Little Rock, Arkansas

Background

UST removal activities in 1997 revealed the presence of SPH at the site.  Remedial activities included the excavation of ~930 yards³ of soil.  Multiple dual-phase extraction events by another provider removed ~3,200 equivalent gallons of gasoline/diesel fuel from the site, but failed to reduce the size of the plume.  SPH was still present in 18 monitor wells, ranging in thickness from 0.01 to 1.21 feet and covered an area of ~17,000 to 27,000 feet². The area and shape of the plume changes with the groundwater table fluctuation due to the distribution/morphology of the fluvial deposits underlying the site.

Hydrogeology

The site is underlain by fluvial sediments consisting of silty clay, silt, sand, gravel and cobble that coarsen downward.  These fluvial deposits are underlain by shale at ~15 feet bgs. Groundwater is present at ~7 feet bgs.  

Treatment Methodology

EcoVac Services was retained to utilize its enhanced fluid recovery (EFR^®) and SURFAC^® processes to remove SPH from the site.

 The EFR^® process is best described as a mobile version of dual-phase or multi-phase extraction.  EFR^® simultaneously removes vapors, SPH, and groundwater from the subsurface. It volatilizes adsorbed and free phase volatile organic compounds (VOCs) through a process similar to vapor extraction, but with a much higher vacuum and radius of influence.

EcoVac Services’ patented SURFAC^® process is the combination of dual-phase/multi-phase extraction and surfactant injection. EcoVac Services employs its EFR^®  process for the dual-phase/multi-phase extraction component of EcoVac Services’ patented SURFAC^® process.  The process described herein is patent-protected and represents the intellectual property of EcoVac Services, Inc.

EFR^® and SURFAC^® Implementation

Three week-long EFR^® events were conducted at the site in February, June, and August 2009 to (1) achieve contaminant removal, (2) reduce the aerial/vertical extent of the plumes, (3) determine the surfactant injection volumes/locations/sequence, and (4) determine the duration of the surfactant injection/capture events.

SURFAC^® was implemented thereafter (single application - five field days) in August 2009 to further remove SPH.

Results and Conclusions

SPH was present in four monitor wells, ranging in thickness from 0.02 to 0.21 feet on January 13, 2010.   A 98% reduction in SPH was achieved by EFR^® and SURFAC^® in four field weeks.

Three consecutive 8-hour EFR^® events have been proposed to remove the remainder of SPH at the site.