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In Situ Bioremediation of TPH with Petrox

Petrox reduced the concentration of TPH in soil at a former gas station from 9,500 mg/kg to 52 mg/kg. The impacted soil was at more than 20 feet deep.  Injection of calcium peroxide provided the oxygen needed for metabolism of the petroleum by Petrox microbes.  The post treatment sampling was 90 days after the bioaugmentation, so that even though the average remediation rate was 105 mg/kg/day, the peak remediation rate must have been much higher when the Petrox population was higher.

This is another example of fast, reliable bioremediation by Petrox organisms.

In-situ Bioremediation of BTEX, TPH and PAHs in Groundwater

Convenience Store in Florida

After three underground storage tanks were removed from the location of a convenience store, investigation showed that petroleum contamination was present in small area near the former dispenser island.  The vadose-zone contaminated soil was excavation and disposed off-site.  Ground water monitoring showed that the ground water impact was limited to a small area near the source of contamination. The decision was made to close the site by applying Petrox® bioremediation to the ground water.

Ground Water Contamination

The ground water contamination was in a shallow water table aquifer that had a medium permeability.  The contamination was a suite of BTEX, PAHs, methylnaphthalene isomers and TRPH.

Bioremediation

A pilot study was completed to determine feasibility of Petrox bioremediation combined with a peroxide oxygen supplement.  The pilot study reduced contaminant concentrations by up to 92%.  A full-scale application completed the site remediation.

Results

The pilot study and full-scale applications of Petrox and an oxygen supplement reduced BTEX compounds by >99%, naphthalene by 99%, TRPH by 96% and naphthalene isomers by 88% to achieve the remediation goals and site closure.  The microbial cost for the pilot study and full-scale treatment was less than $2,000.

To learn more, click here to download the case study.

Bioremediation With Horizontal Injection for BTEX and Naphthalene Remediation

In situ remediation is a contact sport, requiring contact between the microbes and contamination.  Clay-rich soils are particularly challenging as the low permeability limits effective distribution of inoculants.  While numerous closely-spaced injection points can improve the distribution of inoculants, this approach is often not possible at active properties and can be costly.  Horizontal drilling was used on the subject site to overcome the combined challenges of low permeability and limited site access to inject Petrox® microbes for bioaugmentation.  The combined technologies reduced the total BTEX concentrations in ground water from 2,771 µg/L to 645 µg/L in less than one year.

Background

The site is a former gas station located in the Florida panhandle.  The site soils are mixed silt and clayey silts that are typical of the coastal setting.  The depth to the water table varied seasonally from 13 to 18 below ground surface.

The underground storage tanks and contaminated soil had been removed prior to the ground water treatment.  Residual ground water contamination exceeded Florida Ground Water Cleanup Target Levels (GCTLs) for benzene, toluene, ethylbenzene, xylene, naphthalene and methylnaphthalene isomers.

The proposed treatment area was approximately 2,500 square feet.  The treatment depth was from 10 to 25 feet below grade.  The treatment depth included the capillary fringe to treat residual contamination above the seasonal low water table.

Horizontal Injection

 Access to the treatment area was limited by the current property use, the proximity of roads on two sides and a building on the third.  Horizontal drilling was selected by the site consultant, Advanced Environmental Technologies (www.aetllc.com) to deliver Petrox® to the contamination.

The horizontal drill rig was set back from the treatment zone on the opposite side of the building.  The horizontal injection wells were set in four horizontal sets of eight wells. The horizontal layers were at 10, 15, 20 and 25 feet deep.  The wells in each layer were five feet apart.  A total of 32 injection wells were closely spaces for excellent coverage through the treatment zone.

Petrox® was injected into the ground water in two treatment events – November 6, 2008 and June 24, 2009.  Petrox® was delivered in each injection well as the drill stem was withdrawn through the treatment zone.  The injection was monitored for accuracy so that 0.2 gallons of Petrox® was injected per foot of injection zone.  A total of 320 gallons of Petrox® slurry was injected.

Following the Petrox® injection, air was injected periodically through vertical sparging wells to increase the oxygen availability for the microbial metabolism.

Results

Ground water samples were collected from a monitoring well inside the treatment area to track the progress of the bioremediation.  Approximately 60 days after the first Petrox® treatment, analysis of ground water samples showed 84% reduction in the benzene concentration and 35% reduction in the total BTEX compounds concentrations.  There was an apparent increase in the xylene concentration due to ground water mixing and induced increase in solubility due to the bioaugmentation injections.

A second sampling event approximately 30 days after the second injection showed additional reduction in the contaminant concentrations.  After the second injection, the total BTEX concentrations were 23% of the original concentration with xylene decreasing from 1,200 to 95 µg/L.

In addition to the BTEX compounds, naphthalene and methylnaphthalene isomer concentrations decreased through both treatments.

  Sampling Date Benzene Toluene Ethylbenzene Xylene Naphthalene
Pre-treatment 11/11/05 3,000 42 1,100 1,100 230
10/23/08 1,700 18 460 454 280
11/6/08 1,600 41 370 760 310
Post-treatment

 

1/22/09 420 43 140 1,200 43
7/30/09 490 2.6 57 95 55

Conclusions

Horizontal drilling and injection made it possible to remediate ground water at this site of petroleum contamination with limited access and low natural permeability.  Without disturbing the property use, the horizontal injection of Petrox® provided effective distribution of the microbes for bioremediation.  The injection may have also made the contamination more available for bioremediation by increasing the contaminant solubility as shown by temporary increases in concentration.

This case study demonstrates that in situ bioaugmentation may be a feasible solution for sites with limited permeability and access restrictions.  For more information contact CL Solutions at www.cl-solutions.com.

PAH Bioremediation

The results of a recent bench-scale test confirmed the effectiveness of a special blend of CL Solutions’ microbes formulated for PAH bioremediation.  The test results showed that after two weeks, the total concentration of 15 PAH compounds decreased by 85% from a total of 358 mg/kg to 50.9 mg/kg.  Benzo(A)pyrene is often a most difficult PAH to remove. The test showed that the custom blend reduced the benzo(A)pyrene concentration from 24.5 mg/kg to 3.68 mg/kg.  Tests will continue to determine whether even greater effectiveness can be achieved over 30 days.

Surface Oil Spill Bioremediation

Petrox microbes provide quick response surface oil spill bioremediation.  Petrox can be applied to the oil surface with a backpack sprayer to initiate rapid bioremediation.  This approach protects surface water and vegetation with minimal surface traffic.

In the following example, an oil spill affected the vegetation and surface water at the edge of a lake. Contractors applied Petrox to the oil surface on vegetation and soil.  Periodic soil samples tracked the results.  After 90 days, the maximum and average concentrations decreased by more than 95% at a very low cost.

Surface Spill Results