Levels of a potential human carcinogen, 1,4-dioxane, have mostly declined in wells in the commercial and residential areas of the Tucson International Airport Area Superfund Site during 2002-2017, according to a new map published by the U.S. Geological Survey.
Industrial activities causing extensive groundwater contamination led to the listing of the Tucson International Airport Area, or the TIAA, as a Superfund Site in 1983. Early groundwater investigations identified volatile organic compounds, including chlorinated solvents, in wells at the site, and cleanup activities began in the late 1980s. In 2002, the compound 1,4-dioxane was discovered in wells in the area and has since been detected in measurable concentrations throughout the site. The U.S. Environmental Protection Agency classifies 1,4-dioxane as a likely human carcinogen. Understanding the current status and trends through time of 1,4-dioxane in groundwater in the area can help the affected community and water managers understand the progress of cleanup activities.
The USGS compiled 1,4-dioxane concentration data from available sources including the City of Tucson Water Department, Pima County Department of Environmental Quality, the Tucson International Airport Authority and wells sampled by the USGS. Concentration data between 2002 and mid-2017 from 63 wells were plotted to show how concentrations have changed through time.
“While computer simulations are valuable to estimate future groundwater conditions, there is really nothing like actual samples from wells for understanding current conditions as well as how those conditions have changed through time,” said Fred Tillman, a USGS scientist and the lead author of the study. “These results indicate that, although concentrations in a few wells in the northern part of the study area have increased somewhat through time, cleanup activities are having a positive effect on 1,4-dioxane concentrations in groundwater in most of the TIAA area, particularly in the southern part of the site.”
The map and accompanying charts provide an easy comparison of concentration levels between wells and through time. Well locations are plotted on an aerial photo of the TIAA Superfund Site using colored symbols to differentiate between monitoring, supply, former supply and private wells. Concentration charts were placed as closely as possible to well locations on the map, with colored arrows linking the chart to the well location.
The development of this map and annual USGS groundwater sampling was supported by the U.S. Air Force Civil Engineer Center to provide unbiased information to regulators, water managers and the general public on 1,4-dioxane groundwater contamination in the area.
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