IMPACTS OF THE SEPTEMBER 2013 COLORADO FRONT RANGE FLOODING ON THE BUILT AND NATURAL ENVIRONMENTS, AND IMPLICATIONS FOR ENVIRONMENTAL HEALTH

From September 9-15, 2013, northern Colorado Front Range foothills and nearby cities experienced rainfall locally exceeding 20 inches (51 cm), close to their mean annual precipitation. Extreme runoff and flooding occurred along the South Platte River basin, from foothill canyons to more than 170 miles (275 km) downstream. The flooding caused extensive physical damage to the natural environment, roads, bridges, houses, other buildings, historical mines, storage ponds, irrigation ditches, urban infrastructure (e.g., wastewater treatment plants, sewer lines), oil/natural gas wells and storage tanks, and agricultural fields. There were concerns of potential environmental pollution and health hazards. For two weeks starting September 17^th, we sampled flood sediment deposits and debris from 63 sites over much of the affected area. We are applying numerous analytical methods to evaluate the levels and forms of inorganic, organic, and microbial contaminants, and whether these contaminants may have posed chronic or acute, environmental or human health hazards. Human uptake of contaminants could come from dermal absorption or hand-to-mouth contact by children playing in the muds, or from inhalation of dusts from dried mud deposits. Results to date suggest that the large volumes of geologic-sourced materials transported by the floodwaters helped dilute many sediment-borne inorganic contaminants. Pb, Hg, Cu, and Zn concentrations in most samples exceeded average US sediment concentrations, particularly in foothill samples from near historical mines, but also in downstream samples. Where elevated, these concentrations did not exceed human health soil screening levels but often exceeded avian or mammalian ecological soil screening levels. Microscopic pulverized asphalt particles from damaged roads were seen in samples from throughout the area. Based on observations made during the sampling and by comparing our photographs to pre-flood online imagery, we documented flood processes, impacts on the natural and built environments, and key vulnerabilities in the built environment. These results illustrate the need for coordinated interdisciplinary responses that rapidly assess the collective physical, environmental, ecological, health, and societal impacts of floods and other disasters.