Streamlined approach for environmental restoration closure report for Corrective Action Unit No. 456: Underground storage tank release site 23-111-1, Nevada Test Site, Nevada

The underground storage tank (UST) release site 23-111-1 is located in Mercury, Nevada. The site is in Area 23 of the Nevada Test Site, (NTS) located on the north side of Building 111. The tank associated with the release was closed in place using cement grout on September 6, 1990. The tank was not closed by removal due to numerous active underground utilities, a high-voltage transformer pad, and overhead power lines. Soil samples collected below the tank bottom at the time of tank closure activities exceeded the Nevada Administrative Code Action Level of 100 milligrams per kilogram (mg/kg) for petroleum hydrocarbons. Maximum concentrations detected were 119 mg/kg. Two passive venting wells were subsequently installed at the tank ends to monitor the progress of biodegradation at the site. Quarterly air sampling from the wells was completed for approximately one year, but was discontinued since data indicated that considerable biodegradation was not occurring at the site