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1627 Hwy 99 – Gridley

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Vapor Extraction Unit

On June 30, 2000, four 15,000-gallon USTs and one 5,000-gallon UST were removed from the former Sierra Superstop retail fueling station. Analytical data from samples collected from the tank pit indicated a petroleum hydrocarbon impact to soil and groundwater beneath the Site.

In order to define the extent of the contamination, seven groundwater monitoring wells  were installed at the Site in 1998. Two additional monitoring wells were installed in 2002 to further define the contamination plume.

In January 2005, E2C was selected to provide environmental consulting services for this site.  A Workplan was prepared which proposed installation of a soil and groundwater remediation system at the Site.  The implementation of the workplan included the installation of the following in May 2005:

  • Two  offsite groundwater monitoring wells to assist in definition of the leading edge of the groundwater plume;
  • Eleven  horizontal vapor extraction wells;
  • Five air sparge wells and
  • Trenching and plumbing of the remediation wells to the equipment compound

After approval from the regional water quality control board, commencement of full-scale remedial operations began in March 2007.  In December 2008, the water quality control board concurred with E2C’s recommendation that remedial actions at the site should be terminated due to the  effectiveness of the remedial system.  At this point, monitoring continued at the site to evaluate contaminant rebound in groundwater monitoring wells.  Between February and November 2010, seven separate extraction events were conducted to remove the remaining pollutants.

In March 2011 E2C submitted a request for no further action to the board due to the low concentrations of pollutants remaining at the site.  In June 2011 the board responded with a no further action required directive, and the site was closed.