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<br />1791 <br /> <br /> <br />Figure 6 near bere. Median seasonal dissolved and total-recoverable cadmium concentrations <br />in tbe upper Arkansas River, April 1990-Marcb 1993 <br /> <br />Figure 7 near bere. Median percentage of dissolved cadmium in tbe upper <br />Arkansas River, April 1990-Marcb 1993 <br /> <br />Cadmium concentrations decreased significantly at several sites after the mine-drainage treatment plants came <br /> <br />on line at the LMDT and Yak Twmel (table 4). The median dissolved-cadmium concenrration in the effluent from <br /> <br />the LMDT and the Yak Twmel (via California Gulch) decreased from 12 to 03 ~gIL and from 48 to 5.2 !!g!L, respec- <br /> <br />lively (table 4). Post-treatment (April 1992-March 1993) dissolved-<:admium concentrations decreased significantly <br /> <br />(p < 0.05) at Leadville, Malta, Granite, Buena Vista, Nathrop, and Parkdale (table 4). Total-recoverable cadmium <br /> <br />concentrations decreased significantly during post-treatment at the LMDT, California Gulcb, and at the main-stem <br /> <br />sites Leadville and Malta (table 4). There were more incidences of significant decreases in dissolved cadmium than <br /> <br />in total-recoverable cadmium at the Arkansas River sites. The fewer number of significant decreases in total-recov- <br /> <br />eable cadmium than in dissolved cadmium is probably a statistical anomaly attributable to the large frequency of <br /> <br /> <br />eccurrence of total-recoverable cadmium concentrations that were equal to or less than the detection limit (I !!g!L) <br /> <br />during the pre-treatment and post-treatment periods. <br /> <br />Table 4 near bere. Results of Wilcoxon rank-sum test (I-tailed) of pre-treatment (April 1990-Marcb 1992) <br />and post-treatment (April 1992-Marcb 1993) instantaneous streamllow and cadmium concentrations in <br />the Arkansas River. <br /> <br />During tbe study period, the incidence of dissolved-cadmium concentrations tbat exceeded stream water-qual- <br /> <br />iry standards was relatively small (table 5). Only one sample exceeded the acute standard (Leadville), while two <br /> <br />samples at Leadville, three samples at Grnnite and two at Buena Vista exceeded the chronic standard (table 5). All <br /> <br />exceedances occurred during the pre-treatment period (ApriI1990-Marcb 1992). There was not any obvious sea- <br /> <br />sonal pattern in the incidence of these water-quality standard exceedances. <br /> <br />.~~il~t.~.AII n'!t!l'~fl <br />Table 5 Dear bere. Number of samples that exceeded tbe aculi' .".,,, . ~"" 1MR1I~~ Ul't~ . <br />water-quality standards in tbe upper Arkansas River, April 199 U9fo Revision <br />DO NOT QUOTEI:AS~ <br />Pending Approval by Director, <br />U.S. G50:09;col Survey <br /> <br />21 <br /> <br /> <br />, <br />