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  Petrox® was delivered in each injection well as the drill stem was withdrawn through the treatment zone.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

New Custom Blend Available for Denitrification

CL Solutions has provided Petrox DN for denitrification for many years.  Petrox DN is a freeze-dried consortium that requires hydration before application.  CL Solutions now provides a custom blend of microbes in a dry powdered form with denitrification capabilities. This dry blend makes for more convenient storage and use.  Additional organisms in the consortium can degrade ammonium and organics including petroleum hydrocarbons, fats, carbohydrates, proteins, starches and cellulose.  These benefits make the custom blend a powerful tool for bioremediation of liquid waste in fixed facility treatment or environmental applications.

Call CL Solutions for more infomation or a site evaluation at 513-284-5940.

Dry Cleaner Bioremediation and Brownfield Redevelopment

Site Description

Dry cleaning solvent spills in a storage area lead to the contamination of soil and ground water on the property of a 50-year-old dry cleaners in the middle of a hot brownfield redevelopment.   After the contaminated soil was excavated for off site disposal to the most practical extent, residual perched ground water contamination impacted the redevelopment of the property.

The soil excavation was used as an infiltration gallery as part of a recirculating ground water recovery and treatment system.  The flushing reduced contaminant concentrations, but the levels were still far above the levels required to achieve no further action status.  CL-Out was added to the recirculating ground water and the cleanup goals were achieved in less than two years and were maintained through two years of  post treatment monitoring.

Site Characteristics

Geology and Hydrogeology

The site is on a fluvial terrace adjacent to the Ohio River.  The shallow soils are clayey silts to sit to eight feet deep.  An interbedded sandy zone that formed the first water-bearing zone was encountered from 8 to 12 feet deep.  Perched ground water occurred in the sandy zone at 12 feet below grade.

Ground Water Contamination

 The size of ground water plume that resulted from the spills was estimated to be 3,500 square feet.    The ground water contamination was mainly PCE with a maximum concentration of 11,000 ug/l prior to soil removal or ground water treatment.  The daughter compounds TCE and DCE were detected up to 17 and 12 ug/l respectively.  After three years of recirculation and flushing, the maximum PCE concentration was reduced to 2.3 ug/l and the daughter compounds were below detection limits.

Results

CL-Out bioaugmentation was implemented to supplement the flushing system.  By adding CL-Out on two occasions over two years, the contaminant concentrations were reduced to below drinking water standards.  During two years of post treatment monitoring the DCE concentrations rebounded to above the MCLs.  CL-Out bioaugmentation was implemented again and within three months the contaminant levels were below drinking water standards and remained below drinking water standards for nine months.  After post closure monitoring verified the cleanup goals would be maintained, the KDEP issued a “No Further Action” letter for the site.

The following chart shows the PCE contaminant trend in one of the key monitoring wells during the remediation and post closure monitoring.

Cost

The CL-Out cost during this remediation project was less than $10,000.

 

Benzo(a)pyrene Bioremediation Using Custom Blend Microbes

Benzo(a)pyrene is a difficult remediation challenge. It is resistant to biological and chemical destruction and extraction from soil.  CL Solutions Custom Blend microbes, however, have successfully remediated benzo(a)pyrene and other PAHs in soil during ex situ land farming treatment.  By placing the contaminated  material in windrows, controlling the temperature and moisture, the addition of Custom Blend microbes has reduced the benzo(a)pyrene concentration by as much as 330 ug/kg/day.

The same approach works on high as well as low concentrations.  At a site in Oregon, the benzo(a)pyrene concentration was reduced from 140 ug/Kg to below detection limits in 7 days.  At a site in Ohio, the benzo(a)pyrene concentration was reduced from 28,000 ug/kg to 3.8 ug/Kg in 60 days.  At both sites, Custom Blend microbes effectively treated the full suite of PAHs along with the benzo(a)pyrene.

New Chlorinated Solvent Results

CL-Out bioremediation continued to show outstanding results in bioremediation of PCE, TCE and other chlorinated solvents at three recent applications. Results show more than 90% PCE removal with a single application of CL-Out for in situ ground water treatment. The PCE remediation did not cause an increase in vinyl chloride showing that the breakdown pathway was by dioxygenase cometabolism and not by reductive dechlorination.

A site in Massachusetts showed the following ground water results:
PCE 1,100 ug/L reduced to 30 ug/L, 97% removed
TCE 39 ug/L reduced to 5.6 ug/L, 85% removed
No other daughter products were detected.

Ground water remediation in Florida showed these results:
PCE 182 ug/L reduced to 16.1 ug/L, 91% removed
TCE 9.82 ug/L reduced to 2.77 ug/L, 71% removed
cis 1,2 DCE 3.26 ug/L reduced to 0.282 ug/L, 91% removed
vinyl chloride was not detected before or after bioremediation.

Ground Water contamination at a site in New Jersey followed the same trend:
PCE 690 ug/L reduced to less than 5 ug/L, 99% removed
TCE 7,980 ug/L reduced to less than 810 ug/L, 89% removed
No breakdown products were detected.

These sites join the hundreds of sites remediated by CL-Out aerobic cometabolism.