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<br />
<br />Cadmium. - Hem [3] notes that the concentrations
<br />of cadmium in water is small, with most studies [7,9],
<br />reporting concentrations generally below 0.010 mg/I,
<br />which is the upper limit of cadmium recommended by
<br />the U.S.PHS5. The results of this study are consistent
<br />with these reported results. Inspection of the data
<br />tables indicates that most samples yielded cadmium
<br />values below the detectable limit of about 0.001 mg/1.
<br />The highest value obtained in the dissolved fraction was
<br />a spurious 0.049 mg/I obtained at site B-3 metre in
<br />August 1975. The highest monthly average was 0.011
<br />:t 0.001 mg/I obtained in May 1975. This is above the
<br />maximum permissible limit for drinking water [14].
<br />These values were not, however, characteristic of the
<br />reservoir at any other time. The average for the sus-
<br />pended cadmium was below detectable limits. Kopp
<br />and Kroner [9] reported no instances of detection of
<br />cadmium in the suspended fraction and detected cad-
<br />mium in only 3 percent of the dissolved samples. These
<br />detectable instances provided a mean of 0.0095 mg/1.
<br />
<br />Cadmium was detected in nearly all the sediments,
<br />averaging 4.2 :t 1.4 mg/I in the pre-impoundment flood
<br />plain and 4.4 :t 1.1 mg/I in the reservoir. Again, how-
<br />ever, site F yielded sediments with a slightly higher
<br />cadmium content of 6.1 mg/I, which points to possible
<br />cadmium loading in the sediments in that area.
<br />
<br />Mercury, - Mercury like lead, cadmium, and arsenic
<br />was included in this study because of its potential del-
<br />eterious effect on publ ic health. Hem [3] noted that
<br />very few natural waters contain detectable concentra-
<br />tions of mercury. That statement was made before the
<br />development and widespread use of the flameless AA
<br />method for the analysis of mercury. In this study mer-
<br />cury levels as low as 0.01 /1g/1 were detected in labora-
<br />tory analyses. The highest concentration measured was
<br />0.54/1g/1 in August 1974, at the inlet of the reservoir.
<br />Approximately half the samples analyzed for dissolved
<br />mercury showed detectable levels. Most of those show-
<br />ing detectable levels were below 1 /1g/1. The mean for
<br />all samples collected in the pool was 0.02 :t 0,01 /1g/1
<br />and 0.02 :!; 0.3 /1g/l, respectively, for the two sampling
<br />years. The reservoir inlet averaged higher during the
<br />first year at 0.01 :t 0.02 /1g/1 and lower in the second
<br />year at less than detectable limits. The high average
<br />month was December 1975, at 0,07 :!; 0.11 /1g/1 and
<br />low average was less than detectable limits which oc-
<br />curred during several months. No discernible trends
<br />
<br />5 "Drinking Water Standards," Title 42-Public Health;
<br />Chapter 1-Public Health Service, Dept. of Health, Edu-
<br />cation and Welfare; Part 72, Interstate Quarantine, Fed-
<br />eral Register 2152, March 6, 1962.
<br />
<br />were noted. Durum, et al. 10] detected mercury in
<br />only 7 percent of their sa pies (detectable limit, 0.1
<br />/1g/I). The highest value 0 tained was 4.3 /1g/1. All
<br />three Arkansas River samplin sites yield concentrations
<br />< 0.1 /1g/1.
<br />
<br />Silver. - Solubility relations ips indicate that silver con-
<br />centrations in natural water hould be between 0.0001
<br />and 10 mg/l [3]. Data on ublic water supplies show
<br />a median concentration of .0002 mg/l and in rivers
<br />about 0.0001 mg/1. The dat from this study appear to
<br />be in this range, varying fr m nondetectable concen-
<br />trations < 0.001 mg/I (actu Iy about 0.0002 mg/l) for
<br />most samples up to a maxim m concentration of 0.009
<br />mg/I at site E-surface in Jun 1974. There were many
<br />more samples that had dete table levels of silver than
<br />appear in the computer ge erated tables because the
<br />program was designed to pint 0.0 for any value that
<br />was fed in as < 0.001, The ilver data could be statis-
<br />tically refined.
<br />
<br />Arsenic. - Kopp and Kro er [9] detected levels of
<br />arsenic in 5.5 percent of th samples collected in lakes
<br />and rivers nationwide over 5-year period at a 0.01
<br />mg/I detection level. Duru ,et al. [10] reported that
<br />79 percent of 727 samples ollected nationwide con-
<br />tained less than 0.010 mg/. At the Arkansas River
<br />Pueblo waterworks site, ar enic was not detectable,
<br />Only 2 percent of the sampls had more than the 0.050
<br />mg/l U.S.PHS maximum per issible limit. In this study,
<br />samples were not as frequen Iy analyzed for arsenic as
<br />for the other parameter; ho ever, the results indicate
<br />that in most cases the disso ved arsenic concentration
<br />was less than the detectable limit of 0.003 mg/1. In the
<br />first year of the sampling, arsenic averaged 0.001 :t
<br />0.001 mg/I and less than dete table limits in the second.
<br />The highest single value obta ned was 0.021 mg/I at the
<br />C bottom site in October 19 4.
<br />
<br />Sediment Chemistry
<br />
<br />Additional statistical analy s of the data in table 4
<br />and more sediment samples nd analyses in the future
<br />will be required before final conclusions can be drawn
<br />regarding which parameters nd how much of each are
<br />being unloaded in Pueblo R servoir as basin sediments.
<br />The data generated to date show definite increases in
<br />iron, manganese, and zinc i the reservoir sediments of
<br />the variable inlet sites (E, F and G) compared to pre-
<br />impoundment flood-plain se iments. In addition, mag-
<br />nesium, copper, cadmium, a d lead concentrations ap-
<br />pear to be increasing.
<br />
<br />Recent inlet sediments (site E, F, and G, table 4) of
<br />Pueblo Reservoir contained copper, iron, manganese,
<br />
<br />30
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