WSP07478

• File Number: 8272.600.60
• Description: Colorado River Basin Salinity Control Program - Basin Member State Info - Utah
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 3/1/1982
• Title: Salt Uptake in Natural Channels Traversing Mancos Shales in the Price River Basin - Utah
• Water Supply Pro - Doc Type: Report/Study

Table 4,9, Comparison of mineral dissolution
rates with time and grain size.
t Level of 800
Comparison Statistic df Significance
;-:-
~-second comparisons /
o 114 vs, 1/10 -0,195 6 NS U /
-.:1 H~ vs. 1120 -2.856 6 * 01.() 600 /
c.o 114 vs. 1/60 -6.173 6 ** N /
1/10 V8. 1120 -3.040 6 * '" {
/110 VS. 1160 -6.350 6 ** e
#20 VS. 1160 -4.132 6 ** ~
.
0
72-hour comparisons ]400
114 vs. 1/10 0.275 6 NS
114 vs. 1/20 -1. 437 6 NS r::
114 vs. 1160 -1. 804 6 NS ....
1110 vs. 1/20 -1. 770 6 NS :>
....
1110 vs. 1160 -1. 925 6 NS Eo<
u
1120 vs. 1160 -1.172 6 NS "
@ 200
0
Null Hypothesis Ho: " " "n u
A

NS - No significant difference between sample means at
the 0.95 level.
* - Significantly different at the 0.95 level.
** - Significantly different at the 0.99 level.

I
,
~

A test was de'signed to estimate the
effect of the number of wet/dry cycles on
salt release rates for various shale size
fractions. Shale samples from the four sites
were crushed and separated into four size
fractions, for a total of 16 individual
samples. From each sample, 50 grams of soil
were saturated with 100 ml of distilled
water and placed within a Brinkmann Roto-
evaporator (rotovap) and water bath. By this
method, numerous wet/dry cycles are possible
within a I-day period. Because salts are
removed in a 5 ml aliquot, a 5 percent
adjustment was assumed to be necessary after
each successive wet/dry cycle. The con-
ductivity values were linearly adjusted and
corrected to 25'C. The results are presented
in Appendix C (Table C.2). The test was
terminated after 10 samples were evaluated.

Figure 4.17 illustrates the results, An
increase in dissolution causing greater
solution conductivity after the first
dry ing cycle was observed for all of the
samples. The increase ranged from 5 percent
to 43 percent with a mean of 21 percent and
standard deviation of 12 percent. Following
the second drying cycle, only three of the 10
samples had an increase in conductivity. The
variation ranged from a minus 8 percent to a
positive 10 percent, with a mean of a minus 2
percent and a standard deviation of 6 per-
cent. Further wet/dry cycles generally
brought additional conductivity declines.

The unexpected decline in conductivity
after just one cycle may be due to experi-
mental error or to characteristics of
the rotovap. During the drying, vigorous

-E-)"'"

-

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..........f)-

o

o Site 2, Fraction

-,
"

- f-) Site 1, Fraction

o

2 3
CYCLE NUMBER

4

5

Figure 4.17. Illustrative effect of wetting
and drying cycles on conductivity.

boiling of the slurry occurred, and the
larger aggregates were rapidly eroded. Thus,
it is possible that the mineral dissolution
was accelerated to the point that most
of the salts were released from the shale
samples after only one cycle. Variation in
the conductivity of the following cycles
might have been caused by irregular mass loss
.during drying. Solids splashed into the
condensor unit during evaporation, and no
adjustment was made for their mass.

The rate of salt release from a shale
surface would be expected to be rapid at
first and then to decline as the supply of
surface salt diminished, leaving the much
slower release of salts entrained beneath the
surface of the relatively impermeable shale.
. Under steady-state flow conditions, the salts
would be released by diffusion-controlled
dissolution from the submerged shale. Oven-
drying of the sample (sun drying in the
field) increases the surface area of the
shale as water of hydration is lost, frac-
turing develops, and diffusion inhibiting
boundary layers are disrupted.

Macrochannel induced
streamflow studies

One problem in measuring salt pickup
from various salinity sources is that of

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