CL Solutions provides a special consortium of microbes for oil-contaminated water treatment. Under various conditions, the oil removal rate was as much as 1,300 mg/L/day. In some situations the remediation goal is simply to remove the visible sheen or separate-phase oil. With aeration, CL Solutions microbes were able to remove the visible oil layer and reduce the TPH concentration from 29% to less than 1% in 30 days at a waste oil lagoon. For more information and other case studies click here.
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.
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.
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.
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.
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.
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.
Recent data from field applications of Petrox bioremediation show degradation rates of 100 to 500 micrograms per liter (ug/ml) per day. These degradation rates are for total petroleum hydrocarbons or total BTEX, depending on the site monitoring requirements.
Achieving high degradation rates requires high initial concentrations. Initial concentrations of 1,000 to 10,000 ug/l were used to develop these degradation rates.
At lower concentrations, the degradation rates depend on effective distribution of microbes for cell to contaminant contact. Secondly, desorption of petroleum constituents from submerged soil may cause rebound and suggest lower degradation rates. For these reasons we cannot calculate a degradation rate for petroleum at low concentrations.
Using a special microbial blend, Delta Environmental has been successfully bioremediating high concentrations of heavy oil in soil around pipelines and oil production equipment. At a typical site, Delta reduced the concentration of petroleum C34 to >C50 from 130,000 mg/Kg to less than 10,900 in 30 days. That is a removal rate of 3,970 mg/Kg/day. This approach not only benefits the environment and meets green cleanup standards, but saves money and equipment downtime for the facility.