MONITORING THE EFFECTS OF ACID MINE DRAINAGE IN THE LAKE FORK WATERSHED NEAR LEADVILLE, CO

Poor water quality in the Lake Fork of the Arkansas watershed dates back to the late 19^th and early 20^th centuries, when the Sugar Loaf Mining District just west of Leadville, CO was heavily mined for Ag, Au, and Pb. Today, mine waste piles, flowing adits and tunnels, and abandoned mine shafts contribute acid mine drainage (AMD) and heavy metals to streams in the watershed, leaving many devoid of aquatic life. In 2000, the Lake Fork Watershed Working Group (LFWWG), a community stakeholder group involving federal and state agencies, non-profit organizations, and private landowners, was established to facilitate voluntary remediation projects in the watershed with the primary goal of improving water quality and aquatic habitat.

For the past two years, GeoCorps participants have supported the LFWWG through the Bureau of Land Management, assisting with water quality monitoring, data analysis, and reporting. In 2013, primary monitoring efforts focused on the Lake Fork of the Arkansas, Little Frying Pan Gulch, and Colorado Gulch. The latter two gulches contribute significantly to Al, Cd, Cu, Fe, Mn, and Zn concentrations in the Lake Fork during periods of high flow. To date, the only remediation project completed in Little Frying Pan Gulch (a tributary to Colorado Gulch) is the relocation and capping of the Tiger Mine waste piles. Despite pile removal, high flow monitoring results indicate that water quality remains poor in Little Frying Pan Gulch, with pH values as low as 2.2 and dissolved Fe and Al concentrations of over 250 ppm. Stream reach water quality results suggest that the Tiger Mine Adit is the major contributor of metals and AMD to the east fork of Little Frying Pan Gulch. During periods of high flow, the combined contributions of the east and west forks of Little Frying Pan Gulch lower the pH of the higher-volume Colorado Gulch from 7.16 above the confluence to 5.15 below the confluence. The upcoming installation of limestone channels and settling ponds at the Tiger Mine Adit aims to increase pH and decrease heavy metal concentrations, improving water quality in both Little Frying Pan and Colorado Gulches. Future work in the area will focus on relocating other significant mine waste piles in the west fork of Little Frying Pan Gulch, and continuing to monitor water quality to measure the effectiveness of these remediation efforts.