Detection of the organic solvent perchloroethylene (PCE) in a shallow public-supply well in 1991 and exposure of workers in 1993 to solvent vapors during excavation activities to depths near the water table provided evidence that the shallow aquifer beneath the capital city of Montgomery, Alabama, was contaminated (Figure 1). Investigations conducted from 1993 to 1999 by State and Federal agencies confirmed the detection of PCE in the shallow aquifer, as well as the detection of the organic solvent trichloroethylene (TCE) and various inorganic compounds. Because the source of the groundwater contamination was not determined, in May 2000 the U.S. Environmental Protection Agency proposed that the site, called the Capital City Plume (CCP) Site, be a candidate for the National Priorities List. Moreover, numerous site-investigation activities that occurred between 2000 and 2007 also did not determine the source of the groundwater PCE contamination.
Figure 1. Location of study area and the approximate extent of the Capital City Plume, City of Montgomery, Alabama, 2008
To investigate the potential source area, contamination pathway, and the probable release history of the chlorinated-solvent-contaminated groundwater.
The methods used to accomplish the objective included the collection of (1) pore water in 2008 from the hyporheic zone of a creek using passive-diffusion bag samplers; (2) tissue samples in 2008 and 2009 from trees growing in areas of downtown Montgomery characterized by groundwater contamination and from trees growing in riparian zones along the Alabama River and Cypress Creek; and (3) groundwater samples in 2009 and 2010.
Figure 2. Locations of tree cores, VOC concentrations, and PCE in groundwater, Capital City Plume, City of Montgomery, Alabama, 2008.
The data collected between 2008 and 2010 (Figure 2) indicate that the PCE and TCE contamination of the shallow aquifer beneath the CCP Site most likely resulted from the past use and disposal of industrial wastewater from printing operations and other activities in which chlorinated solvents entered the sanitary sewer and (or) stormwater systems of Montgomery (Figure 3). Moreover, chlorinated-solvent use and disposal occurred at least between the 1940s and 1970s at several locations occupied by printing operations and other activities.The data also indicate that PCE and TCE contamination continues to occur in the shallow subsurface near potential release areas and that PCE and TCE have been transported to the intermediate part of the shallow aquifer.
Figure 3. PCE and TCE in groundwater, Capital City Plume, City of Montgomery, Alabama, 2008.
Landmeyer, J.E., Miller, S., Campbell, B.G., Vroblesky, D.A., Gill, A.C., and Clark, A.P., 2011, Investigation of the potential source area, contamination pathway, and probable release history of chlorinated-solvent-contaminated groundwater at the Capital City Plume Site, Montgomery, Alabama, 2008–2010: U.S. Geological Survey Scientific Investigations Report 2011–5148, 53 p. http://pubs.er.usgs.gov/publication/sir20115148.