FLOOD10381

• County: Pueblo
• Stream Name: Arkansas River
• Basin: Arkansas
• Title: Effects of Impoundment on Water and Sediment in the Arkansas River at Pueblo Reservoir
• Date: 5/1/1977
• Floodplain - Doc Type: Educational/Technical/Reference Information

Cobalt. - Hem [3] noted that concentrations of cobalt
in natural waters are probably limited by factors other
than simple solubility relationships. One mechanism
suggested is control of cobalt concentrations through
absorption by colloidal particles of oxides and hydrox-
ides of iron, manganese, and other metals. The upper
limit of solubility of Co is about 0.005 mg/l [10] in
river waters.

Durum, et al. [10] reported in their study of the sur-
face waters of the United States that cobalt was most
commonly below 0.001 mg/l, but 37 percent of the
samples were in a range from 0.001 to 0.005 mg/1.
Kopp and Kroner [9] reported dissolved cobalt in only
3 percent of their samples with a mean concentration
of 0.017 mg/1. Durum, et al. [10] reported that the
Arkansas River for a Pueblo waterworks sample was
below 0.001 mg/1. In this study, the reservoir yielded
averages of 0.002 :t 0.001 mg/I and < 0.001 mg/l,
respectively,during the two sampling years. The highest
single concentration recorded was 0.030 mg/I recorded
in August 1974, at site B - 9 metres depth. The high-
est average month was July 1974, 0.006:t 0.006 mg/1.
No discernible trends were noted.

Nickel. - The behavior of nickel in natural water has
been reported to be similar to that of cobalt [3]. The
median concentration in North American rivers reported
by Durum and Haffty [8] was 0.010 mg/1. A median
value of less than 0.0027 mg/I is reported by Durfor
and Becker [7] for 100 water supplies in the United
States. Kopp and Kroner [9] report detecting dis-
solved nickel in 16 percent of their samples with a mean
of 0.019 mg/I and suspended nickel in 3 percent of
samples collected having a mean of 0.029 mg/1. In this
study a mean of 0.002 :t 0.001 mg/I was obtained for
both sampling years. The high average month was De-
cember 1975, with 0.006 :t 0.002 mg/I dissolved N i.
Nickel in the suspended fractions averaged less than
detectable limits. Dissolved nickel levels were generally
near the detectable I imit, resulting in points that were
fairly widely scattered. However, it does appear in plot-
ting the first year data using the inlet, outlet, and pool
averages for each month that there is a classic seasonal
effect. It also appears that the inlet values during the
first year of the study were generally higher than the
pool average and the outlet. This was not, however,
reflected in the spatial plots for the months selected.
These plots, in fact, seem to indicate that the nickel
was lower during those months.

Lead. - Garrels and Christ [17] indicate that the solu-
bility of Pb+2 in natural water is probably controlled
by the solubility of PbC03 and PbS04, both of which
are relatively insoluble. Lead concentration in natural
sources would, therefore, be limited by the solubilities

to about 0.002 mg/1. Lead, however, is widespread par-
ticularly from use as an antiknock additive in gasoline
engines and subsequent dispersal through exhaust [3] ,
and is also found in the mine drainage from the Lead-
ville area [19]. Durfor and Becker [7] reported a me-
dian value of about 0,004 mg/I for public water sup-
plies, while Durum and Haffty [8] reported a median
value of 0.004 mg/I for North American rivers. Durum,
et al. [10] reported lead detected in 63 percent of the
samples in concentrations ranging from 0.001 to 0.050
mg/1. The reports noted that few samples were collected
containing greater than 0.050 mg/1. Lead was reported
as occurring widely in a range from 0.006 to 0.050
mg/1. A single sample collected from the Arkansas River
near the waterworks was reported to contain 0.002
mg/I lead. Kopp and Kroner [9] reported rather high
mean values of 0.023 mg/I for 19 percent of the sam-
ples in which dissolved lead was detected and a mean
of 0.120 mg/I in the 3 percent of the samples in which
suspended lead was detected.

The average dissolved lead level reported for the reser-
voir pool during the 1974-75 sampling year was 0.001
:t 0.001 mg/I and for the second year was less than the
detectable limit. A majority of samples collected dur-
ing the entire study reported in appendices A and B
were at less than detectable limits. The highest reservoir
pool average was 0.003 :t 0.001 mg/I in November
1974. In August 1974, a single sample collected at the
bottom of site A contained 0.022 mg/I Pb. Because of
the preponderence of samples near or below detectable
limits, no discernible trends were observed.

Lead levels in the Arkansas River at the two sites sam-
pled during the pre-impoundment study were 0.006 :t
0.010 mg/1. This average included two unusually high
values of 0.041 and 0.017 mg/I wh ich, if deleted from
the average, gives a mean of 0.003 :t 0.003 mg/1. The
reservoir inlet yielded an average of 0.001 :t 0.001 mg/I
lead for each year of the present study. The lead con-
centration due to suspended matter in all cases was not
detectable.

Lead was considered to be one of the more important
metals to monitor because of the potential for lead
loading into reservoir from the Leadville mining district
[19] and from the operating of gasoline powered boats
on the reservoir. No such effect was observed during this
study. An examination of the dissolved and suspended
data 0 n I y, however, revealed that the average lead
composition of the pre-impoundment sediments (table
4) was 65:t 34 mg/I, while the average fOf the reservoir
at sites B; C, D, E, F, and G,is 10Q:t 68 mg/I with 157
mg/I at site F near the inlet and 209 mg/l at si;lf.p.
Thiswould seem to point toward some lead enrichment
of the sediments, particularly near the inlet of \he
reservoir.

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