobrara Formation.
This value was determined by packer tests conducted in the Niobrara Formation
as part of an evaluation of the water storage potential of the A and C-Pits (Rocky
Mountain Consultants, 1988). The hydraulic conductivity of the Dakota
Sandstone was also assumed to be about 2,000 feet per year. A range of
reasonable hydraulic gradients, 0.1, 0.05, and 0.01, were used in the simulations
since the hydraulic gradient at the site is not known.. These values are typical of
similar hydrogeologic systems. Longitudinal and transverse dispersion
coefficients were estimated using an approach suggested by Gelhar and others
(1985). The downgradient flow direction was assumed to be due east towards
the St. Vrain Creek. The effective porosity for the weathered Niobrara and the
Dakota Sandstone was assumed to be 0.25. This value is considered typical of
weathered soils and sandstone units.
The hypothetical leachate release flux rate for the alluvium transport simulation
was estimated to be about 0.07 feet per year. The leachate flux rate was
estimated using the HELP model described in Section 7.2. A leachate flux rate of
0.03 feet per year was estimated for the Dakota Sandstone transport simulation.
The leachate flux rate used in the Dakota Sandstone simulation is about 100
times higher than the leachate flux rate (0.0004 feet per year) calculated by the
HELP model because it is the lowest value that can be simulated using MYGRT.
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