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Tesoro Refining and Marketing
CLIENT

Tesoro Refining and Marketing

SCOPE OF SERVICES
  • Water Well Survey

  • Advance Soil Borings

  • Conduct Soil Vapor Survey

  • Well Destruction

Arco Service Station, Hawthorne, California

In 1989, it was discovered that the site had been contaminated by leaking underground storage tanks. After two years of assessment activities, including site lithology, groundwater flow direction and magnitude and plume characterization, a soil vapor extraction (SVE) pilot test was conducted. After it was determined that SVE was a viable remedial method, a system was installed and started in 1995. After the removal of approximately 10,000 pounds of hydrocarbons from the subsurface, the system was shut down in 1997, due to low influent concentrations; however, groundwater was still contaminated.

In 2002, two high-volume, dual-phase extraction pilot tests were conducted and based on those results an air sparge pilot test was conducted. Air sparging resulted in higher influent petroleum hydrocarbon concentrations. In 2008 the installation of the air sparge and soil vapor extraction system was completed. At that time groundwater concentrations of gasoline range organics (GRO), benzene, methyl tertiary-butyl ether (MTBE), and tert-butyl alchol (TBA) were 67,000 ug/L, 6,300 ug/L, 4,300 ug/L, and 23,000 ug/L respectively. In December of 2009 Stratus assumed consulting responsibility for the site. A review of the air sparge system revealed that concentrating sparging in certain areas of the site instead of using the entire network of air sparge wells would clean up the site more efficiently. Stratus changed from sparging into 15 different wells to sparging into just four wells. Concentrations of hydrocarbons on site went from 51,000 ug/L of GRO, 7,200 ug/L of benzene, 5,700 ug/L of MTBE, and 43,000 ug/L of TBA to 1,400 ug/L of GRO, 700 ug/L of benzene, 160 ug/L of MTBE, and 530 ug/L of TBA. Once these reductions in petroleum hydrocarbons occurred, all air sparge wells were turned back on to help ‘polish’ the site.