To remediate or not? Source identification in an acid mine drainage stream, Warden Gulch, Colorado

A synoptic water quality study was implemented in Warden Gulch, a headwater stream affected by metals that are contributed by both natural and mining-impacted sources. Warden Gulch is a tributary to Peru Creek (Colorado, USA), where emplacement of a mine tunnel bulkhead and other remedial actions have improved water quality upstream of Warden Gulch. The goal of this study was to identify individual source contributions to Warden Gulch and determine if additional remedial actions were warranted. To this end, trace metal loading was quantified from various sources including an actively draining mine. Although highly concentrated waste streams from mining-impacted sites degrade water quality, natural contributions from unmined areas within the Warden Gulch watershed are the dominant sources of metal loading. Further, some mining-impacted sources are associated with diffuse groundwater inflows that may not be amenable to clean up, due to the diffuse nature of the sources and the associated cost. Mining-impacted sources that are amenable to clean up may therefore represent a small portion of the overall metal loading to Warden Gulch. Remedial measures directed at these sources may not substantially improve the water quality of Peru Creek and the larger Snake River watershed.