COPPER, CADMIUM AND ZINC LOADING INTO LITTLE COTTONWOOD CREEK FROM TRIBUTARIES WHITE PINE FORK AND RED PINE FORK

Little Cottonwood Creek (LCC) is impaired for copper (Cu), cadmium (Cd) and zinc (Zn), and the source of impairment is unknown (DWQ, 2022). The LCC tributaries, White Pine Fork and Red Pine Fork, have legacy copper, lead and zinc (James, 1979) mine audits and dumps. Moreover, rock and stream sediment samples collected in 1981 from White Pine Fork contained traces of molybdenum, tungsten, copper, zinc and silver (Bromfield, 1981). The White Pine Fork Tributary could be a source of metal loading into LCC causing impairment. This study analyzed stream water for trace elements in LCC, White Pine Fork, and Red Pine Fork during the fall of 2023 and spring of 2024 to locate a potential source of impairment. In the fall of 2023, 13 water samples were collected and 18 water samples collected in spring of 2024. Using an ICP-OES, trace amounts of Cu were found to decrease downstream in White Pine Fork Tributary drainage from 30.7 ppb to 3.5 ppb at the confluence with LCC in the fall while the Cu in LCC increased from 0.96 ppb to 1.3 ppb after the confluence with White Pine Fork. Cd in White Pine Fork decreases downstream in the fall from 1.27 ppb to 0.23 ppb while the Cd in LCC decreased from 0.4 ppb to 0.28 ppb after the confluence with White Pine Fork. Comparison of September and May in White Pine Fork drainage show that Cu concentrations were highest during peak discharge.

In addition, in 2012 DWQ sampled water monthly in LCC above and below the White Pine Fork confluence. The highest concentrations of Cu were in May during peak discharge and gradually decreased into the fall. Further, during peak discharge Cu concentrations increased from 6.33 ppb to 8.02 ppb after the confluence with White Pine Fork while Cd and Zn decreased after the confluence. Different audits could be the development of this. These results suggest that White Pine Fork is contributing to Cu loading in LCC but not adding Cd or Zn. Higher concentrations of Cu during peak discharge are interpreted to be from higher water table levels interacting with legacy mine tunnels, however Cd and Zn were lower during peak discharge. The results of this research highlight the importance of monthly monitoring to better understand metal transport and water quality. The cause of seasonal variability needs additional study.