Petroleum Release from Underground Storage Tanks Tucson, Arizona


Releases from underground diesel and gasoline storage tanks had contaminated 300,000 cubic yards of soil at a City-owned facility. A benzene plume extended more than ½ mile downgradient in the regional aquifer. Previous site investigations revealed a multi-layer aquifer and two distinct plumes. An organization of area citizens was concerned with the status of the investigations, the conclusions of the health risk assessment, and the communication of results. As a result, an elementary school was closed and the City officials and consultants in charge of the investigation were replaced. Hydro Geo Chem was brought in to design and construct interim remedial actions for source reduction in site soils, to conduct informational technical presentations to the citizens' group and advisory committee, and to prepare remedial action plans for soils and shallow and deep groundwater.

Hydro Geo Chem's Approach

Field investigations revealed the presence of active biodegradation zones on and off the site. A soil vapor extraction (SVE)-bioventing pilot study and numerical simulation to optimize a full scale system established SVE-bioventing as an applicable remedial technology. Simulations were also performed to assess and optimize a groundwater containment system, including vacuum-enhanced extraction. A source-area SVE system was installed, using catalytic oxidation vapor treatment.


Hydro Geo Chem prepared a full-scale corrective action plan that was presented to and approved by the citizens' group and advisory committee and accepted by the Arizona Department of Environmental Quality. By determining that in-situ biodegradation conditions were favorable, we successfully argued for a reduced area of plume containment that could be achieved through installation on City-owned property without accessing privately owned lands. Our containment design was far less expensive than initial containment cost estimates.




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