The North Fork of Clear Creek (NFCC), located near Black Hawk, Colorado, has been negatively affected by acid mine drainage (AMD) from legacy mining activity. In May 2017, a high-density sludge water treatment plant went into operation to treat multiple point sources of AMD. The water treatment plant has significantly lowered the instream metal concentrations.  Dissolved iron was  99% lower in January 2018 as compared to March 2017.  Instream levels of both dissolved copper and zinc initially decreased, but both metals partially rebounded during Autumn base flow. This observation cannot be fully explained by a decrease in NFCC discharge. Dissolved zinc levels decreased by 57% in the first ten months of remediation, while dissolved copper only decreased by 5%, in the same time frame. These levels of dissolved copper and zinc are of concern for the current and future health of the stream, post-remediation. The Windermere Humic Aqueous Model (WHAM7) was used to examine the geochemical speciation of the metal mixtures in NFCC post-remediation stream water. In separate computations made with dissolved iron, aluminum, or manganese removed, only dissolved manganese had a significant effect on the speciation of copper and zinc. The removal of manganese caused a decrease in the free ion while increasing the amount of metal bound to both fluvic and humic acid. Speciation modeling may provide evaluation of the effects of competitive binding reactions that will have potential consequences for complete recovery of the stream.<br/>

Geochemical monitoring and modeling of water chemistry changes to North Fork of Clear Creek following remediation of acid mine drainage inputs

2019 Spring National Meeting

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