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Solvent
Lancaster, CA
Site 51 is located in Lancaster, California at Edwards Air Force Base on the Main Base Flight Line and is comprised of Aircraft Pad 4. During the 1960’s and 1970’s Pad 4 was used for parking and maintenance of XB-70 aircraft. The fuel tanks were purged and cleaned with TCE and the jet fuel/TCE waste liquids were discharged onto the ground adjacent to the pad. Groundwater sampling showed TCE concentrations of 12 ug/l and PCE at 18 ug/l as well as minor levels of DCE.
The near-surface geology consists of alluvium composed of poorly graded sand and silty and clayey sands interbedded with silts and clays. Groundwater is approximately 40 feet below the land surface.
EcoVac Services Inc was contracted by Earth Tech to perform five one day EFR® events at site 51 extracting on four wells individually and combined to dewater and reduce concentrations of TCE and PCE in the groundwater below the site. Field work was performed once per month between August, 2000 and January 2001. A total of 11,142 gallons of impacted groundwater was removed and vapor phase removal of TCE was 10.6 pounds.
Macon, GA
SITE CHARACTERISTICS
Site Location: Macon, Georgia
Site Use: Prior dry cleaners site
Geology: clayey-silty sand on top of bedrock
Depth to Water: 35 – 50 feet
Initial Plume Dimensions (dissolved PCE >MCLs): ~300 ft x 500 ft
No. of Wells > MCLs: ~10
PCE Concentrations: 1,200 ug/l maximum
SITE BACKGROUND
A plume from a former dry cleaners site from decades ago has emanated a ~300 feet by ~500 feet PCE plume. Remediating the plume will be complicated by topographic differences, access, and the existence of several roads and buildings.
RESULTS
EcoVac Services implemented a two day ISCO-EFR® pilot test on the four source area compliance wells in February of 2008. This short term pilot test yielded a 37% to >95% reduction in PCE concentrations in the four wells compliance monitor wells within the test area. In November of 2009 twelve injection wells (four shallow and eight deep wells) were installed around the compliance wells to be used for ISCO-EFR® implementation. During the well installation phase Shelby Tube samples and groundwater samples were collected for EcoVac to perform a Treatability Study including Soil Oxidant Demand and full scale design parameters. This study is currently ongoing and will be completed in February of 2010 after which ISCO-EFR® will be implemented for source area remediation.
EcoVac Services performed pilot testing on the new injection wells in December of 2009. Results of the second round of pilot testing include the removal of 482 pounds of PCE (23 equivalent gallons) and 2,076 gallons of impacted groundwater. During these tests groundwater drawdown and vacuum response were measured on surrounding injection wells and compliance wells to better understand the connectivity and flow paths in the vadose and saturated zones.
The four shallow vadose injection wells were installed in the area where the PCE tank formerly existed to allow for emplacement of oxidants into the impacted soil horizon above the water table which exists approximately 50 feet below the land surface. The highest PCE concentrations in the groundwater have been found slightly upgradient of the former tank location and it was assumed that the released PCE liquids had migrated laterally to reach that location.
Pilot testing of the shallow vadose injection wells showed a strong vacuum influence on the highest concentration compliance well indicating that a preferential pathway for migration of contaminant did exist and could be utilized during the upcoming ISCO-EFR® remediation phase by extracting on the compliance well while injecting the shallow injection well. Extraction on the deep injection wells produced drawdown on the compliance well but showed very little vacuum influence even though they were very close to the compliance well and will be useful to treat the dissolved contaminants in the saturated zone.
Madison, TN
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SITE LOCATION: |
Former rubber manufacturing plant - Madison, Tennessee |
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CONTAMINATION: |
Separate-phase hydrocarbons (SPH – Stoddard Solvent / Varsol) in ten wells ranging in thickness from 0.12 to 9.24 feet (aggregate total of 19.36 feet) covering approximately 20,000 sq. ft. |
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GEOLOGY: |
Silty clay over limestone and bedrock |
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HYDROGEOLOGY: |
Groundwater contained within a limestone bedrock aquifer at depths of 10 to 40 feet below ground surface. Groundwater flow follows the site topography to the south toward a creek which feeds into the Cumberland River. |
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EFR® EFFECTIVENESS: |
After 10 events, SPH was present in three wells at thicknesses of 0.10 feet, 0.54 feet, and 0.89 feet (aggregate total of 1.53 feet), representing a 92% reduction in aggregate SPH thickness. |
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SURFAC® EFFECTIVENESS: |
SPH was present in two wells at thicknesses of 0.05 feet and 0.07 feet one month following SURFAC®, representing an additional 92% reduction in the aggregate SPH thickness remaining after EFR® (from 1.53 to 0.12 feet) and a 99.4% reduction from the original SPH thicknesses. |
Background
The subject site was a former rubber and tire manufacturing plant. Leaks in piping to an aboveground tank and oil/water separator are believed to have resulted in the SPH plume which covered an area of over 20,000 square feet.
Geology/Hydrogeology
Groundwater is present in a limestone bedrock aquifer at depths ranging from approximately 10 to 40 feet below grade. The bedrock aquifer is overlain by silty clay. Monitor wells utilized for treatment have been drilled and completed into the bedrock aquifer. A network of 1-inch monitor wells and nine 2-inch extraction wells were installed prior to commencement of EFR®. An additional nine 2-inch extraction wells were installed prior to implementing the SURFAC® process.
Treatment Methodology
Ten EFR® events conducted from March 2007 to December 2007 reduced the aggregate (total) SPH thickness from 19.36 feet (in 10 wells) to 1.53 feet (in 3 wells), representing a 92% reduction. The object of EcoVac Services’ patented SURFAC® process implemented in September and October 2008 was to remove all remaining SPH from the site. An expedited remedial timeframe was required due to the demolition and reconstruction activities scheduled for the site.
EcoVac Services’ patented SURFAC® process is the combination of dual-phase/multi-phase extraction and surfactant injection. EcoVac Services employs its EFR® (Enhanced Fluid Recovery) 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® Events
Ten EFR® events were conducted from March 2007 to December 2007. These events removed a calculated total of 3,278 pounds of hydrocarbons (approximately 500 equivalent gallons of Stoddard solvent) and 11,938 gallons of groundwater.
SPH Plume Map (3/21/07 - prior to EFR®)
Aggregate SPH Thickness Graph prior to SURFAC®
SURFAC® Pilot Testing
Three days of SURFAC® pilot testing were conducted at the site to: (1) assess the potential need for additional injection wells, (2) determine if additional EFR® events were necessary prior to surfactant injection, (3) achieve contaminant removal, (4) reduce the aerial/vertical extent of the plume, (5) determine the surfactant injection volumes/locations/sequence, and (6) determine the duration of the surfactant injection/capture events.
The SURFAC® pilot test was conducted at nine extraction wells which had a history of SPH. SPH was detected in three extraction wells (EW?2 – 0.54 feet, EW-5 – 0.89 feet, and EW-12 – 0.10 feet) prior to the pilot testing.
Extraction was conducted individually at extraction wells EW-4, EW-5, EW-9, EW-10, EW-12, EW-14, EW-16, and EW-18. The hydrocarbon removal rates were highest at EW?2 and EW-5 (which both contained SPH). Increasing removal rates were only observed during extraction from EW-2, which was likely a result of the dewatering of the top two feet at the most conductive of the tested wells. Groundwater recovery rates ranged from 0.35 gallons per minute (EW-12) to 5.0 gallons per minute (EW-2).
Differential pressures were only detected at EW?3 during extraction from EW-14, suggesting limited vadose zone permeability. Several feet of groundwater drawdown was observed across the wells during the event. A strong hydraulic interconnectivity between wells was suggested.
A calculated total of 209 pounds of hydrocarbons (approximately 32 equivalent gallons of Stoddard solvent) and 2,817 gallons of groundwater were recovered during the pilot test events.
Importantly, the pilot testing identified that a greater drawdown effect might be achieved by the utilization of dual vacuum truck units at the site. Several factors limited the effectiveness of a single vacuum unit including: 1. distance to the most downgradient well was 150 feet generating significant hose friction 2. nine wells were utilized as treatment wells versus the original eight in the scope 3. depths to groundwater requiring significant lengths of stingers (drop tubes), generating additional frictional loss. By utilizing two vacuum units, the total frictional loss could be divided in half while also doubling total liquid capacity to 5,500 gallons.
SPH Plume Map (9/8/08 - prior to SURFAC®)
SURFAC® Treatment Program
The addition of nine extraction wells to supplement the array of 1-inch monitor wells was necessary to provide the proper treatment well spacing. These wells allowed for more complete coverage of the surfactant/water mixture across the SPH plume.
A SURFAC® injection event was conducted at the subject site in September 2008 immediately followed by three double vacuum truck capture events. Two additional single truck capture events were conducted in October 2008.
A calculated total of 603 pounds of hydrocarbons (approximately 92 equivalent gallons of Stoddard solvent) and 12,190 gallons of groundwater were removed the extraction events. Approximately 1,860 gallons of a surfactant aqueous solution was gravity fed into nine extraction wells during the SURFAC® injection event. Approximately 12,190 gallons of liquid were removed during the five SURFAC® capture events.
Results and Conclusions
The site was allowed to recover for one month following the third capture event. Prior to the fourth capture event, SPH was detected at two wells, 0.09 feet at EW-5 (as compared to 0.89 feet prior to the pilot test events) and 0.02 feet at EW-18 (which did not contain SPH prior to the pilot test events). SPH was not detected after the final two capture events. Approximately one month later, two wells contained SPH (EW-5 – 0.05 feet and EW-10 – 0.07 feet). The aggregate SPH thickness at this time (0.12 feet) represented a 92% reduction from prior to SURFAC® and a 99.4% reduction from prior to EFR®.
Edwards AFB, California
Site 51 is located on the Main Base Flight Line and is comprised of Aircraft Pad 4 as shown on attached figures 6-1 and 6-2. During the 1960’s and 1970’s Pad 4 was used for parking and maintenance of XB-70 aircraft. The fuel tanks were purged and cleaned with TCE and the jet fuel/TCE waste liquids were discharged onto the ground adjacent to the pad. Groundwater sampling showed TCE concentrations of 12 ug/l and PCE at 18 ug/l as well as minor levels of DCE.
The near-surface geology consists of alluvium composed of poorly graded sand and silty and clayey sands interbedded with silts and clays. Groundwater is approximately 40 feet below the land surface.
EcoVac Services Inc was contracted by an environmental contractor to perform five one day EFR® events at site 51 extracting on four wells individually and combined to dewater and reduce concentrations of TCE and PCE in the groundwater below the site. Field work was performed once per month between August, 2000 and January 2001. A total of 11,142 gallons of impacted groundwater was removed and vapor phase removal of TCE was 10.6 pounds.
