1997-11-13_REVISION - M1977493 (50)

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Sulfate The water quality standard for sulfate is 250 mg/L. Sulfate was higher than 250 mg/L in the first three sampling events, however, has been below the water quality standard for all sampling events since Sampling Event 3. Other Anal Analytes that remained below the stream water quality standards throughout the sampling investigation are arsenic (tr), boron (d), cadmium (d), calcium (d), chromium (d), chromium (tr), chromium VI and III, copper (d), lead (d), magnesium (d), mercury (tr), nickel (d), selenium (tr), silver (d), zinc (d), TSS (residue, nonfilterable), fecal coliform and alkalinity. For many of the analytes listed above, the water quality standard is dependent on the hardness of the water. For these analytes, the mean hardness (as CaCO3) concentration for that sampling event was used to calculate the water quality standard. Although a regression analysis is recommended for calculation of an appropriate hardness value, due to the small number of samples available for this investigation a regression analysis was not performed. In lieu of a regression analysis, the mean hardness concentration for each individual sampling event was used to calculate the water quality criteria. Analytes for which the water quality standards are hardness dependent are: cadmium, copper, lead, nickel, silver and zinc. As with the other analytes, hardness as CaCO3 decreased throughout the sampling investigation. • Hardness values for Sampling Events 1 and 2 ranged from 1280 to 1410 mg/L. By Sampling Event 3 (May 20, 1997) hardness had decreased significantly and ranged from 484 to 534 mg/L. Hardness continued to decrease through Sampling Event 7 where it appears to have stabilized. The mean hardness concentrations for Sampling Events 7, 8, 9 and 10, are 86, 87, 100 and 96 mg/L, respectively. As hardness decreases, the water quality standards for the above analytes also decrease. One sample in Sampling Event 10, indicated a copper (d) concentration that was slightly higher than the water quality criteria of 0.01 mg/L. A concentration of 0.023 mg/L was indicated in one sample. This was the only sample out of the 40 samples analyzed which indicated a concentration higher than the standard for copper. Fecal Coliform Fecal coliform was analyzed for in Sampling Events 3, 4 and 5. Fecal coliform was not detected in any of the samples. At the request of the Division of Minerals and Geology for the State of Colorado, aluminum was added to the list of analytes for Sampling Event 7 and will be analyzed throughout the remainder of the investigation. For the most recent sampling event (July 10, 1997), aluminum (total recoverable and dissolved), was not detected. DAPROJECTS\6102-001\SWSUM3.DOC[8-Sep-97] 4