MULTI-SCALE SCREENING TECHNIQUES FOR ASSESSING LEGACY MINE LAND SITES IN COLORADO

The western United States has thousands of legacy mine land (LML) sites that negatively affect water quality and ecosystems. Remediation of LML sites is costly and effectiveness can vary depending on individual site characteristics. Prioritization for remediation is often based on geopolitical, rather than scientific, factors which can lead to expensive and/or ineffective efforts. We aim to develop screening techniques that identify LML-impacted watersheds with metal concentrations slightly above aquatic life standard that either have low natural background metal concentrations or well-defined contaminant inputs where targeted remediation could improve water quality and ecosystem health. Our approach has two parts: 1) use GIS to integrate regional geological and geochemical datasets with known mine features in the western U.S. (USGS USMIN database) and satellite data showing hydrothermal alteration (ASTER) to identify sites fitting the criteria; and 2) select candidate sites for field investigation to further characterize sources, natural or mine-related, and extent of metal contamination. Based on results from part 1, five watersheds in central Colorado were selected for preliminary investigation; 1) McNasser Creek, 2) upper South Fork Lake Creek, 3) Saints John Creek, 4) Hall Valley, and 5) Quartz Creek. Possible sources were identified, and surface water, groundwater, and sediment samples were collected throughout each watershed. Water and sediment chemistry in McNasser Creek indicate that, although there is a source of elevated Cu and Zn, natural attenuation mitigates this source on the watershed scale. Upper South Fork Lake Creek shows no significant metal contributions based on our sampling. Saints John Creek has elevated Cu and Zn in water and sediment despite extensive remediation efforts. The Hall Valley has elevated Zn in surface water at the Missouri Mine adit and elevated Cu and Zn in corresponding sediment samples. Spring water discharging downslope, near the creek, has elevated dissolved Cu and Zn. Quartz Creek water and sediment has elevated Cu and Zn at the Bon Ton Mine adit, and downstream surface- and groundwater sites. Preliminary results show that both Hall Valley and Quartz Creek could potentially benefit from targeted remediation efforts and warrant further study.