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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  Petrox® was delivered in each injection well as the drill stem was withdrawn through the treatment zone.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.

Improving Long-Term Bioremediation Results with Nutrients

The goal of bioaugmentation is to improve the rate of contaminant removal by adding a high population of beneficial microbes to the contaminated media.  The additional microbes  should provide short-term benefit as the microbes begin metabolizing the contaminants immediately upon injection. But what benefit does bioaugmentation provide in the long term? And how much benefit does bioaugmentation provide over biostimulation by adding nutrients to the native organisms?

A client of CL Solutions completed a bench-scale study to answer these questions.  A bench-scale study was preferred to a field study because it removes the potential distribution and time-lag issues associated with the distances between injection and monitoring locations in the field.

Samples of petroleum-contaminated soils were obtained and separated into split samples for treatment with microbes and nutrients. Some were untreated for comparison.  Samples were tested for petroleum concentrations, including C-fraction concentrations after 30, 40 and 60 days.  Heterotrophic populations were measured at 40 and 60 days.

The tests showed the following results in the early stages:

  • All of the treated samples showed more than 80% total petroleum reduction in the first 30 days.
  • The sample treated with nutrients only had the same level of petroleum removal as the bioaugmented samples in the first 30 days.
  • The heterotrophic population of the biostimulated sample was as high as in the bioaugmented samples at 40 days.

After 30 days the situation changed.

  • The bioaugmented microbial population continued to increase  after 40 days and may have increased by a factor of 100 times.  Meanwhile, the biostimulated population appeared to stall.
  • The petroleum removal continued in the bioaugmented samples and reached as high as 93% removal.  In comparison the biostimulated sample stalled at 82% removal.
  • The difference appears to be that the bioaugmented samples removed the C-21 to C-35 concentrations at a much higher rate than the biostimulated sample.
  • Phenanthrene was target chemical for bioremediation. The biostimulated sample showed 39% removal while the bioaugmented samples showed complete removal to BDL.

Overall, the superior performance of the bioaugmented samples appears to be related to having a greater metabolic range that removed the heavier hydrocarbon fractions.  Microbes with the extended metabolic range could continue to multiply as they grew on the heavy hydrocarbon fraction.  The results are consistent with field results showing the recalcitrance of heavier hydrocarbon fractions and compounds like naphthalene and phenanthrene under natural attenuation.

Contact CL Solutions for more information and insights.

 

 

 

 

 

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.

Land Farming Application Reduces TPH by 90% to 99%

Petrox microbes were added to excavated petroleum-contaminated soil to accelerate the degradation of DRO and ERO total petroleum hydrocarbons. Petrox was added by spraying the surface of the soil with a hydrated Petrox solution.  The microbes were mixed into the soil using a tractor-mounted disc tiller.  photo-2              photo-1

After approximately 60 days, soil samples were taken for testing.  The soils showed 90% to 99% petroleum removal.  The following chart shows the range of DRO and ERO concentrations before and after Petrox treatment.

land-farming-results

Bioremediation of Naphthalene and Methylnaphthalene Isomers

Petrox bioremediation accelerates the removal of naphthalene and isomers of methylnaphthalene.  These petroleum compounds are often slow to remediate due to their low volatility and strong affinity for absorption onto soil particles.  The remediation rate of these compounds is slower than BTEX compounds.  They often also rebound as the absorbed phase solubilizes following removal of the compound from ground water to reestablish phase equilibrium.  Petrox bioremediation accelerates the remediation of these compounds by a combination of metabolizing the dissolved phase and a biosurfactant effect that strips the compound from soil to make it available for metabolism.

For example, Petrox achieved more than 90% removal of these compound in less than 9 months at a site of a former underground storage tank (UST) in Florida.  After the UST and surrounding contaminated soil were removed, the residual BTEX compounds were treated by chemical oxidation.  The chemical oxidation, however, did not remove the naphthalene and methylnaphthalene isomers. Petrox was applied to the ground water in and around the former UST cavity.

Nine months after the Petrox application the following reductions in concentrations were achieved.  The concentrations are the average of four ground water sampling locations.

Naphthalene –  367 ug/L reduced to 18 ug/L,  95% removal.

1 Methylnaphthalene – 255 ug/L reduced to 33 ug/L, 87% removal.

2 Methylnaphthalene – 400 ug/L reduced to 30 ug/L, 93% removal.

The Petrox was injected into the ground through a continuous low-volume injection system.  This application method did not impact the use of the property or require major construction. The application was also far less costly than alternatives.

The greatest benefit was the relatively rapid removal of difficult contaminants.  Click here and here to view cases studies of naphthalene bioremediation case studies. Use the search bar to find even more case studies of naphthalene bioremediation.