Managing Global Resources for a Secure Future

With the vast amount of disturbed land created worldwide by landfills, it is of growing importance to find sustainable uses for these sites once they reach capacity and are closed. In Arizona, the City of Tucson is interested in using the sealed Harrison Landfill site for grazing land. The purpose of this study is to complete a vegetation study and to assess the concentration of metals in soil and plants at the site. Depending on these concentrations, the site may be deemed either “safe” or “in need of remediation” for use as graze-land.

The Harrison Road Landfill in Tucson, Arizona was active from 1972 to 1997 and sealed with a compact soil cap in 1999. Since it’s closure, the site has undergone groundwater pump and treat, soil vapor extraction, and landfill gas extraction. The landfill gas extraction continues to operate, though groundwater pump and treat and soil vapor extraction have both been shut down after successful remediation. Both of these systems undergo periodic testing for concentration rebound. The site is currently vegetated with mostly grasses, woody shrubs, and some cacti.

Soil and vegetation sampling was conducted in May 2017. Soil samples were collected to a depth of 12 inches (with 15% of samples going to a depth of 30 inches). The soil and vegetation samples were processed using standard methods and analyzed for metal concentrations (As, Ba, Cd, Cr, Pb, Hg, Se, Ni, Zn, and Ag) via inductively coupled plasma/mass spectrometry. These data were used to conduct an exposure risk assessment and were compared to domestic animal toxicity levels (DATLs). The results of this assessment will be used to evaluate the suitability of the site for grazing. If metal concentrations are above DATLs and/or Arizona soil remediation levels, the use of phytostabilizing plants as a primary cover will be investigated as a potential means to reduce exposure.