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<br />London Mountain Clean Up <br />July 2025 <br /> <br /> <br />G2-2 <br />Colorado DRMS Station DRMS-L-5 - South Mosquito Creek midway <br />through London Mine property <br />• Location: 39.2725028°N, -106.1452386°W <br />• Agency: Colorado Division of Reclamation, Mining and Safety <br />• Station Type: Water quality monitoring (on London Mine property) <br />• Data Period: 2011-2012 (3 sampling events) <br />• Sampling Dates: June 17, 2011; September 30, 2011; May 11, 2012 <br /> <br />3. Data Analysis Summary <br />Temporal Trends <br />The data in tables 1-4 reveal persistent contamination patterns over time, with CDPHE <br />monitoring (1998-1999) occurring during active mining operations and DRMS monitoring (2011- <br />2012) documenting conditions during early remediation efforts. The 10+ year data gap between <br />monitoring periods limits comprehensive trend assessment; however, the persistence of <br />detectable metals concentrations across different time periods demonstrates ongoing <br />contamination impacts requiring remediation. Zinc concentrations show consistency between <br />time periods (0.012-0.049 mg/L downstream in 1998-1999 vs. 0.050-0.117 mg/L on-site in 2011- <br />2012), indicating persistent contamination sources. pH values have remained relatively stable <br />and near neutral (6.34-8.1), suggesting the primary impact is metals mobilization rather than <br />acid mine drainage. <br />USGS physical parameter data spanning 1998-present shows typical high elevation, snowmelt- <br />dominated stream characteristics with temperature ranges of 0.0-14.5°C and highly variable <br />flow conditions (0.09-88 cfs), reflecting the pronounced seasonal hydrology of the Colorado <br />Rockies. The conductivity range of 105-323 µS/cm indicates moderate mineralization consistent <br />with mining-influenced watersheds. <br />The extensive USGS flow record (0.09-88 cfs range) indicates that metals concentrations likely <br />vary inversely with discharge, with higher concentrations during low-flow periods and dilution <br />effects during high-flow snowmelt periods. This relationship suggests that remediation benefits <br />will be most apparent during critical low-flow periods when aquatic life is most vulnerable to <br />metals exposure. <br />Exceedances of Water Quality Standards <br />The detection of zinc (up to 0.117 mg/L), cadmium (up to 0.0003 mg/L), and lead (up to 0.010 <br />mg/L) at measurable concentrations supports the 303(d) impairment listing for these